Reconfigurable Orbital Angular Momentum Mode Generation at 225 GHz Using Cascaded Reflectionless Miniaturized-Element Frequency Selective Surface Phase Plates

This paper presents a device capable of generating different or hybrid orbital angular momentum (OAM) modes at 225 GHz using a mechanically tunable configuration. The device is composed of two 10 cm-diameter reflectionless plates, each 0.6 mm thick, designed to work together such that their combined phase response produces specific OAM modes, once properly aligned. These plates are patterned with metallic traces on thin glass substrates to form a miniaturized-element frequency selective surface (MEFSS) structure. These traces are microfabricated with high precision to achieve accurate transmission phase modulation across the wafer. The mechanism enabling mode flexibility relies on discretizing the plates into finite number of angular sectors, each with a unique phase response. When the plates are properly aligned, the combined phase from corresponding sectors can generate a desired OAM mode. By rotating one plate relative to the other, new alignments between sectors produce different combined phase profiles, allowing for the generation of a different mode. The reflectionless nature of the plates ensures that the overall performance is largely insensitive to the distance between the two plates. Transmission phase measurements of individual and combined plates are validated via near-field measurement and the resulting phase profiles confirmed the generation of distinct OAM modes in agreement with simulation predictions. This device demonstrates an innovative approach to OAM mode generation, with potential applications in near-field communication (NFC) and high-resolution radar imaging systems.