Design of a Compact Broadband Butler Matrix and Its Application in Organic Beam-Former at the 5 GHz Band

Unlicensed spectrum at 5 GHz, from 5.15 GHz to 5.85 GHz, has been proposed by multiple countries as the U-NII (Unlicensed National Information Infrastructure) radio band to be used by IEEE-802.11a. This frequency band of interest of 5 GHz can also be potentially applicable to 5G (the Fifth Generation, a commercial system operating on licensed bands) wireless wide area network (WAN) systems. The 5 GHz band is relatively clean, as compared to the overly crowded 2.45 GHz band. Our space-efficient beamforming design is based on this band. The bandwidth of the patch antennas used in the beam-former was designed to be 0.7 GHz; at the center frequency of 5.5 GHz, it is 13% of the center frequency. Any designed system that satisfies this percentage can be considered as a broadband system. In this paper, we first discuss a preliminary Proof of Concept (two double-layer organic boards) design, then show the preliminary results; and lastly discuss the design improvement (Section IV).