Note on EMI Measurement at Open Field Test Site (4) - Adjustment Range of Receiving Antenna Height

C.I.S.P.R. Publication 22 defines the search range of the receiving antenna height in EMI measurement as 1 to 4 m at distances of 3 m, 10 m and 30 m. With this rule, the maximum point cannot be obtained at a measurement distance of 30 m when the directly transmitted free-space wave and wave reflected from the ground plane are in phase. By modifying the calculation previously reported)), we have made a simulation closer to actual EUT measurement. If the measurement distance is 30 m, the receiving antenna height must be changed to 8 m to obtain the maximum point for horizontally-polarized wave measurements. Practically, a height of at least 6 m is considered necessary. The present FCC rule is therefore reasonable.