The calculation and measurement of the near fields of a surface waveguide

A surface wave structure, consisting of a grounded dielectric slab placed between two parallel conducting plates and perpendicular to them is excited by a slot source. The fields are calculated from a careful approximation to the field integrals. This approximation, using the method of steepest descents, includes the correct treatment of the contributions from poles which lie near to the saddle point. The analysis is verified through comparison of the computed results with experimental data. The measurements are made using a highly accurate field probing technique in which the back-scattered signal from a dipole scatterer is measured at the input to the structure. The agreement between the computed and measured results is extremely good even as close to the source as a half wavelength.