Design of electrically small antennas and electrically small ground planes for maximizing ground wave transmission

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Lim, Sungkyun

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In this thesis, a top-loaded, inductively-coupled, electrically small antenna is designed for high-frequency (HF) ground-wave transmission. The parameters of the antenna are optimized using a genetic algorithm together with the Numerical Electromagnetics Code. Prototypes for two top-loaded antenna designs are tested, and the measured results match well with simulations. Both antenna designs have an electrical size kr of 0.2, an efficiency greater than 65%, and a transmission performance within 1 dB of that of a commercial whip. In the second part of this thesis, the design of a miniaturized ground plane is investigated. It is first shown that when the size of the ground plane is reduced to less than one tenth of a wavelength, the transmission loss increases rapidly due to impedance mismatch. A spiral ground-plane design is then proposed that reduces the ground-plane size without a rapid increase in transmission loss. The spiral ground plane is tested under a quarter-wave monopole, and the measured results match well with simulation. Outdoor transmission test demonstrates that the transmission loss of a 0.43m-diameter spiral ground plane can achieve nearly the same transmission performance as that of a 1.2m-diameter eight-arm radial ground plane


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