Compact Multilayer PCB-Based Marchand Baluns with Maximized Fractional Bandwidth

This manuscript is centred around a unique and comprehensive RF design methodology that allows to accurately predict and maximize the fractional bandwidth (FBW) of multilayer-based Marchand baluns (MBs) while achieving a highly-miniaturized footprint based on a commercially available PCB process. Miniaturization and enhanced coupling between its coupled lines are facilitated using spiral-shaped broadside-coupled lines. Two alternative PCB integration schemes using stripline (SL) and embedded microstrip (EMS) transmission lines are developed and compared. Practical integration design aspects affecting phase imbalance (PI), and amplitude imbalance (AI) are discussed in detail and a new comprehensive simulation-and equation-based design method is described to optimise the balun's balanced signal quality. To verify the potential of the proposed design concept, two MBs using coupled SL and EMS transmission lines are experimentally validated at C-band with footprints of 0.0033λg2 and 0.0022λg2 , and 10 dB return loss bandwidths between 4.6-8.2 GHz (i.e., FBW of 56%) and 3.1-6.5 GHz (i.e., FBW of 71%). Across these FBWs, the power loss, PI, and AI were measured between 0.8-1.5 dB and 1-2.2 dB, 2±2° and 6.5±1° , and 0.35±0.35 dB and 0.45±0.45 dB, respectively.