Technology Explained — Clam Shell Radar

The FA-51MU antenna head subsystem combines a receive and transmit antenna, separated by a shielding structure, which prevents spillover from the transmitter into the receiver. The manual states the antenna design includes sidelobe suppression features. The doubly curved transmit and receive reflectors each measure 9.2ft square. The antenna head is mounted on a hydraulically elevated mast which is supplied in two versions, the taller 39m (127ft) 40V6MD and the shorter 24m (78ft) 40V6M (see photo). The antenna mast and head are mated before elevation on a semi-trailer which is towed by a MAZ-537 tractor.

The Clam Shell transmitter, embedded in the FA52MU Receiver/Transmitter Module, produces a high purity CW signal for search mode operation, with imposed low frequency FM modulation for ranging to targets. Appropriate signal processing provides rejection of clutter, terrain features, precipitation, high density chaff clouds and jamming. Horizontal scan through 360° is achieved by antenna head rotation, using a conventional rotational coupler.

The operator console, signal processing hardware, track data processor, BIT subsystem and PPI display tube are all built into the road transportable F52MU modular shelter. Operation of the radar can be manual or fully automatic and the system maybe remotely controlled via cables from distances up to 500 metres.

Quoted performance figures include the detection of targets with an RCS as low as 0.02 square metres, at speeds of up to 1400kt (2595km/h), with a bearing resolution of 1 degree, velocity resolution of 9.3kt (17km/h) and range resolution of 2.15nm (4km/h). Quoted RMS tracking errors are 0.3 degree in bearing, 4.7kt (8.7km/h) in velocity and 1nm (1.85km) in range. Chaff rejection performance is quoted at better than 100dB, detection range is stated to be 50nm (93km) for targets at 1500ft altitude, and 65nm (120km/h) for 3000ft altitude.

The LEMZ 76N6 Clam Shell FMCW acquisition radar. The unit depicted is deployed on the 24m (78ft) 40V6M elevating mast. (LEMZ) 40 Australian Aviation October 1995

The transmitter delivers 1.4kW of CW power at an unspecified carrier frequency, system MTBF is quoted at 100hr with an MTTR of 0.5hr, though this may be optimistic.

The typical SA-10B Grumble mobile battery comprises a Flap Lid B phased array fire control radar, collocated with the operators’ command shelter on an 8×8 all terrain carrier vehicle, multiple TEL vehicles each carrying four rounds in cylindrical containers, and a pair of search and acquisition radars. The Big Bird F-band acquisition radar provides long range search at medium to high altitudes, and is supplemented by the Clam Shell which provides low level coverage, particularly against cruise missile type targets. A mast mounted semi mobile Flap Lid A phased array may also be used, providing engagement capability against low flying targets. The Flap Lid will provide for concurrent engagements against up to six targets, with two missiles allocated to each target. The SA-10 is reported to use a Track Via Missile (TVM) guidance scheme not unlike that in the Patriot SAM. It is reasonable to expect that the mast mounted Flap Lid A will be used together with the mast mounted Clam Shell, to provide an integrated acquisition and engagement capability against low flying targets up to the radar horizon.

An issue for the Western electronic warfare community is that the Clam Shell uses FMCW techniques, while many older and established radar warning receivers (RWRs) and trackbreaker jammers (ECM) may not have the capability to detect and jam this system. FMCW systems are generally credited with excellent resistance to conventional jamming techniques, and excellent clutter and chaff rejection, both points stressed in the manufacturer’s document. As this system is now being marketed worldwide, with China and India reported as initial export customers, it is likely that it will find other regional users in time. Aircraft not equipped with suitable RWR and ECM will be highly vulnerable to this capable area defence SAM system.

Given the stated performance parameters of the Grumble weapon system, and its regional deployment, we can hope the ADF has given some careful thought to its RWR and countermeasures strategy for the next five to ten years. This particular system could be a serious threat to RAAF aircraft should hostilities (God forbid) take place in the future, and type specific countermeasures will be required as this system is specifically built to defeat terrain following and low flying aircraft and standoff missiles. Should type specific ECM be lacking, substantial defence suppression effort using anti-radiation missiles would be required.

The regional marketing of components of this weapon system underscores the current trend of cutting edge air defence weapons proliferating into regional markets. The arms race we are seeing in Asia today is unlikely to abate as economic and political competition grows in the region. Up to date ECM is therefore a must in what could become a dangerous neighbourhood.