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: $E={\sqrt {{c_{x}E_{x}}^{2}+{c_{y}E_{y}}^{2}+{c_{z}E_{z}}^{2}}}\ \ (2)$

Generic implementation

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.

Correct implementation

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

Decibel