Antennas and reflectors for near-field radiometric remote sensing of temperature in industrial applications

Remote sensing via microwave radiometry has been found to be an extremely useful tool in Earth and space research. In most such applications, sources are in the antenna\´s far field, defined here as the region beyond a distance 2D²/λ, where λ is the free-space wavelength and D is the antenna aperture\´s largest dimension. We have studied the use of microwave radiometry to measure remotely the temperature of materials in industrial heating processes. In many of the proposed applications, the material to be sensed is relatively close to the antenna, but cannot be contacted directly. The antenna\´s far-field radiation pattern does not predict its behavior in near-field remote sensing applications such as these. We present new results showing that a type of overmoded waveguide we call an "infinite-plane simulator" (IPS) improves the coupling between the object whose temperature is to be sensed and the radiometer antenna. When placed in contact with the material, this simulator allows the radiometer to produce temperature data that agree with a simplified theory. When used in a non-contact mode, the simulator-antenna combination is still superior to the antenna alone.