Design Of Millimeter-Wave Bandpass Filter With High Out-of-band Rejection For 5G

With the rapid development of fifth generation?5G?mobile communication technologies,the millimeter wave technology has become one of the key technologies of 5G communication because it can achieve high-speed data rate.As a key device in communication systems,filters play an important role in frequency selection,and its performance has a crucial impact on the transmission quality of communication systems.Therefore,it is of great theoretical and practical significance to study the millimeter wave bandpass filter with high out of band rejection.In this paper,the bandpass filters with high out of band rejection applied in 5G millimeter wave communication system are studied.Based on the substrate integrated waveguide?SIW?technology,a variety of millimeter wave filters with high out of band rejection are designed.The main contents of this paper are as follows:1.A hybrid structure resonator based on dual-mode SIW and microstrip resonator is proposed,in which the microstrip resonator is loaded inside the dual-mode SIW resonator.Firstly,a dual-band filter with independent control of passbands is designed by using the hybrid structure resonator.Two independent passbands can be realized by using odd and even modes of dual mode microstrip resonator and two degenerate modes TE₁₀₂02 and TE₂₀₁ of dual mode SIW resonator.Due to the multi-path transmission effect,three transmission zeros can be introduced into the stopband to achieve high out of band rejection.Furthermore,the two passbands are implemented by dual mode technology,which is beneficial to the circuit miniaturization.Then,a dual-mode SIW filter with quasi-elliptical response is designed based on the hybrid structure resonator.The loaded half wavelength resonator is used as the non-resonanting node to realize the additional coupling path between the source and load.Thus,an additional transmission zero can be introduced into the stopband,which effectively improves the out of band suppression of the dual-mode SIW filter.2.Based on SIW technology and low temperature co-fired ceramic?LTCC?technology,a vertical mixed electric and magnetic coupling?VMEMC?structure is proposed.The structure etches rectangular slots and a circular hole in a specific area of the middle metal layer of the multi-layer SIW.Without affecting the Q value of the SIW resonator,the mixed electric and magnetic coupling between the SIW resonators is realized and the circuit area is effectively reduced.Firstly,the VMEMC structure is applied to the design of second-order SIW filter,and the electric and magnetic coupling characteristics of the VMEMC structure are analyzed.On this basis,two types of third and fourth order SIW filters operating in the Ka band are designed using the VMEMC structure.Both filters have the characteristics of high selectivity,small size and wide stopband suppression,and have good application value in 5G millimeter wave communication system.3.The design of bandpass filters based on defected ground structure?DGS?and SIW structure is studied.Firstly,aiming at the issues that the traditional dual-mode SIW filter can only realize a single transmission zero and the existence of higher-order modes in the upper stopband significantly degrade the out-of-band rejection performance,a novel dual-mode SIW filter with wide stopband suppression is proposed.The filter loads DGS unit directly under the two feedlines respectively to suppress higher-order modes and effectively expand the stopband.Besides,the TE202 mode can be used as a non-resonanting node by introducing additional perturbation vias at a specific position,so that an extra transmission zero on the right side of the passband is introduced,which further improves the out-of-band suppression characteristics of the upper stopband.Next,for the application of millimeter wave filters in wideband communication systems,based on SIW high pass filter and DGS unit,a wideband SIW filter with a passband of 24.82 GHz?33.27 GHz is realized.