FMCW radar for hidden object detection

Abstract

The use of FMCW radar for the detection of hidden objects at short distances is described. The factors which influence the type of radar and the optimum parameters for FMCW radar are discussed. It is shown that FMCW radar is good for situations where a high resolution is needed at a short distance, such as the detection of flaws in building materials. Practical systems are described. Both FFT and nonFourier methods are used for processing the radar returns. Multiple targets hidden in media can be revealed by digital subtraction or template matching using a numerical optimisation procedure. The radar is shown to be capable of producing images of targets. IntroductionThere are many uses for a radar that will detect and recognise hidden objects a short distance in front of the radar. The problem of developing and testing a successful hidden-object radar is a daunting task which is still in a relatively early stage of evolution. The aim of this paper is to review the use of short-distance frequency modulated carrier wave (FMCW) radar for the detection and recognition of hidden objects. This paper is based on research that has continued over a number of years. A number of workers have developed radars for locating underground pipes and for geophysical prospecting [1][2][3][4]. The problem is characterised by the need for a radar with a very large dynamic range and high sensitivity. A version of the FMCW radar was developed for this purpose [5], but as will become clear later in this paper an FMCW radar is not well-suited to these applications, where a relatively low frequency signal has to be used to achieve adequate penetration in lossy soil. Consequently, most of the radars that have been developed for buried-object detection have been pulse radars [2,3,6] or have used holographic imaging [4,7]. There are, however, a range of applications where the detection is required of an object that is hidden only a very short distance in front of the radar. Examples of this type of application are the detection of voids in walls, the testing of homogeneity of building materials and the verification of the presence of reinforcing bars in concrete. In such applications the depth of penetration is less of a problem, the main requirement being high resolution. It is in these Paper 6141F (E15), first

RCS based target recognition with real FMCW radar implementation

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