Research On Inline SIW Filter Based On Controllable Mixed Electromagnetic Coupling

As one of the front-end core devices of RF/microwave circuits,microwave filter assumes the key responsibility of frequency selection and suppression.The performance of microwave filters has a direct impact on the stability of the entire microwave/wireless communication system.With the speed development of modern microwave/wireless communication technology,the performance requirements of microwave filters are also improved to meet the needs of new communication systems.These requirements include simple structure,low machining cost,small circuit size,easy planar integration,large power capacity,low in-band insertion loss,good out-of-band suppression,high frequency selectivity,and controllable transmission zero position.Nowadays,the utilization of spectrum resources of various communication systems is becoming increasingly refined,and the interference between different system frequency bands is becoming increasingly serious.In order to meet people’s growing demand for microwave/wireless communication systems,the realization of high-performance and modular microwave filters has become an urgent problem to be solved.In this thesis,a series of single-layer substrate integrated waveguide(SIW)bandpass filters are designed based on mixed electromagnetic coupling theory.These filters have the advantages of high frequency selectivity,flexible and controllable transmission zeros,inline array arrangement,simple design,compact structure,easy integration,and low processing cost,which are well suited for modern microwave/radio circuits and systems.The main research work and innovations of this paper are as follows:First,a variety of single-layer SIW mixed electromagnetic coupling bandpass filters arranged in an inline array are designed with a hybrid integrated SIW and coplanar waveguide(CPW)structure to introduce controlled mixed electromagnetic coupling and transmission zeros using the different field distribution characteristics of both.Unlike the conventional cross coupling method,the controlled mixed electromagnetic coupling method only requires one physical path to achieve the transmission zeros.Based on this,the asymmetric or quasi-elliptic frequency response characteristics are achieved by cascading multiple sets of identical or different second-order SIW filters,which improves the filter selectivity.Finally,six filters are processed and the accuracy of the simulation results is verified by the actual measurement results.Second,a variety of single-layer SIW cross coupling bandpass filters with asymmetric frequency response and inline array arrangement are designed,using the CPW structure as resonator,which effectively solves the traditional cross coupling filter input/output port isolation problem.At the same time,the design breaks the limitation that inline filters cannot be applied to introduce cross coupling structures between non-adjacent resonant cavities.Compared to conventional SIW filters of equivalent order,the introduction of CPW resonators can reduce the circuit area by about one-third and have a steeper sideband performance.In addition,the introduction of CPW resonators can increase the bandwidth,selectivity,and order of the filter without increasing the circuit size compared to the aforementioned second-order SIW mixed electromagnetic coupling filter.Finally,the two filters are processed and the accuracy of the simulation results is verified by the actual measurement results.Third,a variety of single-layer SIW mixed cross coupling bandpass filters with quasi-elliptic frequency response and inline array arrangement are designed to effectively overcome the problem that conventional CT(Cascaded Triplet)filters can only produce one transmission zero.For the first time,by embedding two parallel sets of CPW structures,both functions of providing hybrid electromagnetic coupling and acting as resonators are achieved,adding more transmission zeros and further enhancing circuit miniaturization,filter design flexibility and performance.Overall,this SIW filter compatible with both CPW resonator and mixed electromagnetic coupling structures takes full account of their structural complementarity,resulting in a more compact overall filter size with excellent frequency selectivity characteristics.Finally,three filters were processed and the accuracy of the simulation results was verified by the actual measurement results.