A Planar, Polarization-Switchable Endfire and ±Broadside Millimeter-Wave Antenna Array Without Lumped Components

A planar antenna array exhibiting polarization-switchable endfire and ±broadside radiation without the employment of lumped components is proposed. The antenna is denoted as symmetrically stacked planar antenna (SSPA), which utilizes the phase difference between the top and bottom patches to enable dual-linear/circular polarized hemispheric radiation. This communication focuses on the dual-linear polarized aspect. One polarization is achieved when a 180° phase difference exists between the first-set of ports, while the perpendicular polarization is accomplished when the second-set of ports are in-phase. A four-element array is constructed to exemplify this concept at 28 GHz, and the main beam is steered across the sphere. A comparison with other designs reported in the literature is conducted to highlight the salient points of the proposed methodology regarding planar, dual-polarized, and lumped-components-free features. To validate the predicted and simulated results, a prototype of the four-element array is fabricated and measured. The measured results show that the proposed array can steer the beam from 0° to 55° in all directions for both linear polarizations.