AP 3302 Pt. 3
Section 1
CHAPTER 2
Basic Requirements Of A Pulse-Modulated Radar System
Introduction
We have seen that a primary radar installation must be able to detect targets at a distance and also provide information on their range, bearing and height. To be able to do this satisfactorily a pulse-modulated radar must have the units shown in Fig 1.
a. A transmitter capable of producing short-duration, high-power pulses of r.f. energy at a given repetition frequency.
b. An aerial system producing a very narrow beam of r.f. energy which may be used for scanning.
c. A sensitive receiver capable of receiving and amplifying the very weak echoes for applica-tion to the indicator.
d. An indicator which measures time intervals of only microseconds duration for range measurement, and which is connected to the aerial system to give indication of the bearing or the height of the target.
Let us now examine some of the stages in a primary radar installation. We can then go on to link the various units together to form a block schematic diagram of a basic system.
The Pulse-modulated Transmitter
The transmitter pulses are produced at a regularly recurring rate, the number of pulses produced each second being known as the pulse recurrence (or repetition) frequency (p.r.f.), measured in pulses per second. The length of time for which the transmitter is switched on to give each pulse is known as the pulse duration, measured in microseconds. Alternative names for pulse duration are pulse width and pulse length.
