MILLIMETER-WAVE SPECULAR AND DIFFUSE MULTIPATH COMPONENTS OF TERRAIN

Multipath interference data were obtained at a frequency of 95 GHz ove r pathlengths of 100-250 m by measuring height-gain interference patte rns over various types of terrain, Data were collected over grass, lak e, ice, snow, concrete, asphalt, and gravel surfaces. The transmit ant enna was kept fixed, while the receive antenna translated vertically r esulting in grazing angles between approximately 0.5-2.0 degrees, Full illumination of the Fresnel zones was accomplished by broad-beamwidth horn antennas at both ends, Measured interference patterns indicate t he presence of both specular and diffuse multipath components. A techn ique was developed to separate these components by filtering in the sp atial Fourier-transform domain by appropriate choice of the notch freq uency for the specular component and the bandpass-filter bandwidth for the diffuse components, The notch frequency is chosen according to sy stem 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 i s known.