# Rectenna - What's the Purpose of the Capacitors?

My current knowledge is a single college introductory EE class. I came across this video which shows the user harvesting electromagnetic (radio?) signals into electricity (using a couple of capacitors and diodes).

I do understand how absurdly inefficient this is, but it's still a project I'd like to try anyways to gain some understanding. (Yes, we have another very abundant electromagnetic radiation called visible light, and yes, I understand if I wanted electricity from "thin air" it would be much better to use a solar panel)

He included this diagram:

And these figures:

• C1 = C2 0.22uF, 100V, Ceramic or Polyester
• Diodes 1N34, OA70, 1N4148
• C3 = C4 100uF 16V, electrolytic

I believe I understand what the diodes do (rectify electromagnetic radiation to energy) and the C3 and C4 capacitors (store energy), but I'm not sure what is the purpose of C1 and C2 capacitors. Would I even need them to complete this project? Could I substitute them?

Thank you! And maybe a follow up secondary question (or perhaps it's required for my main question). Could someone explain in general how this circuit works? I think I somewhat understand, but I feel like there are knowledge gaps. For example, where is ground? Once I understand well enough, I would love to buy the parts to try this out!

• A single-ended antenna without ground won't work well, as you have suggested. Use a loop antenna having two ends. One end goes to junction of C1,C2, the other end goes to junction of C3,C4. A tuned loop may provide more DC. Commented Oct 23, 2019 at 15:31

The capacitors and the diodes together form a voltage multiplier.