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

This paper presents a new class of multi-stub loaded resonators with flexibly controlled resonance modes, which are suitable for both tunable and nontunable filter applications. The proposed resonators, modified from a basic tri-mode resonator, include two quad-mode ones and a six-mode one. One of the quad-mode resonators is utilized to design a reconfigurable dual-band filter with tunable lower passband and fixed upper passband. The other quad-mode resonator is applied to design a bandpass filter (BPF) with very high skirt selectivity. The six-mode resonator is suitable for tri-band BPFs with individually controllable passband frequencies and bandwidths. All three circuits are theoretically analyzed and experimentally demonstrated. Comparisons of the measured and simulated results are presented to verify various applications of the resonators.

Novel Multi-Stub Loaded Resonators and Their Applications to Various Bandpass Filters

The contribution of this paper is to propose novel balanced and dual-band bandpass filters (BPFs), using quarter-mode (QM) and eighth-mode (EM) substrate integrated waveguide (SIW) cavities, for the size reduction of the overall circuit. Two balanced BPFs, which separately demonstrate a third-order Chebyshev response and a fourth-order quasi-elliptic response, are realized by properly choosing, feeding, and coupling those QMSIW and EMSIW cavities. Not only desired differential-mode operation within the passband, but also good common-mode suppression in a certain frequency range have been achieved. Furthermore, a dual-band BPF with improved out-of-band rejection is also realized by properly constructing the coupling topology of four EMSIW cavities. An additional source-to-load coupling path is introduced in this dual-band BPF to obtain more transmission zeros (TZs). The sizes of resonant cavities utilized in the above designs are only one-fourth or one-eighth of those rectangular ones in conventional designs, which lead to a significant reduction in the overall circuit size. All proposed designs have been fabricated and measured to verify simulation predictions. Based on the author’s knowledge, it is the first time using QMSIW and EMSIW for balanced filter designs, and dual-band filter designs with TZs.

Design of Compact Bandpass Filters Using Quarter-Mode and Eighth-Mode SIW Cavities

This letter proposes a novel ultra-wideband (UWB) bandpass filter (BPF) with dual notched bands using triangular defected ground structures (DGS). Two symmetrical dumbbell-shaped interdigital capacitors are formed to improve the BPF's performance. Three pairs of tapered defected ground structures are studied and adopted to suppress the spurious passband by assigning their transmission zeros towards the out of band signal. A small UWB BPF is obtained by combining these two structures. One of the arms in coupled-line sections is extended and folded to create a notched band at 5.3 GHz, and a meander line slot is developed to create another notched band at 7.8 GHz. Simulated and measured results are in good agreement indicating that the proposed BPF has a passband from 2.8 to 11.0 GHz and a wide stopband bandwidth with 20 dB attenuation up to 30.0 GHz.

Compact UWB Bandpass Filter With Dual Notched Bands Using Defected Ground Structures

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 letter, a novel compact ultra-wideband (UWB) microstrip bandpass filter (BPF) with a notched band is presented by using the proposed radial stub loaded resonator (RSLR). The RSLR, on the one hand, is able to control two tunable transmission zeros separately and on the other hand, has the ability to provide a notched band. In addition, the vertical dimension of the UWB BPF can be significantly reduced by using RSLR, as compared with the UWB BPF based on the conventional stub-loaded resonator (SISLR). For validation, two UWB BPFs, one without the notched band and the other with a notched band at 8.0 GHz for rejecting satellite-communication signal, are developed and fabricated. Measured results show two fabricated filters have the merits of low insertion losses, sharp rejections and flat group delays. Moreover, two filters exhibit the simple topologies and compact sizes.

Compact UWB Bandpass Filter With a Notched Band Using Radial Stub Loaded Resonator

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.

Wen Wu

Papers

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

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

Compact UWB Bandpass Filter With a Notched Band Using Radial Stub Loaded Resonator

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

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