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AP3302 Pt3 Contents

AP3302 Pt3 Section 1 Contents

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AP 3302 Pt. 3

Section 1

CHAPTER 1

PULSE-MODULATED RADAR

Introduction

Radar is a method of using radio waves to detect the existence of an object and then to find its position in relation to a known point, usually the site of the radar installation (Fig 1). By means of radar the presence of moving or stationary objects such as aircraft, ships, and landmasses can be detected. In addition, information concerning the exact position of the object (usually referred to as the 'target') and its speed and course, where applicable, can be obtained. The word 'radar' is coined from the initial letters of the phrase: RAdio Detection And Ranging.

Although radar was originally introduced to give warning of the approach of hostile aircraft it has since been further developed to do much more than its original task. Modern radar equipment plays a vital part in all the operational roles of the RAF: as an aid to accurate bombing; in airborne detection and interception equipment; for the control of guided weapons; as navigational and landing aids; in cloud and collision warning devices. It has many other uses in the civilian as well as in the Service field.

Pulse-modulated and CW Radar Systems

Most radar equipments are pulse-modulated, i.e. the radiation from the transmitter aerial is in the form of very short bursts or pulses of r.f. energy, each pulse being followed by a relatively long resting period during which the transmitter is switched off and the receiver is operating. For certain applications pulse-modulated radar has limitations. A form of continuous wave (c.w.) radar is then used. This may be:

a. Pure c.w. radar relying on the 'Doppler shift' in frequency to detect moving objects and to measure their speed.

b. Frequency-modulated c.w. radar where the difference in frequency between the reflected wave from a target and the direct wave from transmitter to receiver gives an indication of the range of the target.

Most of this book deals with pulse-modulated radar systems. However, a basic outline of c.w. radar is given in Chapter 5 and further details are given in section 7.


 

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