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This article presents a ±45° dual‐band dual‐polarized filtering antenna. The filtering antenna element is a dual‐polarized patch antenna that loads a parasitic patch with two rectangle slots to achieve compact multi‐array. Multi‐array consists of three 1×2 subarrays arranged, which are designed for 1.8/2.1 GHz FDD band applications. Very close‐arranged antennas exhibit radiation pattern invariance as well as in‐band radiation property. Radiation patterns are conformal with a compact subarray distance of 45 mm (0.29λ0), which is 56% smaller than that of the array using traditional filtering elements. Moreover, the total width is only 180 mm for three subarray‐composed antenna arrays. The average gain is 8.7 dBi with a low profile of 0.069λ0. The proposed array exhibits the filtering property of the subarrays with a very simple structure. [ABSTRACT FROM AUTHOR]

A novel design concept of multiple‐input and multiple‐output (MIMO) antenna with aiming to improve matching and port isolation at the same time is proposed. As the only additional component, a cross resonator is connected between the two patch antennas. The equivalent circuit model and calculation formula of resonant frequency of cross resonator in differential mode (DM) and common mode (CM) state are given, respectively. The same resonant frequency in the two states is the goal to want, and which is proved to be achievable by the relevant expression. Then, the two port antenna system can obtain good matching and high isolation. The coincidence between simulation and measured results brings the possibility of practical implementation. [ABSTRACT FROM AUTHOR]

In this article, a wideband base station antenna is designed. A new resonant mode is introduced into the antenna. Finally, four U‐shaped slots are added to the dipole of the antenna, and the antenna's third resonant mode is close to the first two resonant modes, which makes the antenna achieve wideband performance. The antenna is fabricated, and its performance is measured. The results show that the antenna has stable gain and radiation patterns. At the same time, the antenna works at 1.6–3.85 GHz with an impedance matching of −14 dB, and the relative bandwidth is 82%, the polarization isolation of the proposed antenna is better than −40 dB. [ABSTRACT FROM AUTHOR]

A novel concept of simultaneous matching, decoupling and miniaturization in multiple input multiple output (MIMO) antenna is proposed. Firstly, the integration of matching and decoupling can be achieved by making the resonant frequency of common mode (CM) and differential mode (DM) consistent. Then, the same resonant frequency of CM and DM will move to lower frequency through changing parameters value of the folded cross resonator. The MIMO antenna will operate normally at lower frequency with low mutual coupling without increase the volume. The operating frequency of antenna is reduced from 3 to 2.5 GHz of achieving 16.7% miniaturization, and the isolation is increased from 20 to 45 dB at 2.5 GHz at the same time. The measurement and simulation results are in good agreement, which verifies the correctness of the design. The goal of matching, decoupling and miniaturization for MIMO antenna will be completed without too much software optimization and other complex structures. [ABSTRACT FROM AUTHOR]

A nonuniform compressed high-order mode dipole with suppressed sidelobe is proposed and investigated. The main performance characteristics, such as directivity, sidelobe, and radiation resistance of a third-order mode dipole with two independent compression coefficients are fully investigated. The investigation shows that enhanced directivity, suppressed sidelobe, and high radiation resistance are achieved simultaneously by selecting the appropriate compression coefficients. The compressed converse current leads to the sidelobe suppression. To verify the investigation, a third-order mode dipole antenna with nonuniform compression is designed, fabricated, and measured. The measurement shows that the reflection coefficient is less than −10 dB over the band of 2.46–2.65 GHz (one of the sub-6 GHz bands of fifth generation). The achieved gain is 4.7 dBi. The sidelobe level is less than −15.4 dB, 9.4 dB lower than the uniform compressed third-order mode dipoles. [ABSTRACT FROM AUTHOR]

A novel electromagnetic transparent high-band (HB) antenna can be achieved by loading dumbbell-like slots, U-shaped slots, square-loop slots, and straight slots on the patch dipoles. The HB antenna operates in the band of 1.71–2.69 GHz (VSWR < 1.5), and the dipoles achieve low-scattering property in the band of 3.4–3.8 GHz. In the design, the impedance matching of HB antenna is very good even scattering suppression technique is applied on the dipoles. The loading of U-shaped slots introduces an additional resonance point, which can alleviate the impedance problem caused by the technique. Besides, a dual-band antenna array has been designed and fabricated for validation. Both simulated and measured results show that the HB antenna has a good performance on electromagnetic transparency. [ABSTRACT FROM AUTHOR]

In this article, a simple dual wideband antenna with a novel feeding structure is designed based on two folded dipoles. Because of the particular antenna structure, the feeding structure of the antenna works as an impedance transformer. Then, four resonance modes are excited to achieve dual wideband performance, which brings a wide impedance bandwidth to the two pairs of dipoles. A prototype of the proposed antenna is fabricated and measured. Results show that the proposed antenna successfully supports the dual wideband operation of 1.4–2.7 GHz (63%) and 3.4–5.2 GHz (41%). [ABSTRACT FROM AUTHOR]

In this article, the realization method and operation mechanism of suppressing cross‐band scattering is introduced, firstly. And then, a SSRs‐loaded electromagnetic transparent antenna (ETA) is designed to suppress the scattering interference existing in the proposed dual‐band shared‐aperture antenna (P‐DBSA). The P‐DBSA is composed of the proposed ETA operating in the lower‐band (LB: 1.7–2.2 GHz) and a 2 × 2 array antenna operating in the higher‐band (HB: 3.4–3.6 GHz). The proposed ETA is obtained by etching folded split‐slot resonators (F‐SSRs) on the entire radiating arms of the LB antenna. In this way, the scattered field formed by the HB‐induced current distributed on the LB radiating arms can be self‐canceled, thereby HB radiation pattern restoration can be achieved. In addition, etching F‐SSRs will not cause the ETA to be difficult to match. The proposed decoupling method has the advantages of simple in structure, high integration, and easy to manufacture, and has important reference value for suppressing cross‐band scattering existing in DBSAs. [ABSTRACT FROM AUTHOR]

A low‐profile dual‐band dual‐polarized base station antenna array is proposed. The dual‐band array is backed by an artificial magnetic conductor (AMC) surface. The AMC achieves profile reduction to 0.159 λL0 in the low band (LB), but it acts as a bandpass metasurface in the high band (HB). The nested design of AMC unit cell creates two out‐of‐phase induced currents with lower intensities, enabling suppression and cancelation of HB scattered fields. The back cavities establish clear and independent radiating environments for the LB and HB antennas. They aid in further radiation pattern restoration and antenna profile reduction. The proposed antenna array was fabricated and experimentally measured. The simulated and measured results are presented. The operating principles of the proposed AMC and back cavities are also investigated. [ABSTRACT FROM AUTHOR]

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]

This article presents a 3-D printed dielectric polarizer. It is constituted by a number of annually arranged dielectric slabs, and each slab is 45° rotated with respect to the azimuth plane. It is able to transform the polarization state of the waves in azimuth plane from linear to circular. Based on the polarizer, two circularly polarized (CP) antenna designs are proposed. One of them is an omnidirectional CP antenna, and the other is a multibeam CP antenna with capability of full azimuthal scanning. They are fed by a dielectric filled biconical structure and six corner reflectors, respectively. Their polarizers are individually designed with different geometric parameters. Both antennas are one-piece configurations and can be directly 3-D printed without assemblies in later stage. Partial surfaces of the antennas are coated with copper films by an electroplating technique to act as the necessary metal components. To validate the design ideas, two prototypes are demonstrated in X-band. Experimental results show that the omnidirectional antenna can achieve a wide 3 dB axial ratio (AR) bandwidth of 28.3% from 8.5 to 11.3 GHz and a peak gain of 3.3 dBic. Meanwhile, the multibeam antenna is with a wide 3 dB AR bandwidth of 22.4% from 8.7 to 10.9 GHz and a peak gain of 9.2 dBic. Within the AR bandwidth, the AR values in full azimuth plane are lower than 3 dB. [ABSTRACT FROM AUTHOR]

This article presents a novel circularly polarized (CP) open‐ended waveguide antenna array based on additive manufacturing technology. It is a one‐dimensional four‐element linear array and has a single piece configuration. Its main body is made of dielectric material and partial surfaces are coated by copper films through electroplating to form necessary metal components. Regarding to each element, it is based on a circular waveguide and employs an inbuilt linearly tapered double‐ridge structure to act as a polarizer. To design such a polarizer, different shaped ridges are analyzed and a design evolution is presented and discussed. Compared to the conventional designs, the proposed element and array can avoid structure partitioning during the processing, and effectively reduce the fabrication difficulty and complexity, meanwhile, attain light weights. To validate the design idea, two prototypes corresponding to the element and the array are fabricated and tested. Experimental results indicate that their axial ratio bandwidth (ARBW) are 22% (8.9–11.1 GHz) and 11.8% (9.6–10.8 GHz), and the gain are 6.6 ± 1.1 and 10.6 ± 0.6 dBic, respectively. The proposed element and array could be potentially applied for satellite and other CP communication systems. [ABSTRACT FROM AUTHOR]

A novel electromagnetic transparent low-band (LB) antenna is given in this article, with a good impedance matching in the band of 0.69–0.96 GHz (VSWR < 1.5). The key feature lies in its great patch dipoles with low-scattering properties. The transparent performance is achieved by loading slots on the dipoles, instead of inserting chokes. Dagger-like slot plays an important role in both impedance matching improvement and scattering suppression. An extra resonance point can be introduced to the reflection coefficient curve in the operating band, so the impedance matching problems can be alleviated. Besides, a dual-band shared-aperture array was designed and fabricated for validation. Both simulated and measured results have proved that the LB antenna has satisfactory impedance characteristics within the operating band and achieves an electromagnetic transparency in the band of 1.7–2.4 GHz. [ABSTRACT FROM AUTHOR]

An antenna decoupling method based on modal control is proposed in this paper. Different from the previous characteristic mode decoupling methods, which excite one of the characteristic modes from each port, a pair of decoupling modes is excited simultaneously at each port. To validate our method, a head‐to‐head antenna pair is analyzed and designed. According to the characteristic mode analysis, an inductor‐loaded coupled sheet is introduced for the head‐to‐head antenna pair. Thus, the resonant frequencies of decoupling modes can be tuned individually. To further demonstrate the flexibility of our design, an eight‐element multiple‐input multiple‐output (MIMO) antenna composed of two integrated four‐element blocks is designed, fabricated, and measured. The proposed antennas show good impedance matching, isolation, and diversity performance varying from 3.35 to 3.71 GHz. Both simulated and measured results show the 8 × 8 MIMO system can achieve isolations of better than 11.5 dB and envelope correlation coefficients of less than 0.2 of each port. [ABSTRACT FROM AUTHOR]

In this article, a radiant metal block structure is proposed for designing reduced-size cavity-backed filtering antenna. The method of characteristic mode analysis is used to investigate the characteristic current modes of the cubic metal block, one of which can maintain a high inherent radiation capacity over a wideband. In addition, the radiation quality factor of the utilized mode is described in detail. Based on this characteristic current mode, metal block antennas with different bandwidths can be designed to realize broadside radiation. The proposed metal block antenna element can maintain stable radiation characteristics in the passband and the realized gain is greater than 9 dBi. To design the filtering antennas, the proposed metal block is cascaded with traditional resonant cavities. A third-order metal block filtering antenna array is fabricated for verification. The measurement results are basically consistent with the simulated ones. The maximum measurement gain is 12.85 dBi and the gain in the passband is flat. [ABSTRACT FROM AUTHOR]

This paper presents a wideband circularly polarized (CP) multibeam antenna array, which is with full azimuth scanning capability and operates in Ka band for 5G applications. It adopts a circular array configuration and consists of 18 elements with a simple structure. Regarding to each element, it is fed by a 90° bent rectangular waveguide and employs a simplified single dielectric slab polarizer to produce CP waves. Within the axial ratio bandwidth (ARBW), the proposed element can achieve a stable half power beamwidth (HPBW) of 29 ± 7°, while, the 3‐dB AR beamwidth is larger than the HPBW. By switching the active elements, the proposed array can realize 360° beam steering in azimuth plane, while, the HPBW and the 3‐dB AR beamwidth cover the entire plane. To simplify the fabrication process, dielectric and metal 3‐D printing technologies are employed for processing. Experimental results indicate that the proposed array can achieve a 40.5% 3‐dB ARBW which almost covers the entire Ka band from 26.2 to 39.5 GHz and a gain of 9.9 ± 1.5 dBic. The front‐to‐back ratio (FBR) of each beam is higher than 19 dB. In contrast to conventional designs, the proposed antenna features wide band, simple structure, and ease of fabrication. [ABSTRACT FROM AUTHOR]

A wideband dual‐polarized planar antenna with triple radiators is proposed for the LTE600/LTE700/GSM850/GSM900 base station in this paper. A novel concept of multi‐radiator for multi‐resonance by close coupling feed is presented and analysed. The proposed antenna is mainly composed of two pairs of loop dipole, L‐shaped radiator, step dipole, two L‐shaped feed lines, balun and reflector. The reflector is designed with a centrosymmetric partible baffle for directional radiations, which contribute to stable radiations as well. Owing to the novel closely coupling scheme for multi‐radiators, three resonances are simultaneously excited within the desired band, producing a wide bandwidth of 47.7% (from 0.59 to 0.96 GHz) for |S11| < −15 dB with high isolation more than 30 dB. Moreover, an average gain of 8.8 dBi as well as stable radiation patterns are achieved simultaneously. [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]

In this article, a height‐reduction dual‐polarized antenna suitable for base station applications with a simple structure is proposed. By adopting the form of bilateral coupling feed, the height of the antenna has been significantly reduced. The working mechanism of height‐reduction of the antenna is given. The experimental results show that the antenna operates at 0.698–0.96 GHz for reflection coefficient <−12 dB with isolation (ISO) of more than 30 dB. It has a stable gain of 8.4 ± 0.6 dBi and a half‐power beamwidth (HPBW) of 66.8 ± 6.8° in the working band, and the height of the proposed antenna is only 0.115λ0, which is much smaller than the traditional 0.25λ0 (λ0 denotes the free wavelength corresponding to the center frequency). [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]

A tri‐band dual‐polarized antenna array for base station applications is presented. The proposed tri‐band antenna array is devised by stacking the 1 middle‐band (MB) + 4 high‐band (HB) interleaved array above the low‐band (LB) patch antenna. The MB antenna yields partial reflection to the HB subarrays, enabling cross‐band and in‐band decoupling abilities without introducing additional decoupling layer. With the aid of spatial cancelation and partition, transmission nulls are successfully generated in the in‐band mutual coupling curves. Measured results show that good impedance matchings and polarization isolations are acquired in the operating bandwidths. The measured co‐ and cross‐polarized in‐band isolations in the HB are improved to >22.4 dB and >29.1 dB, respectively. The HB radiation patterns are well restored. [ABSTRACT FROM AUTHOR]

Difficulty in achieving broadband impedance matching has become a technical problem that limits the development of electromagnetic transparent antennas (ETAs). In this letter, a broadband dual-polarized ETA is designed. It is achieved by etching nested split-slot resonators (N-SSRs) on the entire radiating arms. Etching N-SSRs can form two independently controllable decoupling bands (DB1 and DB2). Combining DB1 and DB2 can achieve broadband scattering suppression. The N-SSRs together form a high-order band-stop filter with good frequency selectivity. Due to the high skirt roll-off performance of the high-order band-stop filter, etching N-SSRs will not increase the difficulty of matching. Therefore, the proposed ETA can obtain well impedance matching performance while having a good cross-band scattering suppression capacity. Then, a dual-band shared-aperture antenna named P-DBSA is designed. The proposed ETA is used as a lower band element of the P-DBSA. Well impedance matching performance of VSWR $< $ 1.5 in both lower band (1.68–2.85 GHz) and higher band (3.3–3.6 GHz) is realized by P-DBSA. Moreover, cross-band scattering is successfully suppressed. [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]

Based on the concept of using controllable mixed electric and magnetic coupling to design planar filters in our earlier work, we propose a novel inline coaxial filter, in which the electric and magnetic coupling can be separately controlled. Due to this controllable mixed coupling, the filter can operate with a quasi-elliptic characteristic. By modifying resonator structure and inserting additional coupling components, the filter size is substantially reduced and the coupling becomes more easily controllable, thus being able to produce a highly selective filter with a compact size. In addition, asymmetric response can be easily achieved. For the N-order filter, a maximum of N - 1 finite transmission zeros can be realized. Practical designs, concerning a global system for mobile communication specification, show the advantages of this filter. Index Terms--Coaxial, elliptic filtering characteristic, inline filter, mixed coupling.

A novel approach for designing tri-band bandpass filters with independently controllable center frequencies and improved stopband rejection characteristic is presented in this paper. The assembled resonator constructed by a stepped impedance resonator and a common half-wavelength resonator is employed to obtain tri-band response. The stepped impedance resonator is designed to operate at the first and third passbands and the other resonator is designed to operate at the second passband. Two kinds of filter configurations with cascaded and pseudointerdigital formats are proposed. Based on lossless lumped-element equivalent circuit, it is found that both filter structures can introduce transmission zeros between passbands. To verify the proposed approach, two filters are designed and fabricated, the measured results exhibit tri-band bandpass responses with high selectivity. Index Terms--Assembled resonator, bandpass filter, equivalent circuit, microstrip, stepped impedance resonator, tri-band.

A triband shared aperture (TBSA) antenna is proposed to meet the new requirements of base station antennas for multiband antennas fusion. The proposed TBSA (P-TBSA) antenna is composed of a lower band (LB, 790–960 MHz) antenna, two columns of middle band (MB, 1710–2170 MHz) subarrays, and a $4\times 8$ array antenna operating at N78 band (higher band (HB): 3.4–3.6 GHz). The LB antenna is located in the center of a shared reflector. The MB subarrays are located around the LB antenna with a side-by-side scheme. The HB array antenna is located below the MB and LB antennas for multi-input–multioutput (MIMO) application. The cross-band coupling interference existing in the P-TBSA antenna can be divided into scattering interference and common-mode interference, which will seriously deteriorate its performance. To suppress the scattering interference, an LB crossed dipole antenna with low radar cross Section (RCS) at both MB and HB and an MB crossed dipole antenna with low RCS at HB are designed. In addition, the method of “path extension” is used to suppress the common-mode interference. By taking the above measures, the distorted radiation pattern of the P-TBSA antenna is significantly recovered. [ABSTRACT FROM AUTHOR]

This paper presents a triple‐band composite antenna array for maritime application. It consists of a three‐element base station antenna array and a waveguide based satellite antenna, which are applied for near‐shore and long distance off‐shore communications, respectively. For the former, it is a ±45° dual polarized array with dipole radiators and covers 2G/3G/4G bands. The three elements are arranged in a form of half hexagon and attain 180° coverage of half power beamwidth (HPBW) in azimuth plane by switching the feeding ports. For the latter, it is a sequentially fed circularly polarized antenna operating in Ku‐band and has a wide HPBW through loading a dielectric structure. To validate the design idea, a prototype is fabricated and measured. Experimental results show that the base station antenna array achieves wide bandwidth of 49.14% from 0.66 to 1.09 GHz and 46.58% from 1.68 to 2.7 GHz with VSWR < 1.5. Meanwhile, the satellite antenna has a wide 3‐dB axial ratio (AR) bandwidth of 20.1% from 12.1 to 14.8 GHz with reflection coefficients lower than −15 dB. Within the band, the HPBW is larger than 90° and the 3‐dB AR beamwidth covers the HPBW. [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]

A high‐isolation dual‐band base station antenna array is proposed. At first, a 5‐element high‐band (HB) dipole antenna array with inter‐element distance of 0.4 λH0 (the free‐space wavelength at the center frequency of the HB) is decoupled. With the main antenna decoupling surface (ADS), metal baffles and auxiliary ADS, the E‐plane and H‐plane couplings can be reduced to <−23.1 dB (<−11.4 dB without decoupling) and <−22.6 dB (<−14.8 dB without decoupling), respectively. The dual‐layer ADS design successfully resolves the contradiction between decoupling performance and matching. The ground plane of the 5‐element array is then exploited as the low‐band patch radiator, forming the proposed dual‐band antenna array. Measured results show that satisfactory cross‐band isolation (>33.1 dB), in‐band isolation (>22.2 dB) and polarization isolation (>30 dB) are obtained. Stable unidirectional radiation patterns are also acquired. [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]

This article presents a circularly polarized (CP) endfire multibeam antenna with wide axial ratio (AR) beamwidth coverage. It is based on a dielectric loaded waveguide structure and consists of a 4 × 4 Butler matrix and four rhombic waveguide elements. Regarding to each element, it decomposes the incoming linearly polarized waves into two orthogonal modes with equal amplitude and obtains 90° phase difference between the two modes via their different dispersion characteristics to realize CP radiation. Study found that the proposed element has low cross‐polarization performance within a wide beamwidth, which contributes to realize wide 3‐dB AR beamwidth coverage in the multibeam array. In fabrication process, injection modeling and electroplating techniques are employed to construct the proposed antenna. By using this way, the structure splitting and misalignment problems, which usually existed in conventional designs, can be avoided, and the antenna weight can be maintained to a moderate level. Through the experiment, it is found that the proposed antenna can achieve an overlapped 3‐dB AR bandwidth of 10.7% from 9.7 to 10.8 GHz and a wide 3‐dB AR beamwidth coverage of 91°. [ABSTRACT FROM AUTHOR]

We propose a compact planar ultrawideband (UWB) antenna with 3.4/5.5 GHz dual band-notched characteristics. The antenna consists of a beveled rectangular metal patch and a 50 [OMEGA] coplanar waveguide (CPW) transmission line. By etching two nested C-shaped slots in the patch, band-rejected filtering properties in the WiMAX/WLAN bands are achieved. The proposed antenna is successfully simulated, designed, and measured showing broadband matched impedance, stable radiation patterns and constant gain. An equivalent circuit model of the proposed antenna is presented to discuss the mechanism of the dual band-notched UWB antenna. A UWB antenna and a single band-notched one are also provided for references. Index Terms--C-shaped slots, coplanar waveguide (CPW) fed antennas, dual band-notched characteristics, equivalent circuits, ultrawideband (UWB) antennas.

Two wideband antennas sharing a common aperture are presented. One antenna consists of an electrically loaded rectangle monopole, an electrically loaded inverse L-shape monopole, and a lowpass matching network between the two monopoles. It covers 30-600 MHz (VSWR Index Terms--Loaded antennas, monopoles, shared aperture, sleeve antennas.

A novel cascaded microstrip open-loop resonator filter with controllable electric and magnetic mixed coupling is presented to have one or more transmission zeros. For two coupled resonators, the coupled sides with the maximum magnetic field are combined with their open gaps with the maximum electric field, creating the electric and magnetic mixed coupling. By adjusting the distances between resonators and the positions of open gaps in a mixed coupled filter, the coupling coefficients can be changed, and controllable transmission zeros can be produced in the lower stopband, upper stopband, or both. Design and fabrication of the proposed second- and fourth-order filters show the advantages: such as a smaller number of resonators, higher rejection level, as well as asymmetrical response; moreover, the location of the transmission zeros can be precisely controlled. Index Terms--Bandpass filter, electric and magnetic mixed coupling, transmission zero.

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 wide‐band circularly polarized reconfigurable antenna based on a pure water dielectric patch antenna is proposed. By changing the shape of pure water in the plexiglass container symmetrically, the circularly polarized states of the antenna can be switched. And the available bandwidth of right‐hand circular polarization and left‐hand circular polarization remain unchanged. The interface between pure water and air with a great difference in relative dielectric constant is equivalent to an electrical wall. When feed with an L‐shaped metallic probe, the axial ratio of a wide band can be formed, and the impedance bandwidth of antenna can be fully utilized. Under the two circularly polarized states of the antenna, the measured results show that the 3‐dB axial ratio bandwidth is above 24.4% for |S11| < −10 dB, the radiation efficiency is concentrated at 58%–71%, and the maximum gain reaches 3.5 dBi. [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]

In this communication, we propose a shared-radiator design concept for dual-band base station antenna arrays. To realize the concept, novel differentially fed dual-polarized slot antenna is devised to be the high-band (HB, 3.4–3.6 GHz) radiator, while the large slot ground can be reused as the radiating arm of the low-band (LB, 0.69–0.96 GHz) crossed dipole. Reflective cavities are introduced to back the HB antennas, building clear and independent radiating environments for the two operating bands. A dual-band base station antenna array with one LB dipole antenna and four HB slot antennas is designed, by adopting the proposed integration concept. Good impedance matching (voltage standing wave ratio <1.5) and high port isolation (>29.5 dB in the LB and >26.6 dB in the HB) are obtained. Stable radiation patterns are also achieved in the two bands. [ABSTRACT FROM AUTHOR]

In this article, we propose a novel reflector-back cavity-low-band (LB)/high-band (HB) configuration for the dual-band dual-polarized base station antenna array design. The HB antennas are embedded in the opening sections of the loop radiating arms of the LB antennas. Clear and independent radiating environments are fulfilled by using two different types of reflectors (large planar reflector and back cavity). The mutual effects between the LB and HB antennas help to acquire good impedance matching and stable radiation patterns. Loop-like LB radiators work as directors in the HB, thereby effectively suppressing the side and back radiations of the HB antennas. Dual-function open slots are loaded on the ground stubs of the LB baluns, serving as impedance transformer in the LB but filtering structures in the HB. The experimental results validate that the proposed antenna array successfully covers bandwidths of 0.69–0.96 and 3.3–3.8 GHz (VSWR < 1.5) for 4G/5G applications. The port isolations are higher than 38 and 25 dB in the LB and HB, respectively. With the two independent radiating environments formed in the two bands, both LB and HB antennas exhibit stable unidirectional radiation patterns. The antenna gains and HPBWs are also satisfactory in both bands. [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, 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]

A compact differentially fed dual‐polarized patch antenna with filtering performance is proposed for 5G applications. By utilizing the half‐wavelength standing current along the open‐ended microstrip line, the out‐of‐phase output signals are obtained. Utilizing the E‐shaped coupled resonator in series with the open‐ended microstrip line, balanced differential feeding with filtering property are realized, as excitation for the patch. The filtering patch antenna was fabricated for demonstration. Measured results show that the antenna has −15 dB impedance bandwidths of 13.7% (3.26–3.74 GHz) and 14.2% (3.25–3.75 GHz) for two polarizations, respectively, covering the 5G band (3.3–3.6 GHz). The patch antenna achieves good port isolation and cross‐polarization discrimination. In addition, the measured gain is higher than 6.8 dBi within operating band. Out of the operating band, the gain drops sharply, exhibiting a bandpass response. The out‐of‐band radiation suppression level of the proposed filtering patch antenna is larger than 16 dB. [ABSTRACT FROM AUTHOR]

A method of designing a printed filtering dipole antenna using codesign of bandpass filter (BPF) and antenna is proposed in this article. The printed dipole antennas consist of two identical arms, which are placed on the opposite sides of the substrate. One arm of the dipole is used to construct the half-wavelength resonator of a typical BPF, and thus filtering and radiation performance can be obtained simultaneously. A third-order filtering dipole antenna is designed and analyzed in detail to demonstrate the codesign method. The measured S11 of the filtering dipole antenna is less than −11 dB in the range of 0.94–1.094 GHz and the peak gain is 7.8 dBi. To extend this design method, a third-order ±45° dual-polarized filtering dipole antenna is designed and measured. The measured S11 and S22 of the ±45° dual-polarized filtering dipole antenna are both less than −11 dB in the range of 0.94–1.08 GHz. Besides, the isolation between them is higher than 20 dB in the passband. The measured radiation patterns show that the dual-polarized filtering dipole antenna would be a potential candidate for base stations. [ABSTRACT FROM AUTHOR]

In this communication, a ±45° dual-polarized antenna for 690–960 MHz base station applications is proposed. The proposed antenna has a crisscross-shaped radiator which is fed by four triangular-shaped couplers. The ±45° dual polarization is achieved by vector synthesis of the currents on the radiator. To further broaden the impedance bandwidth (IBW), a miniaturized lowpass filter is designed and integrated with the baluns of the proposed antenna. With the lowpass filter, a new resonance is introduced and harmonic suppression is also realized. The experimental results which agree with the simulations show that wide harmonic suppression bandwidth which can cover the interference bands (1.69–2.69 GHz and 3.3–3.8 GHz) is obtained. In the operating frequency band (690–960 MHz), a voltage standing-wave ratio (VSWR) of less than 1.5, a polarization isolation (ISO) of more than 35 dB, a half-power beamwidth (HPBW) of 66.8° ± 1.5°, and the gains of 8.3 dBi ± 0.2 dBi are obtained by the proposed antenna. [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]