CHARACTERISTICS OF ANTENNAS

1. Gain of Antenna:

The relative improvement in the received signal of a certain antenna to that which would be received by a half wave dipole put in the same place. The ratio of the voltage received (i.e. gain) is usually quoted in decibels (dB's)

Note: Gain can also be quoted in (dBi's), i.e. comparison made with isotropic radiator (or point source).
This results in a gain figure which is 2.5 dB higher for the half wave dipole. The gain of the half wave dipole is called unity gain.

2. Bandwidth:
The range of frequencies covered by the antenna where the gain does not drop below 3dB. Also defined in terms of voltage standing wave ratio (V.S.W.R.), e.g. the frequency range over which the V.S.W.R. of the antenna does not exceed 2:1.
3. Wide Band, Narrow Band:
Certain antenna designs have wider bandwidths than others, usually achieved at the expense of gain.
Low frequency antennas have narrower bandwidths than higher frequency ones.
4. Beam Width:
The angle of the front radiated beam from a yagi – measured each side of maximum to where the signal falls to 0.7 of maximum. (See section 7. Polar Diagrams).