Usually, it is assumed that the duration of the transmitted pulse is equal to the duration of the reflected echo pulse. Thus, in the ratio of the transmitted power and the received power (which is used in the fundamental radar range equation) can be dispensed with a time specification.
By the reflection of the transmit signal the spectrum may be modified:
- It can occur additional harmonics to the carrier frequency.
- The carrier frequency can be imposed on one or more Doppler frequencies.
- The direction of the polarization can be changed.
The pulse duration of the echo signal is not constant. The duration of the reflected pulse can be considerably stretched by interference from reflections at areas with slightly different distances (and following different run times).
All together: the echo signal is subject to so many influences that the waveform and the shape of the echo signal in the result must be regarded as unknown. Nevertheless, in order to build an optimal matched receiver or an optimal matched filter, multiple receiving channels must be set up in parallel, taking into account all the possible deformations of the signal. In a selection circuit, the echo signal with the best (greatest-of) Signal to Noise Plus Interference Ratio (SNIR) is then further processed. The “position” of the greatest-of-switch is also saved as important information for the identification of this echo signal.
In general, the receiving bandwidth is kept as small as possible, so not much unnecessary noise is received. Therefore, to select the bandwidth only with BHF = 1/τ for a simple pulse radar. The influence of the noise can be suppressed in the receiver using of pulse integration. Here, a sum of pulse periods is formed. The reflecting object is assumed to be stationary during the time of these pulse periods. Since the noise is randomly distributed, thereby the sum of the noise cannot reach the sum of the echo signals. The signal-to-noise ratio is improved by this measure.