Stepped-impedance Sections Research Articles

An Electronically Tunable Delay Line With Continuous Control of Slope and Peak Delay

This article presents a continuously tunable dispersive delay line (DDL). The slope as well as peak value of delay can be controlled electronically. The basic unit consists of a stepped-impedance section and two variable resistors in the form of p-i-n diodes. The slope and peak delay are controlled by changing the bias current of the p-i-n diodes. A transmission line model is used for theoretical analysis. Design equations are derived. Three prototypes with variable delay profiles are fabricated to validate the proposed technique. In all the cases, good agreement is obtained among the predicted and measured results. The implementation provides fast tuning over a given frequency band. Furthermore, a comparison with other reported techniques shows that the design is simple, occupies less area, and provides lower insertion loss. The DDLs operate as a linear device at least up to 23 dBm.

Design of dual/tri-frequency impedance transformer with ultra-high transforming ratio

In this article, the design of a new dual-band impedance transformer with ultra-high transforming ratio (UHTR) is presented. The closed-form expressions are derived analytically using a lossless transmission-line theory. To practically validate the proposed design concept, two examples of dual-band transformer working at smaller and larger frequency ratios are designed for different load impedance of 500, 1000, and 1500 Ω. Finally, three prototypes of dual-band transformer with UHTR are designed, fabricated, and tested. For all these prototypes, different frequency ratios (two operating frequencies can be chosen arbitrarily) are considered. The measured return loss of the prototypes is better than 15 dB at all the operating frequencies. The measured results are matched very closely with the simulated results. This design is then extended to match a complex load at two different frequencies. The multi-band characteristic is obtained by decomposing a shorted stub into a stepped impedance section of the proposed structure. With the necessary derivation and analysis, a tri-frequency matching network is designed for a transforming ratio of 10.

Compact Multiband Interdigital-Coupled-Fed Planar Antenna with Stepped-Impedance Structures for Mobile Handsets

A new compact multiband planar antenna combining an interdigital-coupled feeding line and one stepped-impedance structure is presented here. This antenna is capable of generating five resonant modes to cover the ISM 915/2400/5800 MHz bands, GPS band, and IMT C-band, respectively. The five resonant frequencies covered by the proposed antenna can be adjusted individually by controlling the impedances and electrical lengths of the corresponding stepped-impedance sections. An additional advantage of the proposed stepped-impedance structure is its ability to suppress higher order resonance modes, thus filtering out unwanted interference. The proposed antenna utilizes a simple planar compact structure and occupies a small area of only 12 × 30 mm2. Details of the antenna design and experimental results are presented and discussed.

Miniaturised dual‐band rat‐race coupler with harmonic suppression using synthetic transmission line

A dual-band 90° unit module with harmonic suppression (HS) is proposed. This unit module consists of a pair of back-to-back stepped impedance sections and an open stub. The unit module is realised by synthetic transmission lines, and it is successfully implemented into a novel miniature dual-band (2.45/5.8-GHz) rat-race coupler with HS (suppression level ≥16 dB, 6.8–13 GHz). Compared with traditional 1.5λ microstrip ring hybrid, the proposed dual-band rat-race with HS only occupies 13.84% of its area.

Compact wide-stopband microstrip bandpass filter-based on stub-loaded stepped-impedance resonators

This study presents compact wide-stopband microstrip bandpass filters using stub-loaded stepped-impedance resonators. The resonators consist of three stepped-impedance sections. By adjusting the parameters of the resonators, one can control the frequencies of the resonant modes as well as the frequency of the transmission zero. When the transmission zero frequency is close to the spurious resonant mode frequencies, one can have a wide-stopband bandpass filter without external filtering circuits or increasing the resonator number for suppressing the spurious passbands. To validate the design concept, three dual-band bandpass filters and one wideband bandpass filter are designed, fabricated and tested.

GENERALIZED SYNTHESIS OF RAT RACE RING COUPLER AND ITS APPLICATION TO CIRCUIT MINIATURIZATION

Generalized synthesis of the rat race ring coupler is developed with its four arms being allowed to have difierent characteristic impedances. The transmission line theory incorporated with the even-odd analysis is used to formulate the conditions for solving the circuit parameters. The solution shows that a rat race ring with a normalized area of 41.82% or 0:97‚-circumference can be achieved. Based on the solutions, simulated bandwidths of the new ring hybrids are reported. Two experimental circuits are measured for validation check. One uses stepped-impedance sections to realize the four arms for further size reduction. This circuit occupies only 13.12% of that of a conventional hybrid ring at 1GHz. It is believed that this implementation has the best size reduction for a microstrip ring hybrid in open literature. Measured scattering parameters show good agreement with the simulated results.

Miniaturized Dual-Band Hybrid Couplers With Arbitrary Power Division Ratios

Branch-line and rat-race couplers are designed to have dual-band operation with arbitrary power division ratios. An elementary two-port is proposed to imitate the 90deg section at the two designated frequencies with different characteristic impedances. The two-port consists of a stepped-impedance section with open stubs attached to its two ends, and its circuit parameters are determined by the transmission line theory. The use of the stepped-impedance sections also leads to circuit miniaturization. By the standard microstrip technology, investigated also includes the realizable power division ratios and circuit bandwidths in the two bands, the upper limit of the ratio of the two designated frequencies and the miniaturization factor of the proposed circuit. Hybrid couplers operating at 2.45/5.2 GHz with various power division ratios are designed, fabricated and tested. Experiment results are compared with the theory and simulation.

Compact Bandstop Filters with Extended Upper Passbands

This paper presents new compact bandstop filters (BSFs) with extended upper passbands. In the basic proposed filter configuration, the conventional quarter-wavelength open-stub resonators are replaced with equivalent two-section stepped impedance resonators. Transmission line analysis is used to determine the dimensions of the equivalent stepped impedance sections. The filter structure is analyzed using a full wave electromagnetic (EM) simulator and then realized at 2.3 GHz band. Experiments have also been done to validate the performance of the design concept. Compared with the conventional quarter-wavelength-based bandstop filter, significant extensions of the upper passband beyond 9 GHz and 40% size reduction are achieved. Two other variations of the proposed basic BSF with further size reduction (more than 60%) are implemented and their measured performances are verified.