Development of a defected ground structure wide bandwidth balun on multilayer organic substrate

We present the design and development of a compact wide bandwidth balun on a multilayer organic substrate. A defected ground plane is designed into a multi-layered Marchand balun to achieve wide bandwidth. Our experimental results demonstrate that the balun achieves an average measured insertion loss of 0.5 dB from 1.9 GHz to 18 GHz and ~1dB from 18 GHz to 20 GHz and a return loss better than 10 dB from 1.9 GHz to 21.5GHz. The measured amplitude imbalance is less than ±1.4 dB from 1 GHz to 21.5 GHz. The measured phase imbalance is less than ±5° from 1 GHz to 19 GHz. To the best of our knowledge, this planar balun has the largest bandwidth ratio reported to date.