A Compact Single-Layer High-Gain Omnidirectional-Like Circularly Polarized Array Antenna Based on Complementary Source Radiation

To solve the difficulty of cascading arbitrary antenna elements in a compact single-layer structure for achieving a high-gain omnidirectional-like circularly polarized (OCP) array antenna, a new design methodology based on complementary source radiation is introduced in this letter. By utilizing the inherent quadrature-phase difference of the electric and magnetic fields in a resonant cavity, the parallel magnetic current and electric current with a <inline-formula><tex-math notation="LaTeX">${\text{90}}^\circ$</tex-math></inline-formula> phase difference are realized in the open cavity and two symmetrical arms of the proposed antenna, respectively. The radiation intensity of electric current source is enhanced by reshaping the structure with cutting corners and introducing slots. Thanks to the simple and symmetrical structure of the element, the proposed methodology effectively addresses the cascaded difficulty of existing OCP antennas, making it possible to achieve the required gain of the OCP array antenna by appropriately cascading elements. To verify the design methodology, a seven-element center-fed array antenna is designed and fabricated in a single-layer dielectric substrate. The OCP array antenna achieves a maximum realized gain of 6.5 dBic and its volume is just <inline-formula><tex-math notation="LaTeX">$4.12\lambda _{0} \times 0.58\lambda _{0} \times 0.015\lambda _{0}= 0.035\lambda _{0}^{3}$</tex-math></inline-formula>.