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Electronic Warfare and Radar Systems Engineering Handbook
- Radiation Patterns -

[Go to TOC]

RADIATION PATTERNS



The radiation pattern is a graphical depiction of the relative field strength transmitted from or received by the antenna. Antenna radiation patterns are taken at one frequency, one polarization, and one plane cut. The patterns are usually presented in polar or rectilinear form with a dB strength scale. Patterns are normalized to the maximum graph value, 0 dB, and a directivity is given for the antenna. This means that if the side lobe level from the radiation pattern were down -13 dB, and the directivity of the antenna was 4 dB, then the sidelobe gain would be -9 dB.

Figures 1 to 14 on the pages following depict various antenna types and their associated characteristics. The patterns depicted are those which most closely match the purpose for which the given shape was intended. In other words, the radiation pattern can change dramatically depending upon frequency, and the wavelength to antenna characteristic length ratio. See section 3-4. Antennas are designed for a particular frequency. Usually the characteristic length is a multiple of λ/2 minus 2-15% depending on specific antenna characteristics.

Bandwidth-to-ratio table - RF CafeThe gain is assumed to mean directional gain of the antenna compared to an isotropic radiator transmitting to or receiving from all directions.

The half-power (-3 dB) beamwidth is a measure of the directivity of the antenna.

Polarization, which is the direction of the electric (not magnetic) field of an antenna is another important antenna characteristic. This may be a consideration for optimizing reception or jamming.

The bandwidth is a measure of how much the frequency can be varied while still obtaining an acceptable VSWR (2:1 or less) and minimizing losses in unwanted directions. See Glossary, Section 10.

A 2:1 VSWR corresponds to a 9.5dB (or 10%) return loss - see Section 6-2.

Two methods for computing antenna bandwidth are used:


Narrowband by %, RF Cafe - Bandwidth equation where FC = Center frequency


Broadband by ratio, RF Cafe - Bandwidth formula

An antenna is considered broadband if FU / FL > 2. The table at the right shows the equivalency of the two, however the shaded values are not normally used because of the aforementioned difference in broadband/narrowband.

Object that experiences a plane wave, the resonant mode is achieved when the dimension of the object is λ/2, where n is an integer - RF Cafe


For an object that experiences a plane wave, the resonant mode is achieved when the dimension of the object is λ/2, where n is an integer. Therefore, one can treat the apertures shown in the figure below as half wave length dipole antennas for receiving and reflecting signals. More details are contained in section 8-4.

The following lists antenna types by page number. The referenced page shows frequency limits, polarizations, etc.


Type  Page  Type  Page
4 arm conical spiral 3-3.6 log periodic  3-3.8 
alford loop 3-3.4  loop, circular  3-3.4
aperture synthesis  3-3.8 loop, alfred 3-3.4 
array 3-3.8  loop, square  3-3.4
axial mode helix  3-3.5 luneberg lens  3-3.9
biconical w/polarizer  3-3.6  microstrip patch 3-3.9
biconical 3-3.6 monopole 3-3.3  
cavity backed circuit fed slot 3-3.9 normal mode helix 3-3.5
cavity backed spiral 3-3.5  parabolic   3-3.7
circular loop 3-3.4  patch   3-3.9
conical spiral  3-3.5  reflector 3-3.9
corner reflector 3-3.9 rhombic   3-3.3
dipole array, linear 3-3.8 sinuous, dual polarized  3-3.6 
dipole  3-3.3  slot, guide fed  3-3.9
discone 3-3.4  slot, cavity backed  3-3.9
dual polarized sinuous 3-3.6  spiral, 4 arm conical 3-3.6 
guide fed slot 3-3.9 spiral, conical  3-3.5 
helix, normal mode 3-3.5 spiral, cavity backed   3-3.5
helix, axial mode 3-3.5 square loop  3-3.4 
horn 3-3.7 vee 3-3.3  
linear dipole array  3-3.8  yagi  3-3.8


Antenna Type  Radiation Pattern  Characteristics 
Monopole antenna type - RF Cafe Monopole antenna radiation pattern - RF Cafe MONOPOLE

Polarization: Linear
Vertical as shown

Typical Half-Power Beamwidth
45 deg x 360 deg

Typical Gain: 2-6 dB at best

Bandwidth: 10% or 1.1:1

Frequency Limit
Lower: None
Upper: None

Remarks: Polarization changes to horizontal if rotated to horizontal
λ/2 antenna type - RF Cafe λ/2 antenna radiation pattern - RF Cafe λ/2 DIPOLE

Polarization: Linear
Vertical as shown

Typical Half-Power Beamwidth
80 deg x 360 deg

Typical Gain: 2 dB

Bandwidth: 10% or 1.1:1

Frequency Limit
Lower: None
Upper: 8 GHz (practical limit)

Remarks: Pattern and lobing changes significantly with L/f. Used as a gain reference < 2 GHz.

Figure 1


 
Antenna Type  Radiation Pattern  Characteristics 
Vee antenna type - RF Cafe Vee antenna radiation pattern - RF Cafe VEE

Polarization: Linear
Vertical as shown

Typical Half-Power Beamwidth
60 deg x 60 deg

Typical Gain: 2 to 7 dB

Bandwidth: "Broadband"

Frequency Limit
Lower: 3 MHz
Upper: 500 MHz (practical limits)

Remarks: 24 kHz versions are known to exist. Terminations may be used to reduce backlobes.
Rhombic antenna type - RF Cafe Rhombic antenna radiation pattern - RF Cafe RHOMBIC

Polarization: Linear
Vertical as shown

Typical Half-Power Beamwidth
60 deg x 60 deg

Typical Gain: 3 dB

Bandwidth: "Broadband"

Frequency Limit
Lower: 3 MHz
Upper: 500 MHz

Remarks: Termination resistance used to reduce backlobes.

Figure 2


 
Antenna Type  Radiation Pattern  Characteristics 
Circular loop antenna type (small) - RF Cafe Circular loop antenna radiation pattern - RF Cafe CIRCULAR LOOP (small)

Polarization: Linear
Horizontal as shown

Typical Half-Power Beamwidth:
80 deg x 360 deg

Typical Gain: -2 to 2 dB

Bandwidth: 10% or 1.1:1

Frequency Limit:
Lower: 50 MHz
Upper: 1 GHz
Square loop antenna type (small) - RF Cafe Square loop antenna radiation pattern - RF Cafe SQUARE LOOP

Polarization: Linear
Horizontal as shown

Typical Half-Power Beamwidth:
100 deg x 360 deg

Typical Gain: 1-3 dB

Bandwidth: 10% or 1.1:1

Frequency Limit:
Lower: 50 MHz
Upper: 1 GHz

Figure 3


 
Antenna Type  Radiation Pattern  Characteristics 
Discone antenna type - RF Cafe Discone antenna radiation pattern - RF Cafe DISCONE

Polarization: Linear
Vertical as shown

Typical Half-Power Beamwidth:
20-80 deg x 360 deg

Typical Gain: 0-4 dB

Bandwidth: 100% or 3:1

Frequency Limit:
Lower: 30 MHz
Upper: 3 GHz
Alford Loop antenna type - RF Cafe Alford Loop antenna radiation pattern - RF Cafe ALFORD LOOP

Polarization: Linear
Horizontal as shown

Typical Half-Power Beamwidth:
80 deg x 360 deg

Typical Gain: -1 dB

Bandwidth: 67% or 2:1

Frequency Limit:
Lower: 100 MHz
Upper: 12 GHz

Figure 4


 
Antenna Type  Radiation Pattern  Characteristics 
Axial Mode Helix antenna type - RF Cafe Axial Mode Helix antenna radiation pattern - RF Cafe AXIAL MODE HELIX

Polarization: Circular
Left hand as shown

Typical Half-Power Beamwidth:
50 deg x 50 deg

Typical Gain: 10 dB

Bandwidth: 52% or 1.7:1

Frequency Limit
Lower: 100 MHz
Upper: 3 GHz

Remarks: Number of loops >3
Normal Mode Helix antenna type - RF Cafe Normal Mode Helix antenna radiation pattern - RF Cafe NORMAL MODE HELIX

Polarization:
Circular - with an ideal pitch to diameter ratio.

Typical Half-Power Beamwidth:
60 deg x 360 deg

Typical Gain: 0 dB

Bandwidth: 5% or 1.05:1

Frequency Limit
Lower: 100 MHz
Upper: 3 GHz

Figure 5


 
Antenna Type  Radiation Pattern  Characteristics 
Cavity Backed Spiral antenna type (flat helix) - RF Cafe Cavity Backed Spiral antenna radiation pattern - RF Cafe CAVITY BACKED SPIRAL
(Flat Helix)

Polarization: Circular
Left hand as shown

Typical Half-Power Beamwidth:
60 deg x 90 deg

Typical Gain: 2-4 dB

Bandwidth: 160% or 9:1

Frequency Limit:
Lower: 500 MHz
Upper: 18 GHz
Conical Spiral antenna type - RF Cafe Conical Spiral antenna radiation pattern - RF Cafe CONICAL SPIRAL

Polarization: Circular
Left hand as shown

Typical Half-Power Beamwidth:
60 deg x 60 deg

Typical Gain: 5-8 dB

Bandwidth: 120% or 4:1

Frequency Limit:
Lower: 50 MHz
Upper: 18 GHz

Figure 6


 
Antenna Type  Radiation Pattern  Characteristics 
4 Arm Conical Spiral antenna type - RF Cafe 4 Arm Conical Spiral antenna radiation pattern - RF Cafe 4 ARM CONICAL SPIRAL

Polarization: Circular
Left hand as shown

Typical Half-Power Beamwidth:
50 deg x 360 deg

Typical Gain: 0 dB

Bandwidth: 120% or 4:1

Frequency Limit:
Lower: 500 MHz
Upper: 18 GHz
Dual Polarized Sinuous antenna type - RF Cafe Dual Polarized Sinuous antenna radiation pattern - RF Cafe DUAL POLARIZED SINUOUS

Polarization: Dual vertical or horizontal or dual Circular right hand or left hand with hybrid

Typical Half-Power Beamwidth:
75 deg x 75 deg

Typical Gain: 2 dB

Bandwidth: 163% or 10:1

Frequency Limit:
Lower: 500 MHz
Upper: 18 GHz

Figure 7


 
Antenna Type  Radiation Pattern  Characteristics 
Biconical antenna type - RF Cafe Biconical antenna radiation pattern - RF Cafe BICONICAL

Polarization: Linear,
Vertical as shown

Typical Half-Power Beamwidth:
20-100 deg x 360 deg

Typical Gain: 0-4 dB

Bandwidth: 120% or 4:1

Frequency Limit:
Lower: 500 MHz
Upper: 40 GHz
Biconical w/Polarizer antenna type - RF Cafe Biconical w/Polarizer antenna radiation pattern - RF Cafe BICONICAL W/POLARIZER

Polarization: Circular,
Direction depends on polarization

Typical Half-Power Beamwidth:
20-100 deg x 360 deg

Typical Gain: -3 to 1 dB

Bandwidth: 100% or 3:1

Frequency Limit:
Lower: 2 GHz
Upper: 18 GHz

Figure 8


 
Antenna Type  Radiation Pattern  Characteristics 
Horn antenna type - RF Cafe Horn antenna radiation pattern - RF Cafe HORN

Polarization: Linear

Typical Half-Power Beamwidth:
40 deg x 40 deg

Typical Gain: 5 to 20 dB

Bandwidth:
If ridged: 120% or 4:1
If not ridged: 67% or 2:1

Frequency Limit:
Lower: 50 MHz
Upper: 40 GHz
Horn w/Polarizer antenna type - RF Cafe Horn w/Polarizer antenna radiation pattern - RF Cafe HORN W/POLARIZER

Polarization: Circular,
Depends on polarizer

Typical Half-Power Beamwidth:
40 deg x 40 deg

Typical Gain: 5 to 10 dB

Bandwidth: 60% or 2:1

Frequency Limit:
Lower: 2 GHz
Upper: 18 GHz

Figure 9


 
Antenna Type  Radiation Pattern  Characteristics 
Parabolic (prime) antenna type - RF Cafe Parabolic (prime) antenna radiation pattern - RF Cafe PARABOLIC (Prime)

Polarization:
Takes polarization of feed

Typical Half-Power Beamwidth:
1 to 10 deg

Typical Gain: 20 to 30 dB

Bandwidth: 33% or 1.4:1
limited mostly by feed

Frequency Limit:
Lower: 400 MHz
Upper: 13+ GHz
Parabolic antenna type - RF Cafe Parabolic antenna radiation pattern - RF Cafe PARABOLIC

Polarization:
Takes polarization of feed

Typical Half-Power Beamwidth:
1 to 10 deg

Typical Gain: 20 to 30 dB

Bandwidth: 33% or 1.4:1

Frequency Limit:
Lower: 400 MHz
Upper: 13+ GHz

Figure 10


 
Antenna Type  Radiation Pattern  Characteristics 
Yagi antenna type - RF Cafe Yagi antenna radiation pattern - RF Cafe YAGI

Polarization: Linear
Horizontal as shown

Typical Half-Power Beamwidth
50 deg X 50 deg

Typical Gain: 5 to 15 dB

Bandwidth: 5% or 1.05:1

Frequency Limit:
Lower: 50 MHz
Upper: 2 GHz
Log Periodic antenna type - RF Cafe Log Periodic antenna radiation pattern - RF Cafe LOG PERIODIC

Polarization: Linear

Typical Half-Power Beamwidth:
60 deg x 80 deg

Typical Gain: 6 to 8 dB

Bandwidth: 163% or 10:1

Frequency Limit:
Lower: 3 MHz
Upper: 18 GHz

Remarks: This array may be formed with many shapes including dipoles or toothed arrays.

Figure 11


 
Antenna Type  Radiation Pattern  Characteristics 
RF Cafe - Linear Dipole Array (corporate feed) antenna type RF Cafe - Linear Dipole Array (corporate feed) antenna radiation pattern LINEAR DIPOLE ARRAY
(Corporate Feed)

Polarization: Element dependent
Vertical as shown

Typical Half-Power Beamwidth:
Related to gain

Typical Gain: Dependent on
number of elements

Bandwidth: Narrow

Frequency Limit:
Lower: 10 MHz
Upper: 10 GHz
RF Cafe - Aperature Synthesis antenna type RF Cafe - Aperature Synthesis antenna radiation pattern APERATURE SYNTHESIS

All characteristics dependent on
elements

Remarks: Excellent side-looking, ground mapping where the aircraft is a moving linear element.

Figure 12


 
 
Antenna Type  Radiation Pattern  Characteristics 
RF Cafe - Cavity Backed Circuit Fed Slot (and microstrip patch) antenna type RF Cafe - Cavity Fed Circuit Fed Slot antenna radiation pattern CAVITY BACKED
CIRCUIT FEED SLOT
(and microstrip patch)

Polarization: Linear, vertical as shown

Typical Half-Power Beamwidth:
80 deg x 80 deg

Typical Gain: 6 dB

Bandwidth: Narrow

Frequency Limit:
Lower: 50 MHz
Upper: 18 GHz

Remarks: The feed line is sometimes separated from the radiator by a dielectric & uses capacitive coupling. Large conformal phased arrays can be made this way.
RF Cafe - Guide Fed Slot antenna type RF Cafe - Guide Fed Slot antenna radiation pattern GUIDE FED SLOT

Polarization: Linear,

Typical Half-Power Beamwidth
Elevation: 45-50E
Azimuth: 80E

Typical Gain: 0 dB

Bandwidth: Narrow

Frequency Limit:
Lower: 2 GHz
Upper: 40 GHz

Remarks: Open RF Waveguide

Figure 13


 
 
Antenna Type  Radiation Pattern  Characteristics 
RF Cafe - Corner Reflector antenna type RF Cafe - Corner Reflector antenna radiation pattern CORNER REFLECTOR

Polarization:
Feed dependent

Typical Half-Power Beamwidth
40 deg x variable

Typical Gain: 10 dB above feed

Bandwidth: Narrow

Frequency Limit
Lower: 1 GHz
Upper: 40 GHz

Remarks: Typically fed with a dipole
or collinear array.
RF Cafe - Luneburg Lens antenna type RF Cafe - Luneburg Lens antenna radiation pattern LUNEBURG LENS
(also LUNEBERG)

Polarization:
Feed dependent

Typical Half-Power Beamwidth:
System dependent

Typical Gain: System dependent

Bandwidth: Narrow

Frequency Limit
Lower: 1 GHz
Upper: 40 GHz

Remarks: Variable index dielectric sphere.

Figure 14



Table of Contents for Electronics Warfare and Radar Engineering Handbook
Introduction | Abbreviations | Decibel | Duty Cycle | Doppler Shift | Radar Horizon / Line of Sight | Propagation Time / Resolution | Modulation | Transforms / Wavelets | Antenna Introduction / Basics | Polarization | Radiation Patterns | Frequency / Phase Effects of Antennas | Antenna Near Field | Radiation Hazards | Power Density | One-Way Radar Equation / RF Propagation | Two-Way Radar Equation (Monostatic) | Alternate Two-Way Radar Equation | Two-Way Radar Equation (Bistatic) | Jamming to Signal (J/S) Ratio - Constant Power [Saturated] Jamming | Support Jamming | Radar Cross Section (RCS) | Emission Control (EMCON) | RF Atmospheric Absorption / Ducting | Receiver Sensitivity / Noise | Receiver Types and Characteristics | General Radar Display Types | IFF - Identification - Friend or Foe | Receiver Tests | Signal Sorting Methods and Direction Finding | Voltage Standing Wave Ratio (VSWR) / Reflection Coefficient / Return Loss / Mismatch Loss | Microwave Coaxial Connectors | Power Dividers/Combiner and Directional Couplers | Attenuators / Filters / DC Blocks | Terminations / Dummy Loads | Circulators and Diplexers | Mixers and Frequency Discriminators | Detectors | Microwave Measurements | Microwave Waveguides and Coaxial Cable | Electro-Optics | Laser Safety | Mach Number and Airspeed vs. Altitude Mach Number | EMP/  Aircraft Dimensions | Data Busses | RS-232 Interface | RS-422 Balanced Voltage Interface | RS-485 Interface | IEEE-488 Interface Bus (HP-IB/GP-IB) | MIL-STD-1553 & 1773 Data Bus |
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