A dual circularly polarized (CP) magnetoelectric dipole antenna is presented in this article. The dual-CP antenna was devised to form a circular ring shape and fabricated using 3-D printing technology. To overcome the conflict between high (broadside) gain and wide (half-power) beamwidth, a new beamwidth broadening technique was proposed. Twelve metacolumns were placed evenly along the circumference close to the ring-shaped dipole. A design approach is elaborated, where the number and size of meta-columns were decided according to the design curves. Symmetrical beamwidth of 108° in orthogonal planes with a broadside gain of 6 dBic was achieved across a wide effective bandwidth from 3.2 to 5.4 GHz (51%), sufficiently covering the 5G new radio (NR) bands: n77, n78, n79. The antenna owns a compact size of 0.83×0.83×0.18 λ ³ at 4.15 GHz. A planar subarray composed of four dual-CP elements was also investigated and compared with the existing arrays.

A low-profile microstrip antenna with stable radiation pattern in a relatively wide band is presented for 5G operation. Four resonant modes with different frequencies are integrated in a single structure to enhance the bandwidth with stable gain, and well matched by introducing the folded walls. An impedance bandwidth of 58.3% has been achieved from 2.84 to 5.17 GHz with a compact structure of 0.84λ ₀ × 0.68λ ₀ × 0.06λ ₀ , where λ ₀ is the free-space wavelength at the center frequency of 4 GHz. The measurement results show that the proposed antenna is with the merits of average gain of 5 dBi, stable radiation patterns, low cross polarization, and low backlobes, exhibiting potentially use for the applications of 5G wireless communication systems.

A compact wideband circularly polarized (CP) magneto-electric (ME) dipole antenna array is proposed. In order to achieve compact size and wideband characteristics, a novel substrate integrated waveguide (SIW) to coaxial transition (SCT) was designed to connect the lightning-shaped ME-dipole antenna element and a SIW feeding network. Particularly, a SCT-based power divider network together with the sequential-rotation (SR) technique was employed to improve the axial ratio (AR) bandwidth of the 4×4 antenna array. The antenna array prototype was fabricated to verify the design. Measured results show that an impedance bandwidth of 27.7% (23.3-30.8 GHz) and 3-dB gain bandwidth of 25.3% (23.5-30.3 GHz) were achieved. Moreover, a 3-dB AR bandwidth of 27.8% (23.2-30.8 GHz) with a peak gain of 20.2 dBic were also recorded. Therefore, it is a good candidate for the fifth generation (5G) millimeter wave (mm-wave) communications.

A tri-polarized antenna with diverse radiation characteristics is proposed in this paper. This design mainly consists of two pairs of loop radiating dipoles and an omnidirectional monopole antenna element, which are used for the fifth generation (5G) and vehicle to everything (V2X) communications, respectively. By adding eight pairs of inverted L-shaped patches with unequal sizes around the proposed dipoles, wide beamwidths in both E- and H-planes can be obtained across the desired lower and upper frequency bands. Furthermore, by employing eight fork-shaped microstrip stubs to combine the circular monopole antenna element and the L-shaped patches, the flare angle of the conical beam can be increased to 180°, which results in gain enhancement in the azimuth plane. Finally, the proposed loop radiating dipoles are excited by a pair of symmetrical differentially-fed feeding lines. Consequently, high port isolation for the proposed loop radiating dipoles as well as low gain variations for the monopole antenna element can be achieved. Measured results show that the impedance bandwidths of 32.84% (2.8-3.9 GHz) and 18.18% (4.5-5.4 GHz) can be achieved for the 5G communications. Wide half power beamwidths (HPBW) of larger than 103° in E-plane and 91° in H-plane can be achieved across the operating bands. In addition, a bandwidth of 5.5% (5.82-6.15 GHz) with gain of 2.47 ± 0.69 dBi in the azimuth plane can also be obtained for V2X communications.

A dual-wideband dual-polarized antenna using metasurface for the fifth generation (5G) millimeter wave (mm-wave) communications is proposed. It is designed and analyzed based on characteristic mode theory (CMT). The proposed metasurface is mainly composed of a 3×3 square-patch, in which its four corner patches are further sub-divided into a 4×4 sub-patch array, while the size of the other four edge patches is reduced and the center patch is etched with a pair of orthogonal slots. By doing so, the side lobe level can be effectively reduced and the main beam radiation can be enhanced. The metasurface is excited by a pair of orthogonally arranged substrate-integrated-waveguide (SIW) to grounded-coplanar-waveguide (GCPW) dual-polarized feeding networks that help to reduce the insertion loss and expand the frequency bandwidth of the feeding ports. In order to yield higher gain, four proposed metasurfaces are fed by a pair of 1-to-8-way power divider feeding networks including a pair of low-transmission-loss E-plane phase shifter. Measured results show desirable impedance bandwidths of 13.85% (24.2-27.8 GHz) and 14.81% (36.9-42.8 GHz) in the lower and upper frequency bands, respectively, and their corresponding average gains are 13.96 and 15.46 dBi.

In this communication, a dual-polarized filtering magneto-electric dipole (FMED) antenna and arrays are proposed for 5G n258 (24.25–27.5 GHz) operations. The FMED antenna was devised to incorporate filtering mechanisms using a built-in substrate integrated waveguide (SIW)-based filter plus slot-and-notch etching on the dipole element. As such, lower and upper radiation cutoffs and nulls were produced and tuned, independently. To overcome the problem of “high selectivity” of a filtering antenna that has not been correctly quantified and thus has no comparison, a new skirt measure metric named as radiation suppression index is initiated here. Design steps of the FMED element and novel feeding techniques are elaborated, where the SIW-based series-parallel slot-coupled feeders and the slot-coupled differential power divider were conceived for large-size array, to combat with the insertion losses. A prototype of 4 $\times $ 4 FMED array was implemented and tested for experimental verification. A high gain of 16.8 dBi ± 1.4 dBi with a 3 dB gain bandwidth of 24–27.7 GHz and a radiation efficiency of 78% were accomplished.