Transient Analysis of the Thin-Wire Equiangular Spiral Antenna

The study of large antenna structures, compared to the duration of the input pulse times the speed of light, allows a better understanding of the pulse propagation and reflection by the antenna structure. Identifying which part of the antenna geometry contributes to radiation makes it possible to identify the relationship between the radiated field impulse response and the acceleration of charges due to the antenna geometry. To this end, this paper analyzes the thin-wire equiangular spiral antenna from a time-domain perspective and shows the role of the centripetal acceleration on its radiated field. An analytical expression for the time-domain radiated field is also presented with good match with the simulation results. This approach leads to a more complete physical understanding of the radiation process and, thus, to a more guided design process of thin-wire antennas in general.