THz Near Field Focusing using Cassegranian Configuration for EM Side-channel Detection

This paper presents near field focusing at THz frequencies using cassegranian antenna configuration used for the electromagnetic side-channel detection. The antenna is designed to produce the focused beam 30cm away from the aperture. The focusing is done in the near field region by moving the sub-reflector from the focal point along the axis. It is observed in the simulations and measurements that the subreflector position has to shift approximately 11 wavelengths along the axis to create the focus at the required location. The 3dB focus width of the antenna is ~4 mm. Finally, simulation results of near field gain are compared with measurements and good agreement is observed.