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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

aerial rotation rate. However, to get the increased accuracy required at the shorter ranges, it may be desirable to operate at a shorter wavelength. S band (10 cm) radars may be used in this role, with parameters such as the following:

 

Frequency

3 GHz

Peak power

650 kW

Pulse duration

1 us

PRF

700 p.p.s.

Slant range

up to 75 nm.

 

The aerial used is a solid reflector, measuring 16 feet (5 m) across and 6.5 feet (2 m) high, which is rotated at the relatively high rate of 15 r.p.m. The shape of the reflector is such that it produces a half-power horizontal beamwidth of 1.5o and a cosec2 pattern in the vertical plane. This provides coverage in excess of 75 nm up to heights in excess of 40,000 feet. The aerial gain is 31 db.

This radar (like all modern air traffic control radars) uses MTI to reduce ground clutter, and circular polarization to reduce clutter and attenuation due to weather phenomena.

Height-finding in air traffic control. It will be noted that the air traffic control radars considered above are capable of providing accurate measurements of range and bearing in azimuth of aircraft within their control area, but no mention has been made of height-finding. The reason for this is that aircraft flying under air traffic control arrangements are flying at known pre-arranged heights according to a 'flight plan'. Furthermore, they can be expected to be in radio communication with air traffic control and can confirm the height at which they are flying by reference to the altimeter readings. In other words, aircraft flying under air traffic control-unlike enemy aircraft in an air defence radar system-are co-operative targets. Nevertheless, there may be a requirement for a height-finding radar in the air traffic control environment, if only as a back-up measure. In such cases, it will take the form described earlier in this chapter.

Precision (runway) approach radars. When an aircraft is coming in to land in conditions of extremely poor visibility, it may be necessary for a ground controller to give instructions to


 

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