Multimode Stepped-impedance Resonators Research Articles

Design of UWB Filtering Impedance Transformers and Power Dividers Using Stepped-Impedance Resonators

This study presents a novel design of ultra-wideband (UWB) impedance transformers and power dividers with filtering capabilities. Based on the UWB impedance matching network, the UWB filtering impedance transformers are designed, and the UWB filtering power dividers are achieved by impedance transforming one port of one or more impedance transformers. The transformers consist of a multi-mode stepped-impedance resonator (SIR) and defected ground structures (DGSs). The SIR is tightly coupled to two ports of different impedance levels via the unsymmetrical two-sided coupled lines and DGSs. In addition, two transformers that convert impedance from 50 Ω to 100 Ω are connected to form a UWB power divider with filtering function. The 25 Ω port of an impedance transformer with a 50 Ω to 25 Ω conversion is impedance matched to two 50 Ω ports connected in parallel, resulting in another power divider with filtering function. Thus, two prototype UWB impedance transformers from 50 Ω to 100 Ω and from 50 Ω to 25 Ω are designed and their corresponding power dividers are also designed and fabricated. The simulated and measured results are consistent, demonstrating good features, such as return loss greater than 10 dB and insertion loss less than 4.5 dB in the passband, UWB filtering capacity with out-of-band rejection greater than 20 dB, and compact size smaller than 1.2λ × 2.1λ (λ is the wavelength of the central frequency).

Wideband Balanced Filters With Intrinsic Common-Mode Suppression on Coplanar Stripline-Based Multimode Resonators

In this paper, two types of coplanar stripline (CPS)-based multimode stepped-impedance resonators are proposed for exploration of wideband balanced filters with intrinsic common-mode (CM) suppression. Such CPS multimode resonators (MMRs) can be readily terminated with either a pair of open- or short-circuited ends with no need of via holes. With resorting to a proper impedance ratio, the first three modes of each MMR are assembled to construct a wide differential-mode (DM) passband. Afterwards, two distinctive broadside-coupled sections are further investigated based on their open- and short-ended circuit models, respectively. Characteristic impedances and effective dielectric constants can be adequately obtained by virtue of an efficient quasi-static approach under the odd- and the even-mode operations. As such, two types of CPS-MMR-based bandpass filters each with five transmission poles are synthetically designed. For experimental validation, the proposed balanced filters are finally fabricated and measured with the help of two identical pairs of balanced-to-balanced microstrip-to-CPS transitions. Theoretical, simulated, and measured results are found in reasonable agreement with each other with/without the transitions, thus demonstrating that the proposed CPS-based MMRs are well characterized with the wideband DM transmission and intrinsic CM suppression.

Compact superconducting single- and dual-band filter design using multimode stepped-impedance resonator**Project supported by the National Natural Science Foundation of China (Grant No. 61371009) and the Fund from the Chinese Ministry of Science and Technology (Grant No. 2014AA032703).

This study presents two multimode stepped-impedance structures to design single- and dual-band filters. Transmission zeroes are introduced for the single-band filter by using dual-mode stepped-impedance resonators. The single-band filter with high selectivity is centered at 6.02 GHz and has a fractional bandwidth (FBW) of 25.6%. Four stubs (two low frequency and two high frequency ones) are connected to the rectangular patch in the center to construct a quadruplemode resonator. The independent conditions of the center frequencies of the high and low bands of the resonator are analyzed. A dual-band filter, which operates at 1.53 GHz and 2.44 GHz with FWBs of 12.1% and 14.1%, respectively is designed. The single- and dual-band filters are both fabricated with double-sided YBCO films and they can be used in mobile and satellite communications.

Design of microstrip tri‐mode balun bandpass filter with high selectivity

A new microstrip tri-mode balun bandpass filter (BPF) with good filter-type and balun-type functions is presented. To realise the tri-mode BPF performance, the multimode stepped-impedance resonator is introduced and parallel coupled to both the balanced and the unbalanced ports. To achieve 180° phase difference, two types of transition structures, i.e. the microstrip–coplanar waveguide–microstrip transition and the microstrip–coplanar stripline–microstrip transition, are adopted for the two balanced output ports design, respectively. A balun BPF operating at 2.6 GHz is designed and fabricated to validate the feasibility of the new approach. Results indicate that the proposed balun BPF exhibits not only high selectivity with two transmission zeros locating at 1.7 and 3.7 GHz but also good balance performance with 0.5 dB magnitude imbalance and 5° phase imbalance between the balanced outputs.

Tri-band filter with multiple transmission zeros and controllable bandwidths

This paper presents a compact microstrip tri-band bandpass filter (BPF) using two multimode stepped-impedance resonators (SIRs) with a 0° feed structure. The fundamental odd-mode and even-mode resonant frequencies and the third resonant frequency are utilized to determine the center frequencies of the tri-band filter. The mode-splitting technique is used by combining two SIRs with electrical coupling. Therefore, two modes generate one passband and the bandwidths can be controlled by the electrical coupling strength. The 0° feed network is applied to create one pair of transmission zeros at each side of all the triple passbands, resulting in high selectivity. Finally, a tri-band BPF with the central frequencies of 1.8, 2.4, and 5.8 GHz, and respective fractional bandwidths of 8.9, 12.5, and 5.3% are designed and fabricated. The simulated and measured results show a good agreement.

Compact and High Selectivity Tri-Band Bandpass Filter Using Multimode Stepped-Impedance Resonator

In this letter, a miniaturized tri-band bandpass filter (BPF) using a multimode stepped-impedance resonator (SIR) with a 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> tapped-feed structure is presented. The odd- and even-mode fundamental resonant frequencies and the first high-order resonant frequencies of the SIR are utilized to generate dual-mode dual-band response and the tapped side-coupled feed-lines construct an additional passband avoiding occupying extra size. Owing to the 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> tapped-feed structure and the intrinsic characteristics of the SIR, multiple transmission zeros are created to improve the selectivity of the filter. The bands of the designed tri-band BPF are located at 1.57 GHz (GPS application), 3.5 GHz (WiMAX application) and 5.8 GHz (WLAN application). Good agreement between the simulated and the measured results is observed.

Design of a Wideband Bandpass Filter with a High Band Selectivity and a Wide Stopband

In this paper, a wideband bandpass filter (WBPF) with a wide stopband by using a multimode stepped impedance resonator (SIR) and tapping a stepped-impedance open-circuited stub is designed and implemented for the 3.1–4.9 GHz low band specification. The wide passband performance with a wide stopband is formed by allocating the first three resonant modes of the multimode SIR, and the band selectivity is further improved by using the stepped-impedance open-circuited stubs to have sharp attenuation rates at both lower and upper sides of the passband. Moreover, the insertion loss of the designed filter is improved by two aperture-backed structures under the inter-digital input/output ports. The fabricated WBPF exhibits a high performance, including the bandwidth of 3.3–5 GHz (3-dB fractional bandwidth of 45%), low insertion loss of 1±0.3 dB at center frequency f 0 of 4 GHz, and a wide stopband from 5.1 GHz to 11 GHz. Experimental results also show a good agreement with the simulated ones.

PLANAR MULTIBAND BANDPASS FILTER WITH MULTIMODE STEPPED-IMPEDANCE RESONATORS

Planar multiband bandpass fllters are implemented based on the versatile multimode stepped-impedance resonators (SIRs). The resonant spectrum of a SIR can be calculated as functions of the length ratios for various impedance ratios of the high- and low-impedance sections. Thus, by properly selecting the geometric parameters and designing the input/output coupling structure, the SIRs are feasible to realize multiband multimode fllters. Using a single SIR, a dual- mode dual-band, a dual-mode triple-band or a hybrid dual-/triple- mode dual-band bandpass fllter can be realized. Emphasis is also placed on designing specifled ratios of center frequencies and fractional bandwidths of the passbands. To extend the design ∞exibility, extra shunt open stubs are used to adjust the ratio of the passband frequencies. In addition, sharpness of the transition bands is improved by designing the input/output stages. Simulation results are validated by the measured responses of experimental circuits.

Broadband quasi-Chebyshev bandpass filters with multimode stepped-impedance resonators (SIRs)

Planar broadband bandpass filters of order up to 9 are synthesized based on the multimode property of stepped-impedance resonators (SIRs). Based on the transmission line theory, the modal frequencies of the SIRs are calculated based on the impedance and length ratios of its hi- and low-Z segments. In the synthesis, the SIR coupling schemes are determined by the split mode graphs. Using one, two, two, three, and three dual- or triple-mode SIRs, quasi-Chebyshev filters with four, six, six, eight, and nine transmission poles, respectively, are synthesized with a fractional bandwidth (BW) /spl Delta/=50%. Emphasis is placed not only on designing the I/O coupling structures for matching the external Q (Q/sub ext/) and the circuit BW, but also on matching the resonant peaks of the circuit with the nominal Chebyshev poles. Measured results of experimental circuits show good agreement with simulated responses.