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Abstract Balun continues to playa critical role in RF and microwave systems that employ link between symmetrical circuits and asymmetrical circuits. Several balun configuration have been proposed to achieve the appropriate applications requirements. There are tradeoff between the balun size, bandwidth, impedance transformations and fabrication techniques. In this thesis, two previously proposed coupled line baluns are studied namely the five sections coupled microstrip line balun and three sections coupled line balun where suspended coupled line are used for high even mode impedance. They are simulated, optimized, fabricated and measured. The optimized baluns are compared with previous results. Microstrip line and coupled line with defected ground structures are also studied. The structures are simulated with commercial EM simulator. The effect of varying the defected ground structure parameters, as well as the coupled line parameters, on the coupled line characteristics are investigated. A multi-section coupled line balun with defected ground structure is proposed. The proposed balun is examined. The balun is optimized, fabricated and measured. The obtained bandwidth is 112% Fo, the center frequency of operation, with 0.5 dB amplitude balance and 180o± 40 phase difference. |