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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

angles of elevation, and the 23 cm (L band) radar uses a cosec2 reflector for general surveillance and cover at high angles of elevation. Since both aerials may be tilted between - 2o and + 9o from the horizontal, the beams can be adjusted to give almost complete cover out to the maximum range of 250 nm, up to heights of about 100,000 feet. In some installations, the aerials are mounted back to back on the same platform and rotate together, the outputs being displayed on separate indicators.

Height-finding Radars

To enable satisfactory instructions to be given to an interceptor aircraft, the ground radar must supply the controller with all the necessary information on range, azimuth bearing, height, track and speed of both the enemy and interceptor aircraft.

The displays associated with the long-range surveillance radars will provide the information on range and bearing of the target; but they give no indication of target height. For this we require a height-finding radar. Typical parameters for such a system are:

 

Wavelength

10 cm (S band)

 

Frequency

3 GHz

 

Peak power

1 MW

 

Pulse Duration

2.5 to 5us

Preset to order

PRF

300 to 600 pps

Preset to order

Slant range

up to 180 nm

(at low angles of elevation)

 

Once again, the pulse duration and p.r.f. can be pre-set relative to each other within the limits, and for the reasons, discussed earlier.

The aerial used in this role is longer in the vertical plane than in the horizontal plane (typically 40 feet (12 m) high by 7 feet (2 m) across). It is usually a solid reflector with a parabolic shape in the horizontal plane and linear in the vertical. This gives a beaver-tail beam with half-power beamwidths of 0.6o vertically and 3.7o horizontally (Fig 4). The aerial is turned to the required bearing (obtained from the surveillance radar p.p.i.) and is then used for finding the range and elevation of the target on that bearing. Range and elevation may be displayed direct on a Type E display or they may be converted to give range and height on a range-height indicator (see p 21/22).

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