In this paper, a 3-D printed all-metal reflectarray is presented for millimeter-wave applications. The array has sub-wavelength element spacing, so that the elements are non-resonant. A two-stage notch is etched at the top of the element, which provides multiple degrees of freedom for phase tuning. The phase variation range is more than 360 • by changing the height and width of the first stage of the notch. Thanks to the non-resonant property and the two-stage notching, stable phase shift can be maintained in wide frequency range. A reflectarray with 20×20 elements is fabricated by using 3-D printing technique, which has the merits of flexible construction, light weight and low cost. The simulated and measured results on radiation patterns and realized gain are highly consistent. The measured 1-dB gain bandwidth achieves 17.6%, ranging from 31 GHz to 37 GHz. In the whole 1-dB gain bandwidth, the measured aperture efficiency is higher than 47.7%, with a peak efficiency of 53.6% at 31 GHz. The proposed reflectarray has no substrate loss and can provide high aperture efficiency in wide bandwidth.INDEX TERMS Metal reflectarray, wideband, high aperture efficiency, 3-D printing.

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