Overview

Military radar applications must generally take into account hostile countermeasures in the form of irradiation of interference signals from jammers, which emit different waveforms occupying the frequency band of our own radar as an electronic countermeasure (ECM). Usually for the investigation of countermeasure against this threat the assumed interference waveform is noise. The signal-to-noise ratio for target echoes at the output of the radar receiver would be dramatically decreased by this interference and target detection would be impossible or a lot of false alarms generated. Therefore we have to develop adequate electronic counter countermeasures (ECCM) to maintain the operation of our radar [1]. One common technique is to spread our own frequency band by changing the operating frequency using a random pattern for the frequency selection. This technique is named frequency agility. We thus force the enemy also to spread his noise power over a wider frequency band and therefore the spectral power density of the jammer in our receiver is minimised.

Several radar functions rely on coherent processing of a train of pulses within a so-called coherent processing interval (CPI) without any frequency change. This is especially the case in the Doppler processing mode for moving target detection and location in the presence of clutter. The operator of the jammer may then learn our frequency quickly, and concentrate his noise power on our operating frequency band.

The jammers may be carried by special aircraft flying on holding patterns in a stand-off mode or may be installed on the...