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).

Antenna Vendors page

Narrowband BW (%) = (f_U - f_L) / f_C

Broadband BW = f_U / f_L

%	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

%	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/λ) + 10 log (a) + 9.938 dB

D= diameter
a = illumination factor
(typ = 0.6)
λ = wavelength

Dipole Antenna, 1/2 Wave

1/2-wave dipole antenna coordinates and radiation pattern

Elevation 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.

Azimuth Pattern

Vertical Whip Antenna, 1/4 Wave

1/4-wave dipole antenna coordinates and radiation pattern

Configuration

Elevation 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.

Azimuth Pattern

Log-Periodic Array

Yagi Array

Yagi antenna coordinates and radiation pattern

Elevation 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

Azimuth Pattern

Circular Loop

Elevation 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

Azimuth Pattern

Square Loop

Elevation 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

Azimuth Pattern

Horn

3 dB beamwidth 56 * λ / h
Elevation 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

3 dB beamwidth 70 * λ / w
Azimuth Pattern

Webmaster: Kirt Blattenberger, BSEE, UVM 1989