An analysis of the CTHA´s resonance currents and the resulting radiation shapes

The contrawound toroidal helical antenna (CTHA), a novel low-profile antenna, is a bifilar antenna with four terminal connections. The two filaments of the antenna can be thought of as a two-wire transmission line whose resonances are determined by the boundary conditions present at the ends of the line. The CTHA is then approximated by a circular array of vertical loops for certain resonance modes. This structural approximation is used in an analytical approach to estimate the general shape of the radiation pattern of the CTHA for these cases. The analytical results are compared with simulation. Relatively good agreement was found, validating the structural approximation for rough pattern estimations.