Abstract
In harmonic radar applications, images produced using algorithms of conventional radar applications experience some defocusing effects of the electronic targets’ impulse responses. This is typically explained by the dispersive transfer functions of the targets. In addition, it was experimentally observed that objects with a linear transfer behavior do not contribute to the received signal of a harmonic radar measurement. However, some signal contributions based on a multipath propagation can overlay the desired signal, which leads to an undesired and unusual interference caused by the nonlinear character of the electronic targets. Here, motivated by the analysis of measured harmonic radar data, the effects of both phenomena are investigated by theoretical derivations and simulation studies. By analyzing measurement data, we show that the dispersion effects are caused by the target and not by the measurement system or the measurement geometry. To this end, a signal model is developed, with which it is possible to describe both effects, dispersion and multipath propagation. In addition, the discrepancy between classic radar imaging and harmonic radar is analyzed.
Highlights
Harmonic radar is a niche microwave measurement technique that enables new detection capabilities, especially in security related applications
One of the more widely known descriptions are X-Parameters [15] or the poly-harmonic distortion modeling [16]. These methods are useful for describing interconnected dynamic nonlinear circuit elements, for instance, but are not used in harmonic radar applications
The test target is placed on a rotating platform, so that the measurement setup is comparable to an inverse synthetic aperture radar (ISAR) scenario
Summary
Harmonic radar is a niche microwave measurement technique that enables new detection capabilities, especially in security related applications. One of the more widely known descriptions are X-Parameters [15] or the poly-harmonic distortion modeling [16] These methods are useful for describing interconnected dynamic nonlinear circuit elements, for instance, but are not used in harmonic radar applications. Another aspect in harmonic radar is the influence of surrounding objects and the measurement environment, both viewed as having a strictly linear scattering behavior. In conjunction with the derived Volterra and multipath model, some simple example systems composed using separate static nonlinear elements, as well as dynamic linear transfer-elements, are presented Based on these special cases, simulation studies are performed and analyzed.
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