Research And Design On Microstrip Filtering Antenna

RF(Radio Frequency) front-end circuit is the link connecting the free space and the IF(Intermediate Frequency) signal, higher demands have been proposed for RF front-end circuit owing to the "miniaturization, integration, high performance" development trend of microwave communication system. As the two most important components, antenna and filter determine the quality of the entire communication system. The traditional design method realizes the filtering function by cascading filter and antenna, but this may result in impedance mismatching and lager circuit size. Filtering antenna not only has radiation but also has the function of impedance matching, filtering and balance conversion. Meanwhile, the circuit size can be reduced to make the system more compact. Filtering antenna has become a hot topic in RF filed for its excellent performance. In this thesis, a series of compact, highly integrated, good selectivity microstrip filtering antennas has been researched.First of all, research status of microstrip filtering antenna at home and abroad is summarized, significance and content of the work are presented. Furthermore, the basic theories of filters and antennas are introduced, coupled bandpass filter theory and methods are described.Secondly, an endfire filtering antenna is designed by integrating wideband balun and quasi-Yagi antenna. The multilayer wideband balun is designed based on a closed loop resonator. The balun is compact,easy to be integrated. This filtering antenna has wide bandwidth, good selectivity and compact structure.Then, three high performance filtering antennas have been proposed based on synthesis of the filter. The last resonator and port in filter can be replaced by antenna, thus filtering antenna is realized. Filtering antenna has the function of filtering and radiation. Meanwhile, annular slot, dual-mode resonator and stepped impedance resonator are utilized to design second-order, forth-order and dual-band filtering antenna. All designed filtering antennas have compact structure, as well as the flat gain and smaller cross-polarization in passband.Finally, a MIMO filtering antenna is designed based on coupled transmission line resonator. Due to the two controllable transmission zeros produced by coupled line resonator, the filtering antenna has higher frequency selectivity. By introducing the decoupling unit and the slot on the floor, isolation between the two ports has been proposed without changing the filtering and radiation characteristics of the filtering antenna.