Inkjet-printed capacitively loaded Marchand baluns with enhanced fractional bandwidths

A comprehensive design methodology for the realization of ultra-wideband and highly miniaturized capacitively loaded Marchand baluns (MBs), suitable for integration into balanced antenna systems is presented. A design technique to maximize the fractional bandwidth (FBW) for a given manufacturing process is demonstrated for the first time. Furthermore, a novel MB integration scheme using broadside-coupled lines and 3D vertically integrated capacitors in a two-material inkjet printing process is uniquely proposed. The concept has been experimentally validated within the S and C bands. It exhibits a footprint of 0.128 × 0.098 λ_g², centre frequency of 4.4 GHz, and FBW of 121%. Its power loss, phase imbalance and amplitude imbalance were measured between 0.8 and 2.2 dB, 3 ± 2°, and 0.4 ± 0.4 dB, respectively.