Compact Reflection-Type Phase Shifter MMIC for Ka-Band in Aligned Carbon Nanotube Array

This letter presents a novel Ka-band reflection-type phase shifter (RTPS) monolithic microwave-integrated circuit (MMIC) implemented in aligned carbon nanotube (CNT) technology. The design integrates a single-layer, wire-bonded Lange coupler loaded with CNT-based tunable Schottky diodes, offering a compact and efficient solution for monolithic integration. It features a lateral diode structure with a cut-off frequency beyond 200 GHz, fabricated using aligned CNT (A-CNT) arrays characterized by high density and exceptional semiconducting purity on a silicon substrate. The proof-of-concept prototype achieves better than 10 dB return loss across a 12% fractional bandwidth. It further demonstrates a maximum phase shift of 65° at 42 GHz with a compact chip area of only 1 mm².