A wideband microwave balun is designed to adapt unbalanced to balanced transmission line networks. The balun is realized by a planar microstrip line configuration on a double copper c1added teflon-ceramic C0I11posite board. The microstrip line conductor pattern was formed on the board using the chemical etching process. The fabricated balun is measured and evaluated in both the time domain and frequency domain, indicating a 5 GHz bandwidth. The time domain modeling technique is used to characterize the balun's performance. Based on physical analysis of the balun's configuration, the discontinuities through the transmission paths are modeled as distributed and lumped elements, resulting in an equivalent network model for the balun structure. The obtained model successfully simulates the balun's performance. / Master of Science