On the resonant frequency of the normal mode helical antenna excited by a loop

The resonant performance of the electrically small helical antenna excited by a loop is investigated by the moment method, using second order B-spline functions as basis functions. Although the antennas studied are electrically very small, the program provides convergent results which agree well with those of the experiment. It is shown that the resonant frequency of the antenna is closely related to the helix parameters. When the wire length is held constant, the resonant frequency increases with the pitch and decreases when the radius of the helix is increased. With a fixed helix diameter, a critical turn spacing exists which determines whether the resonant length is greater or less than one half wavelength. By adjusting the turn spacing of the helix, a specific resonant frequency can be obtained