Waveguide presentation

University of Engineering & Technology PeshawarDepartment of Telecommunication Engineering ,Mardan Campus1 |

04-10-2012 First FYP Presentation,Batch-08



Wave Guides

Syed Muhammad Umar Muhammad Fawad khan

Reg.# 11MDTLC0510 Reg.#11MDTLC0483



The first waveguide was proposed by J. J. Thomson in 1893

and experimentally verified by Oliver Lodge

In 1894 the mathematical analysis of the propagating modes

within a hollow metal cylinder was first performed by Lord

Rayleigh in 1897. (McLachan, 1947)

History



Dow-Key, ANRITSU Company are the manufacturer

of Waveguides as well as are the pioneers of making

waveguides and their components in the world.

Companies:



A hollow conductive metal pipe used to carry high frequency radio

waves, particularly microwave”(A type of a transmission line)[1]

Form of RF feeder used for microwave applications[2]

A waveguide is a device that confines electromagnetic energy and

channels it from one point to another[3]

System of material that is designed to confine electromagnetic waves in

a direction defined by its physical boundaries[4]

What is a Waveguide?



Only carry or propagate signals above a certain frequency, known

as the cut-off frequency.

Waveguides



Waveguide

TYPES



Parallel Plate wave guide

Rectangular waveguide

Circular waveguide

Dielectric waveguide

a). Optical waveguide

b). Slab waveguide

Types



Parallel metallic plates

Dielectric permittivity

Width in y-direction

Height in x-direcion

Length in z-direction

Parallel plate waveguide



This is the most commonly used form of waveguide and has a

rectangular cross section.

Rectangular waveguide



Circular waveguide is less common than rectangular waveguide.

They have many similarities in their basic approach, although

signals often use a different mode of propagation.

Circular waveguide



This form of waveguide is used on printed circuit boards as a

transmission line for microwave signals. It typically consists of

a line of a given thickness above an earth plane. Its thickness

defines the impedance.

Circuit board stripline



Shapes



• Optical wave guide

• Optical frequencies

• Core dielectric

• Refractive index “n-one” (r<a)

• Cladding dielectric constant

• Refractive index “n-two” (a<r<b)

Dielectric Waveguide



• Slab wave guide.

• Optical frequencies

• Symmetric

• Slab region (n-one)

• Refractive index n-one & n-2

• n-2<n-one

Dielectric wave guide Conti…



• Maxwell’s equations can be solved with suitable boundary

conditions at wall of wave guide. In order to determine

electromagnetic field configuration in wave guide.

• After simplification we achieve field configurations of different

number.

• Each configuration is called mode.

• Wave guide have different types of modes.

Electromagnetic Field configuration



• E (Electric field )

• H(Magnetic feild)

• Ex Hx (x-axis)

• Ey Hy (y-axis)

• Ez Hz (z-axis)

Components Of EM wave

O

X

Y

Z

Ex , Hx

Ez, Hz

E y,H y



1. Transverse Electro Magnetic (TEM) wave:

Electric and magnetic field components are transverse, or

perpendicular, to the direction of propagation. Here both electric and

magnetic fields are directed components. (i.e.) E z = 0 and Hz = 0.

2. Transverse Electric (TE) wave:

Here only the electric field is purely transverse to the direction of

propagation and the magnetic field is not purely transverse. (i.e.)

E z = 0, Hz ≠ 0

Possible modes of wave Guide



3.Transverse Magnetic (TM) wave:

Here only magnetic field is transverse to the direction of propagation

and the electric field is not purely transverse. (i.e.) E z ≠ 0, Hz = 0.

Modes of waveguide Conti…



. Hybrid (HE) wave:

Here neither electric nor magnetic fields are purely transverse to the

direction of propagation. (i.e.) E z ≠ 0, Hz ≠ 0.

Modes of waveguide Conti…



• TEM mode of operation

• Parallel plate waveguide

• Creation of Electric field at certain voltage

• Electric field vertical to plates

• Current flow in z-direction

• Magnetic field in y-direction

• The interior fields comprise a plane

Electromagnetic wave which propagate in z-direction.

• Both field are in transverse plane

Basic Operation



Meaning both the electric and magnetic field components were

transverse, or perpendicular, to the direction of propagation.

TEM Mode Conti…



TE & TM Operation



Dimensions of the waveguide which

determines the operating frequency range:



1. The size of the waveguide determines its operating frequency range.

2. The frequency of operation is determined by the dimension ‘a’.

3. This dimension is usually made equal to one – half the wavelength at the

lowest frequency of operation, this frequency is known as the waveguide

cutoff frequency.

4. At the cutoff frequency and below, the waveguide will not transmit

energy. At frequencies above the cutoff frequency, the waveguide will

propagate energy.

Dimensions of the waveguide which

determines the operating frequency range:



• High frequency

• Medium Frequency

• Low Frequency

• Cut off Frequency

Wave paths in a waveguide at various

frequenciesAngle of incidence(A) Angle of reflection (B)

(A = B)



• When a probe launches energy into the waveguide, the electromagnetic

fields bounce off the side walls of the waveguide as shown in the above

diagram.

• The angles of incidence and reflection depend upon the operating

frequency. At high frequencies, the angles are large and therefore, the

path between the opposite walls is relatively long as shown in fig.

Wave propagation



• At lower frequency, the angles decrease and the path

between the sides shortens.

• When the operating frequency reaches the cutoff frequency

of the waveguide, the signal simply bounces back and forth

directly between the side walls of the waveguide and has no

forward motion.

• At cut off frequency and below, no energy will propagate.

Wave propagation Conti…



• The exact size of the wave guide is selected based on the

desired operating frequency.

• The size of the waveguide is chosen so that its rectangular

width is greater than one – half the wavelength but less than

the one wavelength at the operating frequency.

• This gives a cutoff frequency that is below the operating

frequency, thereby ensuring that the signal will be propagated

down the line.

CUTT OFF Frequency



• The general symbol of representation will be TE m, n or TM m, n

where the subscript m indicates the number of half wave variations

of the electric field intensity along the b ( wide) dimension of the

waveguide.

• The second subscript n indicates the number of half wave

variations of the electric field in the a (narrow) dimension of the

guide.

• The TE 1, 0 mode has the longest operating wavelength and is

designated as the dominant mode. It is the mode for the lowest

frequency that can be propagated in a waveguide.

Representation of modes



Expression for cut off wavelength

22

2

b

n

a

mc

For a standard rectangular waveguide, the cutoff wavelength is given

by,

Where a and b are measured in centimeters



A Hollow metallic tube of uniform circular cross section for

transmitting electromagnetic waves by successive reflections from

the inner walls of the tube is called Circular waveguide.

Circular waveguide



• The circular waveguide is used in many special applications in

microwave techniques.

• It has the advantage of greater power – handling capacity and

lower attenuation for a given cutoff wavelength. However, the

disadvantage of somewhat greater size and weight.

• The polarization of the transmitted wave can be altered due to the

minor irregularities of the wall surface of the circular guide,

whereas the rectangular wave guide the polarization is fixed

Circular Waveguide Conti…





• H-type T Junction: The junction acts as a power divider, the signal entering into the

1st port is equally divided among the two ports with the same phase.

• E-Type T Junction: It also acts as a power divider, the signal entering into the 1st port

is equally distributed between the two ports with opposite phase.

Waveguide junction types


Waveguide Tees

Waveguide E-type junction Waveguide H-type junction



The device magic Tee is a-combination of the E and H plane Tee. Arm 3, the H-arm

forms an H plane Tee and arm 4, the E-arm forms an E plane Tee in combination with

arm 1 and 2 a side or collinear arms. If power is fed into arm 3 (H-arm) the electric field

divides equally between arm 1 and 2 in the same phase, and no electrical field exists in

arm 4. If power is fed in arm 4 (E-arm), it divides equally into arm 1 and 2 but out of

phase with no power to arm 3. Further, if the power is fed from arm 1 and 2, it is added

in arm 3 (H-arm), and it is subtracted in E-arm, i.e. arm 4.

Magic Tee

3

4

1

2



Magic T waveguide junction

Magic T waveguide Junction

signal directions

Magic T waveguide junction




• Waveguide E bend

• Waveguide H bend

• Waveguide sharp E bend

• Waveguide sharp H bend

Waveguide bends



• Waveguide E bend

This form of waveguide bend is called an E bend because it distorts

or changes the electric field to enable the waveguide to be bent in

the required direction.

Waveguide E bend

To prevent reflections this waveguide bend must have a radius

greater than two wavelengths

E-bend

Radius greater than 2

wavelengths



• Waveguide H bend

This form of waveguide bend is very similar to the E bend, except that it

distorts the H or magnetic field. It creates the bend around the thinner side

of the waveguide.

wave guide H bend

As with the E bend, this form of waveguide bend must also have a radius

greater than 2 wavelengths to prevent undue reflections and disturbance of

the field.

H-bend

Radius greater

than 2

wavelengths



In some circumstances a much shorter or sharper bend may be

required. This can be accomplished in a slightly different manner.

The techniques is to use a 45° bend in the waveguide. Effectively

the signal is reflected, and using a 45° surface the reflections

occur in such a way that the fields are left undisturbed, although

the phase is inverted and in some applications this may need

accounting for or correcting.

Waveguide sharp E bend

Waveguide sharp E bend



Waveguide sharp H bend

This form of waveguide bend is the same as the sharp E bend,

except that the waveguide bend affects the H field rather than the

E field.

Sharp H bend



Waveguide is an indispensable technology for all industries

that make use of transmitting systems.

Waveguides are used to transfer electromagnetic power

efficiently from one point in space to another.

High power-handling capacity

Lower attenuation for a given cut-off wavelength

The magic-T can be used as a power combiner or divider.

Applications & Uses



Rotating joints in radars to connect the horn antenna feeding

a parabolic reflector (which must rotate for tracking)

TE01 mode suitable for long distance waveguide

transmission above 10 GHz.

Short and medium distance broad band communication

(could replace / share coaxial and microwave links)

Applications of circular waveguide



[1,2,4]Waveguides CALDERON, DE GUZMAN,QUITEVIS source slide share.

• [3] Prof. David R. Jackson Dept. of ECE Waveguides Part 1: General Theory

References:





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Waveguide presentation