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This communication investigated a wideband filtering patch antenna with high gain and high selectivity. The antenna is mainly composed of an aperture-coupled driven patch, a stacked patch, and four center-shorted trapezoidal thin patches. The stacked patch can introduce a higher frequency resonant mode and a radiation null due to magnetic coupling. Four trapezoidal thin patches loaded with shorting vias are located around the driven patch, acting as a vertical split-ring resonator (SRR) and introducing a lower frequency resonant mode and a radiation null due to electric coupling. With two radiation nulls at the edges of the passband, the filtering gain response with high selectivity is achieved. As no filtering circuits are used, the antenna can obtain high gain and high efficiency. Due to the symmetrical structure, a dual-polarized filtering antenna is also presented for base-station application, demonstrating good radiation performances and an isolation of 20 dB. A fabricated dual-polarized antenna is measured, showing a wide bandwidth up to 18.8% (from 3.19 to 3.85 GHz), a peak gain of 9.5 dBi, and two near-band radiation nulls located at 3.13 and 4 GHz. [ABSTRACT FROM AUTHOR]

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]

A new decoupling concept for dual-band shared-aperture base station antenna arrays is proposed. By loading arrow-shaped decoupling structures in the hollowed regions of the low-band (LB) loop dipole arms, the LB antenna can yield partial reflection to the high-band (HB) antennas, canceling the HB-coupled wave. A dual-band base station antenna array is designed, fabricated, and measured based on this decoupling concept. With decoupling, the HB radiation patterns are restored. The copolarized in-band couplings between the HB antennas are reduced by about 9 dB, reaching >26.9 dB. The proposed antenna array possesses both cross-band and in-band decoupling abilities, without extra decoupling layer. [ABSTRACT FROM AUTHOR]

In this letter, a dual-band interleaved base station antenna array with self-decoupling characteristic is studied. The low-band antenna radiator along with its feeding baluns can be considered as compensation and partition structures for the high-band (HB) antennas. The measured co- and cross-polarized in-band isolations between the HB subarrays are enhanced to > 24.6 dB and > 29.3 dB, respectively, without introducing extra decoupling layer. The HB radiation performances are recovered, exhibiting good capability of crossband scattering suppression. The decoupling principles are analyzed and explained. [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]

In this article, a method for designing a tunable coaxial filtering antenna is presented. The proposed filtering antenna has a simple structure, consisting of a standard waveguide and some metal cylinders. Instead of utilizing traditional coupling irises, an all-cylinder coupling structure is employed for flexible tuning. Thus, the center frequency and bandwidth of the coaxial filtering antenna can be conveniently tuned by adjusting the lengths of the cylinders. Theoretical analysis and design process of the filtering antenna are given in detail. A third-order tunable filtering antenna with Chebyshev response is designed to verify this method. The tunable range of the center frequency is from 9.25 to 10.75 GHz, and the tunable range of the fractional bandwidth (FBW) is from 2% to 8%. The measured gain of the antenna is flat and greater than 6.5 dBi along the tuning range. In addition, the antenna maintains good impedance and radiation characteristics throughout the tuning range. [ABSTRACT FROM AUTHOR]

A new antenna decoupling structure by combining metal and dielectric superstrates is studied in this letter. The decoupling concept is elaborated in a 5-element antenna array. Afterwards, the decoupling performances are validated in a 3 × 3 staggered antenna array. The dielectric superstrate serves as magnitude and phase compensators. It achieves the tradeoff design to simultaneously improve decoupling bandwidth and matching in wideband decoupling issue. The E-plane and H-plane isolations are enhanced by at least 9 dB, reaching > 23 and > 27.2 dB in the operating bandwidth of 3.4–4.2 GHz. The radiation performances are also enhanced through decoupling. [ABSTRACT FROM AUTHOR]

A high selectivity and high efficiency filtering antenna is presented in this communication. A double-layer filtering patch antenna is first proposed, which can generate a radiation null due to the mixed electric and magnetic coupling between the two patches. By changing the length of the slot line on the patch, the position of the radiation null can be flexibly set at the lower band edge or upper band edge. Based on this mechanism, a three-layer patch antenna with two radiation nulls is designed. Two radiation nulls are introduced on both sides of the passband, consequently, a quasi-elliptic bandpass response can be obtained. Moreover, the proposed antenna features high efficiency since no extra filtering circuit is utilized. A prototype antenna operating at 1 GHz is designed, fabricated, and measured for validity verification. The measured results agree well with the simulated one, showing that the prototype antenna has a fractional impedance bandwidth of 16% (0.91–1.07 GHz), a flat passband gain response with peak value of 8.83 dBi, a high efficiency about −0.41 dB in the passband. The band-edge selectivity is highly improved by the radiation nulls near the passband edge. [ABSTRACT FROM AUTHOR]

A dual-band dual-polarized antenna array is considered to analyze the operating mechanism of the resonant coupling in multiband multiarray antennas, firstly. The considered antenna is composed of a lower band (LB) antenna operating from 690 to 960 MHz and two columns of higher band (HB) subarrays operating from 1690 to 2690 MHz. Then, a novel method of suppressing the resonant coupling interference by using ferrite cores is proposed. It is implemented by loading ferrite cores on the feed cables of the HB elements. The resonant coupling interference is caused by the LB common-mode currents distributed on the HB feed cables. It will seriously distort the LB radiation patterns. With the ferrite cores, the LB common-mode currents are eliminated, and then, the distorted LB radiation patterns are completely restored. Furthermore, the loaded ferrite cores hardly affect the performance of the HB elements. [ABSTRACT FROM AUTHOR]

In this communication, a high-selectivity and high-gain filtering slot antenna operating in $X$ -band is designed based on a triple-mode cavity resonator. Three modes of the cavity resonator, namely, TE101, TE011, and TM110, are excited by properly selecting the position and size of the coupling aperture. By adjusting the frequency and external coupling of the three modes, transmission zero can be introduced on both sides of the passband, achieving high selectivity of antenna gain. Because the cavity has a high unload quality factor, the radiation efficiency in the passband is high and flat. In order to increase the gain of the filtering waveguide antenna, a grid-slotted patch is added on the top of the slot. To demonstrate the concept, an $X$ -band waveguide filtering antenna is designed and fabricated. Measured results show the filtering antenna can obtain a gain of greater than 8.5 dBi in the frequency range of 9.8–10.2 GHz. [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, 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]

This paper proposes an accurate and general method to calculate and characterize the couplings of patch antennas. It is found that the coupling effects of open-/short-circuited patches can be represented by J/K inverters. Unlike traditional ones, these J/K inverters should be with complex- and frequency-dependent values. Three different patch antennas are used to exemplify how to characterize couplings with J/K inverters. Once the values of J/K inverters are successfully extracted, the total equivalent circuits of these patch antennas can be easily given in a unified way. J/K inverters can also help us see how the couplings affect antenna bandwidth. To present advantages of the proposed method, comparison with traditional coupling calculation approach based on characteristic modes is conducted. Technical limitations and potential applications of the proposed method are also discussed. [ABSTRACT FROM AUTHOR]

This communication presents a wide stopband filtering antenna element and its application in multi-input multi-output (MIMO) system. Microstrip terminated coupled lines and a rectangle patch are utilized to generate the filtering function. By varying the length of the parallel coupled lines and open-circuited stubs, multiple transmission zeros can be introduced in the spurious band. Appropriate positioning the location of these transmission zeros enables a wide harmonic suppression. To demonstrate the proposed method, a wide stopband filtering antenna is designed and further applied in a four-element MIMO array. The measured and simulated results agree well. The proposed MIMO antenna obtains an attenuation of 12.6 dB up to $6.6\times $ the center frequency. [ABSTRACT FROM AUTHOR]

A novel broadband patch antenna with electric- and magnetic-coupled elements and its application in multiple-input-multiple-output (MIMO) system is proposed in this communication. Unlike the conventional gap-coupled patch antennas, the electric and magnetic coupling between adjacent patches is considered and studied. Also, for improved understanding of the broadband nature of the proposed configuration, the phase relationships between patch elements are studied. Two- and three-patch prototypes are designed for validation of the concept, and the three-patch antenna is fabricated and measured showing a good agreement between the measured and simulated results. Considerable selectivity is observed in the results of the three-patch antenna because of the radiation nulls introduced by the electric and magnetic coupling. Apart from the broadband operation, the proposed antenna elements show promise for application in high-isolation MIMO systems due to their inherent band-reject characteristic when they are closely placed. For validation in this application, a four-element MIMO antenna is designed, fabricated, and measured. The measured results agree well with the simulated ones. [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 new modal approach for evaluating $Q$ -factors of antennas based on newly introduced XeR/XmR modes rather than characteristic modes (CMs). In our new approach, $Q$ -factors could be represented as direct linear superpositions of eigenvalues of XeR and XmR modes. We validate the accuracy of the new formula for $Q$ -factors by studying two canonical wire antennas. Moreover, the relations between XeR/XmR, TE/TM, and Xe/Xm modes are presented, which show interesting properties. It is found that eigenvalues of XeR/XmR modes reveal useful information about minimum $Q$ -factors. Compared with the CMs, some disadvantages of the proposed modes are also discussed. [ABSTRACT FROM AUTHOR]

In this article, we propose a compact ±45° dual-polarized dual-dipole (DPDD) antenna for second-, third-, and fourth-generation (2G/3G/4G) long-term evolution (LTE) base stations. The DPDD antenna consists of two perpendicularly crossed dual-dipole elements. Each dual-dipole element is directly fed by a coaxial cable. Two dual-dipole elements are printed on the same substrate, making the DPDD antenna planar and compact. Due to the coupling between two crossed dual-dipole elements, the DPDD antenna can achieve a broad bandwidth of 51% for a return loss greater than 15 dB (1.61-2.71 GHz) with a high isolation of 30 dB. The dual-polarized antenna has a gain of 9 dBi and a halfpower beamwidth (HPBW) of 65 ± 5° for ±45° polarization with a flat metallic reflector. For applications in LTE700/GSM850/900 base stations, a new artificial magnetic conductor (AMC) surface is introduced to replace the metallic reflector. It is shown that the antenna height can be significantly lowered from 105 mm (0.29λ0.83, where λ0.83 is the freespace wavelength at the frequency of 0.83 GHz) for a metallic reflector to 31.52 mm (0.087λ0.83) for an AMC surface while a broad bandwidth of 52% (0.68-1.16 GHz) is still achieved. The broadband ±45° DPDD antenna is described in the "Broadband ±45° DPDD Antenna" section, and the ±45° DPDD antenna with an AMC surface is demonstrated in the "DPDD Antenna with an AMC Surface" section. [ABSTRACT FROM PUBLISHER]

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 method of achieving a single-feed circularly polarized (CP) microstrip antenna with both broad impedance bandwidth and axial ratio (AR) bandwidth is presented. The CP characteristics are generated by employing a resonator to excite the two orthogonal modes of the patch via two coupling paths and the required 90° phase difference is achieved by using the different orders of the two paths. The presented method, instead of conventional methods that power dividers and phase delay lines are usually required, not only significantly enhances the bandwidths of the antenna but also results in a compact feed, reduced loss and high gain. Based on this method, a dual-band shared-aperture CP array antenna is implemented for $C$ -/ $X$ -band satellite communications. The antenna aperture includes a $2 \times 2$ array at $C$ -band and a $4 \times 4$ array at $X$ -band. To accommodate the $C$ - $X$ -band elements into the same aperture while achieving a good isolation between them, the $C$ -band circular patches are etched at the four corners. The measured results agree well with the simulations, showing a wide impedance bandwidth of 21% and 21.2% at $C$ -band and $X$ -band, respectively. The $C$ -band and $X$ -band 3 dB AR bandwidths are 13.2% and 12.8%. The array also exhibits a high aperture efficiency of over 55%, low sidelobe ( $C$ -band: −12.5 dB and $X$ -band: −15 dB), and high gain ( $C$ -band: 14.5 dBic and $X$ -band: 17.5 dBic). [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]

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]

In this paper, a novel dual-band dual-polarized array antenna with low frequency ratio and integrated filtering characteristics is proposed. By employing a dual-mode stub-loaded resonator (SLR) to feed and tune with two patches, the two feed networks for each polarization can be combined, resulting in the reduction of the feed networks and the input ports. In addition, owing to the native dual resonant features of the SLR, the proposed antenna exhibits second-order filtering characteristics with improved bandwidth and out-of-band rejections. The antenna is synthesized and the design methodology is explained. The coupling coefficients between the SLR and the patches are investigated. To verify the design concept, a C-/X-band element and a $2 \times 2$ array are optimized and prototyped. Measured results agree well with the simulations, showing good performance in terms of bandwidth, filtering, harmonic suppression, and radiation at both bands. Such an integrated array design can be used to simplify the feed of a reflector antenna. To prove the concept, a paraboloid reflector fed by the proposed array is conceived and measured directivities of 24.6 dBi (24.7 dBi) and 28.6 dBi (29.2 dBi) for the X-polarization (Y-polarization) are obtained for the low- and high-band operations, respectively. [ABSTRACT FROM PUBLISHER]

This paper proposes a quasi-elliptic filter with slot coupling and nonadjacent cross coupling based on the substrate integrated waveguide (SIW) cavity. The slots etched on the top metal plane of SIWcavity are used to produce electrical coupling, and the cross coupling is realized by the microstrip transmission line above the SIW cavity. The coupling strength is mainly controlled by the width and height of the slot. The length of the open-ended microstrip line controls the sign of the cross coupling. The cross coupling with different signs are used in the filter to produce a pair of transmission zeros (TZs) at both sides of the passband. In order to prove the validity, a fourth-order SIW quasi-elliptic filter with TZsat both sides of the passband is fabricated in a two-layer printed circuit board. The measured insertion loss at a center frequency of 3.7 GHz is 1.1 dB. The return loss within the passband is below −18 dB with a fractional bandwidth of 16%. The measured results are in good agreement with the simulated 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]

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]

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]

A novel design concept of multimode filtering antenna, which is realized by integrating a multimode resonator and an antenna, has been applied to the design of dual-polarized antenna arrays for achieving a compact size and high performance in terms of broad bandwidth, high-frequency selectivity and out-of-band rejection. To verify the concept, a $2 \times 2$ array at C-band is designed and fabricated. The stub-loaded resonator (SLR) is employed as the feed of the antenna. The resonant characteristics of SLR and patch as well as the coupling between them are presented. The method of designing the integrated resonator-patch module is explained. This integrated design not only removes the need for separated filters and traditional {50}{\text - }{\Omega } interfaces but also improves the frequency response of the module. A comparison with the traditional patch array has been made, showing that the proposed design has a more compact size, wider bandwidth, better frequency selectivity, and out-of-band rejection. Such low-profile light weight broadband dual-polarized arrays are useful for space-borne synthetic aperture radar (SAR) and wireless communication applications. The simulated and measured results agree well, demonstrating a good performance in terms of impedance bandwidth, frequency selectivity, isolation, radiation pattern, and antenna gain. [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]

Novel multiband balanced bandpass filters with controllable bandwidths are presented in this letter. Slotline coupled-feed structure (SLCFS) is employed to suppress the common mode (CM), due to its intrinsic CM rejection. For differential mode, the tri-band/quad-band performance is realized by three/four pairsofhalf-wavelength resonators, which are designed for different passbands, respectively. Since the load effects between different resonators are very slight, the passband frequencies and bandwidths can be independently tuned and designed. Moreover, quasi-elliptical bandpass responses could be achieved to enhance the selectivity. Finally, two multiband balanced filters are designed and fabricated to validate the design method. To the best of authors’ knowledge, the quad-band balanced filter may be the first ever reported. [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]

In this letter, an independently 1.1–2.8 GHz tunable four-channel cavity diplexer is proposed and developed. The presented diplexer consists of two tunable dual-band filters. Each filter is separately achieved by putting two identical sets of two metal posts in a single cavity. The variable distance of the posts is selected to provide an appropriate coupling between adjacent modes during the tuning process. Meanwhile, the adjustable screws with capacitive loading are employed to control the prescribed resonant frequency of the cavity. Thus, a wide tuning range of 1.1–2.8 GHz (87% tunable ratio) is obtained in a continuous way. Moreover, the diplexer can achieve an isolation higher than 50 dB. Finally, the proposed diplexer is fabricated, and the measured results agree well with the simulated results. [ABSTRACT FROM PUBLISHER]

This letter reports a new kind of matching network for quad-channel diplexers. The matching network is comprised by some open- and short-circuited transmission lines, which can be chosen based on the design graph. The impact of loading resonators on the network is discussed. The diplexer can be easily realized by the combination of different bandpass filters without complicated tuning. To illustrate the concept, one quad-channel diplexer is designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other. [ABSTRACT FROM PUBLISHER]

A triple-mode wideband bandpass filter (BPF) is proposed. It consists of a single rectangular waveguide cavity with two small metal rods to be inserted into the cavity from input/output feeding ports. As such, one TM110 mode, one TM210 mode, and one TM130 mode can be simultaneously excited in this cavity to form up a wide frequency passband. The fractional bandwidth is 58% at center frequency of 5.5 GHz with low insertion loss (<0.5 dB). Furthermore, this design approach is good for miniaturization compared with traditional single-mode filter. For validation, a proposed filter is fabricated using silver-plated aluminum metal cavity. Both theoretical and measured results are presented with good agreement. [ABSTRACT FROM PUBLISHER]

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]

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]

This letter presents a novel reconfigurable dual- band bandpass filter (DBBPF) with independently controlled passbands and constant absolute bandwidths (ABW). The design procedures follow the traditional synthesis approach of filters. Moreover, in order to meet the requirement of constant ABW, theoretical analysis and calculation are carried out to determine proper parameters of coupling regions. Finally, the proposed DBBPF exhibits 21.8% fractional tuning range of the first passband from 0.98 to 1.22 GHz and 17.9% of the second passband from 1.63 to 1.95 GHz, and 3-dB ABWs are 76 $\pm$ 4 MHz and 100 $\pm$ 4 MHz, respectively. [ABSTRACT FROM PUBLISHER]

A balanced bandpass filter is proposed based on stub-loaded ring resonators (SLRRs) and loaded coupled feed-lines (CFLs) with high selectivity and common-mode (CM) rejection. By controlling the coupling coefficient of the CFLs, three transmission poles within the differential passband are achieved. The CFLs are loaded with open- and short-circuited stubs at the end of the traditional parallel-coupled feed-lines, which resulting in multiple transmission zeros (TZs) in differential mode (DM) and CM to improve the passband selectivity and CM suppression, simultaneously. Finally, the proposed filter is designed and fabricated, the simulated and measured results are in good agreement. The filter shows low insertion loss, multiple transmission zeros, high selectivity and enhanced CM rejection. [ABSTRACT FROM PUBLISHER]

Two types of modified open- or short-circuited stub-loaded \lambda/4 resonator and their applications to second- order dual-band bandpass filters are presented in this letter. Based on the resonance characteristics analysis, it is found that the first two resonant frequencies of the two resonators can be independently controlled. Furthermore, different frequency ratios can be achieved by loading different stubs. Finally, to illustrate the proposed idea, two second-order dual-band filters with controllable bandwidths are designed, fabricated and measured. The measured results are in good agreement with the full-wave simulation results. [ABSTRACT FROM PUBLISHER]

In this letter, stepped-impedance resonators are used in coaxial cavity filter to generate dual-band response. Two key merits of the proposed filter are the helical feeding structure and the introduction of mixed coupling for coupling control and generation of transmission zero. The helical feeding structure makes it possible to conveniently control the external quality factors of two bands. To illustrate the concept, a third-order dual-band coaxial cavity filter is designed, fabricated and measured. The measured results are in good agreement with the full-wave simulation results. [ABSTRACT FROM PUBLISHER]

This letter presents, for the first time, a dual-band filtering quadrature coupler with high skirt selectivity. The proposed coupler employs two sets of resonators, i.e., four half-wavelength resonators and four quarter-wavelength resonators. The former not only operate at the upper passband but also feed the latter. The inherently realized source-load coupling for lower passband contributes two additional transmission zeros close to the two edges of lower passband. The tapped feeding position results in a pair of transmission zeros in the vicinity of the upper passband. The central frequencies and bandwidth of the two passbands can be independently designed. For verification, the simulated and measured results of a dual band filtering quadrature coupler operating at 2.77 and 3.55 GHz are presented showing good agreement. [ABSTRACT FROM PUBLISHER]

Novel compact tri-band bandpass filter (BPF) with controllable bandwidths is presented in this letter. The tri-band performance is realized by using three sets of resonators, i.e., two sets of short-stub loaded dual-mode resonators, which are designed for the first and second passband, respectively, and half-wavelength resonators for the third passband. The three passband frequencies and bandwidths could be independently tuned and designed. The half-wavelength resonators are embedded between the two dual-mode resonators and serve as part of feed lines for the first and second passband, thus compact size is realized. The newly designed tri-band BPF is verified by circuit implementation and good agreement between the simulated and measured results can be observed. [ABSTRACT FROM PUBLISHER]

This letter presents a quintuple-mode ultra-wideband (UWB) bandpass filter (BPF), using a multiple-stub-loaded resonator, consisting of multiple loaded stubs to a uniform transmission-line resonator, i.e., two asymmetrical stepped-impedance stubs at the center and four uniform-impedance stubs at the symmetrical side locations. Six modes including two odd and four even modes are controllable, while the first five modes are allocated within the UWB band. Two transmission zeros generated by the asymmetrical stepped-impedance stub are used to improve the passband selectivity greatly. The resonant mode and transmission zero chart are given, indicating that the higher modes could be suppressed by the transmission zeros generated by the stubs and the parallel-coupled lines. A compact planar UWB BPF is simulated, fabricated and measured, and the 20 dB stopband performance is extended to 29.7 GHz. [ABSTRACT FROM PUBLISHER]