IEC61000-4-3 RS test pre compliance using GTEM Cell.

[ankitvirdi4]

Hi guys,

I have to test an EUT according to IEC61000-4-3 but the lab with an anechoic chamber is not available due to some technical issues there, there are many other labs with GTEM cells, I think GTEM cells are not compliant with IEC61000-4-3.

All, I want to know is, how uniform will the field be in a GTEM with septum height of 1000mm and what will be the area of uniform field? The EUT is small in dimensions , similar to an average smartphone. So the cell will be more than enough for the EUT but I want cables of 1m in length to be in the uniform field area.

All the help is highly appreciated, Thank you!

 

[ravindragudi]

If the set up is having only the EUT then the GTEM cell test results will be close to that in anechoic chamber. But if you want to have 1m cable in uniform field area, it will be difficult to set it up in the GTEM cell unless you wind up the cable to over come the space constraint.
Earlier I have done such tests in GTEM and anechoic chamber and the results were almost same. I used the EUT only in the uniform field and the cable length was not that long.

 

[ankitvirdi4]

Thank you for the reply

But if you want to have 1m cable in uniform field area, it will be difficult to set it up in the GTEM cell unless you wind up the cable to over come the space constraint.

As said, will winding the cable be the right method? I found a pdf online which states out good practices for EMC measurement using GTEM cell,

How to route cables
"
This is probably the most contentious issue in the EMC world and it is by no means a
problem that is restricted to the GTEM cell. However, because the cell is compact, the
relative dimensions of interconnecting cables soon become an issue. Cables pickup can ruin
the performance of an otherwise good EUT and make a lot of difference to the immunity of
the test item at lower frequencies – below 150 MHz where the cables can act as resonant
antennas. Because of the existence of a longitudinal field component in the GTEM, it is
important that cables are not routed inside the cell along the longitudinal axis. To get from
the boundary of the EUT the cable should be routed along the transverse (X) axis or
diagonally towards the penetration plate. This will avoid over-testing the EUT.
" - The Use of GTEM Cells for EMC Measurements, 6.21.

But doesn't the RF come from patch antenna on the septum plane? Should the cables be horizontal or vertical in orientation?

 

[ravindragudi]

No, winding the cable is not correct method in any EMI EMC tests ... unless it is a end application use-case. As said in your reference document, you may have to route the cable along tranverse axis. With the small size of the EUT, I think it is ok to manage routing the cable in this way (serpantine routing)...

 

[ankitvirdi4]

Thank you so much,

There is still one problem, How do I decide how much is the usable volume for a given GTEM Cell,
,

Should I just geometrically calculate or is there a formula or a reference somewhere?

 

[ravindragudi]

I have not done this calculations earlier as there was no need for me. I guess, even for you with a EUT of the smart phone size and a meter cable, there should be sufficient volume/ space for the test set up inside the GTEM cell (the red color area shown in your previous pic). I would recommend you to visit the test facility and take a look at the GTEM cell and the available area for the test set up, if you have not done so. This will clear your doubts.

 

[ankitvirdi4]

I think the usable test volume corresponds to the volume with an uniform field, The red colour denotes the maximum allowable size of the EUT and the green colour denotes the volume with uniform field, It may be one-third of maximum septum height, though this is just a speculation. I am not very sure. I have visited the test facility and although there is a lot of space in the Cell, the volume which will have uniform field is considerably smaller.

 

[ravindragudi]

although there is a lot of space in the Cell, the volume which will have uniform field is considerably smaller.

I am talking about the area/ space which is usable with uniform field, with reference to the smart phone sized EUT you mentioned in the original thread. Do you still think that GTEM cell will not have that volume to support such a small EUT? I used a wooden/ thermocol plank inside the GTEM cell to adjust the EUT set up. And this whole thing was approximately within the red color are shown in previous pic.

 

[ankitvirdi4]

Okay, understood your point. Thank you.