Investigation And Design Of Microwave Filter Based On MMR Technique

As an important component in the microwave communication system, microwave filter has always received enormous attention in both academia and industry research. In recent years, with the fast development of communication systems, higher demand for the performance of filters has been put forward: high Q factor, low insert loss, sharp out of band rejection, high power capacity together with compact size. Multiple-mode resonator technique is an effective approach to solve the above problems. Multiple-mode resonator can be divided into two categories: one is the use of degenerate modes inside the resonator, and the other is a multiple-mode resonator utilizing high-order resonances. The former can be used in the design of the narrowband filter with compact size; the latter can improve the bandwidth of the filter, suitable for ultra-wideband filter design. In this background, this thesis concentrates on multi-mode resonator and its application in filter design. The main work of thes thesis are as follows:1. The principle of degenerate modes and the implementations of multi-mode resonators are described. The basic characteristics of a TM dual-mode dielectric resonator are analyzed in detail. The dielectric rod resonators are short circuited on the top and bottom surfaces to the metallic cavity. Non-resonating modes are exploited so as to produce a direct coupling between the input and the output of the dielectric-loaded cavity. In this way, a single cavity can provide two transmission poles and zeros, thus leading to N-pole and N-zero filters. Two filters based on the proposed resonator are designed for C-band applications. Fractional bandwidth 2.8% and max insertion IL<1.2dB 。 Simulation results show that the newly-designed filters have good performances.2. The fundamental properties of stepped impedance resonators have been analyzed. In particular, multiple resonant modes of a SIR are extensively studied so as to determine the locations of nearby multiple resonances and to utilize them together in forming a wide passband as expected. The resonant circuits and derivations are later applied to the design and implementation of a novel MMR-based UWB filter. Apart from having a basic structure of a slotline multiple-mode resonator and microstrip feed lines, this novel design introduces a cross-coupling between the input and output feed lines to enhance the filter selectivity. The model of the filter was simulated by electromagnetic simulation software HFSS. Simulation results exhibit an UWB passband from 3.4 GHz to 11 GHz with max insertion loss IL<1.1dB and fractional bandwidth FBW = 105.5%. The design strictly follows the theory and verified by electromagnetic(EM) simulation and experiments.3. Based on the proposed UWB filter, a narrow notched band is introduced by embedding a pair of split ring resonators(SRR) in order to reject any undesired existing radio signals that may interfere with the FCC-defined UWB band. By changing the structural parameters of SRR, it can be easily tuned to any desired frequency. This filter can be integrated in UWB communication systems and efficiently improve the interference immunity from undesired signals such as wireless local area network(WLAN).