Design Of Dielectric Waveguide Filters Based On Cross Coupling And Non-Resonant Node

With the continuous maturity of ceramic dielectric technology,dielectric waveguide filters are widely used in RF front-end systems due to their high Q value,low insertion loss,and high-power capacity in recent years.In engineering applications,cross-coupling,which occurs between nonadjacent cavities,is often considered to introduce the transmission zero but increases complexity of structures.By incorporating non-resonant nodes,it becomes possible to flexibly control the positioning of the zero point in the design of the coupling matrix,thereby meeting the specific shape requirements of the linear filter in various scenarios.Combining two different types of filter implementation methods,this thesis mainly studies cross coupled and linear filters in the 5G frequency band.A miniaturized cross coupled filter with transmission zero and a linear filter based on non-resonant nodes are designed,and a dielectric waveguide bandpass filter based on non-resonant nodes is processed and tested.The main work content and innovation points of this thesis are as follows:1.Studied the comprehensive method of the generalized Chebyshev filter polynomial and the pole extraction technology of the non-resonant node filter.The process of extracting circuit parameter component values by polynomial synthesis and input and output admittance extraction method is completed using MATLAB software.Wrote coupling matrix calculation codes for two generalized Chebyshev bandpass filters of different orders using MATLAB,and the coupling matrix synthesis process of non-resonant node-based filters is realized.2.A sector structure resonator is proposed,and a circular dielectric waveguide cavity is divided into eight π/4 sector-shaped resonators to realize an eight-order cross-coupled dielectric waveguide filter.It can be found that the bandpass filter model is designed to work at 3.505 GHz with an insertion loss of less than 0.06 d B and an in-band return loss of more than 19.39 d B in the field simulation.This filter has a fractional bandwidth of 8.27%,with two transmission zeros located at 3.31 GHz and3.7 GHz giving an out-of-band rejection lobe of 39.06 d B.The results show that the filter based on the sector structure resonator has excellent filtering performance.The structure realizes the miniaturization of the filter,improving the out-of-band suppression characteristics,and has good industrial application value.3.The design theory based on the non-resonant node filter is used to extract the results of the coupling matrix synthesis using the input-output admittance method.A straight-in and straight-out third-order dielectric waveguide band-pass filter is designed,and two-dimensional circuit simulations and electromagnetic three-dimensional designs are performed.The designed third-order bandpass filter has a center frequency of 3.515 GHz,featuring return loss of over 12.84 d B and an insertion loss of less than 0.68 d B.The-3 d B bandwidth spans from 3.41 GHz-3.62 GHz,while the extractedpole section introduces a transmission zero at 3.3 GHz.Additionally,the proposed filter boasts an out-of-band rejection of at least 24.23 d B.The third-order bandpass filter is processed.The test results reveal good consistency with the simulation results,confirming the accuracy of the proposed theory.The filter cavity has a simple and compact structure,with final dimensions of 50.99mm×12.8mm×6.9mm.Overall,the experimental results validate the feasibility of the proposed theory.4.A fourth-order bandpass filter was designed,which has a the out-of-band zero at the right of passband.The filter has a geometric structure of 48.65mm×8.98mm×6.6mm and operates at 3.495 GHz with a 6.58% fractional bandwidth and 0.66 d B ripple within the passband.The coupling matrix is synthesized from a generalized Chebyshev filtering function resulting in a return loss level of 14.3d B and a transmission zero at 3.7 GHz.The filter also achieves high out-of-band rejection of more than 24.5 d B.The filter structure is linear and does not require cross-coupling,enabling the realization of a transmission zero point and miniaturization of the filter.