Research And Implementation Of Miniaturized Passive Mixers Based On Impedance Transformation

This thesis focuses on miniaturized passive mixers based on impedance transformation and summarizes the overseas and domestic research status.Mixers are widely used to convert the baseband signals to radio frequency signals that can be transmitted by antennas,or to shift the radio frequency received by antennas to baseband signals.Therefore,mixers are playing a great role in radio transmit-receive system.Researches about mixers are hot issues for both RF engineers and other researchers.Mixers studied by this thesis consist of coupler,mixing component and filter.As an important part of mixer,performance of filter has great effect on performance of mixer.There are two microstrip filter designing schemes proposed in this thesis.Three single balanced miniaturized passive mixers based on diode characteristics are designed by using one five-port circuit structure and two different impedance-transformation branch-line couplers,respectively.The circuit configurations mentioned above are simulated by ADS and HFSS.The correctness of the circuit configurations are verified by the fabrication examples.The main works and innovation points of this thesis are mainly reflected in the following three aspects:(1)Two different planar microstrip filters are designed.The first one,which is a low-pass filter,consists of cascaded non-uniform radial stubs and transmission lines.However,the other one,which belongs to the dual-band band-pass filter,is based on quad-mode resonator.The fabricated filters show perfect performance at compact size and can be used to realize miniaturization.(2)A passive mixer with flexible layout is realized by using a five-port circuit structure.The whole circuit structure consists of five-port unit located on the radio frequency substrate,the mixing components-Schottky diodes and a low-pass filter.The Schottky diodes can be connected directly to the five-port unit without the request for additional matching circuits,reducing the circuit size.The measured and simulated results show that the mixer has a good performance on low loss(measured conversion gain=-9.7dB)and high linearity(P1dB=6 dBm).(3)Two kinds of compact passive mixers are proposed by adopting a single-band branch-line coupler based on impedance-transformation from real impedance to complex impedance and a dual-band branch-line coupler which has the impedance-transformation between different real impedances,respectively.The mixers both omits redundant impedance transformer,which simplifies the origin four-tier structure into three-tier structure.Therefore,the mixer proposed in this thesis has a compact size and can contribute to device miniaturization.Finally,simulated and measured results are presented,verifying the validity of above circuit's configuration.