On the dispersive properties of the conical spiral antenna and its use for pulsed radiation

Conical spiral antennas can have an input impedance and gain that are nearly frequency independent over a wide bandwidth. However, these antennas normally have dispersive properties that produce significant distortion when they are used to radiate a pulse. In this paper, we examine this dispersion in detail and the possibility of compensating for the dispersion so that the antenna can be used for pulse radiation. First, a simple, qualitative model for this antenna is described. This model provides physical insight into the causes for the dispersion. Next, the antenna is examined using an accurate, full electromagnetic analysis done with the finite-difference time-domain method. Results from this analysis support the conclusions reached with the simple model and provide additional insight into the dispersion. Finally, an approach for compensating for the dispersion in the antenna is described, and the interesting features of the pulse radiated from this antenna, after compensation, are discussed.