The Research Of Novel Multiband Dielectric Resonator Filters

With the rapid development of mobile communication, communication spectrum resources have been increasingly crowded, and communication systems have often operated in multiple frequency bands. This requires high-performance multi-passband filters to increase the communication system capacity, and to avoid interference between adjacent channels. At the same time, owning the high unloaded Q-value, high dielectric constant, small size and other characteristics, dielectric resonators have been widely used in communication systems. Therefore, it’s of great practical significance to do the research on the higher performance multiband dielectric resonator filters.Based on TE01δ mode and TM01 mode dielectric resonators, some multi-band dielectric resonator filters and balanced dielectric filters are designed, and the main contents are as follows:1. Based on TE01δ mode dielectric resonators, and frequency conversion comprehensive theory proposed by Giuseppe Macchiarella, and the theory that the transmission zeros can be controlled by the change of filter feeding way, a second-order dual-band and a second-order triband dielectric resonator bandpass filter are designed, respectively. Wherein the center frequencies of the dual-band filter’s two sub-bands are 1.80 GHz and 1.84 GHz respectively, and the corresponding relative bandwidths are 1.9% and 1.1% respectively; besides, the center frequencies of the tri-band filter’s three sub-bands are 1.79 GHz, 1.82 GHz and 1.85 GHz respectively, and the corresponding relative bandwidths are 0.9%, 1.3% and 1.1% respectively. Both filters are designed with symmetric transmission zeros, improving frequency selectivity, and avoiding the complex port coupling structures caused by the source-load coupling, or the complex tuning structures caused by the mixture of electromagnetic coupling.2. Based on TM01 mode dielectric resonators, a second-order balanced dielectric resonator filter is designed. Using the ring coupling feeding structure, the feed probe can effectively excite the second-order mode HE11 mode when differential mode signals are input. Also it can excite the fundamental mode TM01 mode when common mode signals are input, suppressing the second-order mode HE11 mode simultaneously. The center frequency is 3.31GHz; the relative bandwidth is 1.6%, and the common mode rejection is greater than 70 d B. Compared with the existing filters in the same order, it has the improvement of 30 dB in the common mode rejection, and the improvement of stop-band rejection.3. Based on TM01 mode dielectric resonators, a second-order dual-band TM mode dielectric resonator filter is designed. Dual passband response is achieved by simultaneous excitation of the fundamental mode TM01 mode and the second mode HE11 mode of the dielectric resonator. Center frequencies of the two sub-passband are 2.47 GHz and 3.20 GHz respectively, and the corresponding relative bandwidth are 1.4% and 1.7% respectively. Compared with the existing studies, the design can halve the number of dielectric resonators, greatly reducing the size of the filter and the processing costs.