The radar receiver collects echoes return as pulses of rf energy and provides a visual display of object information.
The Superheterodyne receiver is almost always used in microwave radar systems..
A mirror frequency occurs during the mixer operation, cause the difference and the sum of both are
accepted by the IF amplifier stage. This mirror frequency must be eleminate by special filters.
Double Heterodyning is a commonly used method to avoid that
mirror frequencies pass through the rather broad tuned input circuit.
For best visibility of nearby and far away target return signals,
STC (or GTC) circuits are used to adjust amplifier gain with time
as swept gain attenuator, which can be
static or
dynamic.
AGC, Automatic Gain Control is necessary to adjust the receiver sensitivity
for the best reception of signals of widely varying amplitudes. It is
a simple method to minimize jamming signals.
The logarithmic amplifier prevents, that very strong echo signals
will saturate the receiver.
The phase shift of the echo signals must be preserved during
demodulation, for moving target indication.
