The off-axis, time-domain response of conical log spiral antennas

The time-domain response of the wire conical log spiral antenna is examined for directions off of the principal axis using numerical simulation. The impetus for this is that the wire conical log spiral antenna, which incorporates an infinite balun, is a single-port, circularly-polarized antenna which does not contain any mechanisms that intrinsically limit the frequency response, e.g. transformer-based balancing networks or 90-degree hybrid networks. It is shown that the time-domain pulse distortion is similar to that of other frequency-independent antennas and that antenna-to-antenna transmission is not rotation invariant in the time domain, but rather undergoes a fractional Hilbert transform with rotation angle. The fractional Hilbert transform due to rotation about the line of sight is shown to hold off the bore sight axis.