(Received November 16, 2008; accepted February 25, 2009; published online July 21, 2009)
A new approach of frequency-modulated pulse compression for target ranging using ultrasonic pulse-echo is discussed. To acquire a receiving signal with a broader bandwidth, a flatter spectrum, and a higher signal-to-noise ratio, the use of a sensitivity-compensated transmitting signal is proposed. To compensate for the uneven and narrow bandwidth of the receiving signal brought forth by the sensitivities of ultrasonic transducers, the sensitivity-compensated signal is calculated by inversing the spectrum of the response function majorly composed of the sensitivities of transmitters and receivers. Moreover, instead of the transmitting signal, a reference receiving signal with an expanded flat spectrum measured priorly is employed for cross-correlation calculation with the receiving signal. The efficiency of the proposed method, compared with both the inverse and matched filtering methods using a chirp wave as the transmitting signal, is studied by a target ranging experiment in air. The results show that the spectrum of the receiving signal is compensated for and expanded using the sensitivity-compensated signal, and that unevenness of less than -20 dB in the spectrum of the receiving signal of the chirp wave is compensated for efficiently. Furthermore, the results of pulse compression show that, using the proposed method, the signal-to-noise ratio of the compressed pulse can be expected to be improved by more than that derived by the inverse filtering method, while the pulse width is shortened and the resolution is improved up to about 1/3 of that acquired by the matched filtering method with a chirp wave.