Wideband phased array radar with digital adaptive beamforming

Future defence radar systems, and in particular the ballistic missile defence (BMD) application, demand radar with high resolution in both angle and range. The high resolution angle estimation requires a large antenna aperture of many wavelengths. The high range resolution requires a wideband waveform of several hundreds of MHz. This paper considers architectures and waveforms for wideband phased array radar and in particular the application of advanced digital adaptive beamforming. A typical wideband waveform used in this class of radar is linear frequency modulation (LFM). It is shown that this waveform is particularly well suited to digital adaptive beamforming. The large electrical aperture demands the use of time delay units for beamsteering, at least at subarray level. A new approach for digitally synthesising the time delay steering is presented. The importance of employing irregular (randomised) subarraying for time delay steering is presented to avoid the problem of wideband grating lobes. This is also a requirement of adaptive beamforming. Finally, an architecture for wideband digital adaptive beamforming which fits well with the use of LFM waveforms is presented.