Millimeter-Wave Array Antennas Using Broadband 3D Folded Strip Elements for B5G/6G Communications

Linearly polarized (LP) circularly polarized (CP) array antennas using broadband 3D folded strip elements which can easily realize diverse polarizations in millimeter-wave (mm-Wave) band are developed. The operating principles, analyses, and corresponding design processes of the proposed LP and CP 3D folded strip elements are provided. Both of these two different polarized elements are excited by slot coupling using a microstrip line laid on an ultrathin (i.e., 0.127 mm) substrate, contributing to the possibility of straightforward integration with mm-Wave front-end circuits. It indicates that the impedance bandwidths (
$\vert S_{11}\vert < -10$
dB) of the LP and CP elements are 51% (27–45.5 GHz) and 54% (30–50 GHz), respectively. The axial ratio bandwidth of the CP element is 51.1%. Both of the LP and CP elements can be easily expended into a corporate-fed array, and design considerations concerning the array performance are also provided. Prototypes of
$2\times $
2 LP,
$4\times $
4 LP, and
$2\times2$
CP array antennas are designed, fab- ricated, and measured. Convincing experimental results validate the correctness of these designs. The exhibited performance metrics make the proposed array antennas good candidates for fifth-generation (5G)-beyond (B5G) and 6G mm-Wave communications.