Research On Dielectric Waveguide Filter Technology

The research object of this thesis is dielectric waveguide filter technology.Compared with planar microstrip filter and substrate integrated waveguide filter,the filter has higher Q value and higher power capacity.Moreover,compared with metal waveguide filter and dielectric resonant waveguide filter,it has a smaller size,which is very convenient for integration in modern RF and microwave circuits.In recent years,with the continuous maturity of ceramic technology,dielectric waveguide filters have been widely used in modern wireless communication systems such as base stations and terminals due to their excellent performance.A larger number of technical studies and related engineering applications have been carried out by scholars in China and abroad.In this thesis,the straight-in and straight-out,the cross-coupling,the new-structural and the dual-mode filter are studied.In addition,the straight-in and straight-out coupling filter with transmission zeros,miniaturized crosscoupling filter,the new-structure coupling technology and the new dual-mode dielectric waveguide filter are proposed,which provide certain application value for academia and industry.The main work and innovation of this thesis are as follows:1.In order to meet the straight-in and straight-out requirements of filter’s configuration in industrial applications,the full-inductive coupling linear dielectric waveguide filter structure and the full-capacitive coupling linear dielectric waveguide filter structure are proposed through theoretical research on linear coupling filters.For the straight-in and straight-out coupling filter,it is generally difficult to achieve cross-coupled transmission zeros.In order to overcome this shortcoming,the new capacitively coupled linear dielectric waveguide filter is designed and implemented.Based on capacitive coupling,weak inductive coupling is generated,so a transmission zero is generated at the high end of the passband.The linear dielectric waveguide filter with full-inductive coupling and fullcapacitive coupling is fabricated and tested.The results show that the filter has excellent performance and can meet the application requirements of base station communication.2.To further improve the out-of-band performance of the filter,this thesis carried out research based on the cross-coupled filter technology,and the new magnetic coupling configuration and electrical coupling configuration are proposed.Based on the new coupling configuration,a T-shape coupling configuration and a I-shape coupling configuration dielectric waveguide filter are designed respectively.By drilling through holes or blind holes on a square medium surface,and then coating all the thin metal on its surface,this unique full-hole design realizes the fourth-order cross-coupled dielectric waveguide filter.In addition,a circular hole is set in the middle of the square cavity to suppress the parasitic response of the filter.Through the design,analysis,simulation and processing test of the filter configuration,the results show that the filter has excellent performance such as 3.5GHz center frequency,less than 0.5 d B insertion loss,more than 15 d B return loss,5% relative bandwidth,and two transmission zeros outside the band.The configuration is very convenient for engineering production and debugging,which is suitable for large-scale mass production,and it has good industrial application value.3.For the cross-coupled filter,this thesis proposes the design of four novel coupled structure dielectric waveguide filters starting from the isosceles right-angle triangular resonator and the sector structure resonator.Firstly,a square dielectric waveguide cavity is divided into four isosceles triangle cavities,each cavity as a resonator.By controlling the coupling between resonators and the coupling position between input and output,two dielectric waveguide filters with different input and output coupling positions are designed.One is based on the traditional cross-coupling structure,and the other is based on the new cross-coupling structure.The new coupling structure realizes the straight-in and straight-out requirements of the filter,which has certain industrial application value.Secondly,a circular dielectric waveguide cavity is divided into four π/2 sectoral resonators or six π/3 sectoral resonators,and a fourth-order and a sixth-order cross-coupled dielectric waveguide filter are realized respectively.Compared with square dielectric waveguide filter,the test results of circular dielectric waveguide filter show that the filter based on fan-shaped resonator has better filtering performance.4.Finally,the dual-mode dielectric waveguide filter is studied.A novel dual-mode dielectric waveguide resonator is proposed,which consists of three blind holes embedded in the surface of the dielectric waveguide at different positions.Based on this theory,a single-cavity dual-mode dielectric waveguide filter and a dual-cavity dual-mode dielectric waveguide filter with controllable transmission zeros are designed respectively.By controlling the I/O coupling of the dual-mode resonator,the single-cavity dual-mode filter can realize the left and right movement of the transmission zero outside the passband.The dual-mode dielectric waveguide filter is cascaded by two single-cavity dual-mode dielectric waveguide resonators.The position of the out-of-band transmission zero of the filter can be controlled by changing the relative position of the three blind holes or rotating the dual-mode dielectric waveguide cavity.The method can set the transmission zero at the low end of the passband,can be set at the high end of the passband,and can also produce transmission zeros at the low end and the high end of the passband to improve the out-of-band selectivity of the filter.Three dual-cavity dual-mode dielectric waveguide filters are fabricated and measured respectively.The results verify the feasibility of the theory.