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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.

The 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 %, where FC = Center frequency

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.

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 MONOPOLEPolarization: LinearVertical as shown Typical Half-Power Beamwidth45 deg x 360 deg Typical Gain: 2-6 dB at best Bandwidth: 10% or 1.1:1 Frequency LimitLower: NoneUpper: None Remarks: Polarization changes to horizontal if rotated to horizontal λ/2 DIPOLEPolarization: LinearVertical as shown Typical Half-Power Beamwidth80 deg x 360 deg Typical Gain: 2 dB Bandwidth: 10% or 1.1:1 Frequency LimitLower: NoneUpper: 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 VEEPolarization: LinearVertical as shown Typical Half-Power Beamwidth60 deg x 60 deg Typical Gain: 2 to 7 dB Bandwidth: "Broadband" Frequency LimitLower: 3 MHzUpper: 500 MHz (practical limits) Remarks: 24 kHz versions are known to exist. Terminations may be used to reduce backlobes. RHOMBICPolarization: LinearVertical as shown Typical Half-Power Beamwidth60 deg x 60 deg Typical Gain: 3 dB Bandwidth: "Broadband" Frequency LimitLower: 3 MHzUpper: 500 MHz Remarks: Termination resistance used to reduce backlobes.

Figure 2

 Antenna Type Radiation Pattern Characteristics CIRCULAR LOOP (small)Polarization: LinearHorizontal 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 MHzUpper: 1 GHz SQUARE LOOP Polarization: LinearHorizontal 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 MHzUpper: 1 GHz

Figure 3

 Antenna Type Radiation Pattern Characteristics DISCONEPolarization: LinearVertical 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 MHzUpper: 3 GHz ALFORD LOOPPolarization: LinearHorizontal as shown Typical Half-Power Beamwidth:80 deg x 360 deg Typical Gain: -1 dB Bandwidth: 67% or 2:1 Frequency Limit:Lower: 100 MHzUpper: 12 GHz

Figure 4

 Antenna Type Radiation Pattern Characteristics AXIAL MODE HELIXPolarization: CircularLeft hand as shown Typical Half-Power Beamwidth:50 deg x 50 deg Typical Gain: 10 dB Bandwidth: 52% or 1.7:1 Frequency LimitLower: 100 MHzUpper: 3 GHz Remarks: Number of loops >3 NORMAL MODE HELIXPolarization: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 LimitLower: 100 MHzUpper: 3 GHz

Figure 5

 Antenna Type Radiation Pattern Characteristics CAVITY BACKED SPIRAL(Flat Helix)Polarization: CircularLeft 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 MHzUpper: 18 GHz CONICAL SPIRALPolarization: CircularLeft 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 MHzUpper: 18 GHz

Figure 6

 Antenna Type Radiation Pattern Characteristics 4 ARM CONICAL SPIRALPolarization: CircularLeft 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 MHzUpper: 18 GHz DUAL POLARIZED SINUOUSPolarization: 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 MHzUpper: 18 GHz

Figure 7

 Antenna Type Radiation Pattern Characteristics BICONICALPolarization: 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 MHzUpper: 40 GHz BICONICAL W/POLARIZERPolarization: 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 GHzUpper: 18 GHz

Figure 8

 Antenna Type Radiation Pattern Characteristics HORNPolarization: Linear Typical Half-Power Beamwidth:40 deg x 40 deg Typical Gain: 5 to 20 dB Bandwidth:If ridged: 120% or 4:1If not ridged: 67% or 2:1 Frequency Limit:Lower: 50 MHzUpper: 40 GHz HORN W/POLARIZERPolarization: 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 GHzUpper: 18 GHz

Figure 9

 Antenna Type Radiation Pattern Characteristics PARABOLIC (Prime)Polarization:Takes polarization of feed Typical Half-Power Beamwidth:1 to 10 deg Typical Gain: 20 to 30 dB Bandwidth: 33% or 1.4:1limited mostly by feed Frequency Limit:Lower: 400 MHzUpper: 13+ GHz PARABOLICPolarization: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 MHzUpper: 13+ GHz

Figure 10

 Antenna Type Radiation Pattern Characteristics YAGIPolarization: LinearHorizontal as shown Typical Half-Power Beamwidth50 deg X 50 deg Typical Gain: 5 to 15 dB Bandwidth: 5% or 1.05:1 Frequency Limit:Lower: 50 MHzUpper: 2 GHz LOG PERIODICPolarization: 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 MHzUpper: 18 GHz Remarks: This array may be formed with many shapes including dipoles or toothed arrays.

Figure 11

 Antenna Type Radiation Pattern Characteristics LINEAR DIPOLE ARRAY(Corporate Feed)Polarization: Element dependentVertical as shown Typical Half-Power Beamwidth:Related to gain Typical Gain: Dependent onnumber of elements Bandwidth: Narrow Frequency Limit:Lower: 10 MHzUpper: 10 GHz APERATURE SYNTHESISAll characteristics dependent onelements Remarks: Excellent side-looking, ground mapping where the aircraft is a moving linear element.

Figure 12

 Antenna Type Radiation Pattern Characteristics 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 MHzUpper: 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. GUIDE FED SLOTPolarization: Linear, Typical Half-Power BeamwidthElevation: 45-50EAzimuth: 80E Typical Gain: 0 dB Bandwidth: Narrow Frequency Limit:Lower: 2 GHzUpper: 40 GHz Remarks: Open RF Waveguide

Figure 13

 Antenna Type Radiation Pattern Characteristics CORNER REFLECTORPolarization:Feed dependent Typical Half-Power Beamwidth40 deg x variable Typical Gain: 10 dB above feed Bandwidth: Narrow Frequency LimitLower: 1 GHzUpper: 40 GHz Remarks: Typically fed with a dipoleor collinear array. LUNEBURG LENS(also LUNEBERG)Polarization:Feed dependent Typical Half-Power Beamwidth:System dependent Typical Gain: System dependent Bandwidth: Narrow Frequency LimitLower: 1 GHzUpper: 40 GHz Remarks: Variable index dielectric sphere.

Figure 14