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This study presents the signal processing techniques applied on a 9.4/18.8 GHz harmonic radar, which is used to investigate behaviours of small insects such as bees, beetles and butterflies. It is still a challenge to achieve high accuracy and long detection range simultaneously in a harmonic pulse radar system. The authors combine the spread spectrum technology with the classic pulse harmonic radar system to overcome the dilemma between accuracy and detection range. The processing gain of the pseudo-random code from the spread spectrum technology is used to increase the sensitivity and makes the system able to detect the signal with the weak power strength below the system noise level. To eliminate the effect caused by the local leakage, the signal-processing method provided to cancel the leakage through applying the symmetric property of the autocorrelation function of the pseudo-random code. In the field tests, the proposed system achieves a 60 m detection range within 1 m ranging accuracy by using 1.75 W transmitting power corresponding to 40.430 dBW equivalent-isotropically radiated power (EIRP). It is estimated to extend to at least 900 m detection range by using a 3 kW transmitting power corresponding to 72.771 dBW EIRP.

This paper presents a 9.4/18.8-GHz harmonic radar to investigate the behavior of bees with colony collapse disorder. The challenges of using harmonic radar for bee searching include the requirements of high range accuracy and high sensitivity. A new harmonic radar using the pseudorandom code positioning technique to simultaneously achieve high range accuracy and high sensitivity is proposed. This study also proposes a new method to cancel the local leakage to further improve sensitivity. To realize the transponder, a compact antenna is designed using the topology characteristics of the composite right/left-handed transmission-line concept. The measured sensitivity of the transceiver is -120 dBm, which is 27 dB lower than the noise level. Field testing results demonstrate a 60-m detection range within 1-m distance error with 1.75-W transmitting power. The significant improvement of the sensitivity and the range accuracy reveal the advantages of applying the code-positioning technique to the harmonic radar.

This paper demonstrates a 9.4/18.8 GHz harmonic radar for bee searching to investigate the phenomenon of colony collapse disorder (CCD). The radar system transmits a pulsed coarse/acquisition code (C/A code) signal with 0° and 90° shift key modulation and then receives the C/A code signal from transponders attached on the bees in BPSK modulation. Using the technique of C/A code positioning, a distance resolution of 0.15 m is achieved. The transponders are designed to minimize the effect from the bodies of bees. The outdoor experiments indicate the sensitivity of the radar system to be −95 dBm and with the distance of 65 m with 6-W peak power. With 3-kW peak power, the distance at which the bees can be located is expected to be 450 m.