Research On Planar/Quasi-planar Wideband Passive Circuits In Radio Frequency Front-end Systems

As an important component in modern RF front-end systems,microwave passive circuits have been a research focus in the field of microwave technology.Although there are many kinds of researches about passive circuits in decades,the demands for design technologies of various wideband passive circuits(such as wideband bandpass filters,wideband differential multifunction-integrated circuits,and wideband filtering phase shifters)are increasing with the development of modern communication systems.With the advantages of simple structure,low cost,simple fabrication,and easy integration,various planar/quasi-planar passive circuits are widely used in modern RF front-end systems.In this dissertation,the researches of fundamental theories,circuit topologies,and synthesis methods of various wideband passive circuits based on planar/quasi-planar structure are presented.These wideband passive circuits include wideband bandpass filters,wideband multifunction-integrated circuits based on hybrid microstrip/slotline structure and double-sided parallel strip line(DSPSL)structure,wideband filtering phase shifters,and so on.The main research of this dissertation includes the following aspects:1.The polynomial synthesis method and topology of wideband fully canonical bandpass filters are studied.Firstly,the characteristic function of wideband fully canonical bandpass filters with complex transmission poles is proposed.A recursion relation for the characteristic function is derived.With the circuit synthesis technology,the recursion polynomial formula of characteristic function is verified.Then,the group delay of wideband fully canonical bandpass filters with complex transmission poles is analyzed.Secondly,to expand the stopband of wideband fully canonical bandpass filters with all transmission zeros located at the right side of the passband,a modified topology of planar wideband fully canonical bandpass filters with wide stopband is proposed.By pushing the parasitic resonances to higher frequencies,a wide stopband can be obtained.2.Quasi-planar wideband multifunction-integrated passive circuits based on hybrid microstrip/slotline structure are studied.Firstly,a wideband differential-to-single-ended out-of-phase power divider is proposed.It can achieve wideband common-mode rejection and realize wideband differential-to-single-ended out-of-phase power division.Secondly,an ultra-wideband single-end-to-differential power divider with intrinsic common-mode rejection is designed to realize the single-end-to-differential power division.Finally,based on the vertical transition structure of the microstrip line and slotline,a high selectivity wideband 180° phase shifter is presented.By introducing step impedance resonators,a pair of out-of-band finite frequency transmission zeros are introduced into the phase shifter.The input/output ports of the phase shifter are located at different metal layers to realize the functions of phase shift and vertical transition.3.Quasi-planar wideband differential multifunction-integrated passive circuits based on DSPSL are studied.Firstly,by changing the reference planes of DSPSL feedlines,the differential-mode signal is converted to an in-phase signal,while the common-mode signal is converted to an out-of-phase signal.With this type of DSPSL feedlines,a differential low-pass filter with a wide stopband and an ultra-wideband common-mode absorption differential transmission line are proposed.Then,based on the coupled DSPSL structure,a common-mode absorption differential wideband bandpass filter is presented.By converting the common-mode noise into heat energy with resistors,a differential wideband bandpass filter with wideband common-mode suppression and absorption can be obtained.4.To overcome the limitation of the traditional wideband filtering phase shifter in realizing large phase shift value and low phase deviation simultaneously,a new design method of the wideband filtering phase shifter is proposed.The proposed wideband filtering phase shifter is composed of two units: one unit is a Schiffman phase shift unit and another unit is a pair of wideband bandpass filtering units with Chebyshev responses.Different from the traditional wideband filtering phase shifter,the proposed wideband filtering phase shifter replaces the delay line with the Schiffman phase shift unit into the main and reference branches.By introducing the Schiffman phase shift unit,the proposed wideband filtering phase shifter can achieve wide phase shift bandwidth,large phase shift value,and low phase deviation simultaneously.The working principle and phase characteristics of the proposed wideband filtering phase shifter are analyzed.A generalized synthesis design method is proposed to design the wideband filtering phase shifter with specific phase shift value,phase deviation,return loss,and bandwidth.