Passive Beam-Steering of High-Gain THz Planar Lens Antenna by Frequency-Orthogonal Spatial Spreading

This paper presents the first demonstration of a high-gain planar THz lens antenna with beam-steering capability by frequency-orthogonal spatial spreading, operating in the 610–685 GHz range. The antenna is based on integrating a Fresnel zone planar lens with a graded-index silicon interposer. The concept enables passive beamforming of four simultaneous beams from a single feeding port, covering a field of view from -30° to -14° for 20 GHz bandwidth with a 4° separation of the beam direction. The beams can be swept continuously over that field of view by mapping the signal to different frequencies. Furthermore, when using four feeds, 16 simultaneous beams can be created, of which two frequency-orthogonal beams are separated by 40 GHz in frequency can be mapped into the same spatial direction. Thus, it is demonstrated that high-gain multibeam beam steering can be achieved without the hardware complexity of conventional phased-array antenna systems requiring a large number of RF chains. An antenna prototype is implemented using silicon micromachining, resulting in a compact 15.8 mm × 15.8 mm device with a thickness of 526μm, which is directly mounted on a standard WM-380 waveguide feed. Measurement results include a realized gain of 32.1 dBi, only a 0.8 dB beam steering loss across the field of view, an effective side-lobe suppression better than -22 dB, and a high radiation efficiency of -1.25 dB. The measurements are in excellent agreement with simulations, and the worst-case deviation of the measured beam direction from the simulated one is only 0.1° out of 16 beams.