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A broadband high‐gain slot grid array antenna (SGAA) is proposed in this paper. Based on the electromagnetic complementarity principle, the metal elements in the traditional microstrip grid array antenna (GAA) are replaced by a wide slot element. Compared with the GAA, the proposed SGAA achieves broadband and high‐gain performance. In order to demonstrate this concept, a prototype with 9‐element SGAA is designed using wide slot radiation elements and fabricated on Rogers 5880 printed circuit board (PCB) substrates, which is fed by a 50 Ω coaxial probe. The measured and simulated results show a good agreement. The proposed SGAA achieves a measured peak gain of 14.8 dBi at 26.0 GHz, a 10‐dB impedance bandwidth from 22.2 to 28.5 GHz with a fractional bandwidth of 24.9%. These results indicate that the SGAA is with high performance and it is suitable for the fifth‐generation (5G) millimeter wave (mmW) wireless communication system. [ABSTRACT FROM AUTHOR]

In this article, a low‐profile ultra‐wideband (UWB) circularly polarized (CP) antenna array with metasurface is presented. The antenna array consists of a 2 × 2 polarization conversion metasurfaces (PCMs) and a sequential feeding network. The PCM is composed of 4 × 4 polarization conversion unit‐cells. The unit‐cell is obtained by putting an ellipse patch into a rectangular ring, connecting the ellipse and the ring with two stubs, and then rotating it by 45°. A linear polarization (LP) slot antenna with a PCM can achieve a CP antenna, which has an impedance bandwidth of about 33.8% (5.4‐7.6 GHz) of |S11| < −10 dB and a 3‐dB axial ratio (AR) bandwidth of about 24.8% (5.8‐7.3 GHz), respectively. The UWB CP characteristics can be achieved when a UWB sequential feeding network is added to the 2 × 2 PCMs. Simulated and measured results show that the proposed antenna array has an impedance bandwidth of about 117% (1.75‐6.75 GHz) of |S11| < −10 dB and a 3‐dB axial ratio (AR) bandwidth of about 105.7% (2.24‐7.35 GHz), respectively. The usable bandwidth can reach 100.3% (2.24‐6.75 GHz). Besides, the proposed antenna array achieves a higher gain compared to the traditional slot array and the peak gain of 12.5 dBic at 6 GHz. The overall size of the antenna is 0.6λ × 0.6λ × 0.03λ (λ refers to the wavelength of the lowest operating frequency in free space). The proposed antenna array can be widely applied to various wireless communication systems. [ABSTRACT FROM AUTHOR]

A class of circularly‐polarized cavity‐backed slot antenna arrays with simplified feeding structure are proposed. Power dividing network is an essential feeding structure for the design of conventional antenna arrays, which results in complicated antenna structure. A novel feeding technique based on the electric field of cavity modes is introduced to feed the array elements. The slots on the top wall are directly fed by the electric field without additional feeding structure. Crossed slots with different lengths are introduced to achieve the self‐phased CP radiation as they produce different perturbation on the two degenerate cavity modes. Therefore, high efficiency and simple antenna structure of the CP slot antenna array are achieved. Then, two CP slot arrays with 3 × 3 and 8 × 8 elements are presented to show the designed feasibility. Finally, the 3 × 3 CP antenna array is fabricated and measured to validate the design concept, which can achieve 12.6 dBic gain, 94% total efficiency, 80% aperture efficiency, and −25 dB cross polarization. [ABSTRACT FROM AUTHOR]

This article introduces a simple wideband circularly polarized (CP) S‐shaped slot antenna for ISM band wireless communication applications. By using a wide curve S‐shaped slot patch on the top side and a T‐shaped feeding line on the bottom side of the substrate, the wideband CP wave is generated. The overall size of the proposed antenna is 0.85λ × 0.85λ × 0.011λ (λ is the wavelength of the lowest operating frequency) and it has a broad impedance bandwidth of 68.1% between 1.66 and 3.44 GHz for S11 < –10 dB and a 3 dB axial‐ratio bandwidth of 57.1% between 1.68 and 3.06 GHz. Within the axial‐ratio bandwidth, the measured gain of the proposed antenna ranged from 2.1 to 5.4 dBic. The measured results are in good agreement with simulated results. The new type of slot antenna with wide bandwidth and simple structure is a good candidate for various RFID applications. [ABSTRACT FROM AUTHOR]

Abstract: In this article, a double‐T‐shaped stub centrally loaded uniform impedance resonator (UIR) is introduced and its resonant characteristics are well clarified, which provided a simple approach for triple‐mode wideband bandpass filter (BPF) design. The double‐T‐shaped stub consists of a T‐shaped stub at the center of UIR and two shunt uniform‐impedance stubs at the T‐shaped stub. Furthermore, loading technique for zero‐voltage point is employed to guide design procedure from UIR to the proposed resonator. The resonant frequencies of the first three modes for the resonator can be free to adjust by the length of the UIR and the two kinds of stub. Finally, a compact wideband BPF is designed, fabricated, and measured. The measured results are in good agreement with the full‐wave simulation results. The realized wideband filter exhibits a 3 dB fractional bandwidth of 69.1% with good in‐band filtering performance, wide stopband, and sharp out‐of‐band rejection skirt. [ABSTRACT FROM AUTHOR]

This article tries to address the unstable radiation pattern issue of the planar‐coupled patch antennas with two different methods. First, characteristic mode analysis (CMA) reveals that the coupled patch antennas generate three characteristic modes with distinctive radiation patterns. A slot‐loading scheme is proposed to reshape the current distribution of the higher mode and reduce its sidelobe level significantly. Then a 13.4% bandwidth with consistent radiation patterns and high gain is achieved by exciting modes 1 and 3 while suppressing unwanted modes with an aperture‐coupled feeding. Second, the radiation pattern stability of the coupled patch antennas is further improved by employing shorted parasitic patches. The presented antenna can be equivalent as the same magnetic current array model under the in‐phase and out‐of‐phase modes, and thus the radiation patterns hardly get changed. Moreover, the non‐radioative nature and high radiation quality factor of the higher mode improve the radiation performance in a new principle. It not only enhances the bandwidth up to 18.5% but also results in a sharp filtering edge of gain response. [ABSTRACT FROM AUTHOR]

This article presents a fully integrated design of probe‐fed open‐ended waveguide filtering antenna by adopting 3‐D printing technology. As for the conventional processing technologies such as computer numerical control machining, they usually suffer from mutually separated parts and inquire post‐processing assembly in the fabrication of complex waveguide structure. Compared with them, the 3‐D printing technology can provide possibility to directly form an all‐in‐one architecture after reasonable design to avoid unexpected concave, thus eliminating the error caused by assembly as can as possible. In this article, the aforementioned manufacture strategy has been successfully applied to waveguide filtering antenna. By adopting a tilted setting in selective laser melting process that is a kind of 3‐D printing technologies, the proposed waveguide antenna with internal structure can be fabricated without flaw and extra supporter. The probe‐fed waveguide antenna is designed herein by reforming the first‐ and last‐order cavities of a waveguide‐fed metal‐insert filter to achieve similar filtering characteristics. This design offers a feasible example of all‐in‐one waveguide filtering antenna and can be extended to other waveguide components. [ABSTRACT FROM AUTHOR]

A printed dual‐band dipole filtenna with flexible frequency ratio and improved band‐notched performance is proposed. It consists of a driven dipole and three parasitic elements. For the driven dipole with short and long arms, a radiation null is found between two passbands, which achieves a band‐notched filtering characteristic. Two parasitic elements are introduced to enhance the passband bandwidth and an additional parasitic element is utilized to improve the band‐notched performance. In addition, the characteristics of the proposed design including flexible frequency ratio, independent controllable operating frequency, and controllable band‐notched bandwidth have also been demonstrated. A filtenna prototype is fabricated and tested. Measured results show that a fractional bandwidth of 21.1% and 18.1% is obtained in the lower and upper passbands, respectively. The measured efficiency is 84% in the lower band and 74% in the upper band but the efficiency sharply decreases to about 13% within the notched band. [ABSTRACT FROM AUTHOR]