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	Broadband BW = fU / fL
% 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
	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
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
	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