Phenomenology of signals in FSR for surface targets detection

Abstract

In this paper the Doppler phase signature forming in Forward Scatter Radar (FSR) is analyzed to show the rationale for "true" forward scatter radar where a target actually crosses the baseline and the whole Doppler signature is used for target detection, speed and trajectory estimation. Several measured Doppler signatures are compared where the target is in one of diffraction zones with the view to separate between pure shadow radiation and bistatic scattering. Two identical objects, metallic and magnetic absorber covered, are chosen to demonstrate the difference in shadow and bistatic scattering mechanisms.

Signal characterisation and processing in the forward scatter mode of bistatic passive coherent location systems

“…From this figure, it is seen that the SLR can be as small as -60 to -80 dB. The measured SLR from a car (Land Rover Discovery) at the same frequency with a 300-m baseline is about −70 dB which reasonably well corresponds to value of −58 dB calculated by Equation (19). The next step is to estimate the leakage signal phase noise level.…”

“…Rectangular and spherical targets with FSML width defined at the -3 dB level correspond to K ≈ 1, but for more complex targets and/or a lower reference level, K may be between 1 and 4. In practice, a simplified approach could be used [19,28] whereby a target is approximated as a rectangular plate with length L and height H. Hence, the -3 dB level of FSML in azimuth plane will be θ FS,az ≈ λ/L and in elevation θ FS,el ≈ λ/H. A simplified definition can now be made, such that if the FSML is pointing to the radar receiver, the system is referred to as FSR, omitting any conditions on scattering region to provide enhanced RCS.…”

“…The simplified FS receiver block diagram is shown in Figure 11 (see also Figure 1). The nonlinear element has the transfer characteristic S out = (S in ) 2 , and there are two signals present at its input, the leakage signal (phase noise free in this example) and a signal scattered from a target with Doppler shift ω d [19]. At the output of the nonlinear element, the signal will be…”

“…However, commonly shared opinion is that FSR has rather limiting capabilities, such as limited coverage due to narrow angular width of the main shadow lobe, strong clutter, presence of the Doppler dead zone, and, therefore, will not significantly contribute into the performance of PCL. In [17][18][19][20][21][22][23], however, it was shown that dedicated FSR can provide excellent Doppler resolution and its algorithms enable both estimation of target trajectory and speed and classification. This article aims to show that FSR when integrated into PCL systems will have the same capabilities as in the case of dedicated FSR, will add extra benefits to the existing bistatic mode of operation of PCL and can practically be implemented on both hardware and software levels without requiring significant restructuring.…”

“…FSR signatures are formed in a specific way, which govern the signal processing algorithms used. Depending on the scenario, signatures are composed of varying contributions of both FS shadowing of the direct path signal and bistatic scattering when the target is in the vicinity of the baseline [19,24,25]-to note, in PCL systems the direct path is usually referred to as the transmitter-receiver leakage signal [15,16] and in bistatic configuration is typically unwanted. This highlights an advantage of FSR: the ability to detect stealth targets through observing perturbations in the direct path signal.…”