Presentation Information
[B-1C-19]Feasibility of Non-Far-Field Region Multiplex Beam Transmission Using Butler Matrix and Lens
◎△Taiga Sugimoto1, Jiro Hirokawa1, Takashi Tomura1 (1. Institute of Science Tokyo)
Keywords:
Butler matrix,non-far field region,multi-beam transmission,lens antenna,signal-to-interference ratio
Non-far-field region wireless communication is expected to enable high-capacity spatial multiplexing, but interference between adjacent beams degrades the signal-to-interference ratio (SIR). This paper proposes an antenna system in which a plano-convex lens and a matching layer are placed in front of a Butler matrix, with two such sets arranged face to face, and presents a feasibility study of its transmission characteristics. Since a Butler matrix alone has a high adjacent-beam crossover level of about −4 dB, an anti-phase two-way divider is added to each output port to suppress the crossover level and sidelobes, and the lens then collimates each beam toward the broadside direction. Using a one-dimensional four-beam, eight-aperture array (aperture spacing 0.55λ, aperture width 0.51λ), four beams with phase differences ΔΦ = ±45° and ±135° are formed at 66 GHz. The lens surface is designed to flatten the phase region by region at z = zR, almost canceling the inter-beam phase difference at the center plane. Evaluating an opposing lens system, at a convex-tip distance ls = 6 mm the SIR of all four beams simultaneously exceeds the required 10 dB (12.24 dB for ±45°, 11.46 dB for ±135°), demonstrating the feasibility of multiplex beam transmission in the non-far-field region using a Butler matrix and a lens.