The Research Of Out-of-Band Zero Design Technology For Dielectric-Filled Cavity Filters

With the rapid development of wireless communication system,the increasing communication rate and the increasing shortage of spectrum resources lead to the increasingly serious mutual interference between communication systems,which puts forward higher requirements for the performance of base station filter.In recent years,the research on dielectric materials has made continuous progress,making the dielectric filled cavity filter with high unloaded Q value,small temperature drift,small volume,low cost and other unique advantages,becoming the first choice of base station filter.By introducing the out-of-band zeros into the filter,the out-of-band suppression performance of the filter can be greatly improved,and the number of required filter cavities can be reduced to achieve miniaturization,which brings great improvement to the overall performance of the filter.Therefore,it has broad application prospect to study how to introduce the out-of-band zeros into the dielectric filled cavity filter.Cross-coupling technology is the most commonly used method for introducing outof-band zeros.The principle is simple and easy to understand.An auxiliary circuit is constructed by adding additional coupling elements between non-adjacent cavities to introduce out-of-band zeros.However,the dielectric-filled cavity filter is very different.Its interior is a solid ceramic dielectric block,and the surface is silver-plated as a metal shielding cavity.Since the entire cavity is filled with ceramic dielectric,it cannot be arbitrarily placed inside like a dielectric-loaded filter.Add coupling elements,thereby introducing out-of-band zeros to improve out-of-band rejection.Based on the dielectricfilled cavity filter,the cross-coupling of the linear topology and the introduction of outof-band zeros in the closed-end topology of thesis are studied.The main research contents of thesis are:1.Based on the dielectric-filled cavity filter,the cross-coupling technology is introduced into the linear topology,and a new path is constructed for the coupling between non-adjacent resonators by rotating the resonant column,combined with the method of field analysis the realization principle of linear inductive and capacitive structure is expounded,and the structure mechanism and influencing factors of linear capacitive cross-coupling are verified by inference and simulation.The influence of different window opening positions on the direct coupling coefficient and cross-coupling coefficient of the structure is simulated and analyzed,and the main factors affecting the position of the out-of-band zero point and the fine-tuning method are studied.2.Applying the closed-end topology to the dielectric-filled cavity filter provides a structure that can introduce multiple out-of-band zeros and only needs one capacitive coupling;basic closed-end topology zero control for two symmetrical zeros Research is conducted,and it is concluded that it is different from the control method of the conventional cross-coupling introducing the zero point,which is not controlled by the size of the added coupling element but by the coupling between the intermediate square structures;the realization of the different zero points of the seventh-order closed-end filter It can achieve symmetrical and asymmetrical frequency responses with the same structure and number of cavities,and summarizes the methods of zero position control with different number of zeros.