Coupled-resonator Bandpass Filters Research Articles

Frequency-Variant Double-Zero Single-Pole Reactive Coupling Networks for Coupled-Resonator Microwave Bandpass Filters

In this work, a family of frequency-variant reactive coupling (FVRCAFVC) networks is introduced and discussed as new building blocks for the synthesis of coupled-resonator bandpass filters with real or complex transmission zeros (TZs). The FVRCAFVC is a type of nonideal frequency-dependent inverter that has nonzero elements on the diagonal of the impedance matrix, along with a nonlinear frequency-variation profile of its transimpedance parameter. The distinctive feature of these new FVRCsAFVC is that they can be modeled with a simple bridged-T network consisting of four reactive elements. Such FVRCsAFVCs can introduce one pole and up to two TZs—so that they are referred to as double-zero single-pole (DZSP) networks. DZSP networks allow the pole to be located above, below, or in-between the TZs. Depending on the choice of the elements in the bridged-T circuit, the position of the TZs and the pole can be controlled independently. The coupling matrix for filters with DZSP networks can be found by solving an inverse-structured nonlinear eigenvalue problem (ISNEVP). Examples of possible implementations of DZSP couplingAFVC networks are provided for both lumped and quasi-lumped-element circuits, as well as for transmission-line-based and waveguide technologies. The application of DZSP coupling networks to the design of microwave bandpass filters with generalized Chebyshev-type characteristics is illustrated by means of the synthesis of three microstrips and two waveguide coupled-resonator bandpass filters. The waveguide filters are verified through electromagnetic (EM) simulations and the microstrip filters are manufactured and characterized for proof-of-concept demonstration purposes, showing a fairly close agreement between EM simulations and measurements.

Exhaustive Synthesis Framework of Coupled Resonator Microwave Bandpass Filters

The synthesis of coupled resonator bandpass filters has been a classic theme of research for the past half century. Continuous efforts have been paid to explore new coupling topologies. Needless to say, the ultimate goal for filter synthesis is to find all the viable coupling topologies and their real-valued circuit models. In this article, a rigorous and straightforward framework for exhaustive search of not only all the viable coupling topologies but also all their real coupling matrices for a given filtering function is presented. The proposition that provides sufficient and necessary condition for a viable coupling topology with finite real coupling matrices is proved. The uniqueness of the folded coupling matrix is also proved and is used to establish the simultaneous equations for a well-behaved numerical solution search process. The special cases of the proposition are discussed with illustrative examples. Demonstration examples, including a prototyped filter in a novel “grid” coupling topology, have shown that the framework can systematically find all the viable coupling topologies and their real-valued solutions numerically, through which many new useful coupling configurations can be found, including the “trapezoid” configuration that is highly suitable for a dual-mode realization for a symmetric/asymmetric filter response.

New Design Approach of “3rd - Order Dipole Antenn” Based on Direct Coupled Resonator Bandpass Filter

ABSTRACT In ultra-wideband (UWB) antennas used with the applications of wireless communication systems (WCS), the following five antenna parameters; radiation patterns, directivity, bandwidth, efficiency and antenna gain should be well optimized. A new design approach-based on coupling matrix theory of synthesis antenna has been presented. The most important parameters of this matrix are; external normalized quality factor, normalized un-loaded quality factor, radiation quality factor and coupling coefficients between the resonators. Accuracy in calculating these parameters will greatly facilitate control of the antenna bandwidth to be designed. The design approach included a BPF which was also expanded to become an antenna arrays-filter in the hope of increasing the gain and bandwidth of the antenna. Further, a matching unit is placed between the designed BPF and the antenna, to overcome the mismatching situation, and to achieve a high transmission power. The paper presented a new design approach for an active BPF at frequency “2.45 GHz” and then its integration with a 3rd-order dipole antenna [1]. This design is followed by the creation of another efficient couple-resonant filter (CRF), in which each resonant grid is represented by a radiator. Moreover, a lossless two-port dipole antenna was introduced. Here, each of the poles is integrated with an inductor, to sure that the bipolar antennas can exploit as a resonator. The scores of the simulation-sketches and the computed results were convincing. Finally, the performance efficiency of the designed filter at the resonant frequency 2.45 GHz and for both “H-plane” and “E-plan” were summarized in Table 1.

Ka‐band coupled‐resonator bandpass filter based on printed ridge gap waveguide for millimetre‐wave application

A low-loss Ka-band coupled-resonator bandpass filter based on the printed ridge gap waveguide (PRGW) technology is presented for millimetre-wave communication applications. The PRGW is employed to allow electromagnetic-wave propagation in the air gap in order to avoid dielectric loss and improve transmission performance which is suitable for millimetre-wave applications. The bandpass filter is implemented with two transmission zeros which are easily obtained by adjusting the stub length of two T-shape stub-loaded resonators (SLR). From its simulation frequency response, the filter has an insertion loss of 0.8 dB, a return loss less than −20 dB during the passband and high selectivity in cut-off frequency. The prototype of the proposed filter is fabricated and tested and a good agreement can be observed between the measured and simulated results.

General method for synthesizing dispersive coupling matrix of microwave bandpass filters

AbstractIn this paper, a general method for synthesizing dispersive coupling matrix (DCM) of coupled-resonator bandpass filters with the general dispersion is proposed. Compared to the dispersion-less coupling matrix synthesized by classic approaches, the DCM incorporates the identity of the physical realization and provides an accurate description of the filter. Moreover, the DCM can accurately describe the complex resonators and coupling elements with intentional strong dispersion. A DCM consists of two parts: the frequency-invariant part that corresponds to the coupling matrix at the center frequency and the frequency-variant part that reflects the dispersion of the physical realization. By iteratively adjusting the transmission zeros governed by the given filter topology and ignoring the transmission zeros brought by the dispersion, the synthesis method can directly obtain the frequency-invariant part so that the overall DCM leads to an equal-ripple response. To illustrate the general synthesis method, two design examples are presented, which include a filter with unintentional weak dispersion and a filter with intentional strong dispersion. The examples are validated by EM simulation, demonstrating the effectiveness, accuracy, and generality of the proposed synthesis framework. Key words: dispersive coupling matrix, filter synthesis, microwave bandpass filter

Design of a Microstrip Low-Pass-Bandpass Diplexer Using Direct-Feed Coupled-Resonator Filter

Previous systematic low-pass-bandpass diplexer was using coupled-feed line to design its bandpass channel response. However, a coupled-feed line coupled-resonator bandpass filter typically leads to the realization problem in the external quality factor because of the line space limitation between the coupled-feed line and the resonator. Based on our investigation, systematic low-pass-bandpass diplexer design using direct-feed coupled-resonator bandpass filter to relax this problem has never been published in the literature. Therefore, a low-pass-bandpass diplexer using direct-feed coupled-resonator bandpass filter is presented and a systematic matching design is also included in this letter.

Analysis of a compact size second order composite right/left handed coupled resonator band pass filter for wireless applications

A microstrip compact size second order bandpass filter for wireless applications is presented. The band pass filter is based on Composite Right/Left handed transmission line. The two resonators are designed using only one composite right left handed unit cell. The bandpass filter has the advantage of compactness (its size is only 2.3 X 2.3 cm2). A second order band pass filter with centre frequency of 4.77GHZ is designed, simulated and measured. The filter has bandwidth of 200MHz and insertion loss lower than 1.8 dB is achieved within pass band. A good agreement between simulated and measured result was achieved.

A new computer-aided tuning scheme for general lossy coupled-resonator bandpass filters based on the Cauchy method

In this paper, a novel analytical circuit model extraction scheme for the computer-aided tuning (CAT) of general lossy coupled-resonator bandpass filters is proposed based on the Cauchy total least squares (TLS) method. The new approach enforces the realisable condition of a set of scattering rational functions that is required for a lossy two-port network in extracting the transfer and reflection characteristics of a filter. Thus, a lossy circuit model can be synthesised from the extracted scattering polynomials using the well-known coupling matrix synthesis method from the literature. To illustrate the effectiveness of the new scheme, measured data of two different kinds of dual-mode filters are used. Using the proposed method, the extracted coupling matrix can give nearly identical frequency responses with the measured data, regardless of whether the filter is well-tuned or badly detuned.

Synthesis Method for Substrate-Integrated Waveguide Bandpass Filter With Even-Order Chebyshev Response

A synthesis method for an even-order Chebyshev bandpass filter of a substrate-integrated waveguide (SIW) is proposed in this paper. The transformation of a Chebyshev polynomial is studied and applied to achieve an equal source and load termination for an even-order filtering response. This transformed Chebyshev polynomial is used to design a millimeterwave (mmW) SIW bandpass filter through electric coupling of SIW resonators or cavities. The cascaded resonators are formed by properly etching the slots on the top metal plane of a single SIW cavity, and these slots create electric coupling as desired in a filter design. The proposed synthesis procedure of coupled-resonator bandpass filter with an even-order Chebyshev response is given and discussed here in detail. The theoretical and extracted external quality factor (QE) and coupling coefficient (K) are utilized to determine the filter circuit dimensions. Two fourth-order bandpass filters are designed at 140 GHz under a Chebyshev response using magnetic coupling and electric coupling as design examples. These two filters are used to prove the correctness of the proposed synthesis method as well as the advantages of electric coupling in mmW. In order to prove the validity, the previously proposed fourth-order filter using electric coupling is fabricated. The filter is fabricated in a single substrate layer using a low-temperature cofired ceramic technology and measured in a frequency band around 140 GHz. The measured results are in good agreement with simulated results.

Flexible Design Method for Multi-Repeater Wireless Power Transfer System Based on Coupled Resonator Bandpass Filter Model

It has been verified that wireless power transfer (WPT) system with multiple relay resonators (repeaters) inserted properly between the transmitter and the receiver can increase the transmission distance significantly. Based on the coupled resonator bandpass filter model, a flexible design method for wireless power transfer system with arbitrary number of repeaters is proposed in detail. The transmission efficiency and the transferred power of the proposed wireless power transfer system are derived under the design theory of filters. It is illuminated the reason that Butterworth type is preferred type for designing WPT with multi-repeater. Moreover, the relation between transmission distance and bandwidth is examined and a technique is further introduced to increase the transmission distance. An RS=50 Ω WPT system with three repeaters is tested and another RS=0 Ω WPT system with one repeater is simulated, and the effectiveness of the proposed method is confirmed as well.

Metamaterial-Inspired Bandpass Filters for Terahertz Surface Waves on Goubau Lines

This paper is focused on the application of split ring resonators (SRRs) to the design of compact bandpass filters for terahertz surface waves on single-wire waveguides, the so-called planar Goubau lines (PGLs). Through equivalent circuit models, electromagnetic simulations, and experiments, it is shown that, while a pair of SRRs coupled to a PGL inhibits the propagation of surface waves along the line, introducing a capacitive gap to the PGL switches the bandstop behavior to a bandpass behavior. In order to highlight the potential application of the proposed structure to the design of practical higher order terahertz bandpass filters, two types of compact bandpass filters are designed and fabricated: 1) third-order periodic bandpass filters based on SRR/gap-loaded PGL and 2) coupled-resonator bandpass filters. It is shown that, while the frequency response of the both filter types can be controlled by altering the physical dimensions of the structure, a wider bandwidth can be achieved from the coupled-resonator filters. The design concept and simulation results are validated through experiments.

Frequency-Agile Bandpass Filters Using Liquid Metal Tunable Broadside Coupled Split Ring Resonators

A fluidic-based approach for designing tunable coupled resonator bandpass filters is presented. These filters employ broadside coupled split ring resonators (BC-SRR) with one of their open loop resonators constructed from liquid metal. The tuning mechanism is based on dynamically moving the liquid metal to reshape the resonator. To demonstrate the concept, a second order Butterworth filter with continuous tuning range from 650 to 870 MHz is designed and experimentally verified by utilizing PTFE tubing filled with liquid metal and Teflon solution. Due to an inductive external coupling mechanism and 180° rotated resonators, the filter exhibits a near constant 5% fractional bandwidth throughout its tuning range with > 10 dB return and <; 3 dB insertion loss. The filter is realized over a 1.27 mm thick Rogers 6010.2LM substrate and has an approximate footprint of 20 × 40 mm2.

Small aperture evanescent‐mode waveguide antenna matched using distributed coupled resonators

Presented is a design methodology which permits the application of distributed coupled resonator bandpass filter principles to form wideband small-aperture evanescent-mode waveguide antenna designs. This approach permits matching of the complex antenna aperture admittance of an evanescent-mode open-ended waveguide to a real impedance generator, and thereby to a coaxial feed probe. A simulated reflection coefficient of <; - 10 dB was obtained over a bandwidth of 20%, from 2.0-2.45 GHz, in a 2.58 GHz cutoff waveguide. Dielectric-filled propagating waveguide and air-filled evanescent-mode waveguide sections are used to form the resonators/coupling elements of the antenna's coupled resonator matching sections. Simulated realised gain variation from 3.4-5.0 dBi is observed across the bandwidth. The antenna's maximum aperture dimension is <; 0.47 λ 0 at the upper operating frequency and so it is suitable for use in a wide angle scanning phased array.

Design and Diagnosis of Wideband Coupled-Resonator Bandpass Filters

A method for circuit elements parameter extraction of wideband filters from their electromagnetic (EM) simulated response is presented. A combline-like resonator for filter realization is introduced. Several possible electric and magnetic coupling structures are investigated. The equivalent lumped element circuit has electric and magnetic couplings modeled by capacitors and inductors instead of frequency-independent reactance or impedance inverters. The parameter extraction method of direct-coupled-resonator filters is developed and is applied to symmetric canonical filters. For filters with nonadjacent spurious couplings, optimization is used to extract the lumped element parameters to reproduce the EM simulated response. Excellent agreement between the EM simulation, lumped elements extracted responses and measurements is obtained. Filter synthesis is carried out by an optimization process. Several filter designs are presented to illustrate the design procedure and validate the circuit modeling. Measured results of an eight-pole filter verified the design process.

Active tuning of a microstrip hairpin-line microwave bandpass filter on a polycrystalline yttrium iron garnet substrate using small magnetic fields

Active magnetic tuning of a microstrip hairpin-line coupled resonator bandpass filter fabricated on a polycrystalline yttrium iron garnet substrate has been demonstrated. The filter exhibits a five-pole Chebyshev response with passband center frequency tunability from 8.3 to 9 GHz under low applied H fields of 50–200 Oe. The instantaneous bandwidth was measured to be approximately 1 GHz. During tuning, passband center frequency insertion loss varies between 1 and 1.4 dB. Good agreement between simulated and measured device performance was demonstrated. Advantages of the proposed filter design include planar geometry, compact size, low insertion loss, and low field tunability. The proposed design approach lends itself to the implementation of a wide range of filter responses, including low pass, high pass, bandpass, and band stop, as well as passband characteristics, including center frequency, fractional bandwidth, passband ripple, out-of-band rejection, etc.

A Highly Integrated Triple-Band RF Front-End Module for WiMAX Applications

This paper presents a compact and highly integrated triple-band RF front-end module (FEM) for worldwide interoperability for microwave access (WiMAX) applications using multilayer low temperature co-fired ceramic (LTCC) technology. The proposed RF FEM is composed of a TX triplexer, an RX triplexer, and a TX/RX switch. Both TX and RX triplexers are fully embedded in an LTCC substrate and the TX/RX switch is placed on the substrate. The TX triplexer consists of 2- and 5-GHz lowpass filters, a 3-GHz highpass filter, and a matching circuit. On the other hand, the RX triplexer consists of miniaturized 2-, 3-, 5-GHz coupled-resonator bandpass filters and a matching circuit, which are stacked up for space saving. In TX path, the RF FEM provides an insertion loss of 1.8dB, 2.1dB and 2.5dB at 2-, 3-, and 5-GHz band, respectively, with a high second-harmonic suppression characteristic. In RX path, the RF FEM also provides a low insertion loss at three passbands with high attenuation at other passbands. The size of the proposed RF FEM is only 4.0mm × 5.0mm with a substrate thickness of 0.73mm. The measured results are in good agreement with the simulated results.

버렉터 다이오드를 이용한 가변 대역통과여파기 설계

This paper proposed a tunable band pass filter. It is two-poles direct capacitive coupled resonator band pass filter which the capacitors of parallel resonators are changed by varactor diodes. The DC bias controls to change the value of capacitance in the parallel resonator for tunning the pass band. To validate the proposed design method, we fabricated the band pass filter which has tunable center frequency from 200MHz to 245MHz.

Comments on "The design of coupled resonator bandpass filter with wide stop-band"

In the above letter [1], Wang, Wang, and Wang presented a coupled resonator bandpass filter with wide stop-band. Before [1] was published, the authors proposed various novel ring resonators among which a coupled double half-ring resonator had been realized by placing two identical open half-ring configuration, leading to suppression of multiple harmonics [2], [3]. Even though the above letter [1] designed a filter using only one element composed of a single ring resonator, the resonator used is conceptually the same as the single element filter in terms of the layout and resulting performance.

The Design of Coupled Resonator Bandpass Filter With Wide Stop-Band

A compact four-pole bandpass filter with multi-order spurious response suppression is proposed. The combination of dissimilar resonator structures with the same fundamental frequency but with different spurious frequencies may improve the stop-band rejection by the mutual cancellation of spurious responses. The measured results show that better than -20 dB rejection levels in the stop-band up to 4.5 f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> have been obtained. Moreover, an embedded-resonator topology is used, which makes the structure of filter to be more compact.

Balanced Coupled-Resonator Bandpass Filters Using Multisection Resonators for Common-Mode Suppression and Stopband Extension

Novel fourth-order balanced coupled-resonator bandpass filters are proposed using suitably designed half-wavelength (lambda/2) multisection resonators for common-mode suppression. By properly designing the input/output (I/O) resonators associated with the filter composed of four bi-section resonators, a balanced filter with good common-mode suppression is realized, but its rejection bandwidth is rather limited. To widen the rejection bandwidth, the I/O bi-section resonators are replaced by the tri-section ones so that a balanced filter with good common-mode suppression and wide rejection bandwidth may be realized by suitably arranging the composed bi-/tri-section resonators. Specifically, a stopband-extended balanced filter with good common-mode suppression (>50 dB) within the differential-mode passband is implemented and its stopbands are also extended up to 5f0 d with a rejection level of 30 dB, where f0 d is the center frequency in differential-mode operation.