Resonance frequency prediction for the CTHA

The contrawound toroidal helical antenna (CTHA) consists of at least two helices wrapped about a toroidal (donut shaped) core with opposite chirality (handedness) and fed from opposite directions. The CTHA is circularly polarized and nearly isotropic. This paper summarizes the work to date for predicting resonant frequencies of the CTHA. The Numerical Electromagnetics Code (NEC2) is used to generate trend plots of basic parameters and predicted resonant frequencies. Parameters considered include the major diameter of the torus, the minor diameter of the torus, the wire thickness, and the number of helical windings about the torus. A brief dimensional analysis is applied to the trends observed from the computer models to get the first estimate of a predictive resonant frequency model and to reduce the number of studied variables. Experimental data is graphed by various parametric groupings to help determine the underlying relationships. The graphs themselves represent the latest design tool for the CTHA.