Near-field probe measurements of microwave scattering from discontinuities in planar surfaces

In microwave scattering, nonradiating fields may contribute to radiating fields by local perturbations such as geometric discontinuities or variations in impedance or electromagnetic properties. Near-field measurements of scattering bodies provide insight into these scattering mechanisms by measuring both radiated and nonradiated fields. In this research, an Hfield probe measured scattering from simple discontinuities in planar bodies at frequencies between 2 and 10 GHz. Illumination of the test-body was furnished by a focused lens system with a Gaussian-like tapered beam that locally illuminated inhomogeneities on the body. Measured data and model calculations are presented for scattered H-fields near canonical discontinuities (e.g. gaps and edges in conducting planes). Calculations of the plane wave spectrum of the measured and modeled data were used to distinguish specular reflected components from surface modes. A focused beam was simulated in a finite-difference time-domain (FDTD) model with a weighted sum of plane waves. FDTD results agreed with the measured near-field data.