Pulsed Signals with Zero Autocorrelation Zone for Synthetic-Aperture Radars
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RY AND METHODS OF SIGNAL PROCESSING
Pulsed Signals with Zero Autocorrelation Zone for Synthetic-Aperture Radars R. N. Ipanov* National Research University MEI, Moscow, 111250 Russia *e-mail: [email protected] Received July 10, 2019; revised March 13, 2020; accepted April 3, 2020
Abstract—A sounding signal with zero autocorrelation zone (ZACZ) that represents a series of two phasecode-shift keyed (PCSK) pulses encoded with complementary sequences of the binary D code is synthesized for synthetic-aperture radars (SARs). Discretes of pulses of the synthesized signal are additionally linearly modulated with respect to frequency for suppression of side lobes (SLs) of the autocorrelation function (ACF) in the presence of the Doppler frequency mismatch. Correlation characteristics of the synthesized signal are compared with the characteristics of the signal without modulation of discretes and PCSK signal encoded with the M sequence (MS). Total correlation characteristics of an ensemble of signals are analyzed in the regime of synthesis of the SAR aperture. In the presence of the Doppler frequency mismatch, the level of all ACF SLs in the ZACZ of the synthesized signal is lower than the level of the MS-encoded PCSK signal. The total ACF of an ensemble of four signals has zero SLs along the entire time axis τ. In the presence of the frequency mismatch, the SL level of the ACF is lower than the SL level of the total ACF of the ensemble of four MS-encoded PCSK signals. DOI: 10.1134/S1064226920080069
1. FORMULATION OF THE PROBLEM The following requirements are imposed on the sounding signals to obtain high-quality radar images (RIs) in the synthetic-aperture radars (SARs) and inversed SARs. (i) The signals must be coherent within time of the aperture synthesis to provide relatively high spatial resolution with respect to azimuth. (ii) The signals must have intrapulse modulation to simultaneously provide high mean power of radiation and high spatial resolution with respect to elevation. Spaceborne SARs that are used for land remote sensing still employ signals with linear frequency modulation (LFM) [1–4] owing to the fact that the LFM signals have been comprehensively analyzed as the first complicated signals in radar applications. The phase-code-shift keyed (PCSK) signals were used as sounding signals in spaceborne SARs for radar mapping of Venus in 1983–1984 [4, 5]. Truncated M sequences (MSs) were used as a code for such signals. Recent interest in the PCSK signals [4, 6, 7] has been driven mainly by the fact that the application of discrete encoding of a coherent ensemble of sounding pulses in the SAR allows a significant increase in the RI quality with respect to parameters related to the properties of the total correlation functions of the ensemble.
In this regard, the PCSK signals with the zero zone (ZZ) of side lobes (SLs) in the region of the central peak of the autocorrelation function (zero autocorrelation zone (ZACZ)) are promising for the SARs [8–13]. Such signals represent periodic trains of coherent pulses encoded
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