Wideband planar balun using microstrip to CPW and microstrip to CPS transitions

A wideband planar balun is proposed using microstrip to coplanar waveguide (CPW) and microstrip to coplanar stripline (CPS) transitions. This structure shows broadband characteristics and does not rely on resonant circuits. Moreover, it does not require tight coupling sections and can be easily fabricated on a printed circuit board substrate. Out-of-phase characteristic between two output ports is inherently achieved by field transformations through physical transitions of two microstrip to CPS transitions. The fabricated balun shows return loss, isolation, amplitude imbalance, and phase imbalance better than 13, 10.8, 1.1 dB, and 8 , respectively, with an 83.2 bandwidth from 16.5 to 40 GHz.