Chen Miao

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

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

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

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.

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

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 f_c 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 f_c to 13.7f_c 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 λ_gc ×0.083 λ_gc and 0.123 λ_g0 ×0.073 λ_g0, respectively. Good agreement can be observed between the simulation and measurement.

Application of Cross-Shaped Resonator to the Ultra Wideband Bandpass Filter Design

An ultra-wideband (UWB) bandpass filter (BPF) with two cascaded cross-shaped resonators is proposed and implemented. As the starting work of this letter, a cross-shaped resonator with wide passband is introduced. With the use of even- and odd-mode approach, this initial resonator is characterized and designed to build up a UWB BPF. And then, a cascaded UWB BPF is fabricated to satisfy Federal Communications Commission indoor mask.

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

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 and Sharp Rejection Microstrip UWB BPF with Dual Narrow Notched Bands

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.

DESIGN OF UNEQUAL WILKINSON POWER DIVIDER FOR TRI-BAND OPERATION

This paper presents a novel tri-band unequal Wilkinson power divider. The proposed structure is derived from the conventional unequal Wilkinson power divider by replacing the quarter-wavelength branch lines and quarter-wavelength transformers with the extended T-shaped short stubs and three-section transformers respectively. The flrst and third operating frequencies of the proposed Wilkinson power divider can be ∞exibly controlled, while the second frequency is equal to the mean value of the other two frequencies. Both of the closed- form equations and design procedure are given. For veriflcation, a tri- band unequal power divider with the power dividing ratio of 2 : 1 and operating frequencies of 1.3, 3.0 and 4.7GHz is designed, fabricated and measured. The measurement results are in good agreement with the simulation ones. It is shown that the proposed power divider has simple topology and good performances in terms of insertion loss, port matching and isolation at all three operating frequency bands.

Novel Sub-Miniaturized Wilkinson Power Divider Based on Small Phase Delay

In this letter, admittance matrix and arbitrary phase delay is investigated for the design of sub-miniaturized Wilkinson power divider (WPD). A theoretical model based on admittance matrix is derived and discussed to find the relationship among arbitrary phase delay, characteristic impedance and electrical length of WPD. The presented method is validated by building a modified configuration which is centered at 500 MHz with 14.18% fractional bandwidth (FBW) using both microstrip lines and lumped elements. The measured results show that the proposed WPD exhibits excellent performances, including less than 0.27 dB insertion loss, better than 26.1 return loss and greater than 39.2 dB isolation. Moreover, more than 85% size reduction is achieved, compared with conventional WPD.

A High Performance Balun Bandpass Filter with Very Simple Structure

A high performance balun bandpass fllter (BPF) with very simple structure is proposed in this letter, this structure realizes superior performance in bandpass flltering meanwhile with good difierential performance of the balun. The proper balanced outputs and BPF characteristic by the symmetric feeding and skew-symmetric feeding have been obtained, and the theory of this simple structure for unbalanced input to balanced outputs has been studied. The center frequency of the fabricated balun-BPF was operated at 2.4GHz with 5.8% fractional bandwidth (FBW), and this frequency is used for Bluetooth and some other communication systems. The difierences between the two outputs are 180 - § 5 - in phase and within 0.39dB in magnitude. At f0, the amplitude imbalanced and phase difierence are within 0.37dB and 179.2 - , respectively. The measured frequency responses agree well with the simulated ones. With the theoretical analyses and practical results, it is shown that the proposed one has the advantages of simple structure, convenient analysis and good performance of both BPF and balun.