D-Band High-Gain Circular-Polarized Plate Array Antenna

This paper represents a low-profile large-scale circular-polarized (CP) plate array antenna in the D-band. To achieve the high gain, high efficiency, and wideband at the same time, a CP 2 × 2 subarray antenna is proposed at first, consisting of integrated horns, complementary phase shifters, and a dual-polarized power divider (PD). The complementary phase shifter includes a parallel capacitance phase shifter and a parallel inductance phase shifter. Phase shifts generated by inductance and capacitance structures present opposite tendencies versus frequency. Therefore, an appropriate combination of them will make the phase shift almost constant over a wideband, which is important to generate a wideband CP beam. Besides, the capacitance phase shifter can be implemented by inserting irises at waveguide broadsides, while the inductance phase shifter can be achieved by inserting irises at the waveguide narrow side. Such a simple configuration can guarantee the element spacing limitation and the fabrication accuracy. The dual-polarized PD consists of an octagon cavity with rotated symmetrical coupling slots for wideband equal-amplitude and in-phase outputs. In addition, some matching layers and matching ridges in the octagon cavity are introduced to achieve wideband matching. Finally, a wideband array feeding network is used to build a 16 × 16-element left-handed CP array antenna. The S₁₁ below -10 dB bandwidth is about 15.1%, and the co-gain is more than 30 dBi from 130 to 149 GHz. The radiation efficiency is higher than 65% and a 3 dB axial ratio can be satisfied over the whole band.