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A novel structure of 26 GHz bandpass filters using TM/sub 11/spl delta// rectangular-mode dielectric cavity resonators is introduced. The resonator of high-permittivity ceramics shows a high quality factor (Q) value of 2600, which is roughly comparable to that of waveguide type ones, in spite of its small structure. A three-stage Tchebyscheff bandpass filter with 0.4% relative bandwidth was fabricated and the passband insertion loss was measured to be 1.7 dB. The filter has input/output ports of microstrip lines for the surface mounting. A duplexer, consisting only of two TM/sub 11/spl delta// mode filters and a microstrip T-junction, is also presented. These filter and duplexer have a configuration compact and easy to manufacture as well as the high-Q performance.