Electromagnetic Compatibility

Current Loop Area & Emission

The current loop area on a PCB which will cause problems with regard to legislative emission  requirements.

The E field strength limit at 3 m distance in Standards is 40 dBuVm-1 or 100 uVm-1.

Considering OATS measurement with +6 dB in-phase reflection from ground plane, the max loop area  that will not exceed specified level can be determined from:

            A    =  380 E r
                          f2 I                         cm2


    E is radiation limit in microvolts per metre
    r is distance to measurement in metres
    f is frequency in MHz
    I is current in milliamps

See page 301 of "Noise Reduction Techniques in Electronic Systems" by Henry Ott.