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In this paper, a low-profile filter using an open circular dual-mode dielectric resonator is proposed as a filter for a mobile communication base station. The basic configuration of the dielectric resonator consists of two dielectric disks with electrodes on both sides stacked in the axial direction; they are installed in a shielded cavity. The doubly degenerate fundamental mode has an electric field parallel to the axial direction of the dielectric disks, and the resonator can be made low profile without significantly changing the resonant frequency. The equivalent circuit of the dual-mode resonator is given in terms of a ring-shaped transmission line with its electric length of ZR. The equivalent circuit of the multistage filter using this resonant circuit can be designed by the Chebyshev filter design method. A six-stage filter with the center frequency of 985 MHz and the passband width of 10 MHz was fabricated. The results agreed well with those of the simulation. The insertion loss at the center frequency is 1.3 dB, and the external dimensions are 158 X 54 x 23.5 mm.

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