Field Measurements within a Large Resonant Cavity Based on the Perturbation Theory

Due to the sensitivity of the field distribution within a resonant cavity to the presence of an object, conventional measurement techniques employing a probe suffer from a limited accuracy. Therefore we propose a new measurement technique of the electric field distribution that avoids the use of a probe. Based on the perturbation theory, it consists of a measure of the cavity resonant frequency variation while displacing a small perturbing object within the cavity. The choice of the perturbing object shape, dimension and material is discussed with the help of simulation and measurement results in a canonical case. The case of reverberation chamber equipped with a mode stirrer is also considered, as well as the insertion of a metallic box within the cavity. Our measurement setup is very low-cost, simple to set up and to use, and adapted to any cavity geometry.