Wideband Bandpass Filters And Fabry-Perot Resonator Antennas Based On Substrate Integrated Waveguide

With the development of the fundamental theory research of substrate integrated waveguide (SIW), studies on microwave and millimeter-wave components based on SIW have made great progress. Filter, especially the bandpass filter, and antenna are two important research areas among them. They are also the key components of wireless communication systems. The antenna is used for transmitting or receiving radio waves which carry signals through the air, while the main function of the filter is allowing the desired frequencies and eliminating the unwanted band including the image frequency, in order to ensure the integrity and correctivity of the signals in the required frequency range. Due to the advantages of high transmission data rate, low energy density and extremely low transmission energy, ultra wideband (UWB) techniques have been utilised for many applications. The UWB bandpass filter is a crux component of UWB system. The highly selective UWB bandpass filter rejects the unwanted signals and improves the UWB system performance. On the other hand, high-gain, low-cost planar antennas are preferred in the applications of wireless LAN, satellite reception and various point-to-point radio links. The conventional array antennas have primarily been good candidates, but their feeding network becomes complicated, and will decrease the antenna efficiency. Therefore, the high-gain Fabry-Perot resonator antennas with a simple feed have attracted a lot of interest. The dissertation will focus on the UWB bandpass filters with high selectivity and low-profile fully substrate-integrated Fabry-Perot resonator antennas based on SIW.Firstly, an overview of the development of the filter design based on SIW-like structures, and the historic background and trends of the Fabry-Perot resonator antennas is given. In Chapter4, the basic theory and operation principle of Fabry-Perot resonator antenna are introduced. The characteristic parameters are deducted for the FP antennas with two kinds of cavities, one is constructed from two partially reflection sheets (PRS), the other is comprised of a PRS and a totally reflective ground plane. Classification analysis on the low-profile mechanism is performed in detail. In Chapter2,3and5, highly selective UWB bandpass filters by cascading HMSIW and IADGS lowpass filter, highly selective wideband bandpass filters using ADGS-loaded SIW/HMSIW, and SIW-slot-fed substrate-integrated subwavelength Fabry-Perot resonator antennas are studied respectively. An intuitive approach has been proposed to design UWB bandpass filters by using cascaded highpass and lowpass filters. The asymmetric defected ground structure (ADGS) with quasi-ellptical response is introduced. Then the theoretical explanation on the advancement of the return loss and suppression level is made for the improved ADGS (IADGS). Accordingly, the design procedure for the IADGS with high cut-off frequency is suggested. Following that, two or three IADGS cells are employed for the lowpass filter design to achieve low return loss in the passband and good enough suppression level. At last, the sharp-transition IADGS lowpass filters are cascaded with the inherent steep-cutoff high-pass HMSIW section to realize highly selective UWB bandpass filters with the passband of about5.8-10.6GHz.When the ADGS cell is directly applied to the center of both the bottom and top broadwall of SIW, or the ground plane near the open boundary of HMSIW, the same quasi-elliptical band-reject performance can be observed in the upper band. So the ADGS cell integrated with SIW/HMSIW can be regarded as an EBG-loaded structure for the wideband bandpass filter design with a more compact size. An ADGS-loaded HMSIW UWB filter with a passband of about5.8-10.6GHz, and a C-band ADGS-loaded SIW wideband filter with a fractional passband of about30%are implemented, respectively, both with steep skirt selectivity.Finally, the novel SIW-slot-fed substrate-integrated subwavelength Fabry-Perot cavity (FPC) antennas are proposed and studied. The longitudinal slots symmetrically cut on the upper broadwall of the SIW are introduced to excite the FPC antennas. A ground plane and an artificial-magnetic-conductor-loaded partially reflective planar sheet act as two reflecting sheets of the FPC, which is fully filled with dielectric to decrease the cavity height to meet the need of integration with the circuit board. The effects of the SIW slot feed on the realized gain and gain bandwidth are analysed. As compared to the substrate-integrated FPC antenna with an embedded microstrip feeding patch, the main beam direction of the proposed antennas are shown to be insensitive to operating frequency and maintained at the boresight direction. Furthermore, the radiation efficiency is improved due to the significant reduction of dielectric loss and ohm loss. The simulated and measured results demonstrate that the proposed antennas have the merits of low profile, high gain, high efficiency, and consistent boresight radiation. Moreover, the easy integration with the circuit board and mechanical robustness make them suitable for low-cost mass production.