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A novel method for the development of a reconfigurable cavity bandpass filter using fluid dielectric is proposed. Dielectric material can produce an effective permittivity ϵeff of the resonant mode when it is loaded into the cavity. Thus, a tube filled with fluid dielectric, e.g., distilled water, can achieve controlled and reversible ϵeff by adjusting the amount of water in the tube. The same manner of resonant frequency can be achieved as the resonant frequency is related to ϵeff, and then frequency tuning is realized. The fluid property can realize easier and faster tuning mechanism than conventional solid dielectric. As ϵeff is affected by the loaded dielectric parallel to the electric field, a triple-mode resonator with resonant modes TE101, TE011, and TM110, which have orthogonal electric fields, is investigated to realize tri-band reconfiguration. The ϵeff, as well as the resonant frequencies, corresponding to each mode can be individually controlled by adjusting their related water posts. Then, reconfigurable single-band and tri-band bandpass filters are designed. A reconfigurable tri-band cavity filter using a triple-mode cavity resonator and fluid dielectric with individual and continuous frequency tuning is reported for the first time. Finally, the reconfigurable tri-band filter is fabricated and measured to validate the concept. [ABSTRACT FROM AUTHOR]

A novel band‐stop filter (BSF) using coaxial‐fed slotted substrate integrated waveguide (SIW) is proposed in this article. The proposed BSF is designed using coaxial‐fed line with extended probes penetrating through the substrate and connecting each other, instead of using the main transmission line to dispose the resonators. The SIW cavities perform the resonators excited by the probes to produce a stopband. Then, two BSFs with one and two SIW cavities are firstly designed, both of them have SIW cavity resonator modes and lower‐band reflection zeroes. Then, two types of third‐order BSFs using two cavity resonators and one slot resonator are presented, the high selectivity is achieved by the RZs at both sides of the stopband. Finally, one of the proposed third‐order BSFs is fabricated and measured to verify the design method. [ABSTRACT FROM AUTHOR]

A triple-passband filter is proposed by exploiting the first three resonant modes in a single rectangular cavity: TE101, TE011, and TM110 modes. Triple-passband frequency response is realized by generating one transmission zero (TZ) between any of two adjacent modes so that each mode contributes one passband. Beside TZs between modes, the three resonant modes are excited by properly placing two coupling apertures at input/output ports of the cavity. When cascading two single cavities, three pairs of slots are used to independently control the coupling between two respective modes of different cavities. As a result, not only two TZs between different passbands but also a pair of additional TZs below the first passband and above the third passband could be realized, respectively, thereby attaining a high selectivity of a triple-passband filter. Finally, a dual-cavity filter with triple-passband and four out-of-band TZs is fabricated and tested. The measured results have verified the validity of the proposed design well. [ABSTRACT FROM AUTHOR]

In this paper, the design of a cavity crossover with three intersecting channels is presented. The three fundamental modes of a cavity resonator, namely, TE011, TE101, and TM110 modes, are adopted to resonate at each of three channels, respectively. Due to the modal orthogonality of these fundamental modes, high isolation among three channels can be achieved. Two kinds of crossovers, for narrowband and broadband applications, are presented. For the narrowband case, the proposed crossover resonates at 2.91 GHz with the fractional bandwidth of 1.4%. For the broadband case, the proposed crossover resonates at 3 GHz with the fractional bandwidth of 24%. The isolations of both designs reach more than 50 dB. For a proof of concept, the broadband example of the cavity crossover structures is fabricated and measured. A good agreement between the simulated and the measured results verifies the accuracy of the proposed design methodology. [ABSTRACT FROM AUTHOR]

Two third‐order continuously tunable bandpass filters featuring single‐/dual‐band operations, respectively, are presented in this letter. One requires a set of three metallic posts in a single metallic cavity, while the other needs one more set to achieve the desired dual‐band operation. The length of each post is adjusted through a screw from its top to establish the center frequency of the passband. Moreover, the coupling among these three resonators can be controlled by varying their locations to determine the bandwidth of the passband. At the bottom of the cavity, grooves are created to linearize and extend the frequency tuning range. In addition, compared to traditional coaxial cavity filters, the proposed designs offer the advantages of ease in fabrication and low in weight. A practical example for the dual‐band design is presented for experimental verification. The simulated range for the tunable passband is from 0.8 to 3.2 GHz, which amounts to a fractional bandwidth of 120%. The simulated results agree well with the measured data. [ABSTRACT FROM AUTHOR]

A novel concept for the two-in-one design with the integration of filters and antennas, using a single cavity, is presented in this communication. Basically, a triple-mode resonator (TMR) is utilized as a common feeder to achieve filtering and radiating functions at three different frequency bands. Each of the three bands adopts one of the three fundamental modes, namely, TE011, TE101, and TM110, in a single TMR to realize the relevant functions. Owing to the modal orthogonality of these fundamental modes, high isolation can be effectively realized among these three channels. Based on the proposed TMR, three different prototypes are designed for different applications. For the first prototype, the structure of a dual-band filter plus an antenna is presented using a second-order TMR. Based on the combination of a duplexer plus an antenna, the second prototype is attained. To further explore the function of the proposed TMR, the structure of a filter plus a dual-polarization antenna is depicted as the third prototype. For verification, the third prototype is fabricated and tested. Good agreement between the simulated and the measured results is achieved, which proves the feasibility of the proposed design methodology. [ABSTRACT FROM PUBLISHER]

A novel approach for design of a miniaturized cavity triplexer is proposed in this paper by using triple-mode resonator (TMR) as a common feeder of three frequency channels in a triplexer. Three frequency channels are generated by three fundamental modes of a single rectangular triple-mode cavity resonator. Without installing any connection-oriented junction network, i.e., T-junction or star junction, only coupling slots are adopted herein to achieve required coupling coefficients and external quality factors toward the specified Chebyshev responses in the three passbands simultaneously. High isolation among these three separated bands can be effectively achieved owing to the modal orthogonality via sharing a common TMR structure as a feeder. Two triplexers are then designed and fabricated using varied topologies. The hybrid resonator triplexer method is presented as the first approach by using a TMR as a feeder to feed three sets of single-mode cavity bandpass filters. As the second approach, the triple-mode triplexer (TMT) method is developed by cascading a few TMRs to form a multistage higher order TMT. Finally, two fabricated triplexer prototypes are tested for experimental verification of the proposed design methodology. Good agreement between measurement and simulation is achieved. [ABSTRACT FROM PUBLISHER]

ABSTRACT A novel substrate-integrated waveguide (SIW) dual-band bandpass filter fabricated on a double-layer substrate is presented in this article. Each layer uses two rectangular cavities to create a passband, so the two individual bandpass filters are formed by setting the different locations of loaded posts for dual-band operation, that is, 4.6 and 5.3 GHz. In design, the coupling between the upper and lower layers is realized via two slots on the middle metal layer between two substrates. The double-layer structure not only provides a degree of freedom to control the center frequency of two passbands, but also improves the out-of-band rejection skirts with the help of produced transmission zeros. In final, the proposed SIW bandpass filter is fabricated to prove the predicted results in experiment, and good agreement is obtained. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:155-158, 2016 [ABSTRACT FROM AUTHOR]

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 millimeter-wave (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. [ABSTRACT FROM AUTHOR]

This paper proposes a novel diplexer based on triple-mode dielectric-loaded cylindrical cavities. Such two metal cavities are designed to achieve two different frequency bands, while three resonant modes of a single cavity are classified as a TM mode and a pair of hybrid (HE) degeneration modes. An off-centered dielectric resonator instead of a traditional corner cuts perturbation or screws perturbation properly perturbs the two degenerate modes in the same cavity. Extensive study is then conducted to design this proposed diplexer. Finally, a diplexer prototype is fabricated using a brass cavity and it is tested for experimental verification of the predicted results. Good agreement between measurement and simulation is achieved. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel class of wideband metal cavity multiple-mode bandpass filters (BPFs), consisting of a triple-mode filter and a quadruple-mode filter. Two TE11 degeneration modes in a single metal cavity are excited by using an off-centered approach instead of a traditional corner-cut approach. They work together with the TM10 mode to constitute a three-pole wide passband with a fractional bandwidth of 30% at the central frequency of 3.2 GHz. Moreover, an off-centered metal cylinder can properly excite an extra TM11 mode in the passband. As such, this TM11 mode, TM10 mode, and a pair of degeneration TE11 modes can be simultaneously utilized to form a quadruple-mode BPF. Compared with the triple-mode BPF, the quadruple-mode BPF has better performance in term of the steepness of rejection skirt. The fractional bandwidth of this BPF can achieve up to 31%. In final, the two proposed BPFs are fabricated by using the silver plated aluminum technology. Measured S-parameter frequency response and group delay have satisfactorily matched with the simulated results. [ABSTRACT FROM PUBLISHER]

Millimeter-wave (mmW) bandpass filter using substrate integrated waveguide (SIW) is proposed in this paper. The propagation constants of three different types of electromagnetic bandgap (EBG) units are discussed and compared with their passbands and stopbands performance. The slotted-SIW unit shows a very good lower stopband and upper stopband performance. The mmW bandpass filter with three cascaded uniform slotted-SIW-based EBG units is constructed and designed at 40 GHz. The extracted coupling coefficient ( K ) and quality factor ( Q ) are used to determine the filter circuit dimensions. To prove the validity, the previous proposed structure is fabricated in a single circuit layer using low-temperature co-fired ceramic technology and measured at 40 GHz, respectively. The measured results are in good agreement with simulated results in such frequency and the measured insertion losses at 40 GHz is 1.42 dB, respectively. [ABSTRACT FROM AUTHOR]

Millimeter-wave (mmW) bandpass filters (BPFs) using substrate integrated waveguide (SIW) are proposed in this paper. The propagation constants of two different types of electromagnetic bandgap (EBG) units are discussed and compared for their passbands and stopbands performance. In among, the slotted-SIW unit shows a very good lower and upper-stopband performance. The mmW BPF with three cascaded uniform slotted-SIW-based EBG units is constructed and designed at 40-GHz. This EBG filter exhibits good out-of-band performance. To further improve the in-band performance, a third-order mmW BPF with nonuniformly cascaded slotted-SIW unit is designed at 140 GHz. The filter is investigated with the theory of electric coupling mechanism. The extracted coupling coefficient (K) and quality factor (Q) are used to determine the filter circuit dimensions. To prove the validity, the two proposed structures are fabricated in a single-circuit layer using low temperature co-fired ceramic technology and measured at 40 and 140 GHz, respectively. The measured results are in good agreement with the simulated results in such high frequency. The measured insertion losses at 40 GHz and 140 GHz are 0.72 and 1.913 dB, respectively. [ABSTRACT FROM AUTHOR]

An ultra-wideband (UWB) bandpass filter (BPF) using the hybrid microstrip and coplanar waveguide (CPW) structure is proposed in this article.The BPF composes of CPW feed lines and H-shaped microstrip resonator. By a CPW/microstrip back-to-back coupling structure, the UWB BPF was realized with the passband covering the entire UWB band (3.1-10.6 GHz). A narrow notched band achieved by etching slots on the lower impedance part of the H-shaped resonator to form an open circuit stub. At last, three U-slot DGSs are used to achieve a good upper-stopband rejection. The measured results are in good agreement with the simulated results. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1577-1581, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27663 [ABSTRACT FROM AUTHOR]

A new method for frequency selective surface (FSS) with high selectivity, namely, filtenna–filtenna (FA-FA)-based technique, is proposed, which consists of two filtering antennas and impedance matching network. Based on the reciprocity theorem, the radiation null of filtenna can provide a stopband of the proposed FSS. In this work, it is validated by using a periodic array of back-to-back magnetoelectronic (ME)-dipole antennas with split-ring resonators (SRRs), and a slotted GND plane is used to connect the two ME-dipole antennas for impedance matching. Bandpass response of the proposed FSS is realized by the intrinsic high-pass characteristic of ME-dipole antennas and the bandstop characteristic of SRRs. Four transmission zeros (TZs) and three transmission poles (TPs) are generated, exhibiting a high-order filtering response. TZs and TPs are analyzed by equivalent circuit model and current distributions. The 3 dB fractional bandwidth (${\mathrm {FBW}}_{\mathrm {3\,dB}}$) of 38.5% in the passband and the 20 dB fractional bandwidths $({\mathrm {FBW}}_{\mathrm {20\,dB}})$ of 8.7% in the lower rejection band and 13.8% in upper rejection band are obtained in this design. Finally, a prototype is fabricated and measured to further validate the proposed FA-FA-based technique. Simulated and measured results show that the proposed FA-FA-based FSS is with the distinct advantages, including wide passband, low profile, tunable TZs, and dual-polarized application, which verifies the proposed method of FSSs. [ABSTRACT FROM AUTHOR]

ABSTRACT A compact triple-mode dielectric resonator (DR) bandpass filter (BPF) based on a single waveguide cavity is proposed, while three resonant modes of a single cavity are classified as a TM mode and a pair of hybrid degenerate modes (HE modes). Two HE degeneration modes in a single metal cavity are excited by using an off-centered DR approach. They work together to constitute a three-pole passband with a fractional bandwidth of 2.7% at the central frequency of 2.53 GHz. To verify the proposed idea, the proposed triple-mode DR BPF is fabricated by using silver plated aluminum metal cavity, and the simulated and measured results are in good agreement. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1645-1647, 2016 [ABSTRACT FROM AUTHOR]

In this article, a class of wideband bandpass filters (BPFs) using triple-mode coaxial resonators has been introduced. Each triple-mode resonator is utilized with TM010 mode, TE− mode, and TE+ mode orthogonal to each other. Two L-shaped feeding probes and a loading disk are adopted to implement the miniaturization of these wideband BPFs. To observe the degree of miniaturization, we set a design specification of the same fractional bandwidth (FBW) of 40% at the same central frequency of 2.5 GHz. After employing the L-shaped feeding probes and loading disk, the efficient circuit size without cavity thickness is reduced by 80% compared with the triple-mode wideband filter without L-shaped feeding probes and loading disk. In contrast, the unloaded quality factors are slightly changed. In addition, another advantage of this work is that the upper stopband is extended to $2.5f_{0}$. Three experimental wideband BPFs in the large, medium, and small sizes are designed, manufactured, and tested for demonstration. Good agreements are obtained between simulation and experiment. [ABSTRACT FROM AUTHOR]

This article proposes a new class of miniaturized full‐metal bandpass filters (BPFs) and multiplexers using circular spiral resonators (CSRs). The proposed metal CSR is supported on the metal cavity's wall, which serves as a short‐end resonator. This CSR has obvious size reduction compared to traditional cavity resonators and owns low insertion loss, high power capacity and high selectivity. Then, three BPFs using two, three and four CSRs are designed and analysed. All the proposed filters have transmission zeroes (TZs) produced by the source‐load coupling without introducing additional coupling structure. The proposed CSR is further used to design diplexer and quadruplexer. All the proposed filters have ultra‐compact size, especially, the size of quadruplexer is only 0.23λ0 × 0.081λ0 × 0.067λ0. Finally, the fourth‐order filter and quadruplexer are fabricated and measured, the good agreement between the measured results and the simulated results validates the proposed design concepts. [ABSTRACT FROM AUTHOR]

In this article, a class of waveguide bandpass filters (BPFs) is modularly synthesized on dual-mode resonators, which are implemented by the TE102 and TE201 modes in a rectangular cavity. Different from the conventional BPFs, these dual-mode resonators are arrayed in a stacked manner, presenting a transversal topology of BPFs. Therefore, each dual-mode resonator contributes a doublet, and these doublets could be independently realized without nonresonating nodes, due to the modularity property of transversal BPFs. The overall sizes of these transversal BPFs are just half or a fourth of the reported counterparts at the expense of the cavities $Q$ -factor which is reduced 44% or more depending on how many cavities are stacked. These BPFs, including single- and dual-passband filters, are then synthesized, fabricated, and measured. The measured results support the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper, a new transversal configuration is presented for waveguide bandpass filters (BPFs) on stacked rectangular $ H$ -plane waveguide cavities. Different from the conventional ladder BPFs, cavities constituting the proposed transversal BPFs are arrayed in a stacked manner. Odd- and even-mode resonators of transversal BPF are realized by TE101 and TE102 modes of rectangular $ H$ -plane waveguides, respectively. Using the configuration proposed herein, the realization of an $N$ th-order filter could be decomposed into realizations of $N$ first-order subfilters, and each subfilter could be realized independently, which is guaranteed by the unique array of resonators of transversal filters. Therefore, the complexity of realizing BPFs could be reduced, especially for filters with multiple transmission zeros (TZs). A class of transversal filters, including BPFs and dual-band filter, are synthesized, fabricated, and measured to verify the approach. [ABSTRACT FROM AUTHOR]

This paper presents the proposal and design of multistate diplexer on uniform- and stepped stub-loaded resonators, that is, a three-state diplexer (TSD) and a four-state diplexer (FSD). The two proposed diplexers have an attractive application in a frequency-hopping system with miniaturization in their overall size. Next, three and four sets of second-order bandpass filters are applied to form the three and four filtering channels, respectively. These filtering channels are then used to comprise these multiple-state diplexers. In this way, compact size and high-frequency selectivity have been well achieved. For the purpose of demonstration, the prototypes of TSD and FSD are fabricated and measured. The measured results are found in good agreement with the simulated results. [ABSTRACT FROM AUTHOR]

This paper proposes a triple-mode dielectric-loaded cylindrical cavity diplexer by using a novel packaging technique for long term evolution (LTE) base station applications. Four metal cavities, loaded by a triple-mode dielectric resonator (DR), are designed to resonate at two different frequencies for the diplexer operation. In this context, three resonant modes of a single cavity are classified as a TM mode and a pair of hybrid degenerate modes (HE modes). The two degenerate modes in the same cavity are properly excited by employing an off-centered DR instead of a traditional corner-cut structure as a perturbation element. Finally, such a diplexer is designed and fabricated, and good agreement between measurement and simulation is achieved. [ABSTRACT FROM AUTHOR]

Filtering baluns are proposed based on the hybrid cavity-microstrip structures in this article. The cavity acts as the resonator to obtain the filtering response. In the meanwhile, the microstrip feeding networks are used to excite multiple modes and achieve the balun characteristics simultaneously. The coupling mechanism between the slots and the cavities is utilized to analyze the single- and dual-band filtering baluns. Therefore, by combining the benefits of the cavities and the microstrip lines, multifunctional filtering baluns are realized. Besides, to reduce the volume and insertion loss further, a filtering balun based on the dielectric cavity-microstrip structure is presented and designed. It possesses high selectivity passband response, magnitude imbalance of 0.075 dB, and phase difference of 180° ± 0.2°. It is much smaller than that fed by the waveguide. On the other hand, it is easy to integrate with other components and robust in structure compared to that fed by the probe. Thus, the proposed hybrid structure not only maintains the high performance of the cavity but also has the flexibility of the planar circuit. [ABSTRACT FROM AUTHOR]

In this paper, a novel on-chip circuit design approach is proposed using hybrid coupling technique. Taking advantage of this technique, a microwave bandpass filter (BPF) is proposed as a design example for proof of concept. Based on stub-loaded stepped-impedance transmission lines and folded stepped-impedance meander line from different metal layers, the proposed BPF can generate three transmission zeros (TZs) and two transmission poles (TPs), which are excited through the hybrid mutual couplings between the inductive and capacitive metals. To understand the principle of this configuration, an equivalent LC-circuit model is presented and simplified, of which the TZs and TPs of the proposed BPF are estimated by the extracted transfer function. The calculated results exhibit good agreements with the simulated and measured ones. In addition, the bandwidth and center frequency of the proposed BPF can be tuned flexibly. Finally, to further demonstrate the feasibility of this approach in practice, the structure is implemented and fabricated in a commercial 0.13- $\mu \text{m}$ SiGe (Bi)-CMOS technology. The measurement results show that the proposed BPF, whose chip size is 0.39 mm $\times0.45$ mm (excluding the test pads), can realize a wide bandwidth from 19.7 to 33.2 GHz with a return loss of 15.8 dB and insertion loss of 3.8 dB at the center frequency of 26.5 GHz. [ABSTRACT FROM AUTHOR]