Abstract :
The measurement of incoherent radar-echo powers much smaller than receiver noise can be achieved by using long-period postdetector integration. Suitable very stable integrators usually operate by integrating over successive discrete periods, `dumping¿ the total and restarting at the end of each period. This behaviour is different from that of the continuous integrator of the `sliding rectangular window¿ type, which may be considered as a passive low-pass filter. In the discrete-interval integrator the `dumping¿ phase is independent of the signal and the filtering analogue is not clear. It is shown that the signal/noise improvement produced by the discrete-interval integrator may be calculated by sampling theory, taking into account the continuously varying nature of the signal. Integration over periods ta is found to produce the same improvement as a low-pass filter of equivalent noise cutoff frequency 1/2ta. The relationship between the sampling and filtering approaches is studied, and methods are derived for calculating the reduction of detectable receiver input echo power for c.w. radars and for pulse radars having range gates narrower and wider than the pulse width. The effect of the i.f. filter response on the improvement produced by an integrator is illustrated by examples.
