This type of Electromagnetic Compatibility (EMC) testing is used for the characterisation of passive RF components and equipment such as amplifiers or frequency converters. More specifically, these are reduced versions of tests: a radiated emissions test called "Sniff" and a radiated immunity test called "Spray". Both tests are performed with antennas composed of a series of coaxial - rectangular waveguide transitions provided with dielectric spacers that ensure a constant distance from the device to be tested.
The final objective is to know the shielding effectiveness of a certain RF component or equipment. Considering the component to be tested as an antenna capable of radiating spurious signals, its shielding will correspond to its maximum gain. Thus, it will be possible to determine whether it is capable of withstanding an aggressive electromagnetic environment, or whether it is the source of interference that can damage other neighbouring equipment when operating.