Do I have to protect PCB from radio frequency reflection?

I am designing a system on megahertz frequency bands (~ 400-1000MHz.) This device is connected to a variable antenna which does not necessarily stay in match with the circuit so there will be some reflection of the power back to the circuit. The feeding power would not be more than 0dBm at maximum. Do I ever need to take care of the reflections at all?

PCB Design
December 5, 2023

For low power devices, they are probably safe even if all the power is reflected. If you generate more power than you need then feed the output through an attenuator it will reduce the effects of any reflected power.

For example, a 6dB attenuation will reduce the forward power by a factor of 4, but any reflected power will be reduced by an additional factor of 4 on the return trip, which gives a factor of 16 reduction in any reflected power.

These effects can normally be ignored on low-power devices (VCOs, PLLs, etc) that can tolerate operating into a mismatched load with no ill-effects. They don’t need any special protection.

For special-purpose devices, the datasheet will often have limits or recommendations to protect them.

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Oliver Smith

Oliver is an experienced electronics engineer skilled in PCB design, analog circuits, embedded systems, and prototyping. His deep knowledge spans schematic capture, firmware coding, simulation, layout, testing, and troubleshooting. Oliver excels at taking projects from concept to mass production using his electrical design talents and mechanical aptitude.

Oliver Smith

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