A metasurface (MS) used to convert the linearly polarized (LP) signal from a source antenna into a circularly polarized (CP) signal is proposed and studied. The MS consists of 16 unit cells arranged in a 4 × 4 layout. Each unit cell is a rectangular loop with a diagonal microstrip. By placing close to a source antenna, the MS converts the LP signal generated from the source antenna into a CP signal. Two source antennas (patch and slot antennas) are used for studies. The source antenna together with the MS is here called a MS antenna. A total of four low-profile MS antennas operating at the frequency of about 2.45 GHz are designed using computer simulation. For verification of simulation results, the MS antennas are fabricated and measured. Simulated and measured results show good agreements. Results show that the MS antennas have substantially better performances, in terms of gain, return-loss bandwidth (RLBW), axial-ratio bandwidth (ARBW) and radiation pattern, than the source antennas. Moreover, the ARBW of the MS antennas is mainly determined by the MS.

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.

By coupling a stub-loaded open-loop resonator onto the back of a CPW-fed mirrored-L monopole, a novel triple-band planar antenna has been achieved and is presented. The proposed antenna features a compact structure with reasonable gains. The measured bandwidths for the distinct triple-band are 2.27–2.87 GHz, 3.4–4.15 GHz and 5.11–6.7 GHz. Omnidirectional radiation patterns for the three bands are observed. Simulations are confirmed by the experimental results, which ensure that the proposed antenna is well suited for WiFi and WiMAX applications.

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.