MODERN ANTENNA HANDBOOK
Transcript of 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
Antennas & RF Devices Lab.
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
Antennas & RF Devices Lab.
• 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.
1.2 RADIATION PATTERN
• 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
Antennas & RF Devices Lab.
1.2 RADIATION PATTERN
• 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
Antennas & RF Devices Lab.
• 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
1.2 RADIATION PATTERN
d
Ideal isotropic source
free-space
Hanyang University
7
Antennas & RF Devices Lab.
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
Antennas & RF Devices Lab.
1.2.1 Radiation Pattern Lobes
d
Ideal isotropic source
free-space
major lobe
minor lobe
back lobe
Hanyang University
9
Antennas & RF Devices Lab.
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
Antennas & RF Devices Lab.
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
Antennas & RF Devices Lab.
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
Antennas & RF Devices Lab.
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
Hanyang University
13
Antennas & RF Devices Lab.
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
Antennas & RF Devices Lab.
1.2.5 Radian and Steradian
plane angle
solide angle
Hanyang University
15
Antennas & RF Devices Lab.
• 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.
1.3 RADIATION POWER DENSITY
Hanyang University
16
Antennas & RF Devices Lab.
1.3 RADIATION POWER DENSITY
• 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
Antennas & RF Devices Lab.
• 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.
1.4 RADIATION INTENSITY
Hanyang University
18
Antennas & RF Devices Lab.
1.4 RADIATION INTENSITY
• 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
Antennas & RF Devices Lab.
Thank you for your attention