Abstract
Long time coherent integration is a vital method for improving the detection ability of global navigation satellite system (GNSS)-based passive radar, because the GNSS signal is not radar-designed and its power level is very low. For aircraft detection, the large range cell migration (RCM) and Doppler frequency migration (DFM) will seriously affect the coherent processing of azimuth signals, and the traditional range match filter will also be mismatched due to the Doppler-intolerant characteristic of GNSS signals. Accordingly, the energy loss of 2-dimensional (2-D) coherent processing is inevitable in traditional methods. In this paper, a novel 2-D coherent integration processing and algorithm for aircraft target detection is proposed. For azimuth processing, a modified Radon Fourier Transform (RFT) with range-walk removal and Doppler rate estimation is performed. In respect to range compression, a modified matched filter with a shifting Doppler is applied. As a result, the signal will be accurately focused in the range-Doppler domain, and a sufficiently high SNR can be obtained for aircraft detection with a moving target detector. Numerical simulations demonstrate that the range-Doppler parameters of an aircraft target can be obtained, and the position and velocity of the aircraft can be estimated accurately by multiple observation geometries due to abundant GNSS resources. The experimental results also illustrate that the blind Doppler sidelobe is suppressed effectively and the proposed algorithm has a good performance even in the presence of Doppler ambiguity.
Highlights
Over the past few years, passive radar has attracted more and more attention and developed very quickly, due to its low cost of operation and maintenance, no need for frequency allocations, and difficulty of jamming [1,2]
For normal bistatic geometry in global navigation satellite system (GNSS)-based passive radar, a high receiver antenna gain with extremely long integration duration is highly recommended [13], and the target detection applications are normally focused on medium- or large-sized targets, like aircrafts or marine targets [6,13]
The newly modernized civil signal GPS L5 is adopted, as it is at least ten times wider in signal bandwidth and four times stronger in terms of signal power than traditional civil signal GPS L1 [39,40]. Both of signal bandwidth and signal power are beneficial to aircraft detection, and GPS L5 is a superior option in GNSS-based passive radar
Summary
Over the past few years, passive radar has attracted more and more attention and developed very quickly, due to its low cost of operation and maintenance, no need for frequency allocations, and difficulty of jamming [1,2]. The common problem of passive radar is that the power level is not high enough for detecting target effectively, and the GNSS signal is no exception, because those transmitted signals are not designed for radar application [9]. To overcome the challenge associated with low power level of the transmitted signals in GNSS-based passive radar, the target forward scattering effect can be taken into consideration [10,11,12]. For normal bistatic geometry in GNSS-based passive radar, a high receiver antenna gain with extremely long integration duration is highly recommended [13], and the target detection applications are normally focused on medium- or large-sized targets, like aircrafts or marine targets [6,13]. The cross-ambiguity function method is only applicable in short coherent time case or the Doppler spreading phenomenon could be ignored
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