Research On Novel Substrate Integrated Waveguide(SIW) Bandpass Filters

Substrate Integrated waveguide(SIW) is a new transmission line similar to the rectangular waveguide, it has many attractive properties, such as low insertion loss, compact size, easy design and integration, thus, SIW has been widely applied to design microwave filters with miniaturization and high performance. The main research of this thesis is to design the wideband filters, cross-coupling filters and millimeter-wave filters based on the SIW transmission line. The main innovations of this thesis can be summarized as follows.1. The multiple-modes resonator based on SIW transmission line is proposed to design wideband filters with controllable resonant modes and bandwidth. The multiple-modes feature of the multiple-mode resonator structure is provide by the U-shaped slots on the SIW transmission line, by modifying the size of the U-shaped slots, we can control the variation of the resonant mode, which can make the bandwidth controllable, also, the inband and out-of-band performance can be improved by increasing the slot number and introducing the loaded via-holes. Besides, the U-shaped slots can generate a transmission zero(TZ) in the upper-stopband, which can improve the band selectivity.2. The novel cross-coupling structure is proposed to design high performance filter with transmission zero. On the basis of the SIW filters with electric coupling(generate by the slots), the stub-loaded microstrip-line is introduced, which will provide coupling between the nonadjacent resonators, which called the cross-coupling, and then generate transmission zero. Besides, the electric coupling provided by the microstrip-line with quarter wavelength stub and half wavelength stub have 180 degree phase deference, which allows us to design high performance bandpass filters with transmission zeros below the passband and above the passband, respectively. Furthermore, the microstrip-line with both quarter wavelength loaded stub and half wavelength loaded stub will generate mixed cross-coupling between the nonadjacent resonator, which will provide transmission zero at both sides of the passband, and then a high performance bandpass filter is designed.3. Design two millimeter wave(mm W) filters based on SIW transmission line. The first proposed filter shows that the U-shaped slot-etched SIW transmission line forms a resonator, and then a mm W filter is designed on the basis of the traditional design theory for the bandpass filter, besides, the filter has electromagnetic bandgap(EBG) property, which can improve the upper-stopband rejection, meanwhile, the U-shaped slots can provide transmission zero, and the different orientation of the notches can provide more than one transmission zeros, which can greatly improve the filter selectivity. The other one is design by a SIW cavity with four rotational symmetry via-holes, the four via-holes divide the cavity into four small cavities, each small cavity is served as a resonator, so the SIW cavity can generate four resonant modes, and the existence of the cross-coupling can provide transmission zero.