A high resolution ultra wideband radar prototype is developed for various applications through the wall imaging. The fre-
Figure 9Measured antenna gain against frequency for the proposed antenna studied in Figure 7
320MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. In recent years, ultra wideband (UWB) radars have become very popular for military and medical applications. Several UWB radars have been developed for underground mine detection [1, 2] through the wall imaging [3], cancerous tissue detection applications [4, 5] with promising results. In addition to these imaging type applications, UWB signals are also used for material characterization [6]. UWB radar systems have significant advantages over traditional radar systems. The most important feature of an UWB radar system is the high spatial resolution as a result of employment of ultra narrow pulses [7]. Moreover, the power spectrum is spread over a wide frequency range, providing a low power density and reduced interference to other RF systems. Another advantage is that the UWB signals provide multipath immunity.High resolution and high multipath immunity allows not only the detection of closely positioned targets, but also provides information about the shape and the material content of a target. As the employed bandwidth is increased, these advantages become more apparent. However, the trade-off is the difficulty of obtaining wideband components such as antennas, low noise amplifiers (LNA's), RF switches, UWB pulse generators, and ultra fast signal digitizers. Wide bandwidth operation also causes additional challenges in signal processing. In general, one cannot stipulate the received signal shape and the traditional matched filter detection approach does not yield the optimum result for every target. The reason is that the reflected UWB pulse is distorted as the reflectivity of the target changes with the frequency.In this article, a high resolution UWB radar prototype for detecting targets behind the walls will be presented. There are reports of a few GHz bandwidth operating UWB systems, such as the ground penetrating radars in Refs. 1, 8 (1 GHz bandwidth), the through wall radar presented in Ref. 3 (2 GHz bandwidth). The potential advantage of our UWB radar prototype is its wide operating bandwidth of 4 GHz between 1.85 and 6 GHz.The rest of the article is organized as follows: In Section II, details of our prototype system including the individual RF components will be presented. In Section III, the signal processing algorithms to extract the useful information from the received signal, and the visualization algorithms for the display of the extracted data will be described. Later, the experiments performed for various types of stationary and moving targets will be presented in Section IV. Finally in Section V, the article will be concluded with ideas for future work.
UWB SYSTEM PROTOTYPEOur UWB system has two major building blocks, a transmitter section for generation and emission of the UWB pulses and a receiver section for capturin...