Time-domain analysis of high-Q antennas

Summary form only given. The transient response of antennas becomes significant when antennas are used in a time-varying fashion. Radiation properties of the antennas are usually defined, calculated, and measured in the frequency domain and/or the steady-state time-harmonic regime. Frequency-domain analysis characterizes the antenna irrespective of the physical time-dependent aspects and neglects the transient properties of the antenna. When it is required to switch between different narrowband radiation mechanisms or different sources in a time-varying radiation configuration, it is important to have a comprehensive knowledge of the transient behavior of the antenna. In a high-Q antenna, an extensive amount of energy must be stored in the near-field before effective far-field radiation begins. The higher Q factor results in a longer time duration for the antenna to reach the maximum radiation efficiency. In a switched-antenna application, this transient effect dominates the performance of the antenna if the switching period is not long enough to let the near field build up the entire stored energy.