In order for the antenna to efficiently emit radio waves, the antenna itself must be separate.
However, in practice, electronic circuits are configured around and integrated with the antenna, which degrades the characteristics of the antenna.
The following two methods can be considered as countermeasures.
- Physically separate the audio circuit from the antenna.
- Electrically separate the two elements (isolation).
Due to the increasing circuit density of smart phones in recent years, method (1) is difficult to adopt, which means that the components must be electrically isolated, as in method (2).
In order to achieve isolation, it is important to increase the impedance of the integrated pathways or the circuit junction to make it seem as if the circuits are not connected at all.
Figure 2 shows an example of applying such a countermeasure to the earphone junction. (The measurement result TRP indicates the magnitude of the power radiated by the antenna.)
Using a high impedance audio line noise filter (NFZ Series, LQW Series) in the cellular band ensures isolation and improves the efficiency of radio wave emission compared to the antenna without the countermeasures.