Design of Millimeter Wave Mixer Based on Carbon Nanotube Schottky Diode

This paper presents a millimeter wave mixer using aligned carbon nanotubes (A-CNTs) Schottky diodes for 5G wireless systems. By leveraging the unique properties of A-CNTs, including ultrahigh carrier mobility, near-ballistic transport, and extremely low intrinsic capacitance, a compact Schottky diode is fabricated with a validated equivalent circuit model that accurately represents its nonlinear DC behavior (from −1.5 V to 1.5 V) and RF characteristics up to 67 GHz. The down-conversion mixer incorporates input and output matching networks, designed on a standard RT/Duroid 5880 substrate along with microstrip lines, to achieve optimized impedance matching and signal isolation. Compared to standalone diode-based mixers without matching networks, the proposed mixer can demonstrate a significant reduction in conversion loss (exceeding 15 dB), improved return loss (greater than 30 dB), and enhanced bandwidth performance. This work represents the first implementation of an aligned carbon nanotube-based Schottky diode mixer on a PCB-compatible platform, establishing a scalable framework for high-frequency applications.