Compact Marchand balun circuit for UWB application

This article presents the development of a miniaturized differential coupler for UWB application using the Marchand balun circuit in multilayer technology. The new technique employs double layer substrate where on the bottom layer the two λ/4 short-circuited stubs with balanced outputs are developed and on the top layer the λ/2 open-circuited stub for unbalanced input is etched. These three transmission lines of the Marchand balun circuit are capacitively coupled using overlapping microstrip lines. To demonstrate this technique, a Marchand balun circuit using multilayer technology is designed, simulated, fabricated and measured. The circuit size is about 2.8 mm × 3.7 mm × 0.63 mm excluding the feeding ports. The results from the simulation and measurement show good agreement.