Ultra-wide Bandpass Filters Using Corrugrated Substrate Integrated Waveguide And Periodic Structure

As a vital component among the various RF devices of radio communication systems, the performance of the filter has a great impact on the whole RF system indices. Ultra-wideband(UWB) communication system can realize an extremely wide bandwidth, low power loss, high anti-interference performance, good security and high speed data transmission, thus, to develop high-property filter applying to UWB communication system has a great practical significance.Substrate integrated waveguide(substrate integrated waveguide, SIW) has been a hot topic due to its unique structural advantages and its excellent electromagnetic characteristics. Unfortunately, the SIW has some deficiencies because of its metallic via holes, such as the metal vias have a large machining error, the drilling process is difficult when its dielectric plate is thick and it is hard to integrate with active chips or circuits because of the interconnected metal layers. In recent years, some researchers are committed to explore ways to improve SIW's properties, and the corrugated substrate integrated waveguide(corrugated substrate integrated waveguide, CSIW) is put forward to avoid the negative effects of perforated structure. Derived from the SIW, the CSIW uses two rows of quarter wavelength corrugated microstrip open-circuit stubs, rather than metal vias, on the edges of the metal plates of the dielectric substrate to act as the narrow wall of a waveguide. It simplified the manufacturing process. This thesis focuses on the design of CSIW ultra-wideband bandpass filters(BPF). CSIW technology combined with the structures of defected ground structure(DGS) and electromagnetic band gap(EBG), a compact CSIW-DGS ultra-wideband bandpass filter and a compact CSIW-EBG ultra-wideband bandpass filter are investigated, respectively. The feasibility of the CSIW structure used in the ultra-wideband bandpass filter design is validated.Firstly, this thesis introduces the analysis methods and design principles of the CSIW structure, and illustrates the CSIW's structural features and its electromagnetic properties compared with SIW's. Secondly, this dissertation explains the formation of the DGS and EBG using periodic structures. The equivalent circuit of the periodic structure unit cell is also proposed. Then the electromagnetic performance of the unit cell is explained in regard to different geometric parameters. After that, we design an effective CSIW-microstrip converter; the DGS structure is formed by notching six periodic structure unit cells on the center of the bottom metal layer of the CSIW, as the unit cells etching on the upper metal surface of the CSIW can form the EBG structure. Then a CSIW-DGS ultra-wideband bandpass filter and a CSIW-EBG ultra-wideband bandpass filter are obtained, respectively. In this paper, theoretical design together with electromagnetic simulation is used to design and optimize these filters. Finally, according to the design results, these two filters are fabricated and measured. Simulation and measurement results show each filter exhibits ultra-wideband bandpass characteristic, low return loss, low insertion loss and high frequency-selectivity.