South Africa is one of the a few countries in the world to have successfully developed a passive radar system, capable of detecting both large and small aircraft using only a signal receiver.
At last week’s Aardvark Roost Electronic Warfare Conference held outside Pretoria, Francois Maasdorp, an engineer at the Council for Scientific and Industrial Research (CSIR), told delegates that with passive radar one only needs a receiver to detect signals emitted by other sources, such as FM radio towers, TV transmitters, WiFi and weather radar.
This makes passive radar (also known as passive coherent location, passive bistatic radar, piggyback radar and covert radar) cost effective, highly mobile and covert. By using several antennas one can use triangulation to identify the location of an aircraft, or by using a single receiver one can use the angle of arrival of the signal to determine a target’s location.
Maasdorp said there were many examples where passive radar would be useful, such as border safeguarding, peace mission support, disaster relief, active war support, air traffic control (ATC) support etc. Replacing or complementing ATC radar in Africa is a very useful application of passive radar, according to the University of Cape Town, as it would be fractionally cheaper than buying active radar systems.
One of the most important benefits of passive radar is that it is covert, as it does not rely on a transmitter that can be detected and destroyed. Furthermore, it is possible to detect stealth aircraft using passive radar. Conventional radar relies on a signal bouncing back from a target – in the case of stealth aircraft, this signal is absorbed or reflected away from the radar receiver. A passive radar, on the other hand, measures distortions and disturbances in the soup of signals in the atmosphere and detects the aircraft in this way.
The market for passive radar is still in its infancy with only a few systems available on the market, but a number of countries and institutions are working on the technology. Maasdorp said research is being conducted at a number of universities, including the University of Cape Town, the University College London, University of Pisa, University of Warsaw and elsewhere in the United States, France, German, Russia, China and others.
Craig Tong, a PhD student at the University of Cape Town, said that the university, in association with Peralex Electronics and CSIR Defence, Peace, Safety and Security (DPSS), has developed a prototype system that can be deployed in the field. During testing, three receiver sites were established in the Western Cape and the system was used to detect airliners at ranges of 150 km. Testing was also done at the Paardefontein range outside Pretoria, where a light aircraft (Cessna 172) was successfully detected and tracked.
A small number of companies have developed commercial passive radar systems, according to Maasdorp, such as Lockheed Martin with its Silent Sentry system. This uses FM radio towers as its source and can detect a ten square metre target at 220 km and track hundreds of targets simultaneously.
Other systems include the Selex Aulos, Thales Homeland Alerter 100 (200 km detection range) and EADS/Cassidian multiband system with a 160 km range – the manufacturer claims it can detect cars and cyclists a few kilometres away.
Due to its advantages, passive radar is expected to corner a large portion of the defence, homeland security and civilian radar markets, according to a report entitled ‘The Military and Civil Aviation Passive Radar Market: 2013 – 2023’ by Market Research Reports.
“Few companies have developed effective, marketable systems. However, as the technology becomes more sophisticated and affordable, more and more competitors can be expected to enter the market, particularly in defence and homeland security,” the company said.
“By the end of 2023, we expect passive radar technology investments to account of more than $10 billion in revenue, following a CAGR [compound annual growth rate] of nearly 36% between 2013 and 2023.” Market Research Reports said that passive radar investment will comprise nearly 41% of the total military radar spending between 2013 and 2023.
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