Design Of Ku/Ka Dual-band Mixer Based On Harmonic Mixing Structure

In order to improve the anti-interference ability of the missile-borne detection system,the detection system should have multi-band operation capability with large frequency difference.This paper focuses on the design of high efficiency RF circuits in large frequency difference dual-band detection systems.The research work on Ku/Ka dual-band mixers is as follows:1)For the problem of large frequency difference in dual-band mixers,it is proposed to use harmonic mixing to achieve dual-band mixing.Based on a diode to analyze the feasibility of dual-band harmonic mixer.The principle of harmonic mixing based on anti-parallel diode pair(APDP)structure is analyzed in detail,and the technical scheme of Ku/Ka dual-band mixer is designed based on this structure.2)For the insufficient problems of conversion loss,port isolation and flexibility in the mixer solution,analysis are made from idle frequency recovery,circuit matching,spurious suppression and band control.Reducing conversion loss by introducing a compact microstrip resonant cell(CMRC)and matching circuit.Improved port isolation and spurious suppression with SIR-based microstrip filters and waveguide filters.The switch circuit is designed to realize the function of freely switching between two working bands.3)According to the different performance requirements of each circuit module of mixer.The field-path combination method is used to solve the problem of establishing an accurate model of the mixing diode in MMW band.A novel spiral compact microstrip resonant unit(SCMRC)is used to design the miniaturized signal reflection unit and a wide stopband IF lowpass filter.The LO and RF bandpass filter with fast roll-off characteristics and high out-of-band rejection characteristics are designed based on the SIR coupling loop structure.A E-plane inductive diaphragm waveguide filter is designed to meet the requirements of high-frequency selection of RF bandpass filtering.4)All circuit modules are combined for simulation and optimization,and developed a mixer.After testing,The mixer is in working frequency range of 16.3~17.1GHz and 32.4~33.1GHz.In the on-state,the conversion loss is 11~13.8dB and 12.8~15.26 dB respectively,and the off-state is greater than 26.6dB and 27.2dB.By analyzing the test results of mixer,it is concluded that the use of harmonic mixing method to achieve a large frequency difference dual-band mixer is feasible.