Design Of Multi-Cylinder Coupled Dielectric Filter

Microwave filter is an important component of wireless communication system.It can separate signals from different frequency bands and suppress unnecessary signals.In recent years,with the increasing application of filter in complex electromagnetic environment such as space communication,the miniaturization design of filter has become the focus of research.In this thesis,the writer analyzes the comprehensive method of coupling matrix of Generalized Chebyshev filter,studies of the characteristics of different filter coupling structure and its realization,puts forward a multi cylinder resonant structure coupling.On this basis,two bandpass filters are designed,which can realize multiple transmission zeros and satisfy the design goal of miniaturization.The main works can be summarized as follows:1.Design of Ultra-Wideband Dielectric Filter.We describe the characteristics of UWB system in detail,deeply study the design method of microstrip filter,analyze its advantages and disadvantages and improve it on this basis.Replace the microstrip line with a cylindrical metal coaxial resonator and fill the surrounding media.The cascade trisections(CT)coupling topology is adopted to calculate the parameters of each system,and the equivalent circuit is simulated.Electromagnetic simulation software HFSS is used to scan,analyze and optimize the influence of each structural parameter in the physical model of the filter,and a 3 order dielectric filter is designed: the center frequency is 3GHz,the working frequency band is 1.8GHz-4.2GHz,the relative bandwidth is 80%,the insertion loss is less than 0.5d B,the in-band return loss is more than 30 d B,and the three transmission zero points are generated out of band.Then,the overall size of the filter is 16mm*16mm*28mm by means of physical processing test to meet the design goal of miniaturization.2.Design of dielectric cavity filter based on ridge waveguide.We have studied the structure of the ridge waveguide and the calculation method of the parameters,and analyzed its advantages.That is,on the basis of the waveguide filter to increase the coupling between the resonator strength,thereby reducing the overall size,to achieve broadband function.Then we propose a structure in which a multi-cylinder metal coaxial resonator is combined with a ridge waveguide,and adding ring capacitive loading dielectric over the resonator.We adopt the cascade method of two stage CT coupled topology,and use the design method of Generalized Chebyshev filter to calculate the coupling coefficient of each resonator,and simulate the equivalent circuit of the whole structure.Then we analyze the influence parameters of resonant frequency and inter-stage coupling coefficient by software HFSS,and a 6 order dielectric cavity filter is designed: the center frequency is 15 GHz,the working frequency band is 12.8GHz-16.5GHz,the relative bandwidth is about 25%,the insertion loss is less than 0.5 d B,the in-band return loss is more than 18 d B,and the two transmission zeros are generated out of band.In order to facilitate the physical processing,the central frequency of the filter is adjusted to 5GHz,the overall size is 34mm*70mm*22mm,and the test results meet the design specifications.At the same time,compared with the standard model of rectangular waveguide,the overall size is greatly reduced.