A Dual-Band Butler Matrix-Based Millimeter-Wave Dual-Band Multibeam Antenna Array Using a Simple Dual-Mode Transmission Line Scheme

This article reports a millimeter-wave (mmW) dual-band multibeam antenna array (MAA) based on a dual-bandButler matrix (BM) utilizing a novel dual-mode transmissionline (DMTL) structure. This kind of DMTL scheme enables therealization of distinct operating modes at different frequencybands, facilitating the design of a dual-band device through aninitial determination of the frequency ratio (FR) followed by topo-logical and structural adjustments. Compared to conventionaldual-band design techniques, this scheme significantly simplifiesthe design process while enhancing the efficiency. Based on thisscheme and the proposed DMTL structure, a dual-band BMis designed and implemented with several dual-band couplers,crossovers, and shifters as a proof of concept. The structureincorporates nested sets of BMs operating at two distinct bands,providing antenna excitations with a uniform amplitude and pro-gressive phase. Moreover, four wideband dual-polarized antennasare designed to constitute an MAA to verify its dual-band perfor-mance. A prototype operating at 24 and 30 GHz with FR=1.25 isdesigned, fabricated, and evaluated. The measured results showthat excellent reflection coefficients (-19.2 dB) and port isolations(15.1 dB) are achieved, ensuring a stable dual-band multibeamperformance. Additionally, four beam angles of [14 degrees,-45 degrees,46 degrees,-12 degrees]/[12 degrees,-35 degrees, 35 degrees,-11 degrees] and cross-polarization discrim-ination (XPD) of 12.8 dB are realized across the required bands.