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In this article, a compact 94 GHz multibeam antenna array based on the binary phase-controlled concept is proposed. The feeding network is composed of four unconnected layers, and the ridge or groove gap waveguides are adopted as the guided wave structures. A key planar gap waveguide Magic-Tee is designed to obtain 0° and 180° phase states and then integrates with an $8\,\times \,8$ slot antenna array to achieve multibeam operation for the first time. Compared with the traditional phased array and passive beamforming networks (BFNs), the feeding design is simple in construction, consisting of only Magic-Tees and cascaded power dividers without any phase shifters. Benefiting from the gap waveguide technology, the antenna array does not require electrical contact among the metal layers, so it is simple and low cost to manufacture. The $8\times8$ slot antenna array can easily switch among one-beam and three different dual-beam states that point to ±7°, ±17°, and ±38°. The measurement results of 6.6% bandwidth from 91.7 to 98 GHz for both reflection coefficients $< -10$ dB and isolations >25 dB are achieved. The proposed multibeam antenna array would be an attractive candidate for millimeter-wave multiuser communication where it requires multiple beams simultaneously. [ABSTRACT FROM AUTHOR]

A full corporate feeding $8\times $ 8 circularly polarized (CP) planar antenna array using septum antenna elements for millimeter-wave (mmWave) frequency band applications is reported. Widebands for both the impedance and axial ratio (AR) bandwidths and high efficiency are guaranteed by the antenna array attributed to septum elements and feeding network based on the metal ridge gap waveguide (RGW). For the analyzing $2\times $ 2 sub-array containing a feeding structure, simulated results show that the impedance bandwidth ($\vert S_{11}\vert < -10$ dB) of 31.4%, AR bandwidth (AR < 3 dB) of 32.6%, and maximum gain of 29.2 dBic are realized. For the practical fabricated 8 $\times $ 8 antenna array prototype, measured results reveal that its impedance bandwidth ($\vert S_{11}\vert < -10$ dB) is 31.5%, overlap AR bandwidth (AR < 3 dB) is 33.1%, and maximum measured gain value is 28.4 dBic with a maximum aperture efficiency of 85%. With such performances, the proposed CP antenna array would be a promising candidate for mmWave communication systems. [ABSTRACT FROM AUTHOR]

A broadband stepped tapered slots’ endfire circularly polarized (CP) antenna and a multibeam antenna array are proposed for millimeter-wave (mmWave) applications. First, a modified tapered slot endfire antenna element is designed. Compared with the normal antipodal linearly tapered slot (ALTSA) endfire antenna, the performance of the stepped tapered slots’ antenna shows remarkable improvement, and the size of the antenna reduces effectively. The simulation and measurement results of the proposed endfire antenna show that an impedance bandwidth of 63.5% (75.1–145 GHz), an AR < 3 dB bandwidth of 50% (75.9–125.3 GHz), and a max gain of 8.8 dBic are realized, respectively. Second, to reduce fabrication and assembly requirements, a groove gap waveguide (GWG) feeding network is designed for multibeam array applications. The broadband 2 $\times $ 2 GWG network, interconnections, and transitions are designed and applied in the antenna array. Finally, a multibeam array based on the proposed endfire antenna is designed, fabricated, and measured. An impedance bandwidth up to 37.7% and a wide axial ratio bandwidth of 38.7% with a max LHCP gain of 12.8 dBic are achieved by the proposed 2 $\times $ 2 multibeam antenna array. The proposed multibeam endfire CP antenna array would be an attractive candidate for mmWave wireless applications. [ABSTRACT FROM AUTHOR]

A millimeter-wave (mmW) wideband circularly polarized (CP) antenna based on an air-filled waveguide is proposed. By introducing two symmetrical ridges in the septum antenna, the proposed antenna can obtain a more compact antenna aperture than the septum antenna based on a rectangular waveguide (from 0.99 $\lambda \,\,\times1.25\,\,\lambda $ to 0.66 $\lambda \,\,\times0.91\,\,\lambda $). In addition, the high order modes are suppressed to less than −20 dB from 55 to 70 GHz. Then, the sharp corner in the axial-ratio (AR) and gain plots of the septum antenna based on a waveguide are eliminated. A simulated operating bandwidth of 16.4% for both $\vert \text {S}_{11}\vert < - 10$ dB and AR < 3 dB within half-power beamwidth (HPBW) is achieved from 56 to 66 GHz. To verify the design, the proposed antenna has been fabricated and measured. The differences between simulations and measurements caused by flange are evaluated. The measured operating bandwidth of 20.9% is achieved from 60 to 74 GHz [ABSTRACT FROM AUTHOR]

A novel millimeter-wave (MMW) endfire wideband circularly polarized (CP) antenna with simple structure is reported. By introducing two symmetrical septum blades filled in the widened rectangular waveguide, the proposed antenna can obtain a 40% bandwidth for both axial ratio (AR) < 2.5 dB and $S_{11} < -15$ dB. The CP operating mechanism of the antenna has been explained, using a three-port structure. The parametric studies for all of the antenna parameters are carried out to estimate their influences on antenna performance. The sharp corner in the AR plot is also explained by mode analysis. Its influences on the radiation pattern, gain, and reflection coefficient at this frequency point are evaluated. The proposed antenna has been fabricated and measured. The simulation results are in good agreement with the measurement results. Furthermore, this antenna is an appropriate choice for designing a MMW high-efficiency wideband antenna array. An $8 \times 8$ array with 64 equal amplitude and phase wave ports in HFSS has been designed to evaluate the array performance, which shows that the array can achieve 40% operating bandwidth without considering the bandwidth of feeding network. The simulated aperture efficiency of the array is above 85.34% from 50 to 75 GHz. [ABSTRACT FROM AUTHOR]

This paper presents and characterizes a novel high gain circularly polarized (CP) antenna array for 5G applications. The array element is an antipodal curvedly tapered slot antenna (ACTSA) generating circularly polarized field. The CP ACTSA fed by substrate integrated waveguide (SIW) is convenient to integrate with substrates. By introducing two sheet metals on the two sides of the rectangular Rogers 6002 substrate, an impedance bandwidth of 18.2%, a wide 3-dB axial ratio (AR) bandwidth of 16.9%, and stable gain of 8 ± 0.6 dBic over the operating band are achieved. By employing the proposed CP ACTSA as radiating elements, a 4 × 4 high-gain wideband antenna array is proposed for 5G $E$ -band and $W$ -band millimeter-wave applications. Fabrications are carried out using wire cutting electrical discharge machine and print circuit board process, which have advantages of low cost. The whole feeding network is realized by SIW with low insertion loss at millimeter-wave band. Benefiting from the wide impedance and AR bandwidth of the new antenna element, good impedance matching and AR characteristics can be achieved over the whole working frequency band from 81 to 95 GHz by this antenna array. Gain up to 18.5 ± 1.3 dBic is also obtained. [ABSTRACT FROM AUTHOR]