In general, the attenuation characteristics of band-pass filters can be improved by generating attenuation poles in the stop band. In this paper, a design method for a planar band-pass filter with attenuation poles based on a half-wavelength resonator is proposed. According to this design, the attenuation poles can be obtained at any desired frequency by means of coupling structures. Two kinds of filter with the characteristics of steep skirt and wide stop-band were designed and fabricated with the result that the validity of the design method was demonstrated. Therefore, a filter with excellent attenuation characteristics for various applications can be achieved.

This paper describes bandpass filters using linear tapered transmission line resonators (LTLR's). Bandpass filters are designed on the basis of the approximate description of LTLR's with cascaded multi-sections of uniform transmission lines whose widths are slightly different. By this design method, the fundamental characteristics of LTLR's and filter design parameters can be easily obtained using a general-purpose microwave circuit simulator. Trial LTLR bandpass filters showed excellent performance such as low insertion losses and the ability to control spurious responses, then their measured responses indicated close correspondence with the design results.

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.

Chipless RFID tags that use the higher-mode resonances of a transmission line resonator are presented in this paper. We have proposed multimode stepped impedance resonators (SIRs) for this application and reported the fundamental characteristics of an experimental system composed of multimode SIRs with open-circuited ends and a near-field electromagnetic detector using capacitive coupling (electric field) probes for the detector. To improve the frequency response and widen the detection range, we introduced multimode SIRs with short-circuited ends and inductive coupling (magnetic field) probes and measured their properties. To reduce the size of the tag and reader, we examined the frequency responses and found that the optimal configuration consisted of C-shaped tags and detector probes with a spatially orthogonal arrangement. The experimental tag system showed good frequency responses, detection range, and frequency detection accuracy. In particular, the spacing between the tag resonator and the transmission line of the probe, which corresponds to the detection distance, was 5mm or more, and was at least 10 times greater than that of previously reported RFID tag systems using near-field electromagnetic coupling.

Chipless tag systems composed of multimode stepped impedance resonators (SIRs) and a reader based on near-field electromagnetic coupling have been reported. This resonator structure has advantages including a simple design due to its symmetrical structure and good discrimination accuracy because many higher-order mode resonant frequencies can be used for identification of codes. However, in addition to the disadvantage of long resonator length, the frequency response in the tag system becomes unstable due to deterioration of the isolation between the probes because the same probe structure is used for the excitor and detector. In this paper, we propose two methods to solve these problems. One is to adopt an asymmetrical SIR structure with a short-circuited end and open-circuited end, which reduces the resonator length by half while allowing the same number of codes to be generated. The other is to improve isolation between probes by applying different magnetic field and electric field structures to the two probes for excitation and detection. We also examined assignment and identification conditions and clarified that the available number of codes for a unit tag can be more than 15 bits. It becomes clear that a 75-bit chipless tag on a credit card-sized (55×86mm) printed circuit board can be designed by integrating five unit tags.

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.

This paper describes the fundamental principle of novel push-push oscillators using hairpin-shaped split-ring resonators and their application to voltage controlled and injection locked oscillators for frequency synthesizers. The experimental results make it clear that the synthesizer systems discussed here have the advantages of high frequency operation, compact size and low power consumption. Experimental work has been carried out in the L band, but these systems can be applied to much higher frequencies.