Miniaturized 3D Coupled-Lines Balun for Millimeter-Wave Applications

This work presents the design and experimental validation of a miniaturized three-dimensional (3D) balun transformer for millimeter-wave (mmW) applications, implemented using coupled transmission lines fabricated with low-cost metallic nanowire membrane (MnM) technology. The proposed balun achieves high area efficiency and is compatible with scalable three-dimensional chip integration. Measurements across the 40 – 70 GHz range show a magnitude imbalance of less than 0.5 dB and an insertion loss of better than 1.2 dB, with the phase imbalance maintained within ± 5 ◦ up to 55 GHz and gradually increasing at higher frequencies. Occupying only 0 . 0 3 8 mm 2 in a non-semiconductor platform, the MnM-based balun avoids the complexity and high cost of SiGe, BiCMOS, InP, and GaAs implementations, offering a practical and scalable alternative for next-generation mmW systems.