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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.

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