Parallel plate antennas: field distortion caused by test objects

To facilitate field test procedures several regulations recommend the use of parallel plate antennas or related configurations. The electrical field between the two plates is calculated from the applied voltage and the geometrical separation of the two plates. The field distortion caused by test objects is normally neglected for small objects or only roughly taken into account by special correction factors. In reality the test object induces an antenna mismatch and creates new field components because of reflections and surface currents. The surrounding field is not uniform but is a function of the test object´s geometry. The paper presents an approach for the evaluation of these phenomena by calculating mismatch problems and static field distributions in two-dimensional situations. For this purpose the configuration of antenna and test object is transformed into a parallel plate configuration without boundary effects by the method of conformal mapping together with the Schwarz-Christoffel Transformation. The results¿characteristic impedances, v.s.w.r.-ratios, static field distributions, minima and maxima of field strength¿are presented.