Bee Searching Radar With High Transmit–Receive Isolation Using Pulse Pseudorandom Code

This paper presents an innovative radar architecture to improve the isolation of the harmonic radar between the transmitter and the receiver. The proposed radar transmits two closely located frequencies to the transponder, and the transponder transmits a response signal at a mixed frequency. Because the frequency of the response signal is different from those of the clutter and leakage signals, the isolation is significantly improved. For a traditional harmonic radar, the leakage signals should be suppressed to a sensitivity lower than -106 dBm to avoid interference. The proposed radar requires only attenuation of leakage signals to a level lower than -8 dBm to avoid low-noise amplifier saturation. Harmonic radar transponders are compatible with the proposed radar system without additional design. This paper also proposes a new method for maintaining the correlation of transmitter and receiver phase noise. Field test results demonstrate that leakage signal interference in the proposed radar is far lower than that in the harmonic radar. The significant improvement in isolation reveals the advantages of applying the frequency mixing concept in the proposed radar.