Bandwidth, LNA Noise Temperature, Saturation Flux Density and Polarization.
Bandwidth
Bandwidth is another fundamental antenna parameter. Bandwidth describes the range of frequencies over
which the antenna can properly radiate or receive energy. Often, the
desired bandwidth is one of the determining parameters used to decide
upon an antenna. For instance, many antenna types have very narrow
bandwidths and cannot be used for wideband operation.
Bandwidth is typically quoted in terms of VSWR (Voltage
Standing Wave Ratio, and sounds very complicated. But it is simply a
measure of how much power is reflected from an antenna. ) . For
instance, an antenna may be described as operating at 100-400 MHz with a
VSWR<1.5. This statement implies that the reflection coefficient is
less than 0.2 across the quoted frequency range. Hence, of the power
delivered to the antenna, only 4% of the power is reflected back to the
transmitter. Alternatively, the return lossS11=20*log10(0.2)=-13.98 dB.
Note
that the above does not imply that 96% of the power delivered to the
antenna is transmitted in the form of EM radiation; losses must still be
taken into account.
LNA
Noise Temperature: It is the measure of the amount
of noise generated by the LNA. It is measured in Kelvin-the lower the better.
Typical performance can be achieved for 30K to 70K. LNA noise performance is
sometimes specified in terms of Noise
Figure which is measured in dB.
NF=10*Log (1+T/290), NF in dB, T in Kelvins.
Saturation
Flux Density: Flux density is a measure of
signal strength at a point in space and is measured in Watts/meter2 or
dBW/meter2. It is usually applied to signals received at a satellite.
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