This paper presents a new class of dual-, tri- and quad-band BPF by using proposed open stub-loaded shorted stepped-impedance resonator (OSLSSIR). The OSLSSIR consists of a two-end-shorted three-section stepped-impedance resistor (SIR) with two identical open stubs loaded at its impedance junctions. Two 50- Ω tapped lines are directly connected to two shorted sections of the SIR to serve as I/O ports. As the electrical lengths of two identical open stubs increase, many more transmission poles (TPs) and transmission zeros (TZs) can be shifted or excited within the interested frequency range. The TZs introduced by open stubs divide the TPs into multiple groups, which can be applied to design a multiple-band bandpass filter (BPF). In order to increase many more design freedoms for tuning filter performance, a high-impedance open stub and the narrow/broad side coupling are introduced as perturbations in all filters design, which can tune the even- and odd-mode TPs separately. In addition, two branches of I/O coupling and open stub-loaded shorted microstrip line are employed in tri- and quad-band BPF design. As examples, two dual-wideband BPFs, one tri-band BPF, and one quad-band BPF have been successfully developed. The fabricated four BPFs have merits of compact sizes, low insertion losses, and high band-to-band isolations. The measured results are in good agreement with the full-wave simulated results.

Compact Microstrip Dual-/Tri-/Quad-Band Bandpass Filter Using Open Stubs Loaded Shorted Stepped-Impedance Resonator

A new type of microstrip dual-mode dual-band bandpass filter (BPF) using a single quadruple-mode resonator (QMR) is proposed in this paper. The classical even-/odd-mode method is applied to analyze the characteristics of the proposed resonator, which shows that it has two pairs of symmetrical resonant modes. Owing to the inherent characteristic of a dual-mode resonator and source-load coupling, four transmission zeros can be produced and these four resonant modes can be divided in two groups, resulting in a dual-band BPF with two resonant modes in each passband. As examples, two dual-mode dual-band BPFs, Filter A with central frequencies (CFs) at 1.99/5.58 GHz and -3-dB fractional bandwidth (FBW) of 62.3%/19.7%, while Filter B with CFs at 1.64/5.26 GHz and -3-dB FBW of 32.9%/7.6%, are designed and fabricated. An aperture-backed compensation technique is employed in such two filters to enhance the coupling strength between the feeding lines and QMR. Furthermore, a meander coupled-line section is employed in the Filter A design, while a defected microstrip structure is introduced in Filter B design, so as to increase much more design freedoms for tuning filter performance. The fabricated two filters exhibit simple design procedures, low insertion losses, good return losses, sharp shirts, and compact sizes. Moreover, two BPFs do not need external input/output impedance transformation feeding lines.

Compact and Sharp Skirts Microstrip Dual-Mode Dual-Band Bandpass Filter Using a Single Quadruple-Mode Resonator (QMR)

In this paper, a compact quad-band high-temperature superconducting (HTS) bandpass filter using a quadruple-mode square ring loaded resonator (SRLR) is introduced. The even- and odd-mode method is applied to investigate the equivalent circuits of the proposed quadruple-mode SRLR. The design graphs for the relationship of the parameters of electrical length and resonance performances are then set up. Based on the analysis above, four allocated resonant modes can be simultaneously excited and easily tuned. Meanwhile, multi-transmission zeros are created due to the different propagation paths of the square ring structure. Signal-interference theory is also adopted to explain the generating mechanism of transmission zeros. Moreover, a meander coupled-line technique is realized to adjust one uncertain resonant frequency to meet the target specifications of the designed quad-band filter. To verify this methodology, a second-order microstrip HTS filter operating at 2.45/3.5/5.2/5.8 GHz for wireless local area networks and worldwide interoperability for microwave access potential applications is designed using two quadruple-mode SRLRs. The quadruple-mode SRLRs are coupled with a pseudo-interdigital coupling structure for achieving the desired coupling degree conveniently, which also miniaturize the circuit size. This filter was fabricated on a 2-in-diameter 0.5-mm-thick MgO wafer with double-sided YBa2Cu3Oy thin films. The filter component was measured at the temperature of 77 K. Measured results agree with the theoretical results and show that the insertion losses in passbands are less than 0.3 dB, which exhibit superiority in midband insertion loss.

Quad-Band High-Temperature Superconducting Bandpass Filter Using Quadruple-Mode Square Ring Loaded Resonator

In this paper, a multiple stubs loaded ring resonator (MSLRR) is proposed to design directly coupled multi-band bandpass filters (BPFs) with mixed electric and magnetic coupling (MEMC). The proposed MSLRR exhibits multiple-mode resonant behavior. The increased number of loaded stubs excite many more useful resonant modes, but these resonant modes can be still independently controlled. As examples, a dual-band BPF, a tri-band BPF, a quad-band BPF, and a quint-band BPF using different types of MSLRRs are designed and fabricated. The passband frequencies and return losses (RLs) of these multi-band BPFs can be independently controlled. A dual-mode open loop resonator is then introduced in the quint-band BPF to enhance the sixth resonant mode of the MSLRR to produce the sixth passband so that a sext-band BPF is also presented. Multiple transmission zeros due to the cancelling effect of MEMC and virtual grounds in the MSLRR can be observed around the passbands resulting in sharp passband selectivity and high band-to-band isolation. Moreover, all of the fabricated multi-band BPFs have compact sizes, good RLs, and low insertion losses. Good agreements are observed between the simulated and measured results.

Compact Multi-Band Bandpass Filters With Mixed Electric and Magnetic Coupling Using Multiple-Mode Resonator

This letter presents a compact quad-band bandpass filter for DCS/WLAN/WiMAX/5G Wi-Fi applications It utilizes two resonators One is a multi-stub-loaded resonator operating at the first, second and fourth passband frequencies The other one is a short-end stub-loaded resonator used to yield the third passband Among the four passbands, the highest one is designed to cover a wide bandwidth (515–585 GHz) for 5G Wi-Fi applications The design procedures are discussed in detail and the simulated and measured results are presented

Compact Quad-Band Bandpass Filter for DCS/WLAN/WiMAX/5G Wi-Fi Application

A compact quad-band bandpass filter utilising the proposed quad-mode resonator is presented. The proposed resonator, which has four tunable symmetrical resonant poles, can be treated as a two-side open-circuit stepped-impedance resonator with short-circuit stubs in its low-impedance sections. With the multi-paths propagation mode configuration of the two resonators, transmission zeros among each passband are generated to improve passband selectivity and achieve high isolation. As an example, a quad-band bandpass filter centring at 1.9/2.8/4.3/5.2GHz is designed, fabricated and measured. The measurement results agree well with the full-wave EM simulated responses.

Compact high isolation quad-band bandpass filter using quad-mode resonator

This letter presents a novel lowpass filter (LPF) structure which consists of a section of high-impedance microstrip line (HIML) with a pair of radial stubs (RSs) loaded at its center and a pair of stepped-impedance open stubs (SIOSs) loaded on both ends of HIML. The RSs loaded HIML exhibits a lowpass property and has a wide stopband. The loaded SIOSs not only can improve the roll-off rate of LPF significantly but also is able to extend the stopband. Based on such a LPF structure, a pair of highpass shorted HIMLs are paralleled on both sides of LPF to construct a wideband bandpass filter (BPF) with wide stopband. To validate the proposed method, two filters, i.e., a LPF with cutoff frequency fc at 1.07 GHz and a BPF centered at f0 = 0.89 GHz with -3 dB fractional bandwidth of 87%, are designed and fabricated. The measured results show the fabricated LPF has a -20 dB isolation bandwidth from 1.27 fc to 13.7fc while the fabricated BPF has a -20 dB isolation bandwidth from 1.56 f0 to 15 f0. Moreover, the fabricated LPF and BPF also have the compact size of 0.107 λgc ×0.083 λgc and 0.123 λg0 ×0.073 λg0, respectively. Good agreement can be observed between the simulation and measurement.

Design of Miniaturized Microstrip LPF and Wideband BPF With Ultra-Wide Stopband

This letter presents a new stubs loaded stepped impedance resonator (SsLSIR) to design single-/dual-wideband bandpass filter (BPF). The proposed SsLSIR exhibits multiple tunable transmission zeros (TZs) and transmission poles (TPs), which can be arranged to build up single/dual-wideband BPF. The proposed single-band BPF has a central frequency of 1.91 GHz with -3 dB fractional bandwidth (FBW) of 52.4% and the dual-band BPF has a central frequency of 1.92/5.44 GHz with -3 dB FBW of 66.7%/28.3%. The higher-order spurious frequencies of the single-band BPF are tuned and canceled by the TZs, resulting in a wide stopband with -20 dB spurious suppression from 2.19 to 9.19 GHz. The TZs between two passbands of the dual-band BPF provide a wideband and high band-to-band isolation. Two filters have the merits of low insertion loss, simple physical topology and compact size.

Compact Single-/Dual-Wideband BPF Using Stubs Loaded SIR (SsLSIR)

This paper presents a new ultra-wideband bandpass (UWB) bandpass filter (BPF) based on the half-wavelength (λ/2) stepped-impedance stub-loaded resonator (SISLR). Classical even- and odd-mode analysis shows that the new filter has multiple transmission poles and two tunable transmission zeros on both sides of the filter passband. In order to reject the interfered signals, the technique of generating a notched band inside the UWB passband is studied. As examples, two UWB BPFs, one without the notched band and the other with dual narrow notched bands at 5.8/8.0 GHz, are designed, fabricated and measured. The notched band at 5.8 GHz is realized by an embedded open-circuited stub (EOCS) while the notched band at 8.0 GHz is implemented by a folded stepped-impedance resonator (FSIR). The simulations and measurements agree well with each other. Two filters show the simple topologies, compact sizes, low insertion losses and sharp rejections.

Compact and Sharp Rejection Microstrip UWB BPF with Dual Narrow Notched Bands

By etching slots in the low-impedance section of the conventional stepped-impedance resonator, a novel slotted stepped-impedance resonator (SSIR) is proposed. As two examples, a fourth-order bandpass filter (BPF) operating at 1 GHz with a size of 0.078 λg × 0.062 λg and a miniaturized diplexer operating at 0.9/1.57 GHz with a size of 0.054 λ0 × 0.086 λ0 are designed based on the proposed SSIR. The fabricated BPF exhibits a high selectivity and a wide −30 dB rejection upper stopband from 1.13 f0 to 6.52 f0, while the fabricated diplexer has up to −60 dB output isolation. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

Yu-Xue Ji

Papers

Compact high isolation quad-band bandpass filter using quad-mode resonator

Design of Miniaturized Microstrip LPF and Wideband BPF With Ultra-Wide Stopband

Compact Single-/Dual-Wideband BPF Using Stubs Loaded SIR (SsLSIR)

Compact and Sharp Rejection Microstrip UWB BPF with Dual Narrow Notched Bands

Novel slotted stepped‐impedance resonator and its application to compact and high performance bandpass filter and diplexer design