In the S-300PMU & PMU-1 series the Scientific Research Institute of Radio Engineering (NIIRE) 36D6 "Tin Shield" E/F-band (S-band) 3-D surveillance radar used for target search and acquisition is supplemented by the 76N6 "Clam Shell" low-level acquisition radar. This operates in conjunction with the truck-mounted I/J-band 30N6 "Flap Lid B" engagement radar. "Flap Lid" is a phased array radar which allows simultaneous engagements against up to six targets, with two missiles being allocated to each target. "Clam Shell" provides low level coverage, particularly against cruise missile type targets, and supplies target track information for fire control. Approaching and receding target velocity, range and bearing are provided.

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

An FA-51MU antenna head subsystem combines a receive and transmit antenna, separated by a shielding structure, which prevents RF spillover from the transmitter channel into the receiver. The antenna design includes sidelobe suppression features. The doubly curved transmit and receive reflectors each measure 2.8m (9.2ft) square. Vertical beamwidths of 1 or 6 can be selected, along with beam polarisation.

The antenna head uses 360 scanning via a conventional rotational coupler, and is mounted on a hydraulically elevated mast which is supplied in two versions mounted on a 38.8m (127ft) 40V6MD mast or the shorter 23.8m (78ft) 40V6M. The antenna mast and head are unfolded before elevation, and carried on a 5T58 semi-trailer which is towed by a MAZ-537 tractor. A version directly mounted on a ChMAP trailer is also offered, but this has a shorter effective range due to a much closer radar horizon.

The FA52MU receiver/transmitter module produces 1.4kW of high-purity CW signal at an unspecified carrier frequency, with an imposed low-frequency FM modulation for ranging against detected targets. "Clam Shell" can detect targets at extremely low altitudes in ground clutter in an intense ECM environment. Signal processing hardware provides rejection of clutter, terrain features, precipitation, high-density chaff clouds and jamming. Detection range is 93km (50nm) for targets at 1,500ft altitude, and 120km (65nm) for 3,000ft altitude, says LEMZ, and the radar can track up to 180 low level targets. Quoted performance figures include the detection of targets with an RCS as low as 0.02 square metres, at speeds of up to 1,400kt, with a bearing resolution of 1 , velocity resolution of 9.3kt and range resolution of 4km (2.15nm). RMS tracking errors are 0.3 in bearing, 4.7kt in velocity and 1.85km (1nm) in range. Chaff rejection performance is better than 100dB.

"Clam Shell" will improve the coverage of S-300 batteries tasked with engaging terrain-following strike aircraft and low flying cruise missiles, providing 360 coverage out to the radar horizon. For a target at 500ft altitude, this could be as great as 93km (50nm) subject to terrain, weather, and antenna placement in elevation. While the basic mobile "Flap Lid B" arrangement is unable to exploit this capability effectively, should the mast mounted "Flap Lid A" variant be employed ( a system originally fielded with early S-300P SA-10a), the system can cover a low altitude footprint in excess of 6,700km (1900nm) square. Setup time for the 40V6M mast is quoted at 1hr, while the taller 40V6M2 requires two hours to site, deploy and elevate. These are viable deployment times for strategic fixed deployment, and tactical semi-mobile deployment, should pre-surveyed sites be employed. System mean time between failure (MTBF) is quoted at 100hr, and mean time to repair (MTTR) is 0.5hr.

To date Western manufacturers have not disclosed whether currently deployed anti-radiation missiles such as the AGM-88 HARM and Matra-BAe ALARM have the capability to detect and engage CW emitters such as the "Clam Shell". Should this capability be absent in current inventory rounds, effective suppression of SA-10 site acquisition components will be significantly complicated. Because a "Clam Shell" supported S-300 battery has an effective capability against low flying cruise missiles, the alternative of suppression using cruise weapons, as was performed in Bosnia and Southern Iraq, may not be viable.

The latest models of the S-300 provide significant range improvements over earlier variants. The S-300PMU-1 (SA-10d "Grumble") was the first model to employ the new NII Priborostroyenie 64N6 "Tombstone" 3D surveillance and acquisition radar and the Almaz 86M6 brigade command and control system or its 86M6E export variant. Performance characteristics of the planar/phased array 64N6 have not been publicly disclosed, the use of array techniques suggests substantially lower sidelobe performance in comparison with its predecessors. This combined with newer signal and data processing hardware would provide a significant improvement in ECCM performance against earlier acquisition radars used with the S-300.

The new S-300PMU-2 Favorit (SA-10e) also uses the 64N6 "Tombstone" 3D surveillance and acquisition radar or the latest 96L6E 3D surveillance radar, plus a revised 83M6E2 command and control system and 48N6E2 missile. Reports indicate that the S-300PMU-1 can be upgraded to the latest configuration, but it is unclear whether the older 48N6E rounds used by the S-300PMU-1 retain compatibility with the newer fire control system.

China's PLA, an existing user of the S-300 series, is considered a likely export customer for the Favorit, which the Russians consider a vital source of future hard currency earnings. The S-300PMU-1 was supplied recently to Cyprus. Some sources suggest that Iran and Syria are also likely customers for this capable SAM system. To date export sales of the S-300 series have been very limited, with early variants supplied to Bulgaria, Slovenia, Poland, the GDR, Belarus and Kazakhstan, according to Russian sources. Other reported customers are Croatia, Hungary, and the Ukraine.

The LEMZ 76N6 Clam SHell FMCW acquisition radar is specifically designed to acquire and track ruise missiles and low flying aircraft. The version shown here is mounted on a 23. m (7 ft) 40V6M elevating mast. (LEMZ via Carlo Kopp)