Investigations On The Multilayer Substrate Integrated Waveguide Filters Based On LTCC

With the rapid development of wireless and mobile communication technology, the tendency of modern microwave and millimeter-wave communication systems is miniaturization, low-weight, reliable, multifunctional and low-cost. As an important part of system, the bandpass filters with high-quality, flat group-delay, low insertion loss and good frequency selectivity have caught greater attention from the world. Elliptic and quasi-elliptic filters can meet above requirements because they have transmission zeros. Generally, two methods can be used to produce the transmission zeros, which include cross-coupling theory and one-resonator-multimode theory. It is also well known that the substrate integrated waveguide (SIW) components take a lot of merits such as high-quality, high power capability, low-cost and easy integration etc. Therefore, elliptic and quasi-elliptic SIW filters with good performance have been developed abundantly. Particularly, the introduction of multilayer low temperature co-fired ceramics (LTCC) technology not only improves the performance of SIW filters, but reduces the area of SIW filters dramatically. So the elliptic and quasi-elliptic SIW filters based on LTCC will show tremendous potentials in microwave and millimeter-wave communication systems, and may become an important component of system in package (SiP). My dissertation investigates multilayer SIW filters to develop the novel filters with smaller and better performance.Firstly, a really multilayer SIW configuration of canonical cross-coupled filters is proposed in this dissertation. Compared with the traditional SIW configuration of canonical cross-coupled filters, the filter with the proposed configuration occupies approximately double the area of a single resonator cavity, and the area almost keeps unchanged with the order increasing of the filter. It is also proved that the coupling matrix of the proposed configuration can be obtained by the similarity transformation of the canonical cross-coupling matrix. Then the fourthorder multilayer substrate integrated rectangular and circular waveguide bandpass filters with this configuration are developed using LTCC technology. In addition, a new method is presented to suppress the spurious passband of the SIW filters. What mentioned above has been verified by experiments.Secondly, a multilayer dual-mode SIW filter with a simple structure and good performance is analyzed theoretically, and then is designed and fabricated in this dissertation. The measured results show good agreement with the simulated results and validate the structure of the proposed dual-mode filter.Finally, to reduce the area of multilayer cross-coupled SIW filters, a compact concavo-convex SIW resonator is proposed and analyzed. Then it is used to design the four-pole multilayer cross-coupled filter. The simulated results show that when the work frequency is the same, the SIW filter with this resonator occupies smaller area, and that its spurious passband is a goodish distance from central frequency, so the filter has a good stopband performance.