Research On Balanced And Balun Filtering Circuits Using Dual-mode Dielectric Resonators

The rapid development of wireless communication system puts forward more stringent requirements for radio frequency(RF)circuit designs that the circuit designs should not only meet the requirements of high performance,miniaturization and multifunction but also achieve high integration.Therefore,RF devices of various functions require to be placed closer in a narrow space,resulting in a high level of electromagnetic(EM)interference and signal crosstalk.In order to effectively solve the above issue,the balanced circuit has drawn wide attention from the industry and academia because of its advantages such as high harmonic suppression,high immunity to interference and high stability.Inevitably,single-ended and balanced circuits may coexist in the wireless communication system,three-port balun still plays a key role.In addition,due to that the utilization of spectrum resource is overcrowded and the multi-standard requirement of wireless communication system,the realization of multi-band communication is particularly necessary and important.As one of the most critical RF front-end devices,the filter plays an important role because it has the functions of frequency selection and noise suppression.In the past,single/multi-band balanced/balun filters reported in the literature are mostly designed by utilizing microstrip line,substrate integrated waveguide(SIW)and low-temperature co-fired ceramic(LTCC),which is good to realize the miniature size and high integration.However,the employed resonators all have a relatively low-quality(Q)factor,which can degrade certain performance of the filter such as insertion loss and passband selectivity.On the contrary,the dielectric resonator(DR)has the advantages of high-Q factor,high temperature stability and high power capacity,and has been widely used in the filter designs.Furthermore,as the simplest multimode structure,the dual-mode DR can effectively reduce the volume of filter.Recently,some research groups have successfully used the ring-shaped and rectangular DRs to design types of single-band balanced/balun filters.However,both of them have a relatively large volume because all the employed DRs behave as single-mode resonators.In order to meet the ever-increasing requirements of high performance,miniaturization and multi-band communication of the wireless system,types of single/multi-band balanced/balun filters with good performance are designed by using dual-mode DRs in this thesis.The main contents are as follows.First,types of balanced/balun filters are successfully designed by using dual-mode DR.The employed resonator can be seen as the cross-shaped intersection of two identical rectangular DRs.According to the EM distributions of dominant mode and Ampere's right-hand screw rule,a pair of TE11? modes can be differentially excited by two pairs of feeding probes placed face-to-face to construct the differential-mode(DM)passband through appropriate perturbation.By letting one port of the above balanced filter open,a new balun filter can be easily constructed.Due to the inherent advantages of dual-mode DR,both the designed balanced/balun filters have the advantages of low insertion loss,high passband selective and small volume.Second,a balanced filter is successfully designed by using half-cut dual-mode DR.The employed resonator can be seen as a conventional dual-mode DR which is half-cut along the electric-field symmetry plane(electric wall)of its dominant mode(TE11? mode)and directly contact with the bottom of metal cavity.According to the EM-field boundary conditions,the bottom metal plane functioning as the electric wall will not disturb the EM distributions of dominant mode,but it can realize a half-size reduction.In addition,the dominant mode can have a better separation to the higher-order modes.According to the EM distributions of dominant mode and the Ampere's right-hand screw rule,a pair of TE11? modes can also be differentially excited by two pairs of feeding probes placed face-to-face to construct the DM passband through appropriate perturbation.Due to the inherent advantages of half-cut dual-mode DR,the designed balanced filter not only has a good DM response but also realizes the miniaturization and high harmonic suppression.Third,types of dual-band balanced/balun filters are successfully designed by using half-cut dual-mode DR.By introducing appropriate perturbation,a pair of TE11? modes can be split far away and can still be differentially excited to build the dual-band DM response of the filter.Without changing the circuit size,the proper placement of balanced port pairs can produce a transmission near the center frequency of the two DM passbands.And based on this,a new dual-band balun filter can be designed.Due to the inherent advantages of half-cut dual-mode DR,both the designed dual-band balanced/balun filters similarly have the advantages of low insertion loss,high passband selective and small volume.