Design And Optimization Of The Dielectric Cavity Filter For 5G Band

With the rapid development of modern wireless communication technology,the requirements for the performance of cavity band-pass filter for base station also become higher and higher.The design of cavity band-pass filter also needs to keep pace with the times,accompanied by the development of material science.Compared with metal cavity filter,dielectric cavity filter has better performance,lower loss,higher temperature stability,and smaller size and so on.Although the cost of the medium relative to the metal is much higher,it can be improved by technology to optimize the overall parameters of the cavity and miniaturize the structure to reduce production costs.In the second half of 2017,the Ministry of industry and Commerce put forward a plan on the 3000?5000MHz band of the 5G network.The 3000?3400MHz principle limits the indoor use,3400?3600MHz and 4800?5000MHz are used for the commercial frequency bands.After six months'discussion,China Telecom and China Unicom get 3400?3500MHz and 3500?3600MHz,respectively.The two frequency bands are relatively mature in the exploration of 5G network band.And China Mobile hold 4800?4900MHz and was compensated for 2515?2675MHz at the same time.From the view of frequency division,China Telecom and China Unicom have made great profits since 3.5 GHz in the 5G band is the mainstream in the international scope.From the global 5G spectrum distribution,3.5GHz has the most universal feasibility and the industry chain is relatively mature.In this paper,the center frequency is located at 3500 MHz in the dielectric cavity band pass filter.In this paper,by studying the parameters of single cavity structure,the parameters of single cavity are simulated by high-frequency electromagnetic simulation software(HFSS).After the parameters of the single cavity were determined,three simple filters are designed.The simulation performance parameters were achieved:the central frequency(f₀)is 3.48 GHz,the pass-band bandwidth(BW)is 60?70 MHz,the return loss|S₁₁|of the pass-band is greater than 20 d B,and the insertion loss|S₂₁|is less than 0.5 d B.The out-of-band rejection|S₂₁|is greater than 40d B@f0±60 MHz,and the simulation results reach the expected target value,which preliminarily proves the accuracy of the design direction of the single cavity structure.After several simple filters were designed,it is found that the general out-of-band rejection is very poor.Combined with the previous optimization methods,the introduction of cross-coupling structure is further explored.In this paper,after the five-cavity Z-type and U-type structure were laid out,three-cavity cross-coupling structure(CT)was introduced to realize out-of-band transmission zeros.In the Z-type cavity,under the premise of keeping the index(the center frequency(f₀)is 3.48GHz,the bandwidth is 65 MHz,the return loss in the pass-band|S₁₁|is greater than 20 d B,and the insertion loss in the pass-band|S₂₁|is less than 0.5 d B)not degraded,two transmission zeros are generated at 3.775 GHz in the high frequency band and 3.3198GHz in the low frequency band,respectively.In the U-type cavity,under the premise of keeping the index(the central frequency(f₀)is 3.48GHz,the bandwidth is 65 MHz,the return loss in the pass-band|S₁₁|is greater than 20 d B,and the insertion loss in the pass-band|S₂₁|is less than 0.5 d B)not degraded,two transmission zeros are generated at 3.775 GHz in the high frequency band and 3.3550 GHz in the low frequency band,respectively.At the same time the position of transmission zero is analyzed,since ADS software has advanced electronic design functions for circuit analysis and effective collaborative simulation,the position of zeros can be introduced directly.Finally,the general regulation of the position of zeros is realized,which proves the effectiveness and feasibility of the optimization method.After modification by traditional cross-coupling structure,it is found that the introduction of cross-coupling structure in the past is opened between the cavities.The existence of the opening structure will increase the interference of other uncertain factors when adjusting the coupling coefficient,so a cross-coupling structure--long transmission line structure is redesigned.The introduction of the position of zeros is realized by introducing the long transmission line structure.At the same time,the pass-band performance is maintained well,which proves the feasibility of the long transmission line structure.In addition,the position of transmission zeros can be regulated directly by introducing the long transmission line structure,which proves that the long transmission line structure is more accurate to regulate the position of zeros than the traditional cross-coupling structure.At the same time,the simulation experiment of hybrid control of long transmission line structure and traditional cross-coupling structure,which proves the universal applicability of long transmission line structure.The feasibility and applicability of long transmission line structure are proved comprehensively.