Finger on the Pulse

Radar Electronic Support Measure
Electronic support measures have revolutionised electronic warfare by aiding the detection, geolocation and identification of radars, although current ESM technology does have some significant shortcomings.

Current radar electronic support measure technology has room for improvement, says a leading electronic warfare expert.

The United Kingdom’s Defence Science and Technology Laboratory’s annual Operating in the Future Electromagnetic Environment (OFEME) symposium does not disappoint. This year’s event, which took place in Nottingham, in England’s East Midlands on 20th and 21st November, had some excellent presentations. Among an array of subjects, presentations covered electromagnetic challenges in the maritime environment and optical wireless communications. Dr. Sue Robertson, a leading electronic warfare expert and director of EW Defence, discussed current shortcomings in Electronic Support Measure (ESM) technology.

Highlighting the challenges for electronic support measures to detect radar signals, Dr. Robertson told delegates that ESMs can usually only detect a radar when that signal is pointing at the system’s antennas. At 100 nautical miles/nm (185 kilometres/km) an ESM will see a radar signal for less than one percent of the time it is transmitting. At 25nm (46km) the radar is seen for less than five percent of the time it transmits. A radar will be seen for 20 percent of its scan cycle when under five nautical miles (nine kilometres) away.

Multitracking

ESMs often generate several tracks for the same radar, a process known as multitracking. Multitracking is caused by a myriad of factors. Dr. Robertson said that one of the main causes of multitracking is errors in the measurement of a radar signal’s Direction of Arrival (DOA). An ESM maybe mounted on an aircraft with the system’s receiving antennas spaced several metres apart. The problem, highlighted by Dr. Robertson, is that most ESMs are designed to treat the platform carrying them is a single point in space. This hypothesis leads to a further assumption that radar pulses will arrive at all the ESM’s antennas with an equal signal strength. However, radars can transmit signals with very narrow azimuth beamwidths, sometimes measuring one or two degrees or less. Radars with very narrow main beams might have different parts of the radar pulse at different amplitudes hitting each of the antennas at the same time. This risk causing DOA errors.

Missing pulses also create challenges for ESMs. A radar will transmit a certain number of pulses over a specific time, known as a Pulse Repetition Interval (PRI). PRI measurement is a very important task for an ESM as this information will be correlated with radar tracks to help identify types of radar. Missing pulses creates errors in PRI measurement which has a correspondingly negative effect on the ESM’s performance. Pulses are transmitted by the radar but not detected by the electronic support measure. These missing pulses are caused by the narrow shape of the radar beam, Dr. Robertson added.

Addressing the shortcomings

Dr. Robertson encouraged the Electronic Warfare (EW) community to urgently address these, and other, ESM shortcomings to ensure they can work in today’s and tomorrow’s operating environment. She stressed that the testing of ESM systems in the real world is vital: “However good your system is in theory, or however well it works in the lab environment it will almost certainly work differently, and much, much worse when it is out in the real world.”

To complicate matters, future ESMs will have to deal with much more complicated radar signals than they do today. The advent of active electronically scanned array radars being a case in point. ESMs will need to cope with multitudes of different signals performing different tasks all transmitted by the same system. In addition, ESMs will also have to work in an ever-more congested electromagnetic environment. Dr. Robertson highlighted the advent of satellite communications constellations like SpaceX’s Starlink. Transmissions from Starlink satellites to Earth in the eight to twelve gigahertz range could cause challenges for ESM systems. These wavebands are in the electromagnetic ‘neighbourhood’ where X-band (8.5GHz to 10.68GHz) radar transmission also live.

Dr. Robertson asked what role Artificial Intelligence (AI) can play in future electronic support measure architectures, specifically cognitive electronic warfare. Cognitive EW harnesses AI techniques like machine learning and neural networks to help electronic warfare systems understand and react to their environment. She stressed that technological hurdles to the adoption of cognitive EW techniques along with human trust issues must be addressed. Human trust is imperative, after all a cognitive EW system “only has to fail once and then it will never be trusted again.” Cognitive EW approaches will need to be demonstrated as safe, reliable and capable.

Ultimately, an EW system, cognitive or otherwise, is only as good as the data it receives. Work will need to be done to address existing ESM shortcomings highlighted by Dr. Roberston’s talk. The challenges for the future are as follows: Fix performance errors we know of in ESM systems, develop robust test and assurance methods and use cognitive EW without destroying the credibility of the electronic support system.

by Dr. Thomas Withington