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AP3302 Pt3 Contents

AP3302 Pt3 Section 1 Contents

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AP 3302 Pt. 3

Section 1

CHAPTER 4

Some examples of the uses of pulsed radar

The aerial used in this role is large-typically 45 feet (14 m) across and 15 feet (4.5 m) high. It is usually a solid reflector, capable of rotating at 3 to 8 r.p.m. in winds up to 80 knots (the lower the p.r.f., the slower must be the rate of rotation of the aerial to ensure an adequate number of 'hits' on the target). Two shapes of reflector are available. The one we shall consider here has a parabolic shape in the vertical plane and is linear in the horizontal plane; this gives a fan-shaped beam with half-power beam widths of 1.5o vertically and 0.5o horizontally, with a gain of 45 db. The other shape will be considered later.

It will be noted that the beam produced by the aerial is very narrow (0.5o) in the azimuth plane and so provides good angular discrimination of targets. The bearing in azimuth, obtained by rotating the aerial through 360o (Fig 2a) is indicated on a p.p.i.

The radar coverage for this aerial is illustrated in Fig 2b. The aerial can be tilted in elevation between - 2o and + 9o from its horizontal datum. The tilt in Fig 2b is about + 3.5o and no targets either above or below the beam will be detected. By adjusting the tilt we can obtain radar cover at very low angles of elevation and arrange to detect high-level targets by other means (see later).

23 cm (L band) radar.

An L band radar operating in the long-range surveillance role may have parameters as follows:
 

Frequency

1.33 GHz

 

Peak power

2 MW

 

Pulse Duration

2.5 to 5us

Preset to order

PRF

300 to 600 pps

Preset to order

Slant range

up to 140 nm

 


 

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