Abstract-In this paper, an ultra high frequency (UHF) low-profile antenna is proposed; it is based on the discone antenna but with addition of a back cavity, a short-circuiting structure and a two-plate top structure in order to achieve both low-profile and wideband. It is simulated and prototyped. The test results show that the antenna has an omni-directional radiation pattern in the horizontal plane, is of low-profile, has a height of less than 0.1λ max , and is wideband with an impedance bandwidth of 65% from 430 MHz to 845 MHz for VSWR < 2.5 and an impedance bandwidth of 43% from 440 MHz to 680 MHz for VSWR < 2.0. The proposed antenna can be easily flushmounted on a planar surface and therefore has great potential for uses on aircrafts and high-speed trains due to its conformal capability.

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A genetic and simulated annealing combined algorithm is presented and applied to optimize broadband matching networks for antennas. As a result, advantages of both the genetic algorithm (GA) and simulated annealing (SA) are taken. Effectiveness and efficiency of the presented combined algorithm are demonstrated by optimization of a wideband matching network for a VHF/UHF discone-based antenna. The optimized parameters provide significant improvements of VSWR and transducer power gain for the antenna.

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An optimal design approach which combines the real frequency method and the direct numerical optimization is used to design a broadband matching network for an electrically small antenna. According to the characteristic of electrically small antenna, a network topology which improves the electrically small antenna's efficiency observably is designed with two methods respectively, and the design result is computed and validated with simulation software. Finally, the two methods are compared in the paper. Results show that the VSWR of the antenna is below 2.5 and its efficiency is above 30% in the pass band by optimal design, that is, the performance of the antenna is improved by a wide margin.