Dielectric travelling wave antennas incorporating cylindrical inserts with tapered cavities

Dielectric antenna solutions for industrial radar level measurements are presented to provide monostatic radar operation from 8.5 to 10.5 GHz. Size limited directional antennas having low side lobe levels and marginal ringing properties are needed. Therefore, circular waveguide-fed travelling wave antennas for endfire radiation, incorporating cylindrical dielectric inserts solely made of PTFE (Teflon), are evaluated. Tapered cavities inside the inserts lead to a smoothly raising field expansion far beyond the maximal geometrical antenna diameter. This yields directivity improvements in comparison to a solely radiating conical horn aperture of the same size. A significant length reduction compared to numerically optimized common dielectric rod antennas is achieved as well. Finally, the obtained accuracy gain assuring high-precision radar distance measurements even in the presence of a parasitic reflector scenario is clarified.