AP 3302 Pt. 3
Section 1
CHAPTER 4
Some examples of the uses of pulsed radar
Volumetric (3-D) Radar
A reduction in the number of radars required can be obtained with a volumetric (3-D) radar system which uses a stacked beam principle to provide height as well as plan position information for each aerial revolution. Parameters for a typical system are:
|
Wavelength |
10 cm (S band) |
|
|
Frequency |
3 GHz |
|
|
Peak power |
3 MW |
(shared among 12 separate beams) |
|
Pulse duration |
10 us |
(using pulse compression-see p 617) |
|
PRF |
320 p.p.s. |
|
|
Slant range |
220 nm |
|
|
Height |
up to 100,000 feet. |
|
The aerial consists of a reflector and a feed arrangement to produce a stacked beam system. The reflector is parabolic in both dimensions and measures 40 feet (12 m) across by 15 feet (4.6 m) high. When operating as a transmitter, the transmitter power is divided in the feed system to produce 12 separate beams, as shown in Fig 6 (this is an idealised drawing). The half-power beamwidths are typically 0.6o horizontally and 1.25o vertically and the aerial has a gain of 44 db.
The aerial is rotated in azimuth at a rotation rate of 5 revs per minute, so that all twelve beams are rotated to give the cover shown. Completely gap-free cover up to a range of 220 nm and at heights up to 100,000 feet (to an elevation angle of 30o) is obtained.
When receiving, the echo power in each beam is applied to its own receiver and by comparing the output of each receiver in a computer, information on range, bearing and elevation (height) of each target is obtained for application to the display. All this information is up-dated on each rotation of the aerial. For targets at a range of about 100 nm and at heights of 40,000 feet, the following performance figures are given:
|
Height accuracy |
better than 1,500 feet |
|
Range accuracy |
100 metres |
|
Azimuth bearing accuracy |
0.2o |
|
Range discrimination |
better than 100 metres |
|
Angular discrimination |
better than 0.8o (at low angles of elevation). |
