How to apply the field correction factor

How to apply the field correction factor

Applying the field correction factor can be very hard when there is only one factor can be applied.

The isotropic field is defined by: $E={\sqrt {{E_{x}}^{2}+{E_{y}}^{2}+{E_{z}}^{2}}}\ \ (1)$

If you have a correction for the E-field sensor, you have to correct each axis: $E={\sqrt {{c_{x}E_{x}}^{2}+{c_{y}E_{y}}^{2}+{c_{z}E_{z}}^{2}}}\ \ (2)$

The method of using an average correction factor is the best when one does not have any idea about the direction of the field to be measured. However, during radiated immunity tests, the direction of the field in the test chamber is quite well known (horizontal or vertical polarization). In this case a better way of dealing with this error is to place the probe into the field with the x-axis in the direction of the horizontal field in the chamber and place the y-axis of the probe in the direction of the vertical direction of the field in the test chamber. The customer should apply the x-axis correction factor (in RadiMation^®) when performing horizontal tests and use the y-axis correction factor (in RadiMation^®) when vertical immunity tests are performed.

Average correction factor

When using RadiMation^®, you have to use 1 correction file (for “Field Multiply”) while RadiMation^® is reading out the isotropic field strength. Because of the fact that mostly the 3 correction factors are nearly equal and field probes have an uncertainty, you can assume: $c_{x}\approx c_{y}\approx c_{z}$

Now we can approximate: $c={\frac {c_{x}+c_{y}+c_{z}}{3}}\ \ (3)$

And we would get: $E={\sqrt {(cE_{x})^{2}+(cE_{y})^{2}+(cE_{z})^{2}}}=c{\sqrt {(E_{x})^{2}+(E_{y})^{2}+(E_{z})^{2}}}\ \ (4)$

Example

In this example there is a demonstration of what can go wrong when the $c_{x}\approx c_{y}\approx c_{z}$ does not apply.

Correction factor X-axis: 0.99

Correction factor Y-axis: 1.18

Correction factor Z-axis: 1.22

The average correction(equation 3) is $c={\frac {0.99+1.18+1.22}{3}}=1.13$

The field reading: X=10 V/m, Y = 10 V/m, Z = 60 V/m

The result according equation 2: $E={\sqrt {(0.99*10)^{2}+(1.18*10)^{2}+(1.22*60)^{2}}}\approx 74.8V/m$

The result according equation 4: $E=1.13*{\sqrt {(10)^{2}+(10)^{2}+(60)^{2}}}\approx 65.5V/m$

The difference is 9.3 V/m or 1.15 dB.

Direction correction factor

The correct implementation is to use the correction factor for the antenna that is standing in the field. This means that for horizontal and vertical testing you need to apply 2 different factors. This is due to the fact that other antenna's are in the field. Of course it is also possible to change the antenna of the field sensor with the field.

Example

Correction factor X-axis: 0.99

Correction factor Y-axis: 1.18

Correction factor Z-axis: 1.22

The field reading: X=10 V/m, Y = 10 V/m, Z = 60 V/m

The Z-axis is the axis in the field so the correction factor is 1.22.

The result according equation 4: $E=1.22*{\sqrt {(10)^{2}+(10)^{2}+(60)^{2}}}\approx 68V/m$

The difference is 6.7 V/m or 0.82 dB.

The ability of an EUT to be immune to incoming electromagnetic interference. This is equivalent to the term susceptibility that is used by some standards.

Decibel