reflected power). Unfortunately, improving poor antenna efficiency at the late stage of development where PTCRB testing takes place is very difficult and will almost certainly require a significant re-design of the product enclosure and antenna type. Poor efficiency results from either the choice of antenna or its position and orientation within the product, both of which are fundamental design parameters.
It is possible that the efficiency of the antenna element itself is acceptable but the antenna has become mis-tuned, either in the design process or during final assembly of the device. In this case, restoring the performance can often be quite simple by slightly adjusting the antenna geometry. However, it is critical to understand exactly what the source of the failure is. Simply improving the tuning of an inherently low-efficiency antenna will not yield good results.
6.3 Receive Mode Failures
Receive-mode failures of a device with a module that has acceptable receive sensitivity can be caused by poor antenna efficiency, self-interference or a combination of the two. As is the case with transmit-mode failures, improving antenna efficiency at this stage is very difficult, but re-tuning a mis-tuned antenna is often easily done, even at this late stage of product development. Resolving a self-interference issue at the PTCRB testing stage is possible (although still challenging) and will likely require changes to the hardware. Analyzing the extent of the issue is complex and requires special test equipment and careful analysis. Additionally, antenna tuning and self-interference can sometimes be interactive – the antenna impedance may influence the level of self-interference. For these reasons, taking self-interference into account early in the design phase is critical.
6.4 Harmonic Generation Failures
Antenna Fundamentals – Technical Brief