I have the case where antenna and PCB is inside unknown plastic. Without plastic antenna radiation is very similar to power measured by direct contact measurements. Installing this PCB in plastic enclosure shows radiated power degradation by like 5dB. How to know weather antenna is detuned due to capacitance load of the plastic and additional impedance matching needs to be done or is the plastic degrading performance due to absorption and poor tan delta?
Thank you in advance!
The degradation is likely due to both detuning and losses in the plastic, though I suspect detuning will have the more significant effect. You will need to characterise the epsilon and loss tangent of the plastic to investigate the effect the plastic on radiation.
A quick measurement of radiated power across a wider frequency range might show you a higher power received at another frequency due to the detuning effect. Either way the properties of the plastic enclosure must be considered in the design of the antenna.
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