A 100 GHz Switched Beam Patch Antenna Array With 4 × ${\boldsymbol{\times }}$ 4 Butler Matrix Based on Metallic-Nanowire-Filled Membrane

This paper presents a switched beam patch antenna array fed by a 4 × 4 Butler Matrix (BM) working at 100 GHz for the first time, based on a novel metallic-nanowire-filled membrane technology (MnM). Butler matrix (BM) is well-known as a simple passive beam-forming network with low loss to realize switched beam. For this application, the MnM offers a straightforward and cost-effective fabrication process for micro through-substrate vias (TSVs), optimized for crossovers to ensure high performance up to 100 GHz. This includes high return loss, high isolation, low insertion loss, minimal amplitude and phase imbalance, and a compact size. Based on these features, a compact BM is implemented, targeting operation at 100 GHz. The first measurement on the semi-BM demonstrator validates the design and fabrication with return loss > 17 dB and progressive phase steps with < 10% deviations from 95 to 105 GHz. The second measurement on the patch antenna array fed by the BM indicates rather symmetric switched beams at ±12° and ±45° with low side lobe level (SLL) of −14 and −7 dB. The four switched beams at 100 GHz have a decent gain from 3.3 to 5.5 dBi. The dimensions of the full array and the BM are 4.8 $\times$ 5.3 $\times$ 0.05 mm and 3.1 $\times$ 1.6 $\times$ 0.05 mm, respectively. The obtained results demonstrate that the proposed technology can be used for optimized versions of the Butler matrix, employing techniques to reduce side lobes and compensate for power variation.