Ultra-low Power Beamforming Wideband OFDM Signal with Active GRIN Lens at 19 GHz

We present an active GRIN lens with a flat active frequency selective surface (FSS) for ultralow-power beamforming. The active FSS unit cell consists of an I-shaped metallic patch, a varactor diode, and bias lines to control the voltage across the diode. A five-layer FSS unit cell provides the phase range of 360° at 19 GHz. We fabricated the active gradient-index (GRIN) lens with 32×32 FSS unit cells, 5λ0×5λ0 at 19 GHz. The lens provides the ultralow-power beamforming in the ±40° range. Power consumption for single beamforming is approximately 5.2 μW. The 3-dB gain bandwidth of broadside beam is 15.8%. A 0.8-GHz OFDM signal was successfully steered with the lens. Measured average error vector magnitude (EVM) is about 10%.