Wireless Lab Manual 2008

Wireless Communication Lab 1

LAB MANUAL

WIRELESS COMMUNICATIONS LAB

EEP 776

BHARTI SCHOOL OF TELECOMMUNICATION TECHNOLOGY AND MANAGEMENT

INDIAN INSTITUTE OF TECHNOLOGY, DELHI

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LIST OF EXPERIMENTS

Concept based Experiments Page

1. Study of basic Antennas………………………………………………………………… 3 2. Properties of Antennas: Polarization , Cross Polar Discrimination

Polarization Diversity……………………………………………………………………. 14

3. Antenna Resonance and Gain Bandwidth measurement……………….. 19

4. Characterization of Fading Effects……………………………………………….. 22 5. Fading Counter-measures using Antenna diversity and Frequency

diversity…………………………………………………………….…….................. 32

6. Delay Spread Measurement…………………………………………………………… 38

7. Handover Demonstration………………………………………………………………. 45

Application based Experiments Page

8. 9.




EXPERIMENT NO.1

STUDY OF BASIC ANTENNAS 1. OBJECTIVES

1. To plot the radiation pattern of simple antennas - Dipole, Monopole, Folded

dipole antenna etc, in E & H planes on log & linear scales on polar and

Cartesian plots.

2. To measure the beam width (-3 dB), front to back ratio, side lobe level and its

angular position, plane of polarization and directivity and gain.

2. THEORY Radiation Pattern: The antenna radiation pattern is basically a measure of its

power or radiation distribution with respect to a particular type of coordinates. We

generally consider spherical coordinates as the ideal antenna is supposed to radiate

in a spherically symmetrical pattern. However antennae in practice are not omni

directional but have a radiation maximum along one particular direction. For e.g.

Dipole antenna is a broadside antenna wherein the maximum radiation occurs along

the axis of the antenna. The 3-D radiation pattern of a typical dipole antenna looks

something like this




Directivity: Given a set of spherical polar coordinates (R,,) we can determine the

power density in watts/(square meter) for both the antenna being investigated,

and the isotropic reference antenna, which is radiating the sane total power. The

ratio of these power densities gives the directivity of the unknown antenna in the

direction (,) at a distance R from the antenna. If the direction (,) is not

specified, the “directivity” is taken to be the maximum directivity of any of the

directions of radiation. The quoted definition is: “The directivity of an antenna is

defined as the ratio of the radiation intensity in a given direction from the

antenna, to the radiation intensity averaged over all directions, The average

radiation intensity is equal to the total power of the antenna divided by (4) .If the

direction is not specified the directivity refers to the direction of maximum

radiation intensity”.

Gain: The gain in any direction (,) is power density radiated in direction (,)

divided by power density which would have been radiated at (,) by a loss less

(perfect) isotropic radiator having the same total accepted input power. If the

direction is not specified, the value for gain is taken to mean the maximum value in




any direction for that particular antenna, and the direction along which the gain is

maximum is called the “antenna boresight”. The efficiency of an antenna is the

gain divided by Directivity, in any direction.

3. EQUIPMENT REQUIRED 1. Antenna Digital RF Transmitter, MADL- 2.4.

2. Antenna Digital RF Receiver, MADL – 2.4

3. Antenna Stepper Motor Controller, WCS 860.

4. Dipole Antennas, Folded dipole, Monopole, Yagi antenna

5. Antenna tripod and stepper pod with connecting cables

6. Spectrum Analyser FS300

7. Signal generator SML03

Experiment Setup

Fig. 7.1 4. LAB PROCEDURE PART-I:

a) Connect one of the dipole antennas of length = 24cms (field generator

antenna) to the tripod and set the transmitter frequency to 600 MHz and




keep the attenuator downwards to avoid receiver saturation. Keep the

antenna in horizontal direction.

b) Now connect the second antenna (test antenna whose radiation pattern is

to be measured) to the stepper pod and set the receiver to 600 MHz. Set

the attenuator upwards for maximum sensitivity. Adjust the dipole for

resonance at 600 MHz.

c) Set the distance between the antennas to be around 1 m. Remove any

stray object from around the antennas, especially in the line of sight.

Avoid any unnecessary movement while taking the readings.

d) Now rotate the test antenna around its axis in steps of 5 degrees using

stepper motor controller. Take the level readings of receiver at each step

and note down.

e) Note the maximum reading out of the whole set of readings. This will

form the 0db reference reading. Now subtract all the readings from these

reference readings and note down. Now use this new set of readings for

drawing a plot.

f) Plot the readings on a polar or Cartesian plane with log/linear scales.

g) This plot with both the dipoles in horizontal plane shall form an E-plane

plot.

h) Now without disturbing the setup-rotate the test antenna at receiver from

horizontal to vertical plane by using a polarization connector.

i) And rotate the test antenna around its axis in steps of 5 degrees using

stepper motor controller. Take the level readings of receiver at each step

and note down.

j) Plot the readings also on a polar or Cartesian plane with log/linear scales.

k) This plot shall constitute the H-plane plot of the test antenna.

l) Use a jumper lead to connect the two tripods and take the reading in the

receiver. If the reading is more than 70dB then press another attenuator.

This is the power fed to the Transmitting antenna (Pt).




m) Now connect the two-dipole antennas, in this case, one at Tx pod and

other at Rx stepper Tripod. Take the reading in the receiver. This is the

Power received from the receiving antenna (Pr).

n) Now repeat the procedure for other as well.

PART-II (Calculation):

a) From the E-plane radiation patterns drawn find the following.

b) The –3 db or half power beam width is defined as the angular width in

degrees at the points on either sides of the main beam where the radiated

level is 3db lower than the maximum lobe value.

c) From the polar plot measure the angle where the 0db reference is there.

This shall also be the direction of main lobe or bore sight direction.

d) Measure the angle when this reading is –3db on its either side.

e) The difference between the angular positions of the –3dB points is the E-

plane beam width of the dipole antenna.

f) Side lobe level is usually taken as the level below the bore sight gain.

Strictly all peaks on either side of the main lobe are side lobes. However

in practice only the lobes adjacent to the either side of the bore sight

maxima are referred to as side lobes.

g) Side lobes in this case shall form between the two maximums. Nulls can

be up to –20dB from the bore sight direction gain.

h) If the plot forms distinct side lobes then each one’s angular position and

level can be inferred from the plot.

i) The front to back ratio is a measure of the ability if a directional antenna

to concentrate its beam in the required forward direction.

j) Observe the difference in levels in dB from bore sight direction and the

direction diametrically opposite to it.

k) Measure the H-plane beam width of the dipole antenna from h-plane plot.




l) Calculate the directivity as 41000/(3 dB beam width E-plane X 3dB beam

width H-plane in degrees). Take a log of this value and multiply by 10 for

reading in dBi.

m) As the dipole antenna is itself a reference antenna for gain measurements

hence its absolute gain cannot be directly found out. However the gain of

other antennas can be referred to dipole gain.

n) The received power (Pr) is= Pt*(G * ) 2/ (4 R) 2, where Pt is the

accepted power, G is gain of each dipole antenna (a straight number) and

R is distance between them.

o) Now Gain = Directivity * Efficiency, so find Efficiency.

5. LAB REPORT Give the following information:

1. Antenna Test frequency (f) = ……………………..MHz

2. Antenna Test Wavelength () = ……………….….m

3. Rayleigh Distance, near field-Far field boundary =………………….m (F=2*L2/,

where L is the maximum dimension of the antenna in m.)

3. Distance between the two antennas R=…………….m

4. Theoretical antenna dimension for half wave (/2) Dipole=……………m

5. Practical antenna Dimensions for half wave (/2) Dipole=……….m (/2 – 5%).

6. Power fed to the transmitting antenna (Pt)=………….dBV=……………..nw.

7. Power received from receiving antenna (Pr)= ………….dBV=…………..pw.

8. E-plane –3dB bandwidth of the antenna (HP)=………………….. .

9. H plane –3 dB beam width of the antenna (HP)=…………………. .

10. E plane half power beam width (HPBW) (HP)=…………………..rad

11. H plane half power beam width (HPBW) (HP) = ………………..rad

12. Beam area or Beam solid angle = …………..sr (A =HP*HP (sr). Also

A (sr)=4 (sr)*D where D is Directivity)

13. Beam width between first nulls (BWFN)=………….deg (BWFN=2*HPBW approx.)




14. Front to Back ratio = ………………………dB

15. Directivity of the antenna (D)=………………. (41,0002/ HP*HP)

16. Directivity of the antenna (DdB)=…………………….dB

17. Resolution of the antenna =………..(Beam width between first nulls (BWFN)/2 )

18. Antenna Aperture (A)=…………………m2

19. Gain of the Antenna (G)=……………….

20. Gain of antenna (GdB)=…………………….dB

21. Antenna Efficiency (k)=…………… (k=D/G )

6. QUIZ

1. What will happen if a conducting plate is placed behind the dipole?

2. Identify the type of antenna associated with following radiation pattern?

(a) (b)

(c) (d)

(e) (f)




3. List the factors on which the shape of overall pattern of an antenna array

depends?

4. What will happen if a folded dipole is attached to 5V AC, 50 MHZ signal?

5. What will happen if a folded dipole is attached to 230V AC,50 Hz main supply?

6. When a 5V DC is applied across a folded dipole antenna, will it radiate energy?

Justify your answer.

7. “The Dipole antenna is extremely flexible”. Justify the statement?

8. A Hertz half wave dipole antenna is aligned along X-axis. Where radiation peak

will occur.

9. How does a radiation pattern depend upon the radius on antenna element?

10. What will be radiation pattern of dipole antenna, if it will put on ground?




7. Few more radiation patterns

A typical radiation pattern is shown below with necessary angular explanations

3-D radiation patterns of the dipole for different frequencies




Radiation pattern of the helical antenna

Radiation pattern of the Horn antenna




Radiation pattern of Folded dipole




EXPERIMENT NO.2

POLARISATION OF ANTENNAS, CROSS POLAR DISCRIMINATION AND

POLARISATION DIVERSITY

1. OBJECTIVES 1. To study the phenomenon of Linear and Circular polarization of antennas.

2. To determine the Cross Polar Discrimination(XPD) for the antenna systems in

the lab.

3. To study polarization diversity.

2. THEORY Antenna Polarization for linear antennas is in direction of its elements so if the

dipole is mounted in horizontal plane it is horizontally polarized. If it is made

vertical using polarization adapter then it is vertically polarized. Linear

polarization of an antenna is measured with reference to a dipole antenna. So if

maximum signal is received from a given antenna with test dipole horizontal, then

the given antenna is horizontally polarized. A diagram illustrating polarization is

shown.




As the plane of either of the antennas is changed using a polarization

adapter the received signal strength reduces. A vertical antenna radiates vertically

polarized wave as a vertical whip/ vertical dipole/monopole

discone/endfire/broadside. A horizontal antenna radiates horizontally polarized

waves as a horizontal dipole/biconical/square loop/quad/Vee/Yagi/ Log-periodic.

Cross polarization discrimination is the change in received signal strength with

change in polarization direction for a linearly polarized antenna. In the case of

measurements between dipoles and yagi upto 20dB of change can be observed on

changing plane of polarization. Good polarization discrimination reflects the purity

of an antenna pattern. A circularly polarized wave front has equal power in its

plane. Hence when a dipole antenna is rotated from horizontal to vertical using

polarization adapter in front of a crossed dipole antenna or an axial mode helix

antenna. No appreciable change in signal strength is observed – concluding that

crossed dipole and helix antennas are circularly polarized. The axial ratio of a

crossed dipole and helix antennas would be close to 1 and signal variation would be

a few dBs around all directions in vertical plane. Received signal strength is

maximum between circularly polarized antennas at Tx and Rx when both have same

handedness. Thus it is maximum between RHCP and RHCP or between LHCP and




LHCP antennas. It will be lesser in case of communication between RHCP and LHCP

antennas indicating the polarization discrimination antennas. A practical antenna

using polarization diversity is shown below

3. EQUIPMENT REQUIRED

1. Antenna Digital RF transmitter, MADL 2.4.

2. Antenna Digital RF receiver MADL 2.4.

3. Pair of Dipole antennas, RHCP & LHCP crossed dipole antennas and RHCP &

LHCP axial mode helix antennas.

4. Antenna Tripod and stepper pod with connecting cables, Polarization

connectors.

5. LHCP crossed dipole, RHCP crossed dipole, helix and dipole antennas

Experiment Setup

Fig. 8.1 4. LAB PROCEDURE PART-I:

a) Connect the BNC-RF cable to the transmitter tripod and attach a dipole

antenna to it using polarization adapter. Set the transmitter frequency to

600 MHz and attenuator downwards for low RF level to avoid receiver




saturation. Set the length of the antenna elements to 12 cm. Each from

the center of the boom Keep the antenna in horizontal direction.

b) Now connect another dipole antenna to the receiver stepper tripod using a

polarization connector in between and set the receiver to 600 MHz .Set

the attenuator upwards for maximum sensitivity.

c) Set the distance between the antennas to be around 1m.

d) Keep both the dipoles in horizontal planes and pointing towards each

other. The elements of both antennas should be parallel to each other.

Take the level reading in the receiver.

e) Now rotate the dipole at the stepper pod in vertical plane using

polarization adapter. Take the level reading in receiver with dipole in

vertical plane and note down. Take care not to change the direction of

antenna.

f) Now connect a RHCP/LHCP crossed dipole antenna or RHCP/LHCP axial

mode Helix antenna at the transmitter end and point it towards the

receiver. Take care to Point it precisely towards the other dipole and

ensure that same height is maintained while taking readings. Take the

level reading in the receiver.

g) Now rotate the dipole antenna at the receiver in vertical plane using

polarization Adapter. Observe the change in level reading. Observe its

difference from an ordinary dipole antenna.

h) Try replacing the dipole at receiver tripod with various antennas and

observe the Change in readings on rotating the other dipole from

horizontal to vertical.

i) Now, connect the RHCP/ LHCP crossed dipole antenna at Tx/Rx end and

one RHCP/LHCP axial mode helix antenna at the other end. And find out

which pair of antennas (i.e. RHCP crossed dipole antenna & RHCP axial

mode helix antenna or LHCP crossed dipole antenna & RHCP axial mode

helix antenna or vice-versa) out of four gives maximum Rx reading.




j) See if received signal strength is maximum between circularly polarized

antennas at Tx and Rx when both have same handedness. Measure the

polarization discrimination among antennas.

5. LAB REPORT

Give the following information:

1. Type of polarization = Linear / circular, if linear Horizontal / Vertical.

2. Axial ratio of circularly polarized antenna (A.R.)=………………….dB (Difference of

readings upon rotation of a test dipole in front of a circularly polarized wave

front (crossed dipole) in horizontal and vertical planes.)

3. Cross polarization discrimination (C.P.D) for linear antenna =…………..dB

(Difference of readings upon rotation of a test dipole in front of a linearly

polarized wave front (dipole) in horizontal and vertical planes).

6. QUIZ

1. Compare entire antenna used in this experiment according to their diversity

gain?

2. Find one application of each type of polarization?

3. “The larger the XPD, the less is the energy coupled b/w the cross polarized

channel”. Justify this statement?

4. What is the recommended value (Min.) of polarization discrimination for BTS?




EXPERIMENT NO.3

ANTENNA RESONANCE

&

GAIN BANDWIDTH MEASUREMENTS

1. OBJECTIVES

1. To identify whether an antenna is resonating or non-resonating type.

2. To measure basic antenna’s Gain Bandwidth using log

periodic antenna.

2. THEORY The theory on the different types of antenna mentioned is provided in the Appendix

A.

Basically a resonant antenna is the one which is not terminated in its characteristic

impedance, because of which there will be reflection of the wave transmitted,

whereas a non-resonant antenna is terminated in its characteristic impedance

because of which the transmitted wave is fully absorbed by the antenna.

Dipole antenna’s resonant frequency is a function of its length. A half wave

dipole shall resonate when its length is equal to half the wavelength of its

operating frequency. Hence a half wave dipole whose element length is 12c.m.

shall resonate at around 600 MHz. At the resonant frequency the SWR is minimum

for a resonant antenna. A non-resonant antenna has a broadband frequency

response and its SWR is almost constant over a range of frequencies. A log periodic

antenna comes under the category of non-resonant antenna.





1. Antenna Digital RF Transmitter, MADL -2.4.

2. Antenna Digital RF Receiver, MADL – 2.4

3. Antenna Tripods.

4. Dipole, log periodic, Yagi, Monopole, folded dipole and Biconical antennas.

4. LAB PROCEDURE

a) Connect a log-periodic antenna at transmitter tripod and set the

frequency of the transmitter to 450 MHz. Keep the attenuator downwards

to avoid receiver saturation.

b) Connect the dipole to the receiver pod and set the receiver frequency to

450 MHz.

c) Adjust the dipole for resonance at 600 MHz i.e. set its total length as 24

cms.

d) Now take the receiver readings at 10 MHz interval from 450 to 750 MHz.

Plot the receiver readings against frequency.

e) This will result in plot of gain bandwidth of dipole antenna presuming that

log-periodic antenna have flat response with frequency.

f) The gain shall show some fall at higher frequencies due to various losses

in the system, which increases with frequency.

g) Repeat the above procedure for Yagi, Monopole and Biconical Antennas.

h) At this point you must be able to prove from gain bandwidth plots that a

given antenna is resonating or not.

Note : To adjust the monopole antenna for resonance at 600 MHz , set its

length as 12c.m. For Biconical Antenna biconical elements can be pulled

out completely for broad response.




5. LAB REPORT

1. Gain Bandwidth of the antenna(s) =……………………MHz

(Range of frequencies for which gain is reduced by over 3dB while measuring

with

log-periodic antenna.)

2. Gain bandwidth plot of various antennas

6. QUIZ

1. Compare the entire antenna used in this experiment according to their power

gain, directivity and polarity?

2. What determines the accuracy of antenna array?

3. Why Radomes, Heater and Labeling elements are added in antenna array?




EXPERIMENT NO. 4

CHARACTERIZATION OF FADING EFFECTS

1. OBJECTIVES 1. To observe and characterize the multi-path fading effects in the lab

environment using:

a) CRO

b) Power meter (in-built in the Receiver) and

c) Spectrum analyzer (prefer this to measure the received power)

2. To determine the fade duration at different frequencies.

3. To determine the coherence bandwidth of the wireless channel.

2. THEORY Fading When the waves of multipath signals are out of phase, reduction in signal strength

can occur. One such type of reduction is called a fade; the phenomenon is known

as “Rayleigh fading” or “fast fading.” A typical diagram of multi-path reception is

given below:

A fade is a constantly changing, three-dimensional phenomenon. Fade zones tend

to be small, multiple areas of space within a multipath environment that cause

periodic attenuation of a received signal for users passing through them. In other

words, the received signal strength will fluctuate downward, causing a momentary,

but periodic, degradation in quality.




Fig 1.1. A Representation of the Rayleigh Fade Effect on a User Signal

A phasor diagram of the multipath propagation channel is as shown:

Indoor Propagation Model

The indoor radio channel differs from the traditional mobile radio channel in two

aspects, the distances covered are much smaller, and the variability of the

environment is much greater for a much smaller range of T-R separation distances.

It has been observed that propagation within buildings is strongly influenced by

specific features such as the layout of the building, the construction materials, and

the building type. Indoor radio propagation is dominated by reflection, diffraction,

and scattering. Signal levels vary greatly depending on whether interior doors are

open or closed inside a building. Where antennas are mounted also impacts large

scale propagation. Antennas mounted at desk level in a portioned office receive

vastly different signals than those mounted on the ceiling. Also, the smaller

propagation distances make it more difficult to insure far-field radiation for all




receiver locations and types of antennas. A typical graph of Rayleigh fading

simulated in the lab environment with the receiver moving at 120km/h is as shown

In general, indoor radio channels may be classified either as line-of-sight (LOS) or

obstructed (OBS), with varying degrees of clutter.

Partition Losses (same floor)

Buildings have a wide variety of partitions and obstacles, which form the internal

and external structure. Partitions that are formed as part of the building structure

are called hard partitions, and partitions that may be moved and which do not span

to the ceiling are called soft partitions. Partitions vary widely in their physical and

electrical characteristics, making it difficult to apply general models to specify

indoor installations.

Partition losses between floors

The partition losses between floors of a building are determined by the external

dimensions and materials of the building, as well as the type of construction used

to create the floors and external surroundings. Even the number of windows in a

building and the presence of tinting (which attenuates radio energy) can impact the

loss between floors.




Log-distance Path Loss Model Indoor path loss has been shown to obey the distance power law in equation:

PL(dB)= PL(d0) + 10nlogo

dd

+ X (1.1)

Where

n is the path loss exponent which indicates the rate at which the path loss

increases with distance, the value of n depends on the surrounds and buildings

type. In free space, n=2, it increases if obstructions are present

d0 is the close-in reference distance which is determined from measurements close

to the transmitter

d is the Transmitter-Receiver distance

and X represents normal random variable in dB having a standard deviation of

dB.

Level Crossing Rate

In the design of high speed digital mobile radio transmission systems, it is

important to know the characteristics of multipath fading that induce burst errors.

Provided that burst errors occurs when the signal envelope fades below a specific

threshold value, the level crossing rate can be used as an appropriate measure for

the burst error occurrence rate. The fade duration may also be used to estimate

the burst error length.

The level crossing rate which is generally defined as the expected rate at which the

Rayleigh fading envelope R, normalized to a local rms signal level, crosses a

specified level Rs in the positive-going direction and is given by




RdRRRpN sRs ),(

0

= 2 f D ρ e-ρ2 (1.2)

where ρ = R/Rs

Where the dot denotes a time derivative, p(Rs, R ) is the joint pdf of R, and R for R= Rs .

f D is the maximum Doppler Frequency. ρ is normalized to the local rms amplitude

of the fading envelope. The level crossing rate can be interpreted to be function of

the mobile speed as is apparent from the presence of f D in equation 1.2. It can be

shown that the level crossing rate NRs for a signal received by a vertical monopole

antenna is

2

2

2exp

22

ss

DRRRfN

s (1.3)

Average Fade Duration

It is defined as the average period of time for which received signal is below a specified level R. Average Fade duration (τ),

τ = 1

Nr Pr[rR] , (1.4)

where Pr[r<=R] is the probability that the received signal r is less than R and is given by

Pr[r<=R] = (1/T)*Summation of τi’s

Where each τi is the duration of the fade and T is the observation interval of

the fading signal. Considering a Rayleigh distribution, the equation 1.3 becomes

τ = (eρ2 -1) / (ρ f D 2 ) , f D = v/λ where v is velocity of incident

wave




The average duration of a signal fade helps determine the most likely number of

signaling bits that may be lost during a fade. It depends on the speed of the

mobile, and decreases with increase in f D.

Coherence Bandwidth

Coherence bandwidth is a statistical measure of the range of frequencies over

which the channel can be considered “flat” ( i.e. a channel which passes all

spectral components with approximately equal gain and linear phase ). In other

words, coherence bandwidth is the range of frequencies over which two frequency

components have a strong potential for amplitude correlation. Two sinusoids with

frequency separation greater than Bc are affected quite differently by the channel.

For more details refer to

http://users.ece.gatech.edu/~mai/tutorial_multipath.htm

3. EQUIPMENT REQUIRED 1) Microwave analog digital link transmitter MADL 2.4.

2) Microwave analog digital link receiver MADL 2.4.

3) Scientific Function Generator, HM 5030-4.

4) FS 300 spectrum Analyzer 9KHz 3 GHz.

5) Digital oscilloscope or 100 MHZ analog oscilloscopes, HM 1004-3.

6) Two dipole antennas and antenna tripods.

Experiment Setup: 1. Connecting the Tx [Transmitter] side:

a) Set the length of the dipole antennas to 24 cm end to end.

b) Connect the dipole antenna to the tripod and connect the cable from the

tripod to the RFOUT point of the Microwave Antenna Digital link

Transmitter, MADL 2.4.

c) Set the frequency of the transmitter to 2.4 GHz.




d) Connect the Audio1 point of the transmitter to the output of function

generator, HM 5030-4.

e) Set the waveform knob of the function generator to the sinusoidal, rotate

the frequency knob, so that output is around 2000 Hz.

f) Keep the mic/1 KHz switch of the transmitter in the mic position,

Audio1/Audio2 switch in the Audio1 position and attenuator in the Low

position.

2. Connecting the Rx [Receiver] side:

a) Connect another dipole antenna to the stepper pod and connect it

simultaneously to the RF IN point of the Microwave Analog Digital link

Receiver, MADL 2.4 and RF input point of the spectrum Analyzer.

b) Set the frequency of the receiver 2.4 GHz

c) Set the attenuator of the receiver in the low position.

d) Connect the Audio1 point coming from the receiver to CH-1 of the

oscilloscope, HM 1004-3 (oscilloscope 1) to see the Analog output in the

scope.

3. Connecting the Spectrum Analyzer:

a) Press the SYS key.

b) Select PRESET in the button menu bar using the horizontal scroll keys.

c) Press the PRESET function key.

d) Select FREQ/SPAN in the button menu bar using scroll keys.

e) Press the CENTER function KEY.

f) ENTER 2400 using numerical keys. Terminate the entry by pressing the

unit key MHZ/ms.

g) Select MKR in the bottom menu bar using the scroll keys.

h) Press the MARKER 1 function Key.




i) Press the PEAK function Key in the submenu that appears. The marker

jumps to the signal peak. Turn the rotary knob to change the position of

the marker.

Fig. 1.2

LAB PROCEDURE 1) Transmit a sinusoidal signal of around 2 KHz frequency using a carrier frequency

of 2.4 GHz.

2) Connecting the Audio1 point from the receiver to the CH I of HM 1004-3

oscilloscope will show the sinusoidal signal transmitted and also the tone can be

heard by increasing the volume in the receiver.

3) Keeping the two dipoles parallel to each other, move antenna and receiver

relatively. Observe the 2.4GHz signal amplitude variations in spectrum analyzer

due to multi-path effect (fading effect).

4) Vary the distance between antenna and receiver and note down the distance

between antennas, 2.4 GHz RF signal amplitude in the spectrum analyzer, the

level reading in dBv and plot them. This gives the fade plot.

5) At carrier frequency, say 2.4GHz, keep the receiver at a fade. Now vary the

carrier frequency and note how much frequency change is required to get out of

fade & relate it to Coherence Bandwidth.

6) Repeat the above experiment with carrier frequencies 2.42 GHz, 2.44 GHz.




LAB REPORT

1. Plot of the fades versus the distance between the Tx and Rx. At frequencies f

= 2.4 GHz, 2.42GHz and 2.44 GHz.

2. Plot of the fades for vertical and horizontal polarization. Do you see any

differences ? Explain.

3. Determine the average distance between fades for 2.4 GHz, 2.42GHz and 2.44

GHz.

4. Find the value n for the lab, where

Path loss dB= PL(d0) + 10nlog o

dd

+ X

6. QUIZ 1) Give the values of the IF and RF used in your experiment?

2) What type of modulation the transmitter is using?

3) Is n a function of frequency?

4) What will be the effect on Average Fade Duration if the receiver uses 2

antennas with received signals uncorrelated?

5) If the Coherence Bandwidth is greater than the channel bandwidth, do we need

equalizer? Give reason to support your answer?

6) Point out some WLAN channel models and clearly gives the parameters ranges

under which these models are suitable?

7) Which WLAN channel model may best describe your working environment in lab?

7. MATLAB SIMULATION OF MULTIPATH FADING A typical MATLAB simulation of Rayleigh fading is as shown.







EXPERIMENT NO. 5

DELAY SPREAD MEASUREMENT AND CALCULATION OF COHERENCE

BANDWIDTH

1. OBJECTIVES 1. To measure the rms delay spread of the wireless channel.

2. To determine the coherence Bandwidth.

2. THEORY

Because of multipath reflections, the channel impulse response of a wireless

channel looks likes a series of pulses.

Figure: Example of impulse response and frequency transfer function of a

multipath channel.

We can define the local-mean average received power with excess delay within the

interval (T, T + dt). This gives the "delay profile" of the channel. The delay profile

determines to what extent the channel fading at two different frequencies f1 and f2

are correlated.

Some definitions

The maximum delay time spread is the total time interval during which

reflections with significant energy arrives.




The rms delay spread Trms is the standard deviation (or root-mean-square)

value of the delay of reflections, weighted proportional to the energy in the

reflected waves.

For a digital signal with high bit rate, this dispersion is experienced as frequency

selective fading and intersymbol interference (ISI). No serious ISI is likely to occur if

the symbol duration is longer than, say, ten times the rms delay spread. An

instantaneous impulse influened by delay spread is as shown

In order to compare different multipath channels and to develop some general

guidelines for wireless systems, parameters which grossly quantify the multipath

channel are used. The mean excess delay, rms delay spread and excess delay

spread (X dB) are multipath channel parameters that can be determined from a

power delay profile. The mean excess delay is the first moment of the power delay

profile and is defined to be




kk

kkk

kk

kkk

P

P

aa

)(

)(

2

2

(3.1)

Where P(τ) is the power measured at time τ.

The rms delay spread is the square root of the second central moment of the power

delay profile and is defined to be

22 )(

where

kk

kkk

kk

kkk

P

P

a

a

2

2

22

2

These delays are measured relative to the first detectable signal to at the receiver

at 0=0. The above equations do not rely on the absolute power level of P(), but

only the relative amplitudes of the multipath components within P().Typical

values of rms delay spread are on the order of microseconds in outdoor mobile

radio channels and on the order of nanoseconds in indoor radio channels.

The maximum excess delay (X dB) of power delay profile is defined to be the time

delay during which multipath energy falls to X dB below the maximum. In other

words, the maximum excess delay is defined as x - 0.where 0 is the first arriving

signal and x is the maximum delay at which a multipath component is within X dB

of the strongest arriving multipath signal (which does not necessarily arrive at

0).The figure below illustrates the computation of the maximum excess delay for

multipath components within 10 dB of maximum. The maximum excess delay (X dB)

defines the temporal extent of the multipath that is above a particular threshold.

The value of x –is sometimes called the excess spread of a power delay profile, but

in all cases must be specified with a threshold that relates the multipath noise floor

to the maximum received multipath component.




Fig. 3.1

Coherence Bandwidth

Coherence bandwidth is a statistical measure of the range of frequencies over

which the channel can be considered “flat”( i.e. a channel which passes all spectral

components with approximately equal gain and linear phase ). In other words,

coherence bandwidth is the range of frequencies over which two frequency

components have a strong potential for amplitude correlation. Two sinusoids with

frequency separation greater than Bc are affected quite differently by the channel.

If the coherence bandwidth is defined as the bandwidth over which the frequency

correlation function is above 0.9, then the coherence bandwidth is approximately

Bc1

50 ( 3.2 )

Where the denominator sigma corresponds to the rms delay spread. If the

definition is relaxed so that the frequency correlation function is above 0.5, then

the coherence bandwidth is approximately




Bc1

5

3. EQUIPMENT REQUIRED 1. Microwave Analog Digital Link Transmitter MADL 2.4

2. Microwave Analog Digital Link Receiver MADL 2.4

3. Signal generator SML03 .

4. Digital phosphorous oscilloscope TDS 5104B or100 MHz Analog Oscilloscope HM

1004-3

5. Any 2 antennas – dipole or helix

4. LAB PROCEDURE 1. Transmit a narrow pulse (duty cycle 0.1) using signal generator using a carrier

frequency of 2400 MHz.

2. Connect the external pulse signal to Audio2 input of the transmitter. The Horn

antenna is connected to the RF output of the transmitter. Connect another horn

antenna to the RF input of the receiver. Set the frequency to 2600 MHz at both

transmitter and receiver.

3. Connect the CRO to the Audio2 output of the receiver.

4. Plot the delay profile for the transmitted pulse.

5. Calculate the rms delay spread.

6. Comment on the shape of the received signal on the CRO.

7. Repeat the above steps at frequencies of 2.4, 2.42 and 2.44 GHz.

8. Repeat the above steps with a different antenna (with different HPBW).

5. LAB REPORT 1. Obtain the delay profile for the transmitted pulse. How will your answer change

if you use a narrower pulse for measurement?

2. Calculate the mean access delay, rms delay spread and excess delay spread of

the wireless channel at 2.40, 2.42, 2.44 GHz. Compare the results and explain.




3. Calculate the coherence Bandwidth of the channel based on measurement.

Obtain the approximate dimensions of the lab and theoretically calculate the

approximate value of mean access delay and coherence bandwidth. Compare

the results obtained experimentally. Explain the mismatch.

4. Give the values for mean access delay, rms delay spread and excess delay

spread for antennas with different half power beam width (HPBW). Explain your

result theoretically.

6. QUIZ 1. Explain the sentence ‘One of the ways to reduce multipath interference is to

use an antenna with a very narrow HPBW’. What is disadvantage of using an

antenna with narrow HPBW?

2. What are the HPBW of antennas in the base station and in the handset for a

typical mobile communication scenario (for GSM and for CDMA2000)?

3. Calculate the Coherence Bandwidth for mobile communication in India(GSM and

CDMA 2000)? Will your answer change with degree of urbanization?

4. A signal is said to undergo flat fading if Bs << Bc, where Bs is signal bandwidth

and Bc is coherence bandwidth, otherwise signal undergoes frequency selective

fading . Is your signal transmission in lab undergoing flat fading or frequency

selective fading?

5. For each of the scenario below, decide if the received signal is best described as

undergoing fast fading, frequency selective fading, or flat fading?

(a) A binary modulation has a data rate of 500kbps, and fc=1GHz and a typical

urban radio channel is used.

(b) A binary modulation has a data rate of 5kbps, and fc=1GHz and a typical

urban radio channel is used to provide communication to cars moving on a highway.

6. Which channel has more RMS delay spread between Indoor channel and Outdoor

Channel and why?




EXPERIMENT NO. 6

FADING COUNTER-MEASURES USING ANTENNA DIVERSITY AND

FREQUENCY DIVERSITY

1. OBJECTIVES 1. To observe effects of multiple antennas on the received signal strength.

2. To use antenna diversity as fading counter measure.

3. To use frequency diversity as fading counter measure.

2. THEORY Concepts of Diversity branch and signal paths: Diversity is a powerful communication technique that provides wireless link

improvement at relatively low cost .Unlike equalization it requires no training

overhead.

A diversity technique requires a number of signal transmission paths, named

diversity branches, which carry the same information but have uncorrelated

multipath fadings and a circuit to combine the received signals or select one of

them. Depending on the land mobile radio propagation characteristics, there are a

number of methods to construct diversity branches.

Space Diversity: It is also known as Antenna Diversity. It has a single transmitting

antenna and a number of receiving antennas. Spacing between adjacent receiving

antennas is chosen so that multipath fading appearing in the diversity branches

becomes uncorrelated. A typical element using the antenna diversity technique is

as shown




Angle diversity: It requires a number of directional antennas. Each antenna

responds independently to a wave propagating at a specific angle and receives a

faded signal that is uncorrelated with the others.

Polarization Diversity: In this case two diversity branches are available; it is

effective because the signals transmitted through two orthogonally polarized

propagation paths have uncorrelated fading statistics in the usual VHF and UHF land

mobile radio environment. The concept of Polarisation diversity is shown below:

Time and Frequency Diversity: Difference in frequency and/or time can also be

utilized to construct diversity branches with uncorrelated fading statistics. The

required frequency and time spacing can be determined from the characteristics of

the time delay spread and the maximum Doppler frequency. A common advantage

of these two techniques compared with space, angle and polarization diversity

techniques is that the number of transmitting and receiving antennas can be

reduced to one of each, with the disadvantage that a wider bandwidth is required.

Error-correction coding, which is peculiar to digital transmission systems, can be

regarded as a kind of time diversity technique. Frequency diversity as such is

utilized for large antennas for transmission over large distances. A picture of an

antenna using the frequency diversity is shown at the end of the experiment.




In principle, with an exception of polarization diversity, there exists no limit

to the number of diversity branches. For example, several practical wireless

applications in the 2.4 GHz band have used up to five receiver antennas to achieve

space diversity.

The rationale behind the Frequency diversity is that frequency separated by more

than Coherence Bandwidth of channel will be uncorrelated and will not experience

same fades.

Time diversity repeatedly transmits information at time spacing that

exceeds coherence time of channel so that multiple repetitions of signal will be

received with independent fading condition thereby providing condition for

diversity.

3. EQUIPMENT REQUIRED 1. Microwave analog digital link transmitter MADL 2.4.

2. Microwave analog digital link receiver MADL 2.4.

3. Function Generator, HM 5030-4.

4. FS 300 spectrum Analyzer 9KHz 3 GHz.

5. Digital oscilloscopeTwo or 100 MHZ analog oscilloscope, HM 1004-3

6. Three antenna & three antenna tripods

Experimental Setup

Tx1

Tx2

Rx




Fig 2.1 Transmitter diversity

Fig.2.2 Receiver Diversity

1. Connecting the Tx (Transmitter) side:


b) Connect the dipole antenna to one tripod and the YAGI antenna to

another tripod. Connect the two antenna cables to the RFOUT point of the

Microwave Analog Digital LINK Transmitter, MADL 2.4 with the help of

multiple antenna connectors.

c) Set the frequency of the transmitter to 2.4GHz.

d) Connect the AUDIO 1 point of the transmitter to the output of function


e) Set the waveform knob of the function generator to the sinusoidal,

frequency range knob to 2K and rotate the frequency knob, so that output

is around 2 KHz.

Tx

Rx1

Rx2





Audio1/Audio2 switch in the Audio1 position and attenuator in the low

position.

2. Connecting the Rx (Receiver) side:


simultaneously to the RF IN point of the Microwave Analog Digital link

Receiver, MADL 2.4 and RF input point of the spectrum Analyzer.

b) Set the frequency of the receiver 2.4 GHz

c) Set the attenuator of the receiver at the in the low position..

d) Connect the Audio1 point coming from the receiver to CH-1 of the 100 MHZ

analog oscilloscope, HM 1004-3 (oscilloscope 1) to see the analog signal

output in the scope.







f) ENTER 2400 using numerical keys. Terminate the entry by pressing the unit

key MHZ/ms.


h) Press the MARKER 1 function key. Press the PEAK function Key in the

submenu that appears. The marker jumps to the signal peak. Turn the

rotary knob to change the position of the marker.




4. LAB PROCEDURE

1. Transmit a sinusoidal signal of around 2 KHz frequencies using a carrier

frequency of 2.4 GHz.

2. Connecting the Audio1 point from the receiver to the CH I of HM 1004-3



3. Disconnect one antenna (say, the Yagi Antenna) from the multiple antennas

Connector in the transmitter side and move the two antennas relatively.

4. Observe the 2.4 GHz signal amplitude variations in spectrum analyzer due to

multi-path effect (fading effect). Position the transmitter Antenna in a fade.

5. Now connect the other antenna to the multiple Antenna Connectors and observe

the change in the received signal.

6. Connecting one antenna at a time to multiple antenna connector vary the

distance between antenna and receiver and note down the distance between

antennas and the corresponding 2.4 GHz RF signal amplitude in the spectrum

analyzer, the level reading in dBv And Plot them.

7. Thus two fade plots corresponding to two transmitter antennas are obtained.

Superimpose the two plots to get the overall fade plot.

8. From the plot find out the average distance between fades and average length

of a fade (fade duration in cm).

9. Now repeat the experiments with one transmitter antenna & two receiver

antennas.

10. Frequency Diversity: Use one transmitter & one receiver antenna and set up a

communication link as shown in fig.(ii).

11. Move the Receiver with respect to the transmitter. For every location measure

the received power for four different frequencies separated by coherence

Bandwidth.

12. On the same graph plot the fading profiles for the different frequencies.




5. LAB REPORT 1. Obtain the fade plot with one transmitter antenna and one receiver antenna.

2. Obtain the fade plot with one transmitter antenna and two receiver

antennas(Receive Diversity).

3. Obtain the fade plot with two transmitter antenna and one receiver

antennas(Transmit Diversity).

4. Calculate the average duration of fade (in cm) for

(i) Receive diversity and

(ii) Transmit Diversity.

Compare the values and explain which is better? While commenting make sure

you keep in mind the total transmit power in each case.

5. Obtain the fade profiles for different frequencies (2.40, 2.42 and 2.44 GHz)

using (i) Receive diversity and (ii) Transmit Diversity .Comment on your result.

6. Give the plot of the fade profile using frequency diversity.

6. QUIZ 1. Give an example were Time Diversity Technique is used?

2. What can be the distance between the antennas in Antenna Diversity for signals

to be uncorrelated?

3. Which Diversity Technique is used in Base Station Design?

4. Describe briefly the conditions under which small scale and large scale fading

will occur?

5. Why space diversity technique is considerably less practical at base station?

Which diversity technique will be more suitable at base station?

6. Which diversity technique is suitable for Line-of-Sight Microwave Links?

7. Suggest some other fading countermeasures?




EXPERIMENT NO. 7

HANDOVER DEMONSTRATION

1. OBJECTIVES 1. To demonstrate the concept of handover in a cellular system

2. To plot the received power at the mobile station with respect to the distance

from the two base stations.

3. To set up two overlapping micro cells within the lab.

2. THEORY When a mobile moves into different cell while a conversation is in progress, the

MSC (Mobile Switching Center) automatically transfers a call to a new channel

belonging to the new base station. This handoff operation not only involved

identifying a new base station, but also requires that the voice and control signals

be allocated to channels associated to the new base stations.

Processing handoffs is an important task in any cellular radio system. Many

handoff strategies prioritize handoff requests over call initiation request when

allocating unused channel in a cell site. Handoffs must be performed successfully

and as infrequently as possible, and as imperceptible to the users. In order to meet

these requirements, system designers must specify an optimum signal level at

which to initiate a handoff. Once a particular signal level is specified as the

minimum usable signal for acceptable voice quality as the base station receiver

(normally taken as between –90dBm and –100dBm), a slightly stronger signal level is

used as a threshold at which a handoff is made. This margin, given by =Pr handoff –

Pr minimum usable can’t be too large or too small. If is too large, unnecessary handoffs

which burden the MSC may occur, if is too small, there may be insufficient time

to complete a handoff before a call is lost due to weak signal conditions. Therefore

is chosen carefully to meet these conflicting requirements.




The figure bellow illustrates a handoff situation. Fig. A demonstrates the case

where a

handoff is not made and the signal drops below the minimum acceptable level to

keep the channel active. These dropped call event can happen when there is an

excessive delay by the MSC in assigning a handoff or when the threshold is set too

small for the handoff time in the system. Excessive delay may occur during high

traffic conditions due to computational loading at the MSC or due to the fact that

no channels are available on any of the nearby base stations (thus forcing the MSC

to wait until a channel in a nearby cell becomes free).

In deciding when to handoff, it is important to ensure that the drop in the

measured signal level is not due to momentary fading and that the mobile is

actually moving away from the serving base station. In order to ensure this, the

base station monitors the signal level for a certain period of time before a handoff

is initiated. This running average measurement of signal strength should be

optimized so that unnecessary handoffs are avoided, while ensuring that necessary

handoff are computed before a call is terminated due to poor signal level. The

length of time needed to decide if a handoff is necessary depends on the speed at

which the vehicle is moving. If the slope of the short term average received signal

level in a given time interval is steep, the handoff should be made quickly.

Information about the vehicle speed which can be useful in handoff decisions can

also be computed from the statistics of the received short term fading signal at the

base station.

Today’s GSM systems use something known as Mobile Assisted Handoff (MAHO),

wherein the handoff decisions are mobile assisted. Here every mobile station

measures the received power from surrounding base stations and continually

reports the results of these measurements to the serving base station. The process

Receive power from all the neighboring base stations. Compare the power with that of current base station

Is the power large? No need for handoff.

No Process the handoff and pass the signal to the next base station

Yes




can be explained in short by using a flowchart:

A more comprehensive diagram is as below




Here the cells interact with the original base station as they transmit power

information, and the base station (and sometimes the MSC) takes the decision for

handoff.

For more details refer to http://www.3g4g.co.uk/Tutorial/ZG/zg_handover.html


1. Two Microwave Analog Digital Link Transmitter MADL 2.4

2. One Microwave Analog Digital Link Receiver MADL 2.4.

3. SCIENTIFIC Function Generator, HM 5030-4.

4. FS 300 Spectrum analyzer 9KHz-3GHz.

5. Digital Oscilloscope or 100 MHZ analog oscilloscope, HM 1004-3.

6. Three antennas and three antenna tripod

7. T connectors

Experiment Setup

Fig. 4.2

1. Connecting the Tx [Transmitter] side:


b) Connect the dipole antenna to one tripod and the YAGI antenna to another

tripod. Connect the two antenna cables to the RFOUT point of the Microwave

Analog Digital link Transmitter, MADL 2.4 with the help of multiple antenna

connectors.

c) Set the frequency of the transmitter to 2.4 GHz.




d) Connect the Audio1 point of the transmitter to the output of function


e) Set the waveform knob of the function generator to the sinusoidal,

frequency range knob to 2K and rotate the frequency knob, so that output is

around 2KHz.


Audio1/Audio2 switch in the Audio1 position and attenuator in low position.

2. Connecting the Rx [Receiver] side:


simultaneously to the RF IN point of the Microwave Analog Digital Link

Receiver, MADL 2.4 and RF input point of the spectrum Analyzer Adapter.

b) Set the frequency of the receiver 2.4 GHz.

c) Set the attenuator of the receiver in the low position.

d) Connect the Audio1 point coming from the receiver to CH-1 of the 100 MHZ

analog oscilloscope, HM 1004-3 (oscilloscope 1) to see the analog signal

output in the scope.







f) ENTER 2400 using numerical keys. Terminate the entry by pressing the unit

key MHZ/ms.


h) Press the MARKER 1 function key. Press the PEAK function Key in the

submenu that appears. The marker jumps to the signal peak. Turn the rotary

knob to change the position of the marker.




4. LAB PROCEDURE 1. Keep the two transmitter antennas at a distance from each other pointing to

each other.

2. Keep the receiver antenna in between the two transmitter antennas.

3. Transmit a sinusoidal signal of around 2 KHz frequencies using a carrier

frequency of 2.4GHz.

4. Connecting the Analog Out point from the receiver to the CH I of HM 1004-3



5. Move the receiver antenna in between the two transmitter antennas and

observe the 2.4GHz signal amplitude variations in spectrum analyzer.

6. Connecting one transmitter antenna at a time to multiple antenna connectors

move the receiver and obtain the fade plot.

7. Similarly connecting the other antenna to the multiple antenna connectors

move the receiver and obtain the fade plot for the other antenna.

8. Now connect the two transmitter antennas simultaneously and move the

receiver between them and obtain the combined fade profile (received power

vs. distance).

9. Repeat the above procedures for 2.4GHz, 2.42 GHz, and 2.44 GHz.

5. LAB REPORT 1. Plot the received power vs. distance (fade plot) with one transmitter antenna

at a time. Do this for both the antennas.

2. Obtain the combined fade profile (received power vs. distance) with two

transmitter antennas connected simultaneously.

3. Assume a threshold value for the receiver sensitivity(a power level below the

signal cannot be used by receiver) and create your cell boundaries within the

lab




4. Repeat the experiment for 2.4GHz, 2.42 GHz, 2.44 GHz. Compare the result

and explain the behavior. Theoretically what u can say about the cell size as a

function of frequency ?

6. QUIZ 1. What is threshold level for power in mobile handset?

2. ‘Cells are hexagonal’? Give reasons for hexagonal cells?

3. What could be the other cell shapes possible? Give three examples and explain

the relative merits / demerits.

4. What can be done to increase the capacity of the cell?

5. What is ‘reuse factor’? Give the typical cell reuse factor for GSM networks.

6. In mobile assisted handoff (MAHO), every mobile station measures the received

power from surrounding base station and continually reports the results of the

measurement to the saving base station. In this handoff strategy, when handoff

will initiate?

7. For GSM system, what is the range of and value of handoff duration?

8. What are the practical considerations of handoff?

8. A Little bit extra

In practice there are many more different types of handoffs than MAHO. One

of them is the intertechnology handoff wherein different elements are accessing

the same network and the handoff to different network elements is made based on

different criteria. The diagrammatic representation of such a handoff in Flash-

OFDM technique is as shown.







APPENDIX A Introduction to antennas

An antenna is used to radiate electromagnetic energy efficiently and in desired directions. Antennas act as matching systems between sources of electromagnetic energy and space. The goal in using antennas is to optimize this matching. Here is a list of some of the properties of antennas:

Field intensity for various directions (antenna pattern).

Total power radiated when the antenna is excited by a current or voltage of known intensity.

Radiation efficiency which is the ratio of power radiated to the total power.

The input impedance of the antenna for maximum power transfer (matching).

The bandwidth of the antenna or range of frequencies over which the above

properties are nearly constant.

All antennas may be used to receive or radiate energy. An antenna

radiation pattern or antenna pattern is defined as "a mathematical function or

graphical representation of the radiation properties of the antenna as a

function of space coordinates. In most cases, the radiation pattern is

determined in the far-field region (i.e.in the region where electric and

magnetic fields vary inversely with distance) and is represented as a function

of the directional coordinates." The radiation property of most concern is the

two- or three-dimensional spatial distribution of radiated energy as a function

of an observer's position along a path or surface of constant distance from the

antenna. A trace of the received power at a constant distance is called a power




pattern. A graph of the spatial variation of the electric or magnetic field along

a constant distance path, is called a field pattern.

An isotropic antenna is defined as "a hypothetical lossless antenna having

equal radiation in all directions." Clearly, an isotropic antenna is a fictitious

entity, since even the simplest antenna has some degree of directivity.

Although hypothetical and not physically realizable, an isotropic radiator is

taken as a reference for expressing the directional properties of actual

antennas. A typical linear isotropic dipole antenna is as shown

The linear dipole is an example of an omnidirectional antenna -- i.e. an

antenna having a radiation pattern which is nondirectional in a plane. As the

figure below indicates, a linear dipole has uniform power flow in any plane

perpendicular to the axis of the dipole and the maximum power flow is in the

equatorial plane.




To know more about dipole antennas and their radiation patterns, refer

Appendix B

Yagi-uda antenna: A directional antenna is one "having the property of

radiating or receiving electromagnetic waves more effectively in some

directions than in others." The term is usually applied to an antenna whose

maximum directivity is significantly greater than that of a linear dipole

antenna. One important class of directional antennas is from linear arrays of

linear dipoles as illustrated below. The most famous and ubiquitous member of

this class is the so called Uda-Yagi antenna shown below the array antenna.




There are three kinds of elements (or rods) mounted on a longitudinal

connecting bar or rod. It doesn't matter if this connecting rod conducts, as it is

orientated at right angles to the currents in the elements, and to the radiating

electric fields; it supports little or no current, and does not contribute to the

radiation. It does not matter what it is made of other than that it should have

good structural properties. If it is made of conducting metal as are the

elements, it can be connected electrically to the directors and to the reflector

(but not to the driven element) without disturbing any of the properties of the

antenna. The three types of element are termed the driving element, the

reflector(s) and the director(s).

Only the driving element is connected directly to the feeder; the

other elements couple to the transmitter power through the local

electromagnetic fields which induce currents in them. The driving element is

often a folded dipole, which by itself would have a driving point impedance of

about 300 ohms to the feeder; but this is reduced by the shunting effect of the

other elements, so a typical Yagi-Uda has driving point impedance in the range

20-90 ohms.




The maximum gain of a Yagi-Uda is limited to an amount

given approximately by the gain of a dipole (1.66 numerical) times the total

number of elements. In an end-fire array of N elements the gain is proportional

to N. Consider N isotropic sources, all phased such that the field contributions

in the end-fire direction from each element all add up in phase in the far field.

The field strength (E-field or H-field) of the sum of the phasors will be N times

the field from a single element, so the radiated power density, which is

proportional to the square of the fields, will be N^2 times larger. However, the

total POWER delivered to the N elements will be N times larger than that

delivered to a single element, so the power gain in the far field is (N^2)/N = N .

To broadband a Yagi-Uda, sometimes the individual elements are split into two

in an approximation to a primitive "biconical antenna". An example is shown

here; this shows part of a UHF television receive Yagi-Uda to cover a fractional

bandwidth of around 30 percent. It is vertically polarized.

.

The H-plane radiation pattern of the yagi-uda antenna for 4 elements is as shown:




The E-plane pattern can be obtained by point wise-multiplying this "array

pattern" by the "element pattern", which in this case is a simple half-wave-

dipole E-plane pattern.

To know about the working of Yagi-uda antennas, refer the tutorials on the

website http://www.flickr.com. Courtesy: D.Jefferies email 13th October

2004. You can also access various antenna pictures at

http://www.flickr.com/photos/rabinal/sets/710532/

Antenna arrays: Antenna arrays are formed by assembling identical (in most

cases) radiating elements such as dipoles for example. In the diagram below is

shown an antenna array with its elements along the z axis such that the

distance between each two successive elements is equal to d.




Antenna arrays are characterized by their array factor which is given by the

formula

where

N the number of elements making the array, k = 2Pi / wavelength , is the

polar angle and is the difference of phase between any two successive

elements forming the array.

The examples below explores how each of the parameters N, d and affect

the radiating pattern of the array.




End-fire array: Set N = 10, d = 0.25 (this is 0.25*wavelength) and = kd =

2*Pi*0.25 = 0.5Pi. The main beam (maximum radiation) is directed toward =

180 degrees along the z axis which is also the axis of the array. If you change

to -0.5Pi, the main beam is directed toward 0 degrees along the z axis. For

these values of we have end-fire radiation.

Broad side array: Set N = 10, d = 0.25 (this 0.25*wavelength) and = 0 . The

main beam (maximum radiation) is directed toward = 90 degrees normal to

the z axis which is also the axis of the array. For this value of we have

broadside radiation.

Rod or Monopole Antennas

Rod antennas are the counterparts of loop antennas. They are designed to

respond to electric fields from 30 Hz to 50 MHz. Since rod antennas are so

small compared to the wavelengths (at 30 Hz, the wavelength is 10,000 km),

amplifiers within the antennas are sometimes necessary for small signals. Rod

antennas are typically required for the GR-1089-core standard for network

telecommunications equipment (where radiated emission and immunity tests

for electrical field at 10 kHz are required).




Biconical Antennas Biconical antennas typically cover the frequency range from 20 MHz to 300

MHz. All wire-cage biconical antennas on the market have similar size and

shape (approximately 1.36 m wide). This is because they are based on MIL-STD-

461 specifications from the 1960s, which has become the de facto standard.

Due to their small electrical size below 50 MHz, they have very high input

impedance, resulting in high VSWR.

Balun performance is crucial for biconical antennas. Common mode

current can be easily induced on the feed cable (common mode impedance is

no longer large compared to the input impedance of the antenna). Ferrite

beads are often used on the feed cable to suppress the common mode. In

addition, feed cables should be extended out a meter or more horizontally

before the cable is dropped vertically to the ground to reduce possible

interaction between the cable and the antenna.

Log Periodic Dipole Arrays Log periodic dipole arrays (LPDA) typically cover the frequency range of 80 MHz

to several gigahertz. The phase center of a LPDA moves from the back of the

antenna boom to the front as the frequency is increased. In ANSI or CISPR

standards, emissions measurements are performed from the center of the log

antenna boom. For immunity tests, EN61000-4-3 requires measurements be

made from the tip of the log antenna. The gain of a LPDA is typically around 5

dBi, which provides a good compromise between beamwidth and sensitivity.




For more information on Antenna related definitions and their measurements, please refer http://www.conformity.com/0509/0509emc.html (Article EMC Antenna Fundamentals by Zhong Chen )




APPENDIX B

Dipole radiation patterns

Calculation of array patterns

The radiated field strength at a certain point in space, assumed to be in the far

field, is calculated by adding the contributions of each element to the total

radiated fields. The field strengths fall off as 1/r where r is the distance from

the isotrope to the field point. We must take into account any phase angle of

the isotrope excitation, and also the phase delay which is due to the time it

takes the signal to get from the source to the field point. This phase delay is

expressed as 2 Pi radians times (r/lambda) where lambda is the free space

wavelength of the radiation. Contours of equal field strength may be

interpreted as an amplitude polar radiation pattern. Contours of the squared

modulus of the field strength may be interpreted as a power polar radiation

pattern.

Here is an example of a power polar radiation pattern for two

isotropes spaced 1/4 wavelength apart along the x axis (horizontally on your

screen or paper) and fed with equal amplitudes and phases......-->

Two Isotropes 1/4 Wavelength Apart Fed In Phase




If we increase the spacing to 1/2 wavelength, but still keep the excitation in

phase and equal amplitudes, we see deep nulls developing.......-->

Two Isotropes 1/2 Wavelength Apart Fed In Phase




If we restore the original 1/4 wavelength spacing and feed the isotropes in

phase quadrature (that is, there is Pi/2 phase shift between the excitations),

we see a single lobe develop. This pattern is close to a Cardioid......-->

(To make the lobe face the other direction we would have to reverse the

relative phase, and feed the second isotrope at -Pi/2 phase angle.)

Two Isotropes 1/4 Wavelength Apart 90 Degrees Phase Shift

Returning now to feeding the two isotropes in phase, as we increase the

spacing we see more sub-lobes or sidelobes develop. Here is a picture for

spacing of a whole wavelength.




Two Isotropes 1 Wavelength Apart, In Phase

And if we increase the spacing to six whole wavelengths, there are large

numbers of lobes developing.

This is a method used to make sharp beams for radio telescopes using "Very

Long Baseline Interferometry". In this method two elements are spaced

thousands of kilometres apart, which makes the individual lobes very narrow

indeed.




Two Isotropes 6 Wavelengths Apart In Phase

If we now take two isotropes spaced by a half a wavelength and feed the

elements in antiphase (Pi phase difference) we see the pattern with horizontal

lobes rather than vertical lobes. This radiation pattern is similar to that of a

vertical dipole, which may roughly be regarded as a "doublet" consisting of two

isotropes fed in antiphase. The shape of the radiation pattern is not very

dependent on the separation.




Two Isotropes 1/2 Wavelength Apart Antiphase

Now we turn to arrays of four elements, just to illustrate the ideas further.

Equally excited (same amplitudes and phases) and spaced along the x axis at

intervals of 1/4 wavelength, we see.

Four Isotropes Spaced 1/4 Wavelength in Phase




and again, if we increase the spacing to 1/2 wavelength we get more sidelobes.

Four Isotropes Spaced 1/2 Wavelength, In Phase.

The pictures were obtained from D.Jefferies email 25th March 2003.




APPENDIXC




The ¸FS300 is a highly accurate spectrum analyzer with a frequency range of 9

kHz to 3 GHz. Owing to its modern, digital frequency processing technique; it

offers high measurement quality at a favorable price. The ¸FS315 is

additionally equipped with a built-in tracking generator from 9 kHz to 3 GHz

for scalar network analysis; the tracking generator is also suitable for

generating fixed-frequency signals. Plus, the ¸FS315 includes various detectors

for evaluating measurement results and allows electric field strength

measurements taking into account the antenna factors. The features of the

network analyzer are briefly mentioned below:

Frequency range: 9 kHz to 3 GHz

Resolution bandwidths: 200 Hz to 1 MHz

Dynamic range: >137 dB

Noise level: typ. -120 dBm (300 Hz RBW)

Level uncertainty: <1.5 dB

Frequency counter with 1 Hz resolution

Maximum input level 33 dBm

USB interface

For details on these features and explanation on other features visit

www.rohde-shcwarz.com




How to operate??

A brief overview of the buttons present on the Spectrum analyzer is as shown:







Application Ranges: The FS300/FS315 is a versatile spectrum analyzer for

comprehensive measurements in laboratory, service and production. Some of

the typical applications are as listed:

Measurement of RF spectrum (level and frequency)

Radiomonitoring remote-controlled via USB

Time domain measurements

Measurement of radiated interference (EMC)

Scalar network analysis

The spectrum analyzer also comes with a powerful software package for

remote control from a PC which makes generation of test reports on PC

possible. The software package also enhances the functions of the spectrum

analyzer. Detailed description of the applications can be found in the data

sheet of FS300/FS315 Spectrum analyzer at www.rohde-schwarz.com

Other features:

High-quality measurement characteristics The RF characteristics of the ¸FS300/FS315 are setting new standards in the

lower price class. Since the displayed average noise level is typically –115 dBm

(300 Hz), even weak signals can be reliably detected. Owing to the wide

dynamic range, this is also possible when strong carrier signals are present. The

points in the traces are displayed with an accuracy unrivalled in this price

class. This is an essential prerequisite for any measurement task.

Resolution bandwidths from 200 Hz to 1 MHz With 16 digitally implemented resolution bandwidths from 200 Hz to 1 MHz, the

FS300 can be optimally adapted to the measurement task at hand. The FS315

additionally covers the range up to 20 MHz. Wide resolution bandwidths for

overall measurements ensure short sweep times, whereas narrow bandwidths




are ideal for high frequency resolution and a low noise level. The FS300 and

FS315 fulfill every requirement in between.

Scalar network analysis The ¸FS315 with built-in tracking generator is the perfect solution for cost

efficient testing of the transmission behavior of filters, cables, amplifiers and

so forth. Equipped with an additional VSWR bridge, reflection measurements

can also be performed. Entering any frequency offset between 0 Hz and 3 GHz

allows measurements on frequency-converting DUTs. With simple applications,

the tracking generator can be used as a signal generator with a permanently

set frequency.

Locating EMC weak spots The ¸HZ-15 near-field probes are diagnostic tools used for locating EMC weak

spots on printed boards, integrated circuits, cables, shielding and other trouble

spots. The Near-Field Probe Set ¸HZ-15 is adequate for emission measurements

from 30 MHz to 3 GHz. The Preamplifier ¸HZ-16 up to 3 GHz, with

approximately 20 dB gain and a noise figure of 4.5 dB, increases sensitivity for

measurements. In combination with the FS300/FS315, the preamplifier and

near-field probe set are a cost-effective means of analyzing and locating

sources of interference during development.

For discussion on the rear panel and the slots present therein, visit www.rohde-

schwarz.com




APPENDIX D




FEATURES & BENEFITS

Bandwidths of 15 GHz (TDS6154C), 12 GHz (TDS6124C), 8 GHz

(TDS6804B), and 6 GHz (TDS6604B)

Risetimes to 19 ps 20-80% (28 ps 10-90%) on TDS6154C typical risetime,

with channel-matched, user-selectable DSP

40 GS/s real-time sample rate on two channels*1, 20 GS/s real-time

sample rate on all four channels with 500 fs/sample interpolated points

Up to 64 Megasamples on two channels*1, up to 32 Megasamples record

length on all four channels with MultiView Zoom™ function for quick

navigation

MyScope® Custom Control Windows Enhance Productivity

Right Mouse Click Menus for Exceptional Efficiency

Pinpoint™ triggering provides the most flexible and highest performance

triggering, with over 1400 combinations to address virtually any

triggering situation

Serial pattern triggering up to 3.125 Gb/s with 8b/10b protocol

triggering

Serial data analysis and compliance at rates of 6.25 Gb/s and above

OpenChoice® software with Microsoft Windows XP OS delivers built-in

networking and analysis

Technology specific software solutions provide built-in domain expertise

for serial data, jitter, ethernet, DVI, USB2.0, communications, and

power measurements

System includes: Dual processor system (2.8 GHz Pentium 4 and 583 MHz

PowerPC), high resolution XGA display, front panel CD-R/W, front panel

USB2.0 port, and 1000BaseT network connection

APPLICATIONS

Signal Integrity, Jitter, and Timing Analysis




Validation, Debug, Characterization, and Compliance of Next Generation

Digital Designs

Computer, Datacom, Storage Area Network Equipment Designs and High-

speed Backplanes

High Energy Physics measurements and Data Acquisition

For detailed explanation of features and their benefits, go to

http://www.tek.com/site/ps/0,,55-14873-INTRO_EN,00.html.

Some important features:

Uncompromised Acquisition

You won’t need to need to trade-off bandwidth, record length, and sample

rate for your serial data measurement and analysis needs. The TDS6000C DSOs

provides acquisition architecture with 40 GS/s maximum sample rate and

64 Megasamples record length on two channels (20 GS/s and 32 Megasamples

on each of the four channels simultaneously), for the acquisition power you

need. They provide the ultimate combination of bandwidth, sample rate, and

record length for the fastest signals.

MyScope Custom Control Windows

MyScope control windows allow you to build your own control windows with

only the controls, features, and capabilities that you care about and are

important in your job. You can create your own personalized “toolbox” of

oscilloscope features. MyScope control windows are easily created in a matter

of minutes using a simple, visual, drag and drop process. Once created, these

customized windows are easily accessed through a dedicated MyScope button

and menu selection on the oscilloscope button/menu bar, just like any other

control window. Since the control windows are stored as files on the hard

drive, they can easily be transferred to other TDS5000B or TDS/CSA7000B Series




oscilloscopes, or they can even be e-mailed to a co-worker around the world

when the need arises.

Right Clicks

Right mouse click menus make simple things as they should be – simple.

Virtually all objects on the oscilloscope display have right click menus

associated with them that include all the appropriate actions or features

relative to those objects. There are also right click menus for regions of the

display in addition to just objects.

Pinpoint Triggering

Pinpoint trigger system provides the most advanced, highest performance

triggering available. The ability to trigger an oscilloscope on events of interest

is paramount in high speed debug and validation. Whether you're trying to find

a system error, or need to isolate a section of a complex signal for further

analysis, Tektronix’ Pinpoint triggering provides the solution. The Pinpoint

trigger system uses Silicon Germanium (SiGe) technology to provide trigger

sensitivity of up to 9 GHz (TDS6000C models), and allows selection of all trigger

types on both A and B trigger circuits. An example of triggering using Pinpoint

triggering is as shown:




Front Panel

Fast Edge Output - Front panel SMA connector provides fast edge signal.

Amplitude 440 mV pk-pk, ±20% in a 50 Ω load; VOH +0.3 V, VOL – 0.14 V;

frequency 1 kHz ±5%, 200 ps typical rise time.

Recovered Clock - SMA connector, ≤1.25 Gb/s, Output swing ≥130 mV pk-pk

into 50 Ω. Requires Opt. SM or Opt. ST to enable.

Recovered Data - SMA connector, ≤1.25 Gb/s, Output swing of 1010 repeating

pattern 200 mV into 50 Ω. Requires Opt. SM or Opt. ST to enable.

DC Probe Calibration Output - BNC connector, ±10 V DC for DC probe

calibration. (Signal available only during probe calibration.)

AUX Trigger Output - BNC connector, provides a TTL-compatible, polarity

switchable pulse when the oscilloscope triggers.




USB2.0 Port - One in front. Allows connection or disconnection of USB

keyboard, mouse, or storage device while oscilloscope is on.

Rear Panel

External Time Base Reference In - BNC connector; allows time base system to

phase-lock to external 10 MHz reference.

Time Base Reference Out - BNC connector; provides TTL-compatible output of

internal 10 MHz reference oscillator.

Aux Trigger Input - BNC, see Ext Trigger specification.

Parallel Port - IEEE 1284, DB-25 connector.

Audio Ports - Miniature phone jacks for stereo microphone input and stereo

line output.

USB2.0 Ports - Four in back. Allows connection or disconnection of USB

keyboard, mouse, or storage device while oscilloscope power is on.

Keyboard Port - PS-2 compatible.

Mouse Port - PS-2 compatible.

LAN Port - RJ-45 connector, supports 10BaseT, 100BaseT, and 1000BaseT.

Serial Port - DB-9 COM1 port.

Windows Video Port - 15 pin D-Sub connector on the rear panel; connect a

second monitor to use dual-monitor display mode allowing analysis results and

plots to be viewed along with the oscilloscope display. Video is DDC2B

compliant.

GPIB Port - IEEE 488.2 standard.




Scope XGA Video Port - 15 pin D-Sub connector on the rear panel, video is IBM

XGA compatible. Connect to show the oscilloscope display, including live

waveforms on an external monitor or projector. The primary Windows desktop

can also be displayed on an external monitor using this port.

For more information on the specifications and characteristics of the DSO, visit

http://www.tek.com/site/ps/0,,55-14873-SPECS_EN,00.html



Documents

Wireless Lab Manual 2008