Mainlobe clutter cancellation by DPCA for space-based radars

The author reviews the principle of displaced phase center antenna (DPCA) techniques for the cancellation of mainlobe clutter by introducing correction signals in the first stage of a multistage delay-line canceler. An equivalent network transfer function H(f, theta ) was used to demonstrate the canceler's shifting null response point for scatterers at various azimuthal positions theta off the radar beam center. The moving target indicator (MTI) clutter improvement factor (IF) is formulated in terms of a specified transfer function. Assuming that the radar antenna is a 25798-element rectangular array with unweighted element excitation on transmit and amplitude-weighted according to a Gaussian function on receive, the IF is calculated by an accurate evaluation of the double integrals numerically. The results for an L-band space-based radar with a platform velocity of 7.053 km/s are summarized in a series of curves showing IF in decibels versus clutter internal Doppler spread for various angles of radar beam scan in azimuth and elevation and for different values of radar pulse repetition frequency (PRF). From these results, it is concluded that, even in the worst scan and environment conditions, a 40-dB or better IF can be maintained for the L-band radar if a sufficiently high PRF, about 2 kHz, is used.<
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