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In this article, high selectivity filtering antennas are designed based on a mixed-mode cavity resonator, which is formed by adding a short-circuited metal cylinder at the center of a rectangular cavity. The resonant and coupling characteristics of the proposed resonator are analyzed in detail. The operating modes of the mixed-mode cavity are TE102 mode, TE012 mode, and quasi-TEM mode, which can be utilized to design filtering antennas with different transmission zero distributions. To demonstrate the concept, three slot antennas with 3rd-order filtering performance are designed and simulated, where two transmission zeros are introduced to improve the selectivity. Furthermore, a 5th-order filtering antenna array based on the mixed-mode resonator is designed and fabricated. The measured results are consistent with the simulated results, showing that a gain of greater than 13 dBi is achieved. [ABSTRACT FROM AUTHOR]

In this article, a new class of tunable filters and diplexers operating in $X$ -band is presented. The proposed circuits are based on an in-line dual-post resonator, which consists of a pair of antipodal partial-height posts. The resonance and coupling characteristics of the proposed resonator can be regulated by the height and height difference of the posts. The most interesting feature of using the in-line dual-post resonator is that the input–output coupling and inter-resonator coupling are inversely proportional to the frequency within the tuning range, which is necessary for maintaining the fixed absolute bandwidth of the tunable filter. A prototype tunable filter is designed and fabricated, showing a low variation ($< \pm 3.9$ %) in the absolute bandwidth over a relatively wide tuning range of about 17%. The waveguide $H$ -plane static $Y$ -junction is designed and cascaded with two channel filters to implement the tunable diplexer. Noncontiguous and contiguous frequency plans can be realized by properly arranging the frequency band of the two channel filters. Measured results show that the tunable diplexer can obtain constant frequency spacing and approximately 10% tuning range with an insertion loss of less than 1.5 dB. [ABSTRACT FROM AUTHOR]

This article presents a novel quad-ridge cavity resonator to realize a trimode response based on the TE101, TE011, and TE111 modes. The basic structure of the quad-ridge resonator (QRR) contains four ridges located at the center around the cavities. With an appropriate combination of the main parameters (length and width of the resonator and heights of the ridges), the first three TE resonant modes can be flexibly controlled, and each mode can carry the signal of a channel. Compared with a traditional rectangular cavity, the QRR provides more design freedoms for controlling the first three TE resonant modes and features a wider spurious-free window. The electric field distributions of the QRR are thoroughly analyzed to guide the realization of a filtering response. Intracavity coupling is achieved by an all-iris structure, including horizontal and vertical coupling slots with offsets to the cavity center, capable of easy fabrication and assembly. A nine-pole triple-band filter and a 12-pole triplexer are designed and manufactured to validate the concept. A comparison with other reported multiplexers indicates that the proposed triplexer exhibits the advantages of size reduction and high isolation. [ABSTRACT FROM AUTHOR]

In this article, a novel design approach for designing 4 × 4 and 8 × 8 filtering Butler matrices is proposed. The matrices, composed of combined 90° couplers and 180° filtering couplers as well as phase shifters, provide incremental phase shifts and a bandpass filter performance. The detailed design process and synthesis method for the Butler matrices are presented. A three-layer symmetrical stripline structure is used to realize the Butler matrix, allowing a fully planar structure without interlayer connections. For experimental verification, two prototype 4 × 4 and 8 × 8 filtering Butler matrices, operating at the center frequency of 2.4 GHz with a bandpass response, are devised, manufactured, and tested. The test results match well with the simulation ones. Based on the measurements, array factors have been calculated, which further indicate the acceptance of the measured results. [ABSTRACT FROM AUTHOR]

In this article, we present a design method of high-selectivity filtering antennas based on a dual-probe feeding structure. The first stage of the filtering circuit consists of two or three coupled resonators which are then coupled to the radiating patch acting as the last resonator of the filter. Cross-coupling is used to obtain transmission zero, and thus the selectivity of the filtering antennas is improved. A cascaded triplet (CT) filtering patch antenna, which produces a radiation zero at the high-frequency edge of the passband, and a cascaded quadruplet (CQ) filtering patch antenna, which produces radiation zeros at both edges of the passband, are designed for verification. The process of designing the filtering patch antenna is given in detail. The designed CT filtering patch antenna has a bandwidth of 1.029–1.17 GHz and a radiation zero at 1.19 GHz. The designed CQ filtering patch antenna has a bandwidth of 1.029–1.17 GHz and two radiation zeros at 1.012 and 1.19 GHz, respectively. The peak gain of the CT filtering patch antenna is 9.35 dBi and that of the CQ filtering patch antenna is 9.16 dBi. A dual-polarized CQ filtering patch antenna is fabricated, showing a good performance in measurement. [ABSTRACT FROM AUTHOR]

This article presents a simple design of a coaxial dual-band cavity filter and diplexer using stub-loaded resonators (SLRs). Based on the resonance characteristics of a coaxial SLR, the first two resonant frequencies can be tuned over a wide range by adjusting their structural parameters. Controllable external quality factors can be acquired by using the modified tapping structure for the two designated passbands. A coupling window and a coupling pin are proposed to obtain the expected coupling coefficients in the two bands. To demonstrate this concept, a third-order dual-band bandpass filter and an eight-pole diplexer are designed and fabricated. The measured results agree well with the full-wave simulation results. [ABSTRACT FROM AUTHOR]

In this paper, two novel $4 \times 6$ filtering Butler matrices with uniform and nonuniform power distribution are proposed. The matrices, consisting of a network of coupled resonators and two phase shifters, provide power division and phase shift together with a bandpass transfer function. The analytical synthesis procedures for the $4 \times 6$ filtering Butler matrices are presented. To verify the concept experimentally, two $4 \times 6$ filtering Butler matrices, operating at 2.4 GHz, with uniform and nonuniform power distribution are designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other. Multibeam antenna arrays are realized by using the Butler matrix, and the theoretical analysis has been confirmed by measurements of multibeam antenna arrays, which show reduced sidelobe level (SLL). [ABSTRACT FROM AUTHOR]

In this paper, a novel filtering 180° hybrid coupler is proposed and used to design a $2 \times 4$ filtering Butler matrix. The filtering 180° hybrid coupler can provide power division and phase shift together with a second-order bandpass transfer function, and is based only on coupled resonators. The $2 \times 4$ filtering Butler matrix is easily realized by utilizing several hybrid couplers. The analytical synthesis procedures for the hybrid coupler and Butler matrix are presented in this paper. Finally, broadside and end-fire arrays are realized by using the Butler matrix. To illustrate the concept experimentally, a filtering 180° microstrip hybrid coupler and a $2 \times 4$ filtering microstrip Butler matrix are designed, fabricated, and measured. Simulation and measured results are found to be in good agreement with each other. [ABSTRACT FROM AUTHOR]

This paper proposes a novel design approach for a filtering antenna, which contains an array of 4 by 2 waveguide aperture radiation elements. Coupling matrix theory is introduced in this paper to synthesize the multiple coupled-resonators circuit. Unequal amplitude excitation is applied to the 4 \times 2 elements so as to obtain a low sidelobe level. To demonstrate the concept, an X-band antenna array is designed and fabricated using a three-layer waveguide structure. Measured results show that the filtering antenna array can achieve a gain of more than 15.58 dBi and a radiation efficiency of higher than 90% over the passband (9.91–10.1 GHz). The sidelobe level is −18.3 dB in the {H} -plane and −21.1 dB in the {E}$ -plane. [ABSTRACT FROM AUTHOR]

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]

A helical resonator with two-sectional different pitches is proposed in this paper. The frequency ratios of the first two resonant modes of the helical resonator can be tuned to desirable values in a certain range by adjusting the pitches. The proposed resonator is applied to design dual-band bandpass helical filters. To achieve control over dual-band filtering characteristics, a feeding structure with step-rectangular plate and a coupling window with three apertures are also proposed to realize the expected external quality factors and coupling coefficients in the two bands. To validate the design, a second order and a fourth order dual-band helical filters are fabricated and measured. The measured results show good agreement with simulation ones. [ABSTRACT FROM AUTHOR]

This paper proposes a simple and effective method to designing wide-stopband bandpass filters and diplexers using uniform impedance resonators. Microstrip terminated parallel coupled lines are utilized to generate the filtering functions. By adjustment of the electrical lengths of the parallel coupled lines and open-circuited stubs, multiple transmission zeros can be obtained. Appropriate positioning of these zeros enables the suppression of spurious frequencies. A complete analytic analysis is proposed to fully control the positions of transmission zeros, and the design equations and design rules for both homogeneous and inhomogeneous mediums are given in detail. Different combinations of the frequency position of the transmission zeros can provide various characteristics. To extend the stopband bandwidth, one or more transmission zeros can be distributed on different harmonic frequencies. To demonstrate the proposed method, two bandpass filters and a diplexer are designed and fabricated. The measured results are in good agreement with the simulated ones. The first filter provides a high attenuation of 40 dB up to 6.8 times the fundamental frequency $(f_{{{0}}})$ and the second filter provides a lower attenuation of 28 dB, but this time extending up to $14.9f_{{{0}}}$ . [ABSTRACT FROM AUTHOR]

This paper proposes a novel concept of an integrated duplex antenna for realizing a compact multifunction RF front end by integrating a duplexer and a dual-band patch antenna. First, an all-resonator-based duplexer is designed. It is composed of two sets of split-ring resonators as channel filters, which are joined by a dual-mode stub-loaded resonator as the junction resonator. Then, a novel dual-band patch antenna is achieved by coupling a patch with a hairpin resonator through a slot in the ground. Uniform radiation characteristics have been achieved across the two bands. Finally, the duplexer is integrated with the dual-band patch antenna to form a highly integrated duplex antenna by coupling the hairpin resonator to the junction resonator of the duplexer directly. In this process, the 50- $\Omega $ interface and matching network between them are removed, contributing to a compact footprint. The details of codesign approach have been discussed in this paper. Compared with the traditional cascaded duplexer and antennas, this paper is much more compact and integrated but with an improved frequency response. A prototype of an integrated duplex antenna at S-band is fabricated and measured, showing two operation channels of 2.52–2.65 GHz for transmitting and 2.82–2.94 GHz for receiving with an isolation of over 32 dB. The measured results agree well with the simulation results. [ABSTRACT FROM PUBLISHER]

In this paper, a new design of an antenna array with integrated functions of filtering, harmonics suppression, and radiation is proposed. The device employs a multi-port network of coupled resonators, which is synthesized and designed as a whole to fulfill the functions of filtering, power combination/division, and radiation. The 50- $\Omega $ interfaces between the cascaded filter, power divider, and antenna in traditional RF front-ends are eliminated to achieve a highly integrated and compact structure. A novel resonator-based four-way out-of-phase filtering power divider is proposed and designed. It is coupled to the patch array, rendering a fourth-order filtering response. The coupling matrix of the resonator network is synthesized. The physical implementations of the resonators and their couplings are detailed. Compared to a traditional patch array, the integrated filtering array shows an improved bandwidth and frequency selectivity. In addition, the harmonic of the antenna array is suppressed due to the use of different types of resonators. To verify the concept, a $2\times 2$ filtering array at S-band is designed, prototyped, and tested. Good agreement between simulations and measurements has been achieved, demonstrating the integrated filtering antenna array has the merits of wide bandwidth, high frequency selectivity, harmonics suppression, stable antenna gain, and high polarization purity. [ABSTRACT FROM AUTHOR]

A Ka-band isolated radial power divider via circular waveguide TE01-mode converter is presented in this paper. By redesigning and using the circular waveguide TE01-mode transducer to feed the 20-way radial power divider–combiner, the overall structure is miniaturized. Moreover, the resistive septum is inserted into the waveguide to improve the return loss and the isolation of the output ports. A measured return loss at the output port has improved by around 15 dB, while the worst case isolation is more than 12 dB over 28–36 GHz after using the resistive septum. [ABSTRACT FROM PUBLISHER]

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]

Modified coupled feed-lines (MCFLs) and coupled-line stubs (CLSs)/coupled-line stub-loaded resonators are proposed and applied to design wideband balanced filters to obtain high selectivity and common-mode suppression. MCFLs are implemented by loading short- and open-circuited stubs at the end of the traditional parallel-coupled feed-lines to perform bandpass and bandstop response, respectively. Impedance matching and additional transmission poles guarantee that the filters have wideband differential-mode (DM) passband. Transmission zeros can be allocated to suppress the common mode through different electrical length of stubs. Moreover, the CLSs and its stub-loaded resonators have the property of dual transmission zeros outside the passband, which improves the selectivity of the DM passband. Specifically, two prototypes based on CLSs with second harmonic suppression and CLS-loaded resonators with sharp rejection (\Delta f{{3dB}} / \Delta f{{20dB}}=0.97) are designed and fabricated for demonstration. The simulation and measurement results are in good agreement. [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]

In this paper, an E-plane waveguide power divider and a waveguide-to-microstrip transition are used to form a waveguide magic-T with four arms in the same E-plane. The input port of the original E-plane waveguide power divider acts as the difference port of the magic-T, and a waveguide-to-microstrip transition is utilized to realize the sum port. The four arms are in the same plane, and traditional matching elements, such as cones, wedges, pins, and irises are not needed. The proposed magic-T features easy connection, fabrication, and assembly. The principle and design procedure are described in detail. A Ka-band E-plane waveguide magic-T is designed, fabricated, and measured. A fractional bandwidth of 21% is achieved. The measured and simulated results show good amplitude, phase, and isolation characteristics validating the proposed magic-T. [ABSTRACT FROM AUTHOR]

This paper presents, for the first time, the design and implementation of a planar tunable crossover. This crossover is derived from the conventional two-section branch-line crossover by substituting its three vertical transmission lines with the two fixed capacitors and one tunable capacitor to realize the tunable passband. By designing its horizontal transmission lines as coupled lines and replacing its vertical transmission lines by three capacitors, the circuit size is greatly reduced. Closed-form equations for design parameters are derived to simplify design procedure of the proposed crossover. For verification, a crossover with tunable frequency of 1.2–2.4 GHz is designed based on the given design closed-form equations. Finally, a microstrip tunable crossover with one varactor diode 1sv277 is fabricated and measured. The measured results are in good agreement with the simulated ones. The results show that the passband can be tuned in a frequency range from 1.29 to 2.06 GHz, yielding 46% tuning range with better than 20-dB return loss and isolation, while the insertion loss varies from 0.59 to 1.22 dB. The crossover occupies a small size of 0.25\ \lambda g \times 0.04\ \lambda g, which is only 8% of the area of conventional two-section branch-line crossover. [ABSTRACT FROM AUTHOR]

A Ka-band traveling-wave power divider/combiner, which is based on double ridge-waveguide couplers, is presented. The in-phase output, which is a challenge of the waveguide-based traveling-wave power divider, is achieved by optimizing the equivalent circuit of the proposed structure. The novel ridge-waveguide coupler has advantages of low loss, high power capability, and easy assembly. Finally, the proposed power divider/combiner is simulated, fabricated, and measured. A 15-dB measured return-loss bandwidth at the center frequency of 35 GHz is over 28%, a maximum transmission coefficients amplitude imbalance of \pm\1 dB is achieved, and the phase deviation is less than \pm \12^\circ from 32 to 39 GHz. [ABSTRACT FROM PUBLISHER]

A dual-band planar crossover with simple structure is proposed. This crossover is derived from the conventional single-band two-section branch-line crossover by doubly extending the length of its vertical transmission lines, which realizes the dual-band operation. Closed-form equations for design parameters are derived, which simplifies design procedure of the proposed crossover and shows that the available bandwidth of the passband increases with the increasing frequency ratio. By adding one short-circuited stub and one open-circuited stub to the originally proposed dual-band crossover, two types of modified dual-band crossovers and their closed-form design equations are proposed for smaller and larger frequency ratios applications. For verification, four different dual-band crossovers are designed and simulated, of which two microstrip crossovers operating at 1/1.8 and 1/2.3 GHz are fabricated and measured. The measured results are in good agreement with the simulated ones. [ABSTRACT FROM PUBLISHER]

A method to design TE01\delta-mode dielectric-resonator (DR) filters with transmission zeros is proposed. The feeding probes, extended along ring DRs, are used to excite the TE01\delta mode and introduce transmission zeros. By rotating the angle of the feeding position, transmission zeros can be shifted to the lower or the upper stopband. Thus, TE01\delta-mode DR filters with quasi-elliptic responses are realized with only iris coupling components. Based on this method, second- and fourth-order filters with different responses are designed and fabricated. Measured results confirm the predicted performance. [ABSTRACT FROM AUTHOR]

A compact broadband Gysel power divider with arbitrary power-dividing ratio is proposed. This divider is derived from the conventional Gysel power divider by substituting an ideal phase inverter for the 180^\circ phase shifter, which significantly improves the bandwidth and reduces the circumference to 1 \lambdag evaluated at the center frequency. A wide range of power-dividing ratio (1–6.25) is supported by changing the impedance ratio of the transmission lines, while the dual-band impedance matching characteristic with frequency ratio (1–2.9) is obtained only by varying the impedances of the transmission lines (\20\--\135∼\Omega). Closed-form equations are derived for design parameters. The ideal phase inverter is realized by two transitions: microstrip-to-slotline and slotline-to-microstrip transitions. By utilizing this phase inverter, two microstrip Gysel dividers with power-dividing ratios of 1:1 and 2:1 and operating at 1.5/2.5 and 1/2 GHz, respectively, are designed, fabricated, and measured. The measured results are in good agreement with the simulated ones. The first measured results show a bandwidth of 80% with better than 15-dB return loss and 29-dB isolation from 1.19 to 2.76 GHz. The second measured results show a bandwidth of 95.8% with better than 12-dB return loss and 24-dB isolation from 0.8 to 2.27 GHz. To the authors' knowledge, the most wideband Gysel power divider using microstrip technology is proposed for the first time. [ABSTRACT FROM AUTHOR]

A novel method is presented for the design of a multiband power divider. The method employs network theory and even–odd-mode analysis to derive the equivalent input and output port admittances of a three-port junction, which is based on the conditions of reciprocity, isolation, and matching. If an impedance transformer that transforms the equivalent admittance to normalized unit conductance at multiple frequencies is found, then the multiband power divider can be constructed by attaching the transformer to each port of the junction. To verify the proposed design method, three different tri-band power dividers are designed and simulated, of which one is fabricated and measured. The measured results are in good agreement with the simulations. The return loss and isolation are better than 15 dB, simultaneously, the measured bandwidths of three operating bands are over 100 MHz, and the passband ripple is 0.2 dB. [ABSTRACT FROM PUBLISHER]

Presents a time-domain modular method which consisted of linear components and active devices, to speed up the transient simulation of microwave active circuits. Characterization of the linear components and active devices by time-domain characteristic models; Examination of time-domain characteristic model of a linear network; Application of the transient analysis of a one-dimensional (1-D) discrete-time system.

A response from the authors of the article "Compact broadband Gysel power divider with arbitrary power-dividing ratio using microstrip/slotline phase inverter" in the May 2012 issue is presented.