All-metal Broadband Circularly Polarized Feed Antenna Applied to Millimeter Wave Imaging System

In order to eliminate the tail shadow caused by unstable structure like substrate integrated circularly polarized antenna, an antipodal exponential-logarithmic slot antenna (ALETSA) is improved to achieve an ultra-wideband circular polarization, low side lobe level, low loss and wide beam at W band and F band. The improved ALETSA is directly fed by a standard rectangular waveguide and loaded with rectangular slots. The relative working bandwidth reaches more than 77.7%. The optimized AELTSA realizes that return loss is below -17 dB, side lobe lower than -18 dB and the axial ratio lower than 3 dB from 70 to 140 GHz.