Investigation of the Double-Y Balun for Feeding Pulsed Antennas
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Investigation of the Double-Y Balun for Feeding Pulsed Antennas Jaikrishna Venkatesan 232 Pages Directed by Dr. Waymond Scott, Jr. In this research, a double-y balun implemented with coplanar waveguide (CPW) and coplanar strip (CPS) was investigated for use with pulsed antennas. The balun was modeled using two commercial electromagnetic simulators: Momentum and HFSS. Using these numerical solvers, design information such as the design of CPW bridges, aspect ratio of the double-y balun, and stub lengths of the CPW and CPS open and short stubs were studied. A dipole, along with the outer conductor of a coaxial line was modeled in NEC. The model was used to study the currents along the arms and feedline of balanced and unbalanced dipoles. Normalized amplitude patterns were generated along the azimuth and elevation planes for balanced and unbalanced dipoles. These patterns were used later for comparison with measured patterns. Experimental work was conducted to measure the performance of a double-y balun designed to feed a resistively loaded V-dipole. The performance of the balun was investigated via VSWR, insertion loss, and antenna pattern measurements. Antenna pattern measurements along the azimuth plane were conducted for a 5 cm dipole fed without a balun, a 5 cm dipole fed with the double-y balun, a 5 cm dipole fed with the sleeve balun, a 12 cm dipole fed without a balun, and a 12 cm dipole fed with the double-y balun. The dipoles fed without a balun were fed directly with a 50 W coaxial line. An optical link, consisting of a laser modulator (LM) unit and a laser receiver (LR) unit, was constructed to measure the patterns along the elevation plane of the above dipoles. Resulting patterns agreed closely with patterns generated with NEC models. In addition, the patterns of a resistively loaded V-dipole were measured along the E-plane using the optical link. The measured patterns for the V-dipole were compared with numerical results obtained from literature. The experimental work conducted in this research illustrates the improvement obtained in the patterns of a dipole and a resistively loaded V-dipole with the use of the double-y balun.