Investigation of microwave scattering by tall buildings

The paper describes measurements of the scattering coefficient of a number of tall buildings made at 9.4 GHz using a bistatic pulse-radar method. A helicopter-borne transmitter was flown near the building under investigation, and the direct and scattered signals were compared at a distant fixed receiver. At distances of a few hundred metres from a building, the scattered field was only a few decibels weaker than that incident on the building when specular conditions (Snell´s laws of reflection) were satisfied. In nonspecular conditions, the scattering coefficient was typically of order ¿30 dB; scattering with vertical polarisation (electric vector perpendicular to the horizontal plane of incidence) being generally a few decibels stronger than with horizontal polarisation, owing to the difference between the corresponding reflection coefficients of the building materials. The geometrical factors determining the level of scattering have been considered theoretically, and it has been shown that in simple cases the measured absolute level, and its dependence on azimuth, elevation and range, can be reasonably well explained in terms of scattering from a number of smooth flat elements and corner reflectors which correspond to visible features of the building.