Millimeter-Wave High-Efficiency Endfire Wide-Angle Scanning Circularly-Polarized Array Antenna Using Dual-Ridged Metallic Waveguide and Decoupling Slots

In this communication, a compact millimeter-wave (mm-wave) endfire circularly-polarized (CP) wide-angle scanning phased array antenna is proposed based on circularly-polarized double-ridged waveguides (CPDRW). To begin with, for the realization of a CP wide-beamwidth element, two antipodal trapezoidal grooves are symmetrically etched on the upper and lower broad walls of the air-filled waveguide radiating aperture to enable stable CP radiation via balanced orthogonal polarization coupling, while suppressing cross-polarization and ensuring good impedance matching. Subsequently, to reduce the size of the air-filled waveguide element while maintaining the symmetry of the CP 3dB axial ratio beamwidth, two ridge structures are respectively loaded on the upper and lower broad walls. This design ingeniously decreases the cross-sectional dimensions of the air-filled waveguide to less than half a wavelength. Moreover, to mitigate strong mutual coupling between adjacent elements caused by small spacing, a U-shaped slot is introduced into the inter-element metal walls, effectively suppressing the mutual coupling that propagates through the air. As a validation, these compact CPDRWs are uniformly arranged with a spacing of 0.45λ₀ at 26.5 GHz and the overall size of array is 3.8λ₀ × 1.4λ₀ × 0.35λ₀, simulated, fabricated, and experimentally tested. The proposed array exhibits an impressive CP endfire beam scanning capability with a wide range of ±50°, while maintaining a radiation efficiency of 80.3%~95.4%—a relatively high level. Leveraging the advantages of compaction, endfire radiation, wide-angle scanning, and CP function, the proposed antenna array holds great promise for applications in mm-wave communication systems devices.