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AP3302 Pt3 Contents

AP3302 Pt3 Section 1 Contents

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AP 3302 Pt. 3

Section 1

CHAPTER 3

Factors affecting the performance of Pulse-Modulated Radars

Thus a transmitter rated at I kW mean power can be used to produce 1 MW pulses if the pulse duty factor is TDfr = 1/1000

Factors Affecting Radar Operation

Many factors affect the operation of a radar installation. Some of these factors are external to the radar set and affect all radars, e.g. reflections from unwanted objects and effects of external noise and jamming. We have very little control over such things.

Other factors controlling the performance of the radar are the result of deliberate decisions in design, e.g. the frequency of operation and the values of p.r.f. and pulse duration. These are selected and adjusted to give specific results and thus intentionally limit the operation of the radar.

 

External Factors Affecting Performance

The main external factors limiting the performance of a radar are:

a. Sources of external noise.
b. Reflections from unwanted objects.
c. The dimensions of the target.

Let us examine each of these in more detail.

External Noise

We have previously seen the effects of noise on a c.r.t. display. External noise may be due to any of the factors illustrated in Fig 4. In some circumstances (c) may be the result of deliberate jamming' of the radar by an enemy transmitter; this jamming technique is called "Electronic Counter Measures" (ECM) and uses a specialized radar.

Reflections From Unwanted Objects

We must first define what we mean by 'unwanted objects'! Something which may be an unwanted echo to one type of radar may be the wanted echo to another type. For example, clouds, built-up areas, hills and aircraft all produce radar echoes. For an early-warning search radar the wanted echoes are those produced by aircraft or missiles. For meteorological radar, on the other hand, it is the cloud formations which produce the wanted echoes. For bombing radar the towns and hills produce the wanted echoes, i.e. the 'radar map'.


 

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