MODERN ANTENNA HANDBOOK

Hanyang University

1

Antennas & RF Devices Lab.

MODERN ANTENNA

HANDBOOK

by CONSTANTINE A.BALANIS

chap 1.1 – 1.5

Bang Ji Hun

Hanyang University

2

Contents

1.1 INTRODUCTION

1.2 RADIATION PATTERN

- 1.2.1 Radiation Pattern Lobes

- 1.2.2 Isotropic, Directional, and Omnidirectional Patterns

- 1.2.3 Principal Patterns

- 1.2.4 Field Regions

- 1.2.5 Radian and Steradian

1.3 RADIATION POWER DENSITY

1.4 RADIATION INTENSITY

1.5 BEAMWIDTH

Hanyang University

3


1.1 INTRODUCTION

• This part introduces the fundamental parameters and definitions of antenna.

- To describe the performance of an antenna, definitions of various

parameters are necessary.

- Parameters : Radiation pattern, Radiation power density, Radiation intensity,

Beamwidth

Hanyang University

4


• Radiation pattern or Antenna pattern

: A mathematical function or a graphical representation of the radiation

properties of the antenna as a function of space coordinates.


• In most case, the radiation pattern is

determined in the far-field region and is

represented as a function of the directional

coordinates.

• Radiation properties include power flux

density, radiation intensity, field strength,

directivity, phase, or polarization.

• The radiation property of most concern is the

two- or three-dimensional spatial distribution

of radiated energy as a function of the

observer’s position along a path or surface

of constant radius.

observer’s

position

constant

radius

Hanyang University

5



• Amplitude Field pattern

: A trace of the received electric (magnetic) field at a constant radius

• Amplitude Power pattern

: A graph of the spatial variation of the power density along a constant radius

• Often this patterns are normalized with respect to their maximum value.

• Power pattern is usually plotted on a logarithmic scale or more commonly in

decibels (dB).

Hanyang University

6


• To find the points where the pattern achieves its half-power (−3 dB points),

relative to the maximum value of the pattern, you set the value of (a) the field

pattern at 0.707 value of its maximum. (b) the power pattern (in a linear scale)

at its 0.5 value of its maximum, as shown in Figure 1.2b; and (c) the power

pattern (in dB) at −3 dB value of its maximum.

• To demonstrate this three radiation pattern, the two-dimensional normalized

field pattern (plotted in linear scale), power pattern (plotted in linear scale),

and power pattern (plotted on a logarithmic dB scale) of a 10-element linear

antenna array of isotropic sources, with a spacing of d =0.25λ between the

elements, are shown in Figure 1.2. 1


d

Ideal isotropic source

free-space

Hanyang University

7


1.2.1 Radiation Pattern Lobes

• Radiation Pattern Lobes

: Various parts of a radiation pattern are referred to as lobes, which may be

subclassified into major or main, minor, side, and back lobes.

usually represent radiation in undesirable directions.

should be minimized

(for careful design, side lobe ratio(level) < -30 dB)

** Especially, In most radar system, low side lobe ratios

are very important

Figure 1.3 (a) Radiation lobes and beamwidths of an antenna pattern. (b) Linear plot of

Power pattern and its associated lobes and beamwidths.

Hanyang University

8


1.2.1 Radiation Pattern Lobes

d

Ideal isotropic source

free-space

major lobe

minor lobe

back lobe

Hanyang University

9


1.2.2 Isotropic, Directional, and Omnidirectional Patterns

1) Isotropic pattern

• A hypothetical lossless antenna having equal radiation in all directions.

• Although it is ideal and not physically realizable, it is often taken as a

reference for expressing the directive properties of actual antennas. Ex) dBi

2) Directional Pattern

• A directional antenna is one having the property of radiating or receiving

electro-magnetic waves more effectively in some directions than in others.

3) Omnidirectional Pattern

• having an essentially non-directional

pattern in a given plane (in this case in

azimuth) and a directional pattern in any

orthogonal plane.

Hanyang University

10


1.2.3 Principal Patterns

• For a linearly polarized antenna,

performance is often described in

terms of its principal E- and H-plane

patterns.

- E-plane : The plane containing the

electric-field vector and the direct-

ion of maximum radiation.

- H-plane : The plane containing the

magnetic-field vector and the direct-

ion of maximum radiation

Hanyang University

11


that region of the field

of an antenna where

the angular field distri-

bution independent of

the distance from antenna

that region of the field of an

antenna between the reactive

near-field region and far-field

region wherein radiation field

Predominates

The portion of the near field

region immediately surrounding

the antenna wherein the reactive

field predominates

1.2.4 Field Regions

• The space surrounding an antenna is usually subdivided into three regions.

Antenna

1

2

3

no abrupt changes

infinity

1

2

3

near field

far field

Hanyang University

12


1.2.4 Field Regions

spread out, nearly uniform,

with slight variations

well formed begins to smooth

and form lobes

pattern major lobe major lobe

Parabolic reflector

E field pattern of

Parabolic Reflector Antenna

Reference : Integrated engineering software

https://www.integratedsoft.com/applications/rf-

microwave-antennas/reflector-antennas

https://www.integratedsoft.com/applications/rf-microwave-antennas/reflector-antennas







Hanyang University

13


1.2.4 Field Regions

increase far field distance

from the antenna

first null -25dB

criterion of minimum distance of far-field

Hanyang University

14


1.2.5 Radian and Steradian

plane angle

solide angle

Hanyang University

15


• Since the Poynting vector is a power density, the total power crossing a

closed surface can be obtained by integrating the normal component of

the Poynting vector over the entire surface.

• Power and energy are associated with electromagnetic fields.

• Poynting vector is quantity describing the power associated with an elec-

tromagnetic wave.


Hanyang University

16



• The time-average Poynting vector (average power density) can be written.

• Based on the definition of Eq. (1.5), the average power radiated by an antenna

(radiated power) can be written.

(1.5)

Hanyang University

17


• Radiation intensity

: the power radiated from an antenna per unit solid angle

• The radiation intensity is a far-field parameter, and it can be obtained by simply

multiplying the radiation density by the square of the distance.

• The radiation intensity is also related to the far-zone electric field of an antenna.


Hanyang University

18



• The radical electric-field component (Er ) is assumed, if present, to be small

in the far zone.

• Thus the power pattern is also a measure of the radiation intensity.

• The total power is obtained by integrating the radiation intensity, over the entire

solid angle of 4π.

where d=element of solid angle=sin θ dθ dφ.

Hanyang University

19

1.5 BEAMWIDTH

• The beamwidth of a pattern is defined as the angular separation between two

identical points on opposite sides of the pattern maximum.

half-power beamwidth (HPBW )

first-null beamwidth (FNBW )

FNBW/2 ≈ HPBW

trade-off between beamwidth and the side lobe level

distinguish between two sources

Hanyang University

20


Thank you for your attention

Documents

MODERN ANTENNA HANDBOOK