Reconfigurable Binary-Amplitude Fresnel Zone Plate for Millimeter-Wave Beamforming

This article presents a reconfigurable Fresnel zone plate (FZP) operating at 30 GHz with a low-cost printed circuit board (PCB) process. In general, limited fabrication tolerance greatly limits the optimal design of reconfigurable unit cells at millimeter-wave frequencies. In this work, the freedom of the unit-cell design is improved using a fixed I-shaped element as an impedance matching layer. In addition, N +M control lines like those of the conventional display grid are employed to control N\times M cells in the E- or H-plane. The transmittance of the unit cell was measured to be-3.5 and-24.5 dB in the transparent mode and opaque mode, respectively, at 30 GHz. A binary-amplitude FZP prototype with 32\times32 elements exhibited ±40° beamforming on both the E- and H-planes with a maximum gain at the broadside of 9 dBi. The measured power dissipation was approximately 0.31~\mu \text{W} per single scan at 30 GHz, which is less than 1/100.000 that of the conventional phased array system. Finally, the beamforming of various 5G signals was experimentally demonstrated without signal degradation using the FZP prototype.