Measurements of Cross Polar Effects from Particles using an Open Resonator

The possibility and advantages of being able to measure cross-polar scattering effects from particles which are captive within an open-resonator system are discussed. Experiments using a large X-band open-resonator have identified the existence of a resonant mode, polarised orthogonally to the plane of polarisation of the main fundamental-mode in the resonator, when certain scattering objects are placed in the field. The effect has been observed, when short filaments of wire, short rods of dielectric material or pairs of touching metallic spheres are the scattering objects. The dependency of the magnitude of the orthogonally polarised signal on the orientation of the scatterer with respect to the plane of polarisation of the incident wave is plotted. The problem of relating the results obtained in the resonator to those equivalently obtained for the case of scattering of a progressive wave is discussed. Progress in achieving this by computation is described.