Short-range sea clutter in horizon search radar systems: antenna pattern effects

Short-range clutter can limit the performance of radar systems using high pulse repetition frequency waveforms. The paper evaluates the antenna pattern effects of short-range sea clutter for an example horizon search system. Clutter-to-noise ratio (C/N) and signal-to-noise ratios (S/N) are evaluated for several antenna designs, in which aperture illumination weighting can be achieved on either transmit or receive. Three antenna effects are studied: illumination function (pattern), elevation of the pattern with respect to horizontal (`upspot´), and aperture diameter. Of several cases examined, one with uniform weighting on transmit and Taylor weighting on receive gives the most desirable clutter response. With reference to the case of uniform transmit and receive patterns with no upspot, a Taylor receive pattern with -42 dB sidelobe level in combination with an optimal upspot angle reduces worst-case clutter by ≈14.7 dB at the expense of ≈10.25 dB increase in the transmit power required to equalise S/N to that of the reference. Doubling the aperture diameter further reduces worst-case clutter by ≈13.2 dB, with required transmit power actually decreasing (≈12.41 dB) over the previous case. Here, the cost is a larger antenna. Antenna considerations are shown to have a considerable impact on clutter and to be perhaps the best method of reducing radar dynamic range requirements