Convergence of the Quasi-static Antenna Design Algorithm
SPACE AND NAVAL WARFARE SYSTEMS CENTER PACIFIC SAN DIEGO CA
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The quasi-static antenna-design algorithm uses multipole basis function to model the general thick top load. A sequence of solutions converge in shape and Q. The absolute minimum Q-factor, 1.825, is obtained for a thick disk top load enclosed by a sphere. This is significantly smaller than the thin disk top load Q-factor 2.349 and previously derived thick-disk Q-factor 2.078. An analytic potential is derived for each multipole basis function. The capacitance and effective height is calculated from the potentials on the enclosing sphere. The impedance is computed with Computer Simulation Technology CST Microwave Studio. The impedance data is numerically fit to a dipole eigenmode equivalent circuit. The radiation resistance does not fit the expected omega2 frequency dependence effective height. The error is an omega4 term that is explained by a capacitor approximated for the octupole eigenmode equivalent circuit. The quasistatic antenna design algorithm predicts the DC capacitance and the dipole eigenmode effective height. The octupole eigenmode increases the radiation resistance. The Q-factor, 1.77, is lower than expected. These results are compared to the spherical cap top load. The existence of an omega4 limits the accuracy of the theoretical limits in the Q values for antennas.
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