Antenna Patterns

ANTENNA PATTERNS

Gain for an antenna is expressed in decibels relative to an isotropic radiator (point source that radiates equally in every direction). Physical attributes of an antenna, in conjunction with the operating frequency, results in constructive and destructive interference patterns being set up a points distant from the antenna. Where the fields add constructively a positive gain is experienced, and where fields add destructively a negative gain is experienced (relative to isotropic).

Note:  Keep dimensional units similar; i.e., meters, inches.

Parabolic Antenna

		Gain (typ): 10 to 60 dB Bandwidth: 33% (1.4:1) Frequency Limit: Lower - 400 MHz (due to size)   Upper - 13+ GHz Polarization: Polarization of feed Half-Power Beamwidth: 1 to 10º
G=20 log (D/l) + 10 log (a) + 9.938 dB	D= diameter a = illumination factor (typ = 0.6) l= wavelength

Dipole Antenna, 1/2 Wave

Elevation Pattern Azimuth Pattern

Gain (typ): 2 dB Bandwidth: 10% (1.1:1) Frequency Limit: Lower - none   Upper - 8 GHz (due to size) Polarization: Linear (vertical as shown) Half-Power Beamwidth (typ): 80º x 360º Notes: Pattern and lobing change significantly with L/f. Used as gain reference for f < 2 GHz.

Vertical Whip Antenna, 1/4 Wave

Configuration

Elevation Pattern Azimuth Pattern

Gain (typ): 2 to 6 dB Bandwidth: 10% (1.1:1) Frequency Limit: Lower - none   Upper - none Polarization: Linear (vertical as shown) Half-Power Beamwidth (typ): 45º x 360º Notes: Polarization changes to horizontal if antenna is rotated to horizontal.

Yagi Array

Elevation Pattern Azimuth Pattern

Gain (typ): 5 to 15 dB Bandwidth: 5% (1.05:1) Frequency Limit: Lower - 50 MHz   Upper - 2 GHz Polarization: Linear (horizontal as shown) Half-Power Beamwidth (typ): 50º x 50º

Circular Loop

Elevation Pattern Azimuth Pattern

Gain (typ): -2 to 2 dB Bandwidth: 10% (1.1:1) Frequency Limit: Lower - 50 MHz   Upper - 1 GHz Polarization: Linear (horizontal as shown) Half-Power Beamwidth (typ): 80º x 360º

Square Loop

Elevation Pattern Azimuth Pattern

Gain (typ): 1 to 3 dB Bandwidth: 10% (1.1:1) Frequency Limit: Lower - 50 MHz   Upper - 1 GHz Polarization: Linear (horizontal as shown) Half-Power Beamwidth (typ): 100º x 360º

Horn

3 dB beamwidth 56 * l / h Elevation Pattern 3 dB beamwidth 70 * l / w Azimuth Pattern

Gain (typ): 5 to 20 dB Bandwidth: 120% (4:1) - ridged   67% (2:1) - non-ridged Frequency Limit: Lower - 50 MHz   Upper - 40 GHz Polarization: Linear (vertical as shown) Half-Power Beamwidth (typ): 40º x 40º