Microwave Quasi-elliptic Filters Based On Mixed Electric And Magnetic Tightly Coupling Structure

With the advent of the fifth-generation mobile communication technology(5G)era,wireless communication systems have been rapidly applied and developed.As one of the key components of the wireless communication system,the filter performance directly affects the quality of the entire communication system.Therefore,the research and application of high-selectivity filters are particularly important.At present,the research and application of quasi-elliptic filter based on mixed electromagnetic coupling technology is one of the hot frontier fields.Under the same order,the number and position distribution of finite frequency transmission zeros are the decisive factors affecting the high selectivity of the quasi-elliptic filter.In this paper,a "new" mixed electromagnetic coupling technique of double coupling of amplitude and phase is proposed,and three design methods of high-selectivity quasi-elliptic microwave filters with tightly coupled structure of microstrip line are proposed by using printed circuit board(PCB)technology.The main contents of the paper are as follows:(1)The first chapter briefly introduces the research background and significance of filter technology,the research status and development trend at home and abroad,and also expounds the main work and structure of this paper.(2)In chapter 2,a mixed electromagnetic tightly coupled quasi-elliptic microwave filter based on ?/2 parallel microstrip resonators is proposed.In the second-order filter,a tightly mixed electromagnetic coupling is achieved between two ?/2 parallel microstrip resonators,which produces a transmission zero in the lower or upper stopband.On the other hand,the taped feeding structure is employed in the filter design,which can additionally introduce another transmission zero.Therefore,the second-order quasi-elliptic microwave filter has two transmission zeros outside the passband,which greatly improves the frequency selectivity.In addition,due to the tightly coupled structure of parallel microstrip resonators,the filter can achieve a large bandwidth fraction.This can be easily constructed by higher-order filters with this design method.In this chapter,a third-order quasi-elliptic filter with three transmission zeros is designed,simulated and fabricated in the S-band by using PCB technology.The measured results are well consistent with the simulated results.(3)In chapter 3,a quasi-elliptic ? /2 microstrip resonator microwave filter with tunable mixed electromagnetic tightly coupled structure is proposed.mixed electromagnetic amplitude coupling using parallel microstrip resonators can generate a transmission zero in the lower or upper stopband.On the other hand,another short microstrip line is introduced between the two resonators at the open-circuit end,then the mixed coupling coefficient be tuned,and the position the TZ can be controlled.an additional transmission zero can be introduced by utilizing the signal phase difference formed by the short microstrip coupling line and the parallel microstrip resonator.At the same time,the transmission zeros can be effectively regulated by the distance of the microstrip line and the position of the feeder.This design idea can realize that the second-order filter has two controllable transmission zeros outside the passband.The third-order filter can be easily implemented by cascading second-order filter.Using the PCB printing process,a third-order quasi-elliptic microwave filter with three controllable transmission zeros was designed,simulated and fabricated in the S-band.The measurement results are consistent with the simulation results.(4)In Chapter 4,a SIR quasi-elliptic microwave filter with mixed electromagnetic tight coupling structure is proposed.Using the amplitude coupling of mixed electromagnetic tight coupling structure ?/ 4 SIR,a transmission zero can be generated in the lower or upper stopband.On the other hand,using the signal phase difference between the folded part of the ? / 4 SIR high impedance line and the feed structure,another additional transmission zero is introduced.The design idea can realize that the second-order filter can introduce two transmission zeros outside the passband,and can also achieve better suppression ability out of band.The spurious passband appears at approximately 4 times of the center frequency.Based on the second-order filter,two methods of constructing third-order quasi elliptic microwave filter are proposed.Using PCB printing technology,a third-order high selectivity,high out of band suppression and miniaturized quasi elliptic microwave filter with three transmission zeros is designed,simulated and fabricated in S-band.The measured results are good consistent with the simulation results.