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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).

Narrowband BW (%) = (fU - fL) / fC

% Ratio
5 1.05:1
10 1.11:1
20 1.22:1
30 1.35:1
40 1.50:1
50 1.67:1
60 1.85:1

Broadband BW = fU / fL

% Ratio
67 2:1
100 3:1
120 4:1
133 5:1
150 7:1
160 9:1
163 10:1

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.

Log-Periodic Array
 

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
 
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