I have some doubts to interpret the CISPR standards, one of them is in relation to the test environment for EMI conducted (150kHz up to 30MHz). The minimum size indicated for the vertical or horizontal ground plane is 2m x 2m. Would it be constructively possible to join two planes of 2m x 1m to form one? Some with this knowledge could help me?

Thank you.


1 Answer 1


Yes it is possible to join two coplanar 1m x 2m planes into one 2m x 2m plane for each axis using mu metal foil with conductive glue. (EMI tape) or several machine screw fasteners with some overlap (wavelength for 30MHz is 10m )

The purpose of the 2x2m in each plane is to shunt any radiated fields that might interfere with conducted noise going into the cable to the dual coil LISN up to 30MHz.

Cables can act as receiving antenna to CM noise and may still become unbalanced with a LISN. So the ground plane provides some capacitance to shunt these high impedance fields. The LISN inductance raises this CM impedance with frequency while unintended radiating cable antenna efficiency increases with frequency.

It might look like this with the XY axes joined.

enter image description here

  • \$\begingroup\$ Thank you, now I understand better. In this case instead of using an EMI tape, a thin metal bar and a few equally spaced screws could be used to secure the metal plates. In the same way that the XY plans were joined in the image of your post? Another issue is in relation to thickness, to have low impedance in an aluminum plane it is possible to use as base the depth of penetration at the lowest frequency (150kHz) (δ ≈ 0.2 mm) and choose a commercial value equal or greater. Am I right? \$\endgroup\$
    – Eduardo
    Jan 16, 2019 at 20:32
  • \$\begingroup\$ It seems they use extruded L bracket. Yes Skin depth applies then earth bond connection. \$\endgroup\$ Jan 16, 2019 at 20:34

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