The purpose of this test reduction approach is to eliminate the "zoom scan" session for each single measurement test (6.4.2, Step d) when the measured peak SAR from the "area scan" is below a threshold, by assuring that the maximum peak spatial-average SAR value will be:
• correctly assessed and not underestimated, especially when it could generate a peak spatial-average SAR close to the basic restriction limit;
• correctly identified, even if the "zoom scan" session is not executed.
NOTE This test reduction procedure is different from the fast SAR procedure described in 6.6. In this test reduction protocol, the decision to apply the complete measurement procedure ("full SAR measurement") is taken after looking at values measured from the area scan (not the final peak spatial-average SAR). Moreover, a threshold value is necessary since the goal is to avoid the zoom scan for some particular measurement configurations and not depend on a particular fast SAR algorithm to estimate the peak spatial-average SAR.
In Clause L.3, the rationale and studies supporting this test reduction approach are reported.
These studies consider handsets operating in the GSM900/DCS1800 and UMTS I bands. The protocol described below is only applicable to the above particular operating modes and frequency bands (e.g. it does not apply to GSM850, PCS1900 or GPRS modes), and does not apply to multiple transmissions (6.4.3) compliance testing. The area scan grid spacing parameters used in the Clause L.3 studies were both (x- and y-directions) set to 10 mm, so they meet the requirements reported in this Standard. The area scans were performed at a fixed specified distance of 4 mm spacing between the probe sensors and the internal surface of the SAM phantom.
When applying the protocol described below, it is necessary:
1) to adjust the "area scan" parameters specified in the Table 1 to use grid spacing not larger than 10 mm;
2) to perform the area scans at a fixed 4 mm maximum distance between the measured points (geometric centre of the sensors) and the phantom inner surface.
The single band test reduction protocol (valid for each operating mode supported by the DUT) is described as follows.
a) Measure the local SAR as described in 6.4.2, Step a).
b) Perform the area scan procedure for one of the positions defined in 6.2.4, at the centre frequency of the considered band, as indicated in the complete measurement scheme described in 6.4.2.
c) Determine the peak SAR of the area scan; this is defined as the first absolute peak SAR (APS).
d) Perform the zoom scan, as indicated in the complete measurement scheme described in 6.4.2. Evaluate and manage the measurement drift as indicated in 6.4.2, Step f).
e) For all the other positions and frequency channels to be tested, repeat the following Steps 1) to 5).
1) Measure the local SAR as described in 6.4.2, Step a).
2) Perform the area scan procedure as indicated in the complete measurement scheme described in 6.4.2, Step b).
3) Evaluate the peak SAR of the area scan; if the peak SAR value of the area scan is greater than APS, determined in Step c), then APS shall be assigned to the peak SAR value of the area scan found in this Step 3), after completing Step 4).
4) Perform the zoom scan required by 6.4.2 if the area scan peak SAR is not less than 1,3 W/kg (80 % of 1,6 W/kg) or if the peak SAR is greater than or equal to TH(f) × APS, where the frequency-dependent threshold value TH(f) is defined in Table 4 below and
APS is the absolute peak SAR. If multiple peaks (as in 6.4.2, Step c)) are required to be measured, apply this step to all the peaks.
5) Evaluate the measurement drift as indicated in 6.4.2, Step f). If the drift is higher than 5 %, the drift shall be addressed according to 6.4.2, Step f).
Substeps 1) to 5) of Step e) described above shall be performed sequentially for all applicable bands. The frequency-dependent threshold values used in Step e), Substep 4), are summarized in Table 4.
Table 4 – Threshold values TH(f) used in this proposed test reduction protocol
Operating Mode TH(f)
GSM900 0,75
UMTS VI a 0,75
DCS1800 0,60
UMTS IX a 0,60
UMTS I 0,60
a 3GPP UMTS-FDD Band VI and Band IX have Uplink frequencies very close to GSM900 and DCS1800, respectively. Even if only devices operating in GSM900, DCS1800 and UMTS I bands were considered in Clause L.2, the above thresholds shall be applied for UMTS-FDD Band VI and for UMTS-FDD Band IX.
When the present test reduction procedure is followed:
• The block diagram on the left of Figure 5 shall be applied.
• The block diagram on the right Figure 5 shall be applied only for the first SAR measurement. Subsequent SAR measurements shall be performed according to Figure 9, which is a modification of the procedure described in Figure 5.
a APS = asolute peak SAR. See 6.7.4.
b Apply this step only if zoom scan has been performed.
Figure 9 – Modified chart of 6.4.2
Clause L.3 provides the rationale for the threshold levels used in this test reduction protocol, based on the SAR spatial gradient analysis.
6.7.5 Test reduction based on simultaneous multi-band transmission considerations Simultaneous multi-band transmission means that the device can transmit in multiple frequency bands at the same time, e.g. a WCDMA transmission at 2 GHz and a WLAN transmission at 2,45 GHz. The time-averaged output power of a secondary transmitter (i.e. the lower power transmitter, e.g. Bluetooth, WLAN) may be much lower than that of the primary transmitter (i.e. the higher power transmitter, e.g. WCDMA). In some cases, the
IEC
Measurement 6.4.2 modified
SAR reference measurement 6.4.2 (a)
Area scan 6.4.2 (b-c)
No
No
Yes Yes
Peak SAR ≥ 1,3
Peak SAR ≥
TH3×APSa
Zoom scan 6.4.2 (d-e)
SAR drift measurement 6.4.2 (f)
Peak in cube?b Yes
No Shift cube centre
Select next peak
Yes
No All primary and
secondary peaks required by 6.4.2 (d-e) tested?
secondary transmitter can be excluded from SAR testing when used alone. However, when the primary and secondary transmitters are used together (simultaneous transmission), the SAR limit may still be exceeded. A means of determining the threshold power for the secondary transmitter that allows it to be excluded from SAR testing is required.
One way of determining the threshold power level for the secondary transmitter (Pavailable) is to calculate it from the measured peak spatial-average SAR of the primary transmitter (SAR1) according to Formula (18):
lim 1
lim max
available=P ( SAR SAR ) / SAR
P m× − (18)
where
Pmax,m is the maximum threshold exclusion power level, which is calculated by SARlim× m, where m is an averaging mass.
For example, an exposure limit of SARlim = 2,0 W/kg and an averaging mass of m = 10 g gives total transmitting power of Pmax,m = 20 mW.
For an exposure limit of SARlim = 1,6 W/kg and an averaging mass of m = 1 g give total transmitting power of Pmax,m = 1,6 mW.
The above formula can be easily generalized to the case where more than two transmitters are transmitting simultaneously. If there are N simultaneous transmitters and the peak spatial- average SAR of the first N − 1 transmitters are known (SARi), then the threshold power level for the N-th transmitter can be found from Formula (19):
∑−
=
−
×
= 1
1 lim
lim max
available ( N )/
i SARi SAR
SAR P
P m (19)
NOTE The applicability of power thresholds as defined in Annex B of IEC 62479:2010 to replace Pmax,m in the case where (i) the DUT is measured at the SAM ear and (ii) the radiating parts of the DUT are closer than 5 mm to the phantom surface is currently under investigation. The definition of new power thresholds for such configuration is needed.