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Abstract
In this paper, a wideband compact planar balun with impedance-transforming ratio of 2 : 1 is developed for push pull applications. The proposed balun is composed of broadside coupled strip lines and lumped capacitors. In this design, by utilizing broadside coupled strip lines with large enough spacing between strip and ground plane, even mode impedance of the transmission line and bandwidth is increased. Size reduction is effectively obtained by the use of discrete capacitors. As an example, one balun on a double-sided PCB is designed, simulated, fabricated and measured. Measured results show that the return loss is better than 15 dB over the frequency band from 470 MHz to 860 MHz, or around 59% bandwidth. The amplitude and phase imbalance between the two balanced output ports at worth case are 0.7 dB and 6 degree, respectively, over the operating frequency band.