Analysis And Design Of A New Planar Multi-band Coupler

In recent years,along with the rapid development of wireless communication system,the communication equipment for civil and military applications are increasingly needed.It demands that each device within the communication system can operate at multiple bands with a wide frequency ratio range,and meets the communication requirements of multiple systems at the same time.As a result,the system which can support multiple communication standards to work at the same time becomes a hot research topic.As a key device in the microwave and millimeter-wave systems,couplers directly restrict the performance of the whole system,thus the higher requirements of multi-band features for the couplers are proposed.In order to solve the problems mentioned above,this thesis is devoted to proposing design ideas of novel planar multi-band coupler designs,investigating the theoretical analysis and design,and also extending the multiple-frequency operation to balanced coupler circuits.This thesis is focused on the multi-band designs of single-ended and balanced couplers,and the main contribution of this work is summarized as below:1.The analysis and design of multi-band branch line couplers with high isolation based on coupled lines:Branch line couplers can realize equal power division between the straight output port and the coupling output port,and ensure good port match and isolation.On the basis of the traditional 3-dB branch line coupler circuit,by loading four quarter-wave open/shorted coupled lines to introduce zeros in the passband,dual/tri-band couplers can be realized.The proposed two couplers have advantages of simple structure,high isolation between each passband,and the passband frequency can be adjusted over a wide band just by changing the even/odd-mode characteristic impedances of the coupled lines.These works have been published in IEEE Transactions on Circuits and Systems II-Express Briefs,and one patent entitled with "Tri-band branch line coupler based on shorted coupled lines" has been applied as well.2.The analysis and design of multi-band crossovers with arbitrary frequency ratio based on coupled lines:Crossovers can realize the signal transmission between the cross ports with good port match and isolation.The crossover we proposed is maintained by using two coupled-line sections and two transmission lines.Without no extra loaded stubs,just by changing the electrical length of the middle transmission lines,single-band and dual-band crossovers with large frequency ratios can be easily obtained.The proposed two crossovers have advantages of simple design,compact structure,large frequency ratio,and the center frequency of the single-band crossover and frequency ratio for the dual-band can be easily changed by changing the characteristic impedance of the coupled lines and the transmission lines.This work has been published in IEEE Microwave and Wireless Components Letters.3.The analysis and design of multi-band balanced couplers based on DSPSL:Firstly,the characteristic of the transmission line---double-sided parallel-strip line(DSPSL)and the derivation of the mixed-mode scattering matrix for eight-port balanced networks are introduced.Then,the phase inverter based on DSPSL without frequency sensitivity has been analyzed and designed,to realize differential signal input and output and widen the bandwidth of the common-mode suppression of the balanced coupler.On this basis,according to the multi-band realization of the single-ended branch line couplers above,similarly,by loading open/shorted coupled lines,dual/tri-band balanced couplers with differential-mode equal power division and wideband common-mode suppression have been realized.These works have been accepted by IEEE Transactions on Circuits and Systems II-Express Briefs,and one patent of "Tri-band balanced coupler based on 180°ideal phase inverters:has been applied.