메타물질 기반 능동 빔포밍 렌즈의 설계

Abstract

We derive some equations to effectively simulate our lens based on a principle of beamforming lens. From this simulation, the design requirement for implementing beamforming lens is to have a full 360ᵒ phase range with variable capacitance while keeping low insertion loss. So, we chose a I-shape structure with high refractive index and actively varied transmission phase by adding a variable capacitor in the middle of the I-shape. Based on an equivalent circuit of modified unit cell, we studied design paramters to have a large phase range at 30 GHz by using a FEM solver. To control the active components of each unit cell, bias line became a grid type, so we need to analyze the unit cell with bias lines. Bias lines are modeled as a parallel inductor. This parallel inductor acted as an impedance matching circuit between air and I-shape at 30 GHz. We achieved [-30ᵒ, 30ᵒ] phase range with low insertion loss in single-layer I-shape unit cell and analytically verified the transmission phase limit of single-layer FSS. We have designed 5-layer unit cell with the full 360ᵒ phase range by applying an efficient stacking method. Using this unit cell, we desined an active beamforming lens in simulation. This lens produced a pencil beam that was focused and bended at desired. The gain enhancement at 30 GHz is 4 dB with 16.6% 3-dB bandwidth. We will experimentally verified this lens that can be a solution to build cost-effective 5G base stations that are increasingly needed to provide wide service area.