Low-Profile Wideband Circularly Polarized Complementary Antenna and Arrays for Millimeter-Wave Communications

Low-profile millimeter-wave (mm-Wave) arrays using wideband complementary element combining circularly polarized (CP) electric and magnetic sources are proposed in this article. A pair of centrosymmetric printed $ {\Gamma }$ -shaped strips serve as a CP electric source, and a modified narrow slot with two etched centrosymmetric stubs can be treated as a CP magnetic source. The combination of them can provide a wide 3 dB axial ratio (AR) bandwidth. Operating mechanism of the proposed CP radiating element is investigated and provided. Two differently constructed CP arrays, i.e., a sequentially rotated $4\times4$ CP array and a full-corporate fed $8\times8$ CP array, are then designed based on the proposed CP radiating element, to confirm the expandability of the proposed CP radiating element. Prototypes of these two arrays were fabricated and measured. According to the measured data, the sequentially rotated fed $4\times4$ CP array exhibits an impedance bandwidth ( $\vert S_{11}\vert < -10$ dB) better than 57.1% (i.e., 25–45 GHz), a 3 dB AR bandwidth better than 31.4% (i.e., 29–40 GHz), and a maximum gain of 16.4 dBic, while the corresponding results for the full-corporate fed $8\times8$ CP array are 25.8% (i.e., 29–37.5 GHz), 19.1% (i.e., 29.8–36 GHz), and 24.3 dBic. These competitive performances together with merits, such as compact size, low profile, low cost, and direct integration ability, make these two arrays promising candidates for mm-Wave communications.