ISO 11451-2

Automotive standard according to ISO 11451, 15-04-2001

1 point automotive calibration method, according to ISO 11451, 15-04-2001

1 probe is placed at the reference point in the room, at a height of 1 meter (car roof height < 3 m) or 2 m (car roof height >3 m). The net power, required to achieve the required field strength, is recorded for each frequency point. If the Voltage Standing Wave Ration is below 1,2:1, the forward power method may be used as the reference parameter for calibration and testing

4 point automotive calibration method, according to ISO 11451, 15-04-2001

4 points are taken in a vertical line, 0,5m – 0,8m – 1,0m and 1,2 meter above the floor. (Car roof height < 3 m) or 1,2m – 1,5m– 1,8m and 2,1m (car roof height >3 m).

The net power, required to achieve the required field strength (average of 4 probes), is recorded for each frequency point. If the Voltage Standing Wave Ration is below 1,2:1, the forward power method may be used as the reference parameter for calibration and testing

Room verification, according to ISO 11451, 15-04-2001

Room homogeneity verification:

The room homogeneity is verified at two points. One point 0,75 cm to the left of the vertical reference line and one at the right side of the reference line. Verification is only carried out above 200 MHz! 80% of all frequency points must be within ±3 dB at both points.

Automotive standard according to ISO 11451, 15-04-2005

1 point automotive calibration method, according to ISO 11451, 15-04-2005

1 probe is placed at the reference point in the room, at a height of 1 meter (car roof height < 3 m) or 2 m (car roof height >3 m). The forward power, required to achieve the required field strength, is recorded for each frequency point.

4 point automotive calibration method, according to ISO 11451, 15-04-2005

4 points are taken in a vertical line, 0,5m – 0,8m – 1,0m and 1,2 meter above the floor. (Car roof height < 3 m) or 1,2m – 1,5m– 1,8m and 2,1m (car roof height >3 m).

The forward power, required to achieve the required field strength (average of 4 probes), is recorded for each frequency point.

RadiMation can perform the calibration by reading the field strength of the 4 probes, determine the average of the 4 measured field strength, and level the forward power until the required average field strength is achieved. The forward power to achieve the average field strength is stored by RadiMation for each frequency point.

Using 4 probes will result directly in the required calibration file.

As an alternative, if only 1 field probe is available, 4 separate 1 point calibrations, (at the 4 required heights), can be performed. After the 4 calibration files are made, RadiMation can calculate the final calibration file out of the 4 separate calibration files.

Of course, both methods should result in the same calibration file.

To achieve this, the calibration method, described below is used:

To clarify the calculation method, the following example data is used:

Frequency: 326 MHz

Required field strength:30 V/m

	Pn fwd, cal file [dBm]	Measured field [V/m]
Cal file data@50cm	47,7	30,5
Cal file data@80cm	51,4	30,0
Cal file data@10cm	57,1	30,3
Cal file data@120cm	59,5	30,7

Although RadiMation will have levelled the separate forward powers of the cal files to 30 V/m, the measure field strength will never be exactly 30 V/m. (in the example above, the field strength is 30,5 V/m, 30,0V/m, 30,3 V/m and 30,7 V/m).

First of all, RadiMation will correct the forward power levels to exact required field strength of 30 V/m.

This is done using the following formula:

Pn fwd, corrected [dBm] = Pn fwd, measured [dBm] - 20*log(En measured [V/m] / Rrequired [V/m])

This results in the corrected power levels as mentioned below:

	Pn fwd, cal file [dBm]	Pn fwd, corrected [dBm]	Measured field [V/m]
Cal file data@50cm	47,7	47,56	30,5
Cal file data@80cm	51,4	51,40	30,0
Cal file data@100cm	57,1	57,01	30,3
Cal file data@120cm	59,5	52,30	30,7

After this, RadiMation will normalize the field strength of each point to a power of 1 Watt (30 dBm). I.e. RadiMation calculates which field strength would be generated, if a forward power of 30 dBm was used instead of the measured forward power for this point.

This is done in the following steps:

ΔPn [dB] = Pn fwd, corrected [dBm] – 30 [dBm])

En @ 1 Watt forward power [V/m] = Erequired [V/m] / 10^(ΔP/20)

Te above is repeated for all 4 points.

This results in the normalized field strength (@ 1 Watt) as mentioned below:

	Pn fwd, cal file [dBm]	Pn fwd, corrected [dBm]	En @ 1 Watt forward power [V/m]	Measured field [V/m]
Cal file data@50cm	47,7	47,56	3,97	30,5
Cal file data@80cm	51,4	51,40	2,55	30,0
Cal file data@100cm	57,1	57,01	1,34	30,3
Cal file data@120cm	59,5	52,30	1,03	30,7

After this, the average field strength with a constant power of 1 Watt is calculated by:

E avg, @ 1Watt = { (E1, @ 1 watt) + (E2, @ 1 watt) + (E3, @ 1 watt) +(E4, @ 1 watt) } / 4

So; E avg, @ 1Watt = 2,22 V/m

The relation between the calculated average field strength @ 1 Watt compared to the required field strength is determined by:

ΔE = E required [V/m] / E avg, @ 1Watt [V/m]

Or in dB:

ΔE [dB] = 20 log (ΔE)

So; ΔE [dB] 22,6 dB

So, to find the forward power level to achieve the required average field strength, one should increase the forward power of 30 dBm (1 Watt), with the value of ΔE [dB].

Pcal result = 30 dBm + ΔE [dB]

So; Pcal result 52,6 dB

Verification of the calculation method

To verify the calculated power level will indeed reproduce an average field strength of 30 V/m, one can determine the difference between the calibrated forward power level of each point and the newly found cal. file power level and from this, calculate the field strength, that will be generated in each point if the cal file power level is used.

The average of all 4 field strength should now be 30 V/m

ΔP [dB] = Pn, fwd, cal file – Pcal result

A change in forward power of ΔP [dB] will result in a change in the E field of:

ΔE [lin] = 10^ (ΔP[dB]/20)

So; E predicted [V/m] = ΔE [lin] * Measured field [V/m]

	Pn, fwd, cal file [dBm]	Measured field [V/m]	ΔP [lin]	E predicted [V/m]
Cal file data@50cm	47,7	30,5	1,76	53,62
Cal file data@80cm	51,4	30,0	1,15	34,45
Cal file data@10cm	57,1	30,3	0,60	18,05
Cal file data@120cm	59,5	30,7	0,45	13,87

Egem = 30 V/m

Room verification, according to ISO 11451, 15-04-2005

Room homogeneity verification:

The room homogeneity is verified at two points. One point 0,5 cm to the left of the vertical reference line and one at the right side of the reference line. Verification is only carried out above 200 MHz!

80% of all frequency points must be within 0 to -6 dB at both points. (please note, this is completely different from the rule used in the EN61000-4-3, where 75% of the points in a homogeny area must be within 0 to +6 dB for each frequency point).

International Organization for Standardization

Decibel

Power expressed in milliWatt in dB values.

• 1 mW = 0 dBm

• 2 mW = 3 dBm

• 100 mW = 20 dBm

• 1 W = 30 dBm

• 100 W = 50 dBm