Cobham Antenna Systems

Antenna Primary Specification
Frequency, Gain, Bandwidth
FREQUENCY
Most antennas are designed to operate
efficiently within 10% bandwidth. 2.5GHz ±5%
means a frequency of 2.375 to 2.625 GHz, a
250MHz bandwidth.
For example, at 10GHz an antenna will operate
from 9.5 to 10.5GHz.
Always specify the frequency band or centre
frequency plus bandwidth. L-band or S-band
is not sufficient.
6
GAIN
Antennas passively increase the radiated power
by concentrating it into certain directions.
The gain of an antenna is a measure of its
directionality.
Gain is measured in dB (Isotropic) or dBi and
is usually expressed in dBi or dB relatively to
an isotropic source (equal in all directions).
Antennas are not 100% efficient and have
internal losses. The gain of an antenna
includes these losses:
Gain = Directivity - Internal losses
Gain is the additional signal strength that
the antenna provides in one direction at the
expense of signal strength in other directions.
An antenna is normally a passive device
providing gain by directing the energy to a
required pattern.
The result is a higher signal strength in one
direction and lower in other directions.
Measured pattern of directional antenna
BANDWIDTH
Omni antenna VOA4-
1400/1130
page 41
The bandwidth of an antenna is the range
of frequency where the antenna is operating
effectively. Typically our antennas have a
nominal 10% bandwidth. This may increase
or decrease depending on the antenna and
performance required.
It is important to specify the exact bandwidth
required. Specifying L-band for example is
not sufficient. L-band covers 1 - 2 GHz; much
larger than at 10% bandwidth.
Shows gain relative to isotropic pattern of antenna