Uncertainties in sVSWR and a proposal for improvement using vector response measurements

Site Voltage Standing Wave Ratio (sVSWR) as specified in CISPR 16-1-4 has been adopted broadly for validating test sites above 1 GHz. To measure the standing wave at a location, responses between two antennas are measured with varying separation distances. In a sVSWR measurement, the receiving antenna remains stationary, while the transmitting antenna is moved to six sample positions along a 40 cm transmission path. While it was maintained that six positions were adequate to sample a standing wave [1], another study [2] pointed out that the standing wave is under-sampled, and the site evaluation can be overly optimistic. We further investigate the adequacy of the number of samples, as well as the suitability of the 40 cm travel length. In addition, sVSWR measurements are only required at a frequency interval of 50 MHz. It is shown in this paper that frequency under sampling also takes place. This study investigates the effectiveness of the sVSWR method as defined in CISPR 16-1-4 using geometrical optics simulations and measurements. An alternative method which evaluates sVSWR using vector response measurements is proposed. It overcomes the difficulties with the CISPR sVSWR approach.