Phase shifting metasurfaces typically consist of an ordered metallic geometry that is patterned onto a dielectric substrate and incorporate active devices or materials that enable dynamic tuning. Existing methods at mm-wave and submillimeter bands typically suffer from high losses, which are predominantly produced by the inherent limitations of the tuning elements or materials. This report presents a new, ultra-low-loss and phase-tunable, reflection type metasurface design, which outperforms previously reported technologies in terms of phase shifting and loss. The proposed technique utilizes a variable air cavity, formed between a periodic array and a ground plane, which is controlled by means of a piezoelectric actuator. Two metasurface designs are presented and experimentally tested. Firstly, a square patch element metasurface that is capable of achieving a continuous 180° phase shift across a wide bandwidth, between 35 and 65 GHz. Also presented is a double-cross element metasurface that provides full 360° phase control between 57 and 62 GHz. The variable air cavity is controlled by means of a piezoelectric actuator that supports and varies the height of a ground plane, providing highly accurate, millisecond, displacement. Unlike conventional tuning methods, the tuning mechanism, in this case the moving ground plane, introduces no additional sources of loss and enables an average loss performance of 1 dB. Full-wave simulations are presented and experimentally validated with measurements of both metasurface prototypes. The proposed approach is scalable from microwave up to THz frequencies, due to the electro-mechanical and low loss nature of the tuning.

相移超表面通常由有序的金属几何结构组成，该几何结构被图案化到介电基板上，并结合有源器件或能够实现动态调谐的材料。毫米波和亚毫米波段的现有方法通常会遭受高损耗，这主要是由调谐元件或材料的固有限制造成的。本报告介绍了一种新的、超低损耗和相位可调的反射型超表面设计，其在相移和损耗方面优于先前报道的技术。所提出的技术利用在周期性阵列和接地平面之间形成的可变空气腔，该空气腔由压电致动器控制。提出了两种超表面设计并进行了实验测试。首先，一个方形贴片元件超表面，能够在 35 到 65 GHz 之间的宽带宽上实现连续的 180° 相移。还展示了双交叉元件超表面，可在 57 和 62 GHz 之间提供完整的 360° 相位控制。可变气腔由压电致动器控制，该致动器支撑并改变地平面的高度，提供高精度的毫秒级位移。与传统的调谐方法不同，调谐机制（在这种情况下是移动地平面）不会引入额外的损耗源，并且平均损耗性能为 1 dB。提出了全波模拟，并通过对两个超表面原型的测量进行了实验验证。所提出的方法可从微波扩展到 THz 频率，