- 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.

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

Broadband by ratio,

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: Linear Typical Half-Power Beamwidth Typical Gain: 2-6 dB at best Bandwidth: 10% or 1.1:1 Frequency Limit Remarks: Polarization changes to horizontal if rotated to horizontal |
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λ/2 DIPOLEPolarization: Linear Typical Half-Power Beamwidth Typical Gain: 2 dB Bandwidth: 10% or 1.1:1 Frequency 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: Linear Typical Half-Power Beamwidth Typical Gain: 2 to 7 dB Bandwidth: "Broadband" Frequency Limit Remarks: 24 kHz versions are known to exist. Terminations may be used to reduce backlobes. |
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RHOMBICPolarization: Linear Typical Half-Power Beamwidth Typical Gain: 3 dB Bandwidth: "Broadband" Frequency Limit Remarks: Termination resistance used to reduce backlobes. |

Figure 2

Figure 3

Antenna Type | Radiation Pattern | Characteristics |

DISCONEPolarization: Linear Typical Half-Power Beamwidth: Typical Gain: 0-4 dB Bandwidth: 100% or 3:1 Frequency Limit: |
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ALFORD LOOPPolarization: Linear Typical Half-Power Beamwidth: Typical Gain: -1 dB Bandwidth: 67% or 2:1 Frequency Limit: |

Figure 4

Figure 5

Figure 6

Antenna Type | Radiation Pattern | Characteristics |

4 ARM CONICAL SPIRALPolarization: Circular Typical Half-Power Beamwidth: Typical Gain: 0 dB Bandwidth: 120% or 4:1 Frequency Limit: |
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DUAL POLARIZED SINUOUSPolarization: Dual vertical or horizontal or dual Circular right hand or left hand with hybrid Typical Half-Power Beamwidth: Typical Gain: 2 dB Bandwidth: 163% or 10:1 Frequency Limit: |

Figure 7

Antenna Type | Radiation Pattern | Characteristics |

BICONICALPolarization: Linear, Typical Half-Power Beamwidth: Typical Gain: 0-4 dB Bandwidth: 120% or 4:1 Frequency Limit: |
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BICONICAL W/POLARIZERPolarization: Circular, Typical Half-Power Beamwidth: Typical Gain: -3 to 1 dB Bandwidth: 100% or 3:1 Frequency Limit: |

Figure 8

Antenna Type | Radiation Pattern | Characteristics |

HORN Polarization: Linear Typical Half-Power Beamwidth: Typical Gain: 5 to 20 dB Bandwidth: Frequency Limit: |
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HORN W/POLARIZER Polarization: Circular, Typical Half-Power Beamwidth: Typical Gain: 5 to 10 dB Bandwidth: 60% or 2:1 Frequency Limit: |

Figure 9

Antenna Type | Radiation Pattern | Characteristics |

PARABOLIC (Prime) Polarization: Typical Half-Power Beamwidth: Typical Gain: 20 to 30 dB Bandwidth: 33% or 1.4:1 Frequency Limit: |
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PARABOLIC Polarization: Typical Half-Power Beamwidth: Typical Gain: 20 to 30 dB Bandwidth: 33% or 1.4:1 Frequency Limit: |

Figure 10

Antenna Type | Radiation Pattern | Characteristics |

YAGI Polarization: Linear Typical Half-Power Beamwidth Typical Gain: 5 to 15 dB Bandwidth: 5% or 1.05:1 Frequency Limit: |
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LOG PERIODIC Polarization: Linear Typical Half-Power Beamwidth: Typical Gain: 6 to 8 dB Bandwidth: 163% or 10:1 Frequency Limit: 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 dependent Typical Half-Power Beamwidth: Typical Gain: Dependent on Bandwidth: Narrow Frequency Limit: |
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APERATURE SYNTHESIS All characteristics dependent on 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: Typical Gain: 6 dB Bandwidth: Narrow Frequency Limit: 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. |
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GUIDE FED SLOT Polarization: Linear, Typical Half-Power Beamwidth Typical Gain: 0 dB Bandwidth: Narrow Frequency Limit: Remarks: Open RF Waveguide |

Figure 13

Antenna Type | Radiation Pattern | Characteristics |

CORNER REFLECTOR Polarization: Typical Half-Power Beamwidth Typical Gain: 10 dB above feed Bandwidth: Narrow Frequency Limit Remarks: Typically fed with a dipole |
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LUNEBURG LENS (also LUNEBERG) Polarization: Typical Half-Power Beamwidth: Typical Gain: System dependent Bandwidth: Narrow Frequency Limit 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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