Research And Design Of Multi-Band Microstrip Filters

With the development of modern wireless communication system, multi-band microstrip filters, as important microwave components, have been widely researched. Good bandpass selectivity, high harmonic suppression, compact size, are essential index for modern design. After summarizing recently reported relevant multi-band microstrip filters, several compact structures has been proposed and studied. The work is arranged as follows:Firstly, the background of multi-band microstrip filters and newly reported research progress are investigated. Secondly, some basic theories are introduced, such as odd-/even- mode method, coupling theory, the defected technology, and so on. Thirdly, based on ?/4 resonators, four structures of multi-band microstrip filters are shown. The first one mainly combines two different ?/4 resonators into one resonator unit with common via ground. High harmonic suppression is got with spurline structure. For compact size, the second one uses electric coupling feed structure with magnetic coupling between ?/4 resonators to get dual-band responses. The third one uses magnetic coupling feed structure with electric coupling between ?/4 resonators to achieves dual-band responses; The fourth one realizes the tri-band responses through embedding an comby ?/4 resonator in another ?/4 resonator. It can see that the comby structure can reduce the loss of energy.Finally, based on novel resonators, two compact structures of multi-band microstrip filters are proposed. The first one can realize the tri-band responses based on step-impedance resonators, good selectivity is obtained by employing defected ground structure; The other realizes the dual-band responses with stub-loaded resonators. Tranimission zeros are added by introducing the magnetic coupling between I/O. The measured results are in good agreement with simulated results.