New chapter for naval radars.

The unveiling of the AN/Spy-3, the first order for Herakles, the coming on line of Sampson and the entry into service of the Apar make this an exciting time for naval radar development. It is especially important for the new generation of multi-function sensors with their active elements.

Two decades ago multi-function radars were used only by the United Stales due to its sheer sophistication. Multi-function radars (MFR) have a large number of small gallium arsenide transmitter/receiver modules mounted in a flat array which forms the antenna. Just as electronic scanning in the vertical plane can be controlled by phase shifting, the active ray can be controlled in azimuth as well as in elevation. Because each module has its own radiating and receiving antenna they transmit radar pulses individually. Each is controlled in phase so the whole array produces a beam of energy of the required shape, directed toward the desired location.

This enables radar energy to be concentrated in pencil beams for general surveillance, scanning the whole area around the ship in azimuth and elevation. Scanning is usually provided through angles of up to 60 degrees, although the performance will drop as the angle increases due to the reduction in antenna aperture. Surveillance can also be focused upon an area either because of the presence of targets or because it is a jamming source.

The first production multi-function radar, the Lockheed Martin AN/Spy-1, was at the heart of the Aegis combat system and was so large that it could only be installed on Ticonderoga class cruisers and Arleigh Burke class destroyers. Now a wide range of multi-function radars are becoming available for much smaller hulls, and even the Spy-1 itself has been downsized. It has been selected as the prime sensor for the Norwegian Fridtjof Nansen class frigates.

There are two reasons why a technology once available only to a super power has become more common. The first is technical; the gallium arsenide technology is also a feature of modern cellular or wireless telephones which helps bring a significant reduction in module manufacturing costs.

The second is operational; with the switch from ocean or 'blue water' to littoral or 'brown water' operations. This environment tends to be more densely cluttered in returns from landmasses as well as targets with numerous unidentified or neutral contacts. Local propagation effects may also hinder the tactical picture compilation--severely reducing the time required for track confirmation and generating warnings.

The conventional rotating antennas have many drawbacks in this environment. In search radars all search-and-track functions must be performed at the same rate: while tracker radars are restricted to following one or two targets at a time leaving the ship vulnerable to multiple threats.

Because a multi-function radar steers the beam virtually instantaneously in any direction to perform both surveillance and multi-target tracking, by managing time and energy, functions such as volume surveillance, horizon search or target tracking are performed in very rapid succession under computer control.

Multi-function radars bring several advantages for ship designers and operators: they generate power at the mast-head reducing waveguide losses and maximising the energy in space. This is particularly important for reliably detecting low radar cross-section targets in clutter while the large number of modules provides both redundancy and graceful degradation in case of damage.

The original Spy-1 not only remains in production, having been selected by Japan, Spain and South Korea, but also is being substantially enhanced. The Spy-1D(V) has just successfully completed trials and the Aegis Baseline 7.1 became fully operational during the spring. This version has an improved signal processor, a simplified driver to improve average power, a track-initiation processor and software modifications. These improvements are designed to overcome clutter problems, to reduce high loadings caused by transient tracks and to improve detection performance against stealthy threats.

Further developments are taking place to meet the demands of littoral operations. The sensor is simultaneously being prepared for the ballistic missile defence role, allowing it to detect and to track such missiles after launch and to guide interceptor missiles towards them. The US Navy plans to have 24 Aegis ships configured for ballistic missile defence; Japan will also acquire this technology and there is likely to be interest from South Korea and Australia for their forthcoming destroyers.

Lockheed Martin has also developed a smaller version of the sensor as the AN/ Spy-1F for which Norway is the launch customer. This sensor features smaller aerials (2.4-metre diameter compared with 3.7 metres for the Spy-1D), and 1856 elements per array face compared with 4350 and similar scale electronics. The company has also proposed an even smaller sensor in the form of the Spy-1K for corvettes and light frigates with a 1.7-metre diameter antenna and 912 elements.

A successor is well under development by Raytheon Integrated Defense Systems as the AN/Spy-3, the first production version of which was delivered to the US Navy for functionality tests last year (2003). This is an I/J-band sensor with three arrays each and some 5000 elements in multi-channel modules of eight elements.

The modules slide into the array structure and provide a high-conductivity thermal path to the cooling-array manifold without having a direct link. This simplifies maintenance and reduces coolant leaks within the array.

A single commercial supercomputer acts as signal and data processor and provides improved control. Signal processing features include channel equalisation, clutter filtering, impulse editing, Fast Fourier Transform Doppler, pulse compression and side-lobe cancellation.

The Spy-3 will be used not only in the new generation of surface combatants, DD(X) and CG(X) but also in the new aircraft carrier (CVN-21) and the amphibious warfare ships. The AN/Spy-3 will operate in conjunction with a D-band Volume Search Radar (VSR) as a dualband radar suite providing situational awareness, air control, track identification, counter-battery detection, horizon search and weapon control.

Israel

After the painful sting inflicted to an Eilat class destroyer by an Egyptian Styx missile in 1967, Israel seriously put itself into overdrive to develop not only anti-ship missiles (the Gabriel in this instance) but also detection and self-protection systems for its ships. With the passing years Elta has become a world leader in this department and currently offers the EL/M-2221, which is the fire control radar developed in the context of the Barak point defence missile. Also known as the STGR, the dual-band (X and Ka) radar is able to acquire a missile at a range of 15 km and an aircraft at 30 and can be used to drive self defence guns against, for example, sea-skimmers.

When saturation attacks were a serious threat, Elta developed the EL/ M-2228S. This automatic missile detection radar looks up 70 degrees to also pick anti-radiation missiles in their end dive or television-guided bombs--in other words, non-radiating weapons. The S-band pulse Doppler radar and can track over 100 surface and air targets and is suitable for small ships.

Europe

The first European multi-function radar to have entered service is the Thales Apar (Advanced Phased Array Radar) and is operated by the German and Netherlands navies. Another I/J-band sensor, the Apar has four fixed arrays each of which has 3424 modules with four elements apiece.

The antenna units weigh some eight tonnes; all having 64 column assemblies each with a data-distribution unit, a converter and a part of the beam-steering computer with every face generating a heat load of 85 kW. Consequently there are four cooling supply units within the mast.

The mass of the Apar antenna unit, as with the Aegis', is a major drawback for applications in smaller ships. For this reason studies have been conducted on a smaller version, the Seapar, which was revealed by the company last year. This is designed to incorporate a much smaller element, allowing a reduction of some 50 per cent in masthead weight, a single multi-channel processor (there are four in the Apar) and only two instead of four waveform generators. Ships as small as 1500 tonnes could accept the Seapar, which might be available in three years' time.

The Anglo-Italian company AMS has developed two multi-function radars, the Empar (European Multifunction Phased Array Radar) and the Sampson based upon rotating antennas. Enhancements are planned to provide a tactical ballistic missile interception capability.

The Empar is a G-band sensor and in service on the French carrier Charles de Gaulle. It has a single phased array with 2160 elements driven by a coherent TWT transmitter with a peak power of 120 kW. The sensor, which has a cots management computer, will be used by the Franco-Italian Horizon/Orizzonte class destroyers.

The British equivalent of these ships, the Daring (Type 45) class, will use the Sampson with a dual-face array, each with some 2600 radiating elements (four per module). Essentially the Sampson consists of two independent radars and a common control and an air-cooled antenna that rotates at 30 rpm.

AMS selected a dual rotating antenna to reduce costs and weight. The 4.6 tonne antenna can now be installed higher to extend maximum detection range will the use of air-cooling simplifies the slip-ring assembly.

A rotating solution has also been selected by Thales Naval France (TNF) for its Arabel I/J-band and Herakles E/F-band MFRs; the former used by the French Navy and the latter selected by Singapore for the Formidable class frigates. This has a 50 kW peak-power, coherent, solid-state transmitter and is a single-phase sensor with 1761 phase shifters. The antenna rotates at 60 rpm and four beams can be created simultaneously with the sensor able to track up to 600 targets at a time.

Sea trials of an Australian radar developed by CEA Technologies are anticipated in the very near future in an Anzac class frigate. The E/F-band CEA-Far is being developed to provide considerable flexibility using a modular tile-and-panel active-array concept.

Each panel consists of four tiles and is 674 [mm.sup.2] in size and about 50 kg in weight. Performance is enhanced by adding panels to create a face with the required performance. The sensor can be configured to have either a single common processor for each face or one for all four faces to reduce scan time. While up to six faces can be provided the system to be trialled will have only four.

CEA-Far was a contender for the new Australian destroyer but it appears that the ship's prime sensor will be the AN/Spy-1, although dedicated weapon control versions of CEA-Far are feasible.

In multi-function radars the I/J-band is preferred on the grounds of its superior horizon detection potential but for longer range a dedicated search radar, usually in L-band, (one to two GHz) is needed. AMS is developing the D-band (to provide range) T1850 for the Daring class 3D very-long search radar to augment the Sampson while Thales will provide a similar sensor, Astral, for the Franco-Italian equivalent.

Multi-function radars will retain a conventional surveillance radar for long-range detection, but they remain the prime sensor for smaller warships such as frigates, corvettes, offshore patrol vessels and fast attack craft. These radars are becoming more sophisticated through advances in transmitter technology (exploiting cots products), antenna design, and software-based processing.

They now provide high 2D and 3D performance in terms of detection range, tracking accuracy, false-alarm rate and electronic counter-countermeasures to provide general surveillance, missile detection and target designation. They are also low weight sensors with high reliability. which cuts through-life cycle costs.

A broad range of products is available. of which only a few examples can be mentioned here. The planar array TNF MRR-3D NG has been selected for the South African Valour class frigates while Thales Nederland has supplied the MW 08 with eight stripline antennas to several customers. This was derived from the F-band Smart-S, and the company is marketing the Smart-S Mk 2 as a more modern application of the technology from 2006.

Ericsson Microwave has developed an Agile Multi-Beam version of its successful Sea Giraffe radars. These have been selected by the Swedish Navy for the Visby class corvettes, with a cone-shaped frequency-selective radome to reduce radar cross-section, and by the Polish Navy to upgrade its Orkan class fast attack craft.

Eads also produces a planar phased array sensor in the TRS-3D/16 family. This has been selected for the first of the Malaysian Kedah class corvettes, which will enter service from September and is the sensor of choice for the K-130 corvette programme.