| The application and rapid development of wireless communication technology in various fields in human society,the long-term coexistence of communication systems working in different frequency bands,and the need for tunable RF front-ends to achieve rapid switching in different wireless communication systems.The characteristics of tuning have attracted more and more attention from people.In recent years,with the rapid development of 5G technology,the frequency of signals has become higher and higher,the bandwidth has become wider and wider,the amount of data carried by the signals has become larger,and there is a higher demand on the power capacity and power consumption of filters.Because of its high power capacity and low insertion loss,the body filter can well meet the needs of new technologies.In urban areas,because of the limited installation space,wireless service providers need to package different functions such as multi-standard and multi-band to one site,which imposes higher requirements on the miniaturization of filters.Therefore,the research on miniaturized electrically tunable cavity filter is of great practical value.This thesis investigates and analyzes various implementations of electrically tunable filter and selects suitable methods for use in cavity filters.And compared with the mature microstrip tunable filter structure,the difference between them in the tuning function can be analyzed.The electrically tunable cavity filter mainly achieves the center frequency tuning.In this paper,two kinds of electrical cavity filters were designed and processed and tested.The main work of this article is:(1)In the electromagnetic simulation software AWR,two-step electric coupling,magnetic coupling and electromagnetic hybrid coupling filter circuits are respectively established to analyze the respective tuning characteristics.Through comparison,it is found that the magnetic coupling filter circuit is used in the frequency tuning process.With a minimal change in bandwidth,the filter bandwidth can be made relatively constant by selecting the appropriate magnetic coupling size.Finally,a circuit model is built for the resonant element of the traditional electrically tunable cavityr filter,and the key factors affecting the frequency tunable band width are analyzed,which provides theoretical support for the design of the wideband electrically tunable cavity filter.(2)Based on the coaxial cavity structure,a fifth-order wide-band electrical tuning cavity filter in the 225MHz~400MHz frequency range was designed.A method of connecting the metal screw directly to the resonator has been adopted to realize wide-band adjustment.In order to realize the miniaturization of the filter,a rectangular window is opened at the open end of a rectangular resonator and a notch is formed at a corner of the lower end.Next,an L-shaped metal branch is loaded downward at the open end of the resonant element,greatly reducing the resonant frequency of the resonant element.The electrically tunable cavity filter adopts a frequency hopping scheme.Each resonant element controls the on-off of four chip capacitors through four PIN switches to achieve a resonant frequency distribution at multiple discrete frequency points.All the electrically tunable cavity filter.are fully integrated On the outside of the PCB board.The final simulation results meet the design goals.(3)A 1.1GHz~1.20 GHz fifth-order electrical cavity filter was designed on the suspended stripline metal cavity structure.In order to broaden the tunable frequency bandwidth,a transitional structure composed of interdigital structure and flat-plate capacitance structure was designed.A uniform impedance metal stub is loaded at the open end of the stepped impedance resonator,which can reduce the resonant frequency to realize the miniaturization of the filter.The resonant frequency of each resonator is tuned by a biased varactor diode.The simulation result of this filter is in good agreement with the measured results,and it reaches the design index. |
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