A Wideband Millimeter-Wave Rotman Lens Multibeam Array Using Substrate Integrated Coaxial Line (SICL) Technology

This article presents a wideband Rotman lens multibeam array implemented with substrate integrated coaxial lines (SICLs) for millimeter-wave (mmW) applications. Unlike other dispersive transmission lines commonly used with printed circuit boards, SICL is a nondispersive planar coaxial line that supports the propagation of transverse electromagnetic waves, thus enabling broadband designs of mmW Rotman lenses. Two types of wideband, compact transition structures consisting of small strips and blind vias were designed to transfer energy between the input–output SICLs and parallel-plate lens cavity. Wideband tapered slot antennas excited by SICLs, with a compact lateral size and wide beamwidths, were introduced as the radiating elements to realize a wide scanning range over a large bandwidth. For a proof-of-concept demonstration, a multibeam array prototype that includes seven beam ports and ten array ports connected to ten antenna elements was designed and fabricated. Experimental results agree well with simulation results and show that the proposed multibeam array has an overall bandwidth of 57% (25–45 GHz) with nearly frequency-invariant beam steering performance within ±45°. The desirable wideband operation in conjunction with the ease of integration with planar circuits and low-cost fabrication make the proposed multibeam array design a promising solution for various mmW applications.