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The paper discusses the overall concept of electronic warfare (EW) and defines its three main subsets: electronic support measures (ESM), electronic countermeasures (ECM) and electronic counter-countermeasures (ECCM). The requirements for ESM receivers are reviewed in the context of two specific scenarios: that of intelligence gathering for communications and radar. The different current ESM receiver designs for measuring the presence and frequency of pulsed radar signals, i.e. crystal video, instantaneous-frequency measurement (IFM) and scanning superheterodyne, are described and compared to show their capabilities. Specific ESM receiver equipments for identifying bearing and frequency information are discussed for both the communications and radar scenarios. In comparison, the significance of the new receiver architectures based on surface-acoustic-wave (SAW) channelised, compressive and acousto-optic Bragg cells are also discussed, illustrating their enhanced multiple-signal capability. The paper subsequently discusses active and passive EW techniques such as the use of jamming and chaff and the importance of integrating the ESM receiver and active ECM function into a single equipment. Finally, the paper reports on the use of ECCM coding techniques to retain use of the spectrum when jammers are present in radar and communications systems. The use of adaptive signal processing for cancelling out wide- and narrowband interference is also demonstrated. This outlines the relative significance and areas of application for adaptive antennas, based on fully phased arrays and coherent sidelobe cancellers.