Study On Miniaturization Of Microwave Filters In Wireless Communication Systems

With the development of science and technology, microwave devices demand high performance, multi-function and miniaturization. Filters play an important role in wireless communication systems and are now required to have small sizes without deteriorating filtering performance. It is the reason that the research on the miniaturization of filter has become the melt point in the research area of microwave passive components.With the requirements mentioned above, this thesis focus on the application of substrate integrated waveguide(SIW) technology on cavity filter and their miniaturization with dual-mode resonance, cavity perturbation technology and complementary split-ring resonator(CSRR) structure for the miniaturization of cavity filters, and a series of SIW cavity filters are designed, fabricated and measured. Furthermore, four types of filtennas are designed by using the SIW cavity-filtering structure. The main contents of this thesis contains following parts:1. The design of SIW cavity filter is studied. The resonance characteristics of four shapes SIW cavity, i.e. the rectangular cavity, the circular cavity, the triangular cavity and the hybrid-shape cavities are studied respectively, with which the SIW cavity filters corresponding to each shape are proposed.2. The application of half mode substrate integrated waveguide(HMSIW) technology on SIW cavity-filter designs, which can result in a 50% reduction in size in comparison to the SIW cavity filter.3. A several types of dual-mode SIW cavity filter are proposed. With the dual-mode resonant characteristics, the cavity filters can work in single cavity with the same performance as that SIW filters can achieve with multi-cavity. The perturbations of inductive posts in SIW cavities are also studied to realize the slight miniaturization of SIW cavity filters for better performance.4. The influences of etched slots on the surface of cavity filter are also studied. Cross-slots, T-shape slots and H-shape slots are etched on the top metallic layer of the cavity, respectively, to change the surface current for realizing the miniaturizations of structures.5. The CSRR technology is also used together with the SIW cavity filtering structures for better selectivity, which can provide extra passband below the cutoff frequency with reductions of resonance frequencies to decrease the sizes of the filtering structures.6. Both filtering- and radiating- structures are used in combination on SIW to realize filtennas, which have not only a good radiating performance, but also a better out-of-band rejection.