**5.4 De-Sense measurement**

De-Sense is self-referred to same subjective device operating in different condition and compared the platform noise impact. For example, a GPS module is first performed conducted test in a shielded box and obtains the C/N=40dB at -138dBm receiving level. While the same module is then bundled in a wireless platform and performed the conducted test again, the receiving level become -130dBm for keeping C/N=40dB. In this example, we found that the conducted platform noise causes GPS module de-sensed by 8dB. When the antenna terminal and GPS signal is fed to GPS receiver through a combiner, we now need -123 dBm to keep C/N =40dB and thus a 7dB de-sense caused by platform noise picking up from antenna. Furthermore, when the internal device, like Bluetooth, is active or hand-held device resting on desk, the interaction between platform noise and antenna resulting in different de-sense effect can be easily observed in all those test cases. The noise current at different locations can also be represented with the de-sense Data. The methodology and measuring technique illustrated below in Figure 28 can be applied for investigating GPS degradation of sensitivity caused by platform noise.

Fig. 28. GPS C/N Scanning.

### **5.5 Noise measurement at antenna terminal**

200 Wireless Communications and Networks – Recent Advances

performance, therefore throughput test need to consider how the user interacts with the RF device. For example, 90dB path loss for laptop 802.11g WLAN may represent that AP is 200 meters away in the free space environment, however the hand and head may cause the range for 90dB path loss much less than 20 meters for smart phone VOIP application. Some real-life products throughput test result has been illustrated in Figure 12 and the Root Cause

The current distribution on antenna surface represents the different sensitivity on antenna near field boundary, because the physical geometry of antenna will cause different field intensity coupled via the uniform magnetic flux. Antenna surface current also represents the immunity level for TP and Camera. As to digital noisy components, we can utilize the noise level results to locate the noisy components and identify their noise radiation pattern. We can utilize the near-field surface scanning method to observe the surface current distribution

De-Sense is self-referred to same subjective device operating in different condition and compared the platform noise impact. For example, a GPS module is first performed conducted test in a shielded box and obtains the C/N=40dB at -138dBm receiving level. While the same module is then bundled in a wireless platform and performed the conducted test again, the receiving level become -130dBm for keeping C/N=40dB. In this example, we found that the conducted platform noise causes GPS module de-sensed by 8dB. When the antenna terminal and GPS signal is fed to GPS receiver through a combiner, we now need -123 dBm to keep C/N =40dB and thus a 7dB de-sense caused by platform noise picking up from antenna. Furthermore, when the internal device, like Bluetooth, is active or hand-held device resting on desk, the interaction between platform noise and antenna resulting in different de-sense effect can be easily observed in all those test cases. The noise current at different locations can also be represented with the de-sense Data. The methodology and measuring technique illustrated below in Figure 28 can be applied for

Analysis (RCA) procedure will be addressed later in section 6.

**5.3 Antenna surface current and near-field surface scanning** 

of antenna and locate the noise sources for platform noise analysis.

investigating GPS degradation of sensitivity caused by platform noise.

**5.4 De-Sense measurement** 

Fig. 28. GPS C/N Scanning.

Since the antennas are the most important port for wireless communications as electromagnetic energy receiving component, they are also susceptible to nearby platform noise. Hence the analysis and measurement of noise level at antenna port is critical for RCA of wireless device to improve link performance. Figures 29-31 show the measurement techniques and configuration for noise measurement at antenna terminal.

Fig. 29. LCD panel test fixture and the measurement circuits.

Fig. 30. Platform noise and de-sense measurement at antenna terminal.

Fig. 31. NFS system and measurement setup.

From the various platform noise measuring techniques described above, we can summarize the comparison as Table 3.



Table 3. Measurement techniques comparison.
