Near-Field Coupling Analysis of Butterfly Layouts in Paralleled GaN Half-Bridges for Aerospace Applications

High step ratio isolated DC-DC converters are increasingly used to interface low-voltage, high-current buses with high-voltage distribution networks in aerospace platforms. Paralleled GaN devices in butterfly half-bridge layouts enable high power density, but measurements show that the routing geometry introduces gate-power loop coupling that can be excited during fast switching transitions. This coupling produces ringings on the gate voltage and may affect reliable operation. This paper investigates a baseline butterfly layout and a Shielded Split-AC Butterfly (SSAB) layout that redirects the AC interconnect and encloses the gate network within a quiet ground island to reduce magnetic interaction. Small-signal S₂₁ measurements demonstrate suppression of the dominant coupling mode in the SSAB layout and a shift of the primary resonance into a higher frequency band. Electromagnetic field simulations further confirm reduced current crowding and minimal flux linkage within the gate region. A compact parasitic model is used to relate these observations to loop parameters and provides practical layout guidelines for GaN based high-current stages in high step ratio DAB converters.