Research On Millimeter-wave Front-ended Circuits

With the progress of science and technology,and with the rapid development of various communication devices,the electromagnetic spectrum is increasingly crowded.Millimeter-wave has the advantages of short wavelength,wide frequency band and large information capacity,and has attracted more and more attention from research institutions and communications companies all over the world.The operating frequency of various military and civil systems has gradually expanded from microwave frequency band to millimeter wave band.Especially in recent years,with the development of ultra high speed data transmission,5G communication technology and military communication technology,the demand on millimeter wave system is ever-growing.It is significant to carry out the research on millimeter wave and millimeter wave wireless systems.In this dissertation,we firstly focus on the key circuits,such as filters,power dividers,mixers,and transitions between waveguide and planar transmission lines,and aim to achieve their high performance and miniaturization.Then,based on the application of a 36 GHz fuze,we study a Linear Frequency-modulated Continuous Wave(LFMCW)ranging system based on the previous studied circuits.The main research work includes:(1)Filters in microwave systemsConsidering the different working frequency,two kinds of bandpass filters,namely the microstrip and the SIW bandpass filters,are studied.For microstrip bandpass filters,the study focuses on wide band bandpass filter,tunable bandpass filter and wide stopband bandpass filter.The design equations of the filters are derived according to the transmission line theory.For SIW wide stopband bandpass filter,the field distribution of the cavities with different ratios of width and length are analyzed.A combination of rectangular and square resonant cavities with the same fundamental resonant frequency is adopted to transmit the fundamental frequency and suppress the higher order mode through electrical and magnetic coupling.Finally,these filters are verified by fabricated filters.The results between simulated and measured are in good agreement,which prove the accuracy of the proposed study.(2)Power dividers in microwave and millimeter wave systemsIn this dissertation,the study on power dividers is carried out in three aspects: the dual-band power divider,the miniaturized power diver and the waveguide power divider(3D PD).For the previously reported dual-band power dividers,the frequency ratio range is very narrow,and the characteristic impedances may can not be realized in the real circuits.To solve these problems,a dual-band power divider which is based on stub loaded resonators is proposed.Compared with the previous reported works,the proposed circuit is more flexible in implementation.Moreover,the dual-band power divider has a higher working frequency ratio.Traditionally,filter and power divider are often cascaded to achieve the response of filtering and power splitting.But this approach will result in bulky circuit size and large insertion loss.In order to solve this problem,two filtering power divider are proposed in this dissertation,which can simultaneously realize the function of filtering and power dividing.The design equations are derived by the even-and odd-mode method.These two proposed circuits are verified by fabrication.The results between simulated and measured are in good agreement,which prove the accuracy of the proposed study.The traditional waveguide power divider has the drawbacks of low isolation and non-planar output ports.These drawbacks greatly restrict the application of the waveguide power divider.To solve these problems,we propose a Ka-band WG power divider which has the merits of planar output ports and high isolation.For verification,this power divider is fabricated and the measured results show that the return loss and isolation are better than 15 dB and 20 dB,respectively,in the range of 34.6-39 GHz.In the center operating frequency,the isolation is better than 40 dB.(3)Transitions between waveguide and planar transmission lineIn order to achieve good transition between waveguide and planar transmission line,and taking into account the need of other microwave circuits,such as mixers and power dividers in measurement,three transition structures,namely vertical waveguide to SIW,in-line waveguide to microstrip and vertical waveguide to microstrip transition,are studied.The transitions studied in this dissertation have the advantages of broadband,compact size and low insertion loss.Especially the in-line waveguide-to-microstrip line transition,except for the mentioned merits,this transition integrates two functions into one circuit,which is very beneficial to realize the miniaturization and high performance.In addition,in order to test 3D PD,a waveguide matching load based on the in-line waveguide-to-microstrip line transition,covering the whole Ka-band is studied.Measured results show that the return loss is better than 16.6 dB in the whole band.A microstrip antenna arry based on the previously vertical waveguide-to-microstrip line transition is also proposed.Measured results show that the return loss is better than 13 dB and the gain is better than 17 dBi in the range of 36-37 GHz.(4)Millimeter-wave MixersThe tranditional odd-harmonic mixers have the drawbacks of single-,non-planar structure,and high conversion loss when used as up-conversion.To solove these drawbacks,a planar third-harmonic mixer based on a planar 180° phase shift structure is is presented in this dissertation.In theory,the proposed planar third-harmonic mixer has lower conversion loss than the corresponding waveguide circuits.Measured results show that the conversion loss is less than 14 dB in the IF signal's range of 1.7-2.2 GHz.(5)Miniaturized millimeter-wave front-ended systemFirstly,the principle of FMCW ranging system is analyzed.According to the system's working range,the index of each component is allocated reasonably.Secondly,a 36 GHz FMCW ranging system was assembled based on the previously studied circuits for verification.In this ranging system,a variety of measures are adopted to miniaturize the system.Firstly,sharing one antenna to reduce the size of the system.Secondly,utilizing the power divder to substitute the circulator makes the whole system more compact.Thirdly,the use of single ended mixer makes the whole system further miniaturized.