Design And Research Of Antenna With Chebyshev Filtering Characteristic

With the rapid development of radio technology,the requirements for the Microwave filters and antennas in RF front-end are also getting more stringent.The antenna with filtering characteristic has been becoming a research focus,because it can solve problems of oversize and impedance mismatching caused by connecting the antenna and the band-pass filter directly.Designed by using the synthesis method,filtering antenna is a special antenna with filtering characteristic,and has smaller size and higher performance.In this paper,microwave band-pass filters and microwave filtering antennas have been researched according to the principles of high integration,miniaturization and high performance.Hence,a novel compact cross-coupled band-filter with center frequency of 2.4 GHz and two miniaturization antennas with 2-order Chebyshev filtering characteristic are designed.The frequencies of the two filtering antennas are respectively 915 MHz and 2.4 GHz.The main contents of this thesis are as follows:In chapter 1 and 2,the domestic and foreign research methods and forefront about the passive RF front-end components are summarized,and the relevant theoretical about the design of filters and filtering antennas are collected to set up a theoretical foundation for our studies and designs.In chapter 3,a novel embedded cross-coupled band-pass filter is proposed to illustrate the integrated design process of achieving miniaturization and set the foundation for filtering antenna design.Two kinds of compact stepped impedance resonator structures are designed to realize the miniaturization of the filter.By studying and improving the coupling mechanism between the resonators,an embedded structure is designed,resulting in reducing the area occupied by the feed line.The final geometric structure of the whole band-pass filter is very small,including the feed structure.In order to verify the feasibility of this approach,we design a four-order cross-coupled band-pass filter with center frequency of 2.4 GHz and relative bandwidth of 15%by using filter synthesis method.A sample of the filter is fabricated and measured.The measured and simulated results show that the filter has the generalized Chebyshev characteristic.With its advantages of low insertion loss,good selectivity and edge-of-band rejection characteristics,it can meet the miniaturization requirements of high-performance filters for modern communications systems.In chapter 4,two compact antennas with Chebyshev filtering characteristic are designed by using the synthesis method.Their frequencies are respectively 915 MHz and 2.4 GHz.The specific steps are as follows:(1)Determine the type of response,order and topology of the band-pass filter according to the design goals of center frequency,relative bandwidth and so on;(2)Design resonators which can meet the required coupling type,and of which resonant frequencies should be equal to the target center frequency.Calculate the required coupling coefficient and quality factor which can meet the design specifications.Then design the band-pass filter according the synthesis method;(3)Design the antenna whose resonant frequency and quality factor are respectively equal to the frequency and output quality factor of the filter;(4)Instead the last-stage resonator and output port of the band-pass filter with the designed antenna.Extract the coupling coefficient between the antenna and the former resonator in the case with loss.Use the same value as the coupling coefficient between the last two resonators of the band-pass filter,and then determine the corresponding physical dimensions.However,there was little method in existing filtering antenna literatures to present a clear and simple method of extracting coupling coefficient when dealing with the coupling between the antenna and the former resonator,because the general method of extracting coupling coefficient would be unavailable when the antenna was used as the final stage resonator but it has loss.So,in this chapter,the coupling between lossy resonators has been analyzed in the form of circuit.A method of extracting the coupling coefficient by using the phase information of S21 is proposed and verified by simulating and analyzing many examples with different coupling coefficients and loss.Thereby the design process of filtering antenna is simplified and the design difficulty is reduced.As practical use of the proposed design method of filtering antenna,two compact antennas with two order Chebyshev filtering characteristic are designed and simulated.The results show that the designed filtering antennas have the desired performance.In chapter 5,the main content and work of this article are summarized,and the future work of designing antennas with higher-order generalized Chebyshev filtering characteristics are introduced.