Extended Optimal Filters for Adaptive-Ontransmit Radar Systems Using Binary Codes

Abstract

Abstract-This study introduces an extended optimal filtering technique for adaptive-on-transmit radar based on the transmission of pseudorandom noise waveforms as a method to simultaneously achieve low sidelobe level and spectral purity without degrading the main peak of the cross-correlation function. The proposed method is an extended version of the classical optimal filtering technique, resulting in longer codes with three simultaneously improved features that usually work in trade-off: 1) the cross-correlation function (CCF) sidelobe level is reduced in direct proportion to the filter length, K ; 2) the out-ofband spectral suppression is at least 40 dB for pseudorandom binary sequences (PRBS); and 3) the frequency spectrum tail presents a decay given by K −4 , offering larger out-of-band frequency suppression. The proposed technique provides skew-symmetry to the input signal and is tested on PRBS, Barker, and Golay pair of complementary codes. The proposed codes are also demonstrated to be Doppler resistant and offer better multipath capability.

Estimation of Sidelobe Level Variations of Phased Codes in Presence of Random Interference for Bistatic Wideband Noise Radar

“…Moreover, the SSL in the Golay case depends only on the noise parameters, whereas it also depends on the inherent autocorrelation noise in the PRBS case. So, we conclude that an irreducible noise is present in the ACF for a PRBS sequence, the so-called code noise [18]. The same trend is observed for the ISL parameter.…”

“…An adaptive-on-transmit (AT) system can be derived for wideband radar systems using the information given by the PSL, SSL, and ISL as a design criterion. The minimal out-ofband sidelobe (OBS) level has been pointed out as an additional criterion to choose the correct transmitting waveform [18,19].…”

“…The noise modulated radar technique offers a large number of advantages mainly due to its robustness to interferences [8,18,19], and the wideband version received importance especially in the last decades [13,14,[17][18][19]. Nevertheless, until not long ago, it was very difficult to find practical implementations of these systems.…”

“…This means that we can know the theoretical value of PSL, SSL, and ISL parameters at any instant for the transmitted code; besides, the generating conditions of the transmitted codes could be changed to improve the sidelobe values under the detection of a certain noise level presence. By adapting the sidelobe properties of the transmitted waveform to minimum levels, the overall performance of the system will achieve enhanced performance features to face anomalous or extreme operation conditions [15][16][17][18].…”