Description of the radar set, tactical-technical characteristics
Figure 1: Watchman radar at Basra airport Iraq (© unknown)
|frequency:||2,750 - 3,050 MHz|
|pulse repetition time (PRT):|
|pulse repetition frequency (PRF):||≈ 1,100 Hz (9-fold staggered)|
|pulsewidth (τ):||0.4 and 20 µs|
|peak power:||58 kW|
|average power:||1.3 kW|
|instrumented range:||80 NM|
|range resolution:||60 m (190 ft)|
|beamwidth:||β=1.5 ; ε=30 degrees|
|hits per scan:|
|antenna rotation:||4 Seconds (15 rpm)|
Watchman Surveillance Radar
The Watchman family of S-Band medium-range radars is designed to provide terminal area/approach surveillance and ground controlled approach surveillance developed by Plessey Radar Ltd during the 1970s. The radar can be configured from a number of modules which enables users to match precisely equipments to operational needs. Options include transportable or static aluminium or carbon-fibre antennas; adaptive or eight-filter Moving Target Detector (MTD) signal processing and plot or track outputs. The Traveling-wave tube- based transmitter provides frequency diversity and frequency agility and enables a single radar to provide a variety of detection ranges out to a maximum of 222 km. The transmitter is available in a single tube format or with multi-tubes which accommodates the “graceful degradation” often required by the operator.
A dual pulse train is used; it has a very short pulse (0.4 microseconds) for high discrimination at short ranges and a much longer pulse (20 microseconds) for long-range detection of aircraft with small radar cross sections. The long pulse is compressed in the receiver using a surface acoustic wave equalizer. The basic compressed pulse length is 0.4 μs, giving a 60 m range cell too. The signal separation is achieved by using different radio frequencies for the long and short pulses. Target detection is further enhanced by interchanging frequencies at nine pulse repetition intervals. A recent variant of Watchman (S) uses Solid-state transmitter. There are any upgrades to a new digital receiver design with intelligent tracking routines. CFAR circuit and high definition clutter map clutter map using a process of alpha smoothing (1/8 of current clutter amplitude plus 7/8 of previous sweep clutter amplitude) compensate the influence of noise and clutter by raising the detection thresholds.
The Watchman surveillance radar system provides Air Traffic Services for the vast majority of the UK Ministry of Defence operational stations in the UK and worldwide. There are currently 40 systems in service worldwide. The Tactical variant (mobile equipment) of the Watchman system allows the rapid deployment and installation of Air Traffic Services in locations where British forces are on operational duty.