Wideband Millimeter-Wave Balun-Diplexer Based on a Novel Coupled Marchand Architecture for Compact Footprint and Phased-Array Integration

Journal article, 2025

This letter presents the first reported wideband balun-diplexer for mm-wave applications, designed for shared-aperture full-duplex array systems. By integrating balun and diplexer functionalities in a single component, we enable per-element self-interference suppression, while also facilitating the interface between the balanced feed of the antenna and the unbalanced ports found in many beamformer chips. A novel coupled Marchand topology enables a compact footprint compatible with the strict lattice constraints of grating-lobe-free phased arrays, and facilitates integration with the multilayer stackups commonly used in phased-array systems. The component targets K/Ka-band SatCom applications, with two 3.5-GHz-wide bands centered at 19 and 29 GHz, respectively. Fabricated on a Megtron 6 substrate, the prototype achieves a minimum TX–RX isolation of 20 dB, insertion losses of 1.5 and 2.3 dB in the lower/higher bands, respectively, and a common-mode rejection ratio exceeding 19 dB in both bands. The results confirm the feasibility of the proposed concept and demonstrate the first realization of a compact, mm-wave balun-diplexer for high-frequency phased-array integration.