Millimeter-wave specular and diffuse multipath components of terrain

Multipath interference data were obtained at a frequency of 95 GHz over pathlengths of 100-250 m by measuring height-gain interference patterns over various types of terrain. Data were collected over grass, lake, ice, snow, concrete, asphalt, and gravel surfaces. The transmit antenna was kept fixed, while the receive antenna translated vertically resulting in grazing angles between approximately 0.5-2.0°. Full illumination of the Fresnel zones was accomplished by broad-beamwidth horn antennas at both ends. Measured interference patterns indicate the presence of both specular and diffuse multipath components. A technique was developed to separate these components by filtering in the spatial Fourier-transform domain by appropriate choice of the notch frequency for the specular component and the bandpass-filter bandwidth for the diffuse components. The notch frequency is chosen according to system geometry considerations. Using this unique separation technique, specular and diffuse reflection coefficients were deduced for various terrain types. The separation technique developed in this paper can be readily applied to existing height-gain data if the system geometry is known.