In this paper, an end-fire antenna for 28 GHz broadband communications is proposed with its multiple-input-multiple-output (MIMO) configuration for pattern diversity applications in 5G communication systems and the Internet of Things (IoT). The antenna comprises a simple geometrical structure inspired by a conventional planar helical antenna without utilizing any vias. The presented antenna is printed on both sides of a very thin high-frequency substrate (Rogers RO4003, εr = 3.38) with a thickness of 0.203 mm. Moreover, its MIMO configuration is characterized by reasonable gain, high isolation, good envelope correlation coefficient, broad bandwidth, and high diversity gain. To verify the performance of the proposed antenna, it was fabricated and verified by experimental measurements. Notably, the antenna offers a wide −10 dB measured impedance ranging from 26.25 GHz to 30.14 GHz, covering the frequency band allocated for 5G communication systems with a measured peak gain of 5.83 dB. Furthermore, a performance comparison with the state-of-the-art mm-wave end-fire antennas in terms of operational bandwidth, electrical size, and various MIMO performance parameters shows the worth of the proposed work.

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This paper presents the design and characterization of a via free planar single turn helix for 28 GHz broadband applications. The proposed antenna is designed using ROGERS RO4003 material, having a simple structure and end-fire radiation pattern. The antenna comprises of a compact dimension of 1.36 λ 0 × 0.9 λ 0 with a thickness of 0.0189 λ 0 (where λ 0 is the free-space wavelength at the central frequency of 28 GHz). Parametric study has been carried out to investigate the impact of key design parameters and to achieve an optimum design. Results show a good agreement between the simulated and measured results. A single turn helical inspired antenna covers −10 dB impedance bandwidth of 26.25-30.14 GHz having a peak gain of 5.83 dB and radiation efficiency up to 85%. Moreover, linear array configurations with 2 and 4 elements have been analyzed for applications with higher gain and space constraints. Presented array configurations are suitable for applications having space constraints in one dimension. Results show that peak gain up to 8.2 dB and 11.1 dB can be achieved with 2 and 4 elements, respectively. Due to its simple planar and via free structure, this antenna is suitable for 5G communications and for sensing, imaging, IoT and tracking applications at 28 GHz band spectrum.

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A simple and compact antenna with a switchable beam for millimeter-wave communication is proposed in this paper. The antenna has a planar structure, and the design evolution is discussed. The beam switching functionality was achieved by incorporating two PIN diodes in the ground plane of the antenna. By switching ON either of the PIN diodes, the inverted L-shaped stub becomes connected to the ground plane and behaves as a cavity, which causes the dispersion of the radiation pattern. Therefore, a wide-angle (±18∘) beam-switching property can be achieved using a simple and low-cost technique, without the necessity to implement additional conventional circuits. The proposed antenna is characterized by a good performance in terms of return loss, bandwidth, measured gain up to 7.95 dB, and radiation efficiency up to 84%, making it a proper candidate for IoT technology and millimeter-wave 5G devices.

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A simple, nearfield transformation meta-structure is proposed to increase the directivity of resonant cavity antennas (RCA). The meta-structure is comprised of 14 × 14 meta-atoms or so called “unit-cells”, adding localized phase delays in the aperture of the RCA and thus increasing its broadside directivity. A prototype of the meta-structure is additively manufactured using the stereolithograpy process and has a profile of 0.56λ. With the meta-structure integrated with the RCA, it demonstrates a measured broadside directivity of 20.15 dBi without affecting its half-power directivity bandwidth. Benefiting from additive manufacturing, the proposed approach is a simple, light-weight, low-cost, and planar approach that can be tailored to achieve medium-to-high gains with RCAs.