Akhil,
If you search the literature, you will find attempts to calculate far
field from measured near field values.?? There are several challenges
though:?? the 3-meter and 10-meter regulatory requirements are for
frequencies of 30MHz and higher.?? At 30MHz the free-space wavelength is
around 10 meters, the lambda/(2*PI) near-field boundary is around 1.5
meters.?? This means that for the entire frequency range the regulatory
requirements refer to far-field conditions, but up to 3GHz your measured
values (if we take the average of 2cm and 1cm as 1.5cm) are in the near
field. The impedance of the near field is location dependent and also
depends on the impedance of the source.?? For pure electric and magnetic
sources the E and H fields vary with the second and third power of the
distance.?? So for frequencies below 3GHz you would need to have more
than one measurement points at different distances and measure both E
and H fields.?? The summary: theoretically yes, practically very
challenging...
Regards,
Istvan Novak
Samtec
On 7/10/2019 4:32 AM, Akhil paul wrote:
Hi ,------------------------------------------------------------------
In our lab we have the facility to measure magnatic and electric field of
pcb board at small distances using R&S near field probes . If I know the
maximum magnetic and electric fields strength at 2cm or 1cm from the pcb ,
then can I find field strength at 3meter and 10 meter from the pcb for emc
compliance test. If it's possible please explain the procedures.
-Akhil
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