Additive Manufactured Filtering Lens Antennas for Radar Measurements at 240 GHz

In this work, a novel approach for 3D-printed, frequency selective lens antennas is presented. Modern frequency modulated continous wave (FMCW) radar sensors based on monolithic microwave integrated circuits (MMIC) operating beyond 100 GHz often use system concepts with a signal generation at lower frequencies, followed by frequency multipliers. This often leads to an unwanted feed-through signal of the fundamental tone in the output spectrum. In FMCW operation, this fundamental feed-through signal generates false targets in the range spectrum. Additionally, the unwanted radiation may be problematic for legal conformity or electromagnetic interference compliance. To suppress this fundamental feed-through signal, a filter structure is integrated in a lens antenna, filtering the unwanted signal, while the desired output signal is radiated. The developed lens antenna structures were fabricated by additive manufacturing using Selective Laser Sintering (SLS) and Stereolithography (SLA) techniques, allowing easy and cost effective production of complex structures. Both techniques were compared regarding the printing material and its suitability for high frequency lens antenna design. In the end, radar measurements are shown to demonstrate the successful suppression of false targets caused by fundamental feed-through signals.