The absolute determination of extinction cross-sections by the use of an open resonator

Abstract

A new experimental technique for determining the extinction cross-section of an obstacle at microwave frequencies is described. This method does not involve the measurement of fields but requires only the determination of the Q -factor of an open resonator, which can be done very accurately. By measuring the Q -factor of the resonator with no obstacle present, and then with the obstacle in two different positions a quarter wavelength apart along the axis of the resonator, the extinction cross-section can be deduced. The methodis, however, restricted to a class of obstacles possessing reflexion symmetry in a plane perpendicular to the direction of propagation of the incident wave. Experimental results with brass spheres for which the absorption is negligible (and therefore the extinction cross-section is nearly equal to the total scattering cross-section), give excellent agreement with Mie’s theory. Results are also given for steel spheres.