AP 3302 Pt. 3
Section 1
CHAPTER 3
Factors affecting the performance of Pulse-Modulated Radars
Introduction
Although we now know something of the basic operation of a pulse-modulated primary radar there are still many questions left to be answered (Fig 1). In this chapter we shall attempt to answer these, and similar, questions.
Terms Used in Pulsed Radar
We have already met some of the terms used in pulse-modulated radar. Let us now define those terms more precisely and then go on to show their relationship with other, equally important, terms (Fig 2).
The waveforms shown in Fig 2 are 'ideal', i.e. we have assumed zero rise and decay times. In practice each pulse is more rounded because it takes a finite time to rise and to fall. However the ideal waveforms shown are adequate for our purpose. Note that the axes used in Fig 2 are power against time although more usually the waveform refers to voltage and time.
Pulse repetition frequency. This is the number of pulses occurring in one second. For a p.r.f. of 500 p.p.s. the pulse spacing Tr is 1/500 second or 2,000 microseconds. The value of p.r.f. normally lies between about 200 and 6,000 p.p.s.
Pulse duration. The pulse duration Td is the length of time for which the transmitter is switched on to give each pulse. It normally lies between about 0.l and 10 us.
