A Quasistatic Antenna Design Approach for Minimum-Q Antennas

The quasistatic antenna-design algorithm uses electrostatic methods to calculate the antenna's shape. The asymptotic conical dipole is a classic quasistatic design. A charged disk is added to the asymptotic conical dipole to model a thick top-loaded monopole. The antenna's shape is an equipotential surface. The disk height and radius control the width and height of the top load. The minimum Q for this design is lower than the ideal thin-disk-loaded monopole. A Computer Simulation Technology model confirmed the predicted Q value of twice Chu's limit. Measurements on a 16-wire, 0.5 m physical antenna agreed with the NEC 4 model. The tradeoff in Q and radiation resistance is illustrated with detailed examples. Several designs have a lower Q than the ideal thin-disk-loaded monopole. This design approach gives a very good design with only two degrees of freedom. The computational time for the algorithm is a small fraction of one NEC 4 modeling run. The algorithm can be extended to design antennas with a cylindrical, elliptical, or conical form factor.