This paper describes newly development compact square-shaped stepped impedance resonators (SIR's) and their application to antenna duplexers. The new square-shaped SIR's are devised in consideration of an optimized resonator structure for miniaturization. Fundamental properties such as the effect of the tapered section and unloaded Q of the square-shaped SIR's are studied. Experimental antenna duplexers using the new SIR's perform excellently and have compact size and light weight as expected. These results prove that they are suitable for use in portable radio telephone terminals.

This paper describes newly developed miniaturized stepped impedance resonators with a double coaxial structure (DC-SIR's) and their application to bandpass filters. The new DC-SIR's using dielectric material are devised for more compact and lower frequency bandpass filters. Fundamental characteristics such as resonance properties and unloaded-Q make it clear that DC-SIR's have attractive features that miniaturization can be achieved without Q-factor degradation. Trial 400 MHz bandpass filters incorporating DC-SIR's are also made. Experimental results of bandpass filters proved that DC-SIR's are applicable to lower frequency band radio equipment and able to contribute to the expansion of applicable frequency ranges of dielectric coaxial resonators.