The Type 984 3-D radar.
The Type 984 radar is a high powered high-definition S band unit providing elevation data as well as range
and azimuth. It produces 6 separate beams, five of which scan as a single unit in order to provide the elevation. These
actually scan at 45° to the vertical in order to provide increased coverage, while the sixth is fixed on the
horizon to provide the Early Warning Beam. The scanning beams each cover 4·4° in elevation and (including the
aerial's rotation) 6·6° in azimuth. The set of beams cover 22° of elevation with the bottom of the
beam being 0·5° above the horizon. Unlike most radars -which use a parabolic reflector- the Type 984 has the
beams passing through a massive waveguide lens which focuses them just as an optical lens does with light beams, this gives
the radar its characteristic 'dustbin' shape.
The pulse duration is 2·5 µS with all the beams transmitting simultaneously, and the transmission period is 2·5 mS.
25 pulses are transmitted during each elevation sweep, and one during the fly-back; a point target can expect to
receive up to 10 pulses in a single 'paint'. When the Early Warning Beam sweeps across a target about 40 pulses can
be expected as it has one quarter of the scanning rate.
The two-way radiation pattern is 1·5° at 3dB down, 2·5° at 12dB and 3° at 20dB.
Beam 1 has a range gate of 0 - 192 miles, this is followed an an Automatic Gain Control (AGC) pulse, and the returns
are fed to channel 1 of the delay line. Beams 2 and 3 have no range gate as they have to share delay lines and the
actual delay is determined by the ranges of the other beams. Beam 4 has a range gate of 0 - 72⅔ miles and Beam 5
is 0 - 52⅔ miles. Beams 4 and 3 share channel 2 of the delay line, and beams 5 and 2 share channel 2.
Beam 6 has a nominal range gate of 208 miles, but there are a selection of 3 short-range sacrifices that can be made (as it is
the long-range early-warning beam) which also serve to reduce short-rang clutter; 32⅓ miles, 52⅔ or 74⅔ miles
and these figures are added to the nominal range figure to give 240⅓, 260⅔ or 282⅔ miles respectively.
The delay lines allow for four sets of pulses to be added together to improve the radar's detection rate and also allow for
the effect of clutter to be substantially reduced. The delay line system consists of 11 quartz polygons, each precision
ground, and enclosed in a temperature-controlled 'oven'.
This page copyright SR Jenkins January 2019; reproduction without prior approval is prohibited.
Page last updated: 4th January 2023.
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