Characterisation of an optoelectronically pulsed equiangular spiral antenna

Two-arm equiangular spiral antennas were integrated with ultrafast photoconductive switches and fabricated on silicon on sapphire substrates. Their transient radiation properties were investigated in the time domain using photoconductive excitation. The equiangular spiral antenna is found to be highly efficient, and its transient response exhibits a frequency sweep that is directly related to the antenna structure. In the transient mode of excitation, the antenna remains circularly polarised, as expected from earlier CW measurements. Finally, the antenna pattern for radiation through the substrate is significantly broadened due to the high dielectric constant of sapphire.