Reliable detection of life under rubble and collapsed buildings after disasters like earthquake or air raid is the most important issue in life-detection process. In this paper, the performance of microwave life-detection system (MLDS) based on a continuous wave (CW) radar is analyzed from different aspects such as penetration depth, sensitivity, and total harmonic distortion (THD) of the output signal. A novel quadrature receiver as an appropriate architecture for the MLDS, and harmonic radar system as an alternative structure are proposed in order to resolve the well-known null point issue and improve the sensitivity of the system. Results show that by using these structures in the MLDS, the null points can be completely removed and hence the chance of detecting a trapped victim under the rubble can be improved considerably. Moreover, by using the harmonic structure, the received power in some distances away from the MLDS can be improved by 3 dB compared to that of the conventional systems. By examining different frequencies, 1.15 GHz (L-band) is found to be the most appropriate carrier frequency because of deeper penetration of about 5 meters in the rubble and 7 percent improved output signal THD compared to the previously designed X-band radars for the MLDS.

Keywords: Microwave life-detection system, harmonic radar architecture, modified quadrature receiver, continuous wave radar, penetration depth, total harmonic distortion, heartbeat, respiration.

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