This paper presents a novel 3-D-printed circularly polarized (CP) open-ended waveguide (OEW) antenna array. It aims to provide a lightweight scheme for OEW array design and concurrently address the high fabrication complexity problem of conventional OEW arrays. To realize these, the proposed design adopts dielectric 3-D printing technology to build the main body of the array and employs electroplating to form the waveguide walls. To attain CP radiation, an in-built antipodal exponential groove polarizer is proposed and applied to a square waveguide. With the perturbation of the grooves, degenerate modes T E 10 and T E 01 can be excited simultaneously, and their differential phase can be 90 degrees, resulting in CP radiation. Moreover, a novel matching cube based on effective medium theory (EMT) is proposed for the antenna to mitigate the reflections at the waveguide aperture and therefore realize good impedance matching. To validate the design idea, prototypes for a single element and a 2 × 2 array were fabricated and measured. Experimental results show that their weights are 15 and 76 grams, and their axial ratio bandwidths (ARBWs) are 16% (5.45-6.4 GHz) and 11.1% (5.52-6.17 GHz), respectively.

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