A 60-GHz Passive Broadband Multibeam Antenna System in Fused Silica Technology

In this letter, we present a coplanar-fed, broadband passive multibeam antenna system. The module is composed by a 4 × 4 Butler matrix connected to a linear array of four elements and realized in a via-less two-metal-layer (i.e., top and bottom) fused silica technology. The accurate process resolution (1 μm) allows manufacturing small design features to implement low-loss, broadband (10% relative bandwidth) millimeter-wave building blocks, using conventional microstrip designs. The measured insertion loss of the via-less transition is 0.4 dB at 62 GHz. The Butler matrix exhibits between 59 and 66 GHz maximum simulated phase and amplitude imbalances of ±7° and ±0.8 dB, respectively. The experimentally characterized radiation patterns of the entire system show a half-power beamwidth (HPBW) of 30° at 60 GHz, and the beam-steering angles show a maximum variation of 7° in the 60-66-GHz band.