A planar ultra wide band single layer microstrip BALUN operating from 200MHz to 10GHz

In this paper a new single layer BALUN is presented that covers the frequency range of 200MHz to 10GHz. The structure is composed of a two stage Wilkinson power divider followed by a wideband current flipping structure. Full wave simulations as well as measurements show that an amplitude imbalance of below 0.2dB and a phase imbalance of less than 5 degrees is achieved by this BALUN from 1.5GHz to 10GHz. Maximum phase and amplitude imbalance are 12degrees and 2dB respectively. The structure is very low loss with maximum insertion loss of 2dB and is matched at all the three ports with the maximum reflection coefficients of less than -10 dB in most of the bandwidth. The coupling between the two equally powered output ports is less than -10dB and the total length of the structure including the transitions to the connectors is 6.5cm.