Antenna Types

Warning: The use of gain antenna in some countries is not permitted. Similarly where ERP (transmitted power limits) are imposed the actual transmitted power must not exceed the limit stated. This means that the transmitter output power, less any coaxial feeder losses, plus the antenna gain must not exceed the specified maximum ERP. Before installing your system please check!

Antenna types fall into a number of categories. For the majority of applications the choice lies between portable, fixed, omni-directional and those with gain and directional properties.

True omni-directional antenna in reality do no exist, i.e. those with equal gain in all directions. However the nearest practical equivalent is the 1/2 or 1/4 wave dipole. The 1/4 wave dipole is by far the most popular of all antennas and is found in use on most portable apparatus. Where the frequency is too low and the dipole can become cumbersome and a compressed dipole (helical) antenna has to be used.

Whatever antenna types you choose please ensure that its impedance is 50 Ohms.

name	Gain and Directional Properties	Comments

1/4 wave dipole	< -0.8dB near omni in the	For portable apparatus operating above 400MHz
	vertical plane only.	Requires a ground plane for operation

Helical	< -4 to -10dB near omni in the	For portable apparatus < 400MHz
	vertical plane only.	Requires a ground plane for operation

1/2 wave dipole	+ 1.2 to + 1.8dB near omni-	For portable and fixed apparatus looking for a low
	directional in the vertical plane.	cost antenna that does not require a ground plane

End fed dipole	0db, near omni in vertical plane	For fixed apparatus that does not require a ground
		plane

Colinear	+3dB to +9dB , near omni-	For fixed apparatus that does not require a ground
	directional in vertical plane	plane

Yagi	+3dB to +28dB . Beam width	For point to point links. Where an unwanted signal
	proportional to gain	needs to be blocked from the opposite direction
		choose an antenna with a high front to back ratio