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.

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.

Negative group delay characteristics can be used to improve signal-integrity performance such as equalizer for compensation of the group delay of transmission line (TL). This brief-paper newly attempts to propose a concept of the embedded Folded-Stepped Impedance Resonator (F-SIR) structure with open-stub resonator, for negative group delay and slope characteristics at high-frequency as well as low-insertion loss. The concept of the proposed TL is based on the combination of resonance and anti-resonance due to open-stub resonator in order to establish wideband negative group delay and negative slope characteristics. The proposed TL is fabricated on PCB, and then the concept is validated by measurement and simulation.

Basic left hand mode transmission line (LH mode TL) characteristics made on PCB is an important future issue for the application of the EMC field. In this paper, possibility of a LH mode TL characteristic made by a folded-stepped impedance resonator (F-SIR) type is investigated experimentally and numerically. The experimental and calculated from FEM and equivalent circuit results indicate that some backward propagation characteristic and negative group delay can be established by F-SIR structure.

In this paper, a compact ultra-wideband bandpass filter (UWB-BPF) using pseudo-interdigital stepped-impedance resonators (PIDT-SIRs) is designed and implemented on a commercial printed circuit board (PCB) of RT/Duroid 5880 substrate. The first two resonant modes of the SIR are coupled together and they are applied to create a wide passband. The proposed filter at center frequency f0 of 7.1 GHz has very good measured characteristics including the bandwidth of 3.68-10.46 GHz (3-dB fractional bandwidth of 95%), low insertion loss of -0.50.4 dB, sharp rejection due to two transmission zeros in the passband edge created by the inter-stage coupling. Experimental results of the fabricated filter show a good agreement with the predicted results.

A novel class of microstrip bandpass filter is configured using the impedance transformers and an improved stepped impedance resonator (SIR). This SIR is composed of a central narrow strip section with an aperture on ground and two wide strip sections at the two sides. This low-high-low SIR resonator has a promising capability in achieving an extremely large ratio of first two resonant frequencies for design of a bandpass filter with ultra-broad stopband. The two quarter-wavelength transformers with low and high impedances, referred as to impedance- and admittance-inverters, are modeled and utilized as alternative types of inductive and capacitive coupling elements with highly tightened degrees for wideband filter design. After extensive investigation is made on the two transformers and the proposed SIR, the two novel bandpass filters are constructed, designed and implemented. Two sets of predicted and measured frequency responses over a wide frequency range both quantitatively exhibit their several attractive features, such as ultra-broad stopband with deep rejection and broadened dominant passband with low insertion loss.

A novel microstrip dual-mode bandpass filter with ultra-broad stopband is proposed using the aperture-backed stepped-impedance ring resonator (SIRR). This SIRR consists of low-impedance strips in the four bended corners and high-impedance strips in the four straight sides. With the cross-shaped aperture placed on the ground underneath the SIRR, the upper stopband is significantly broadened. In particular, the 2nd resonant frequency of this proposed SIRR is confirmed to exceed the four times of its 1st counterpart. The dual-mode filter with the passband of 7.5% at 1.59 GHz is then designed and implemented, demonstrating the measured stopband of 1.70-5.80 GHz and size reduction of 56.0%.

An extended configuration of a stepped impedance comb-line filter is presented. The parallel stripline sections of stepped impedance resonators are coupled electromagnetically and a coupling capacitor is introduced. The creation of an attenuation pole near the passband was detailed. A design procedure for the two-pole extended filter is derived from an analysis using even-and odd-mode impedances. Experimental filters were constructed by ceramic lamination technique. They exhibited excellent performances suitable for portable telephones.

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.