The Research Of Novel Cross-Coupling Technique For Dielectric-Filled Cavity Filters

With the commercialization of 5G communication technology,dielectric-filled cavity filters have become the mainstream solution for the usage of filters in 5G applications.The dielectric-filled cavity filters have the advantages of small size,lightweight,low cost,and low-temperature drift.In the research process of dielectric-filled cavity filters,the stopband suppression performance cannot be satisfied by increasing the order.The stopband suppression can be improved by introducing finitude transmission zeros(TZs).The multipath coupling technique was used to explain the principle of the TZs generated in the cascade triptych(CT)and the cascade quadruple(CQ)topologies.In this technique,a pair of symmetry transmission zeros can be produced upper and lower skirts by the capacitive cross-coupling structure in a CQ filter.The selectiveness of the stopband can be improved effectively in the filter.Therefore,the capacitive cross-coupling structure plays an important role in the cross-coupling technique.So far,the research of the cross-coupling structure is the probe-based structure for the air-filled cavity and dielectric-loaded filters.The probe can be implemented in the space of the cavity in these filters.For the ceramic-filled filters,the cavity consists of a ceramic body with silver-coated surfaces.The cavity is filled with ceramic.The capacitive cross-coupling structure is implemented hardly in ceramic-filled cavity filters.A small number of patents on this subject can be founded in publications.And the study for principle is weak.Based on this situation,the new design methods of capacitive coupling structure are proposed by analyzing the EM field distributions in this paper.The innovation point of this paper as follows:1.A novel capacitive cross-coupling structure for ceramic-filled cavity filters is designed.The new design is based on the inductive coupling structure.The novel capacitive coupling structure is implemented on the surface of the silver-coated ceramic.An isolated metal strip for coupling is placed within a window etched on the silver surface.It is located on the top outside surface of the capacity-loaded resonators,where the concentrated gap electric fields are mainly normal to the coupling strip.Therefore,the strip plays the role of the capacitive-coupling substructure connecting the two cavities to be coupled.Besides,for the convenience of the structure stability and fabrication feasibility,the originally apart two nonadjacent resonators to be coupled are cut-through with ceramic to hold the etched coupling window.Therefore,accompanied by the cutting though,an additional inductive coupling channel is introduced by the inter-cavity opening(iris)under the strip.It is obvious that the width of the iris should be small to ensure the capacitive coupling predominates.With the proposed composite structure,the coupling strength is readily adjusted by varying the dimension of the strip,which supports the flexible design TZs.2.A novel capacitive cross-coupling structure for dielectric waveguide filters and dielectric-filled cavity filters is designed.The novel capacitive coupling structure can be designed by analyzing the EM field distributions of the two coupled-resonator cavities.The silver-plated blind hole is introduced at the center of the two coupled cavities.The conventional inductive coupling can be realized by the iris.The EM field distribution pattern is the TE201 and the TE101.The TE201 and TE101 is the odd and even mode,respectively.The resonance frequency of the odd mode is higher than the even mode.The coupling is inductive.The capacitive coupling cannot be realized by the structure.By analyzing the field distributions of the coupled cavities,the TE301 is the even mode.By introducing a deeper silver-coated blind hole embedded in the center of the coupled cavities,the frequency of the TE301-mode and TE101-mode will be decreased.Because the field distribution of the TE201-mode is null at the center of the two coupled cavities.The frequency of the TE201-mode is unaffected.The frequency of the TE301-mode is higher than the TE201-mode.And the TE301-mode and TE201-mode is the even and odd mode,respectively.The capacitive coupling can be realized by the TE301-mode and TE201-mode.The simple structure facilitates the tuning process and mass production.