Research On Miniature Microwave Transceiver Front End Of Harmonic Detector With High Suppression

Harmonic detector is an application of the radar.It can judge whether the target containing metal or semiconductor junction through detecting second harmonic signal and third harmonic signal which reflected by target.Harmonic detector can detect bugs and other small electronic devices,it is mainly used for military counterterrorism,secret security and privacy protection.Because the harmonic detector transmitter channel has nonlinear characteristic,which leads to the harmonic component of the impact performance on the machine,so the improvement of harmonic suppression has been a research focus.At the same time,because of the demand of portability,the miniaturization of harmonic detector is also a focus.In this paper,the high inhibition of miniaturization of harmonic detector transceiver front-end was realized based on the two aspects of designing transceiver front-end circuit and the new type structure of the cavity filter.In the part of designing microwave transceiver front-end circuit structures,The transmitter which used no modulation pulse transmitting structure,produced 2.4 GHz to2.485 GHz signals.The receiver used direct detection structure.The landscape area of transmitting module and receiving module was reduced to 4.5cm×3.8cm and 5cm×4.8cm.Besides,the LTCC filter is added in the transceiver module to enhance the isolation between the channel and harmonic suppression capability.In the part of designing cavity filters,the cavity filter of transmitter was realized by adding metal squares to reduced volume,which using the theory of the load capacitance.It also made the parasitic passband away from 7.2GHz through increasing the bandwidth and improving the center frequency.Finally,I designed a filter which had high out-of-band rejection.Its testing band width was 2.37GHz-3.41 GHz,the rejection of 4.8GHz was more than 130 dBc,and the rejection of 7.2GHz was more than 78 dBc.The two filters of receiver realized high out-of-band rejection and small volume through using the combination interdigital coupled structure and comb-like structure.One of the filters' testing bandwidth was 4.8-4.97 GHz,the rejection of 2.4GHz and 7.2GHz were about116 dBc and 109 dBc.The other filter's testing bandwidth were 7.16-7.5GHz,the rejection of 2.4GHz and 4.8GHz was about 113.5dBc and 101.4dBc.Finally,I realized a transceiver front-end which had small volume and high rejection.The volume was10cm×13cm×2.5cm.The transmission power of transceiver front-end was 33.9dBm,The second harmonic suppression of transmitter can reach 105 dBc,three times of harmonic suppression is greater than 120 dBc.Two receivers' sensitivity was-98 dBm and-93 dBm.Although the power of base signal and harmonic wave signal which input to receivers was 45 dBm,the receiving circuits were not be affected.