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Passive Microwave Repeaters

Passive Microwave Repeaters

3 comments

·August 17, 2025
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scott_h

Interesting stuff, I work with RF and I was curious how a passive component can have such a high gain (given that gain is usually measured as an increase in energy of a signal).

Turns out the way that the gain of a passive reflector seems to be measured is: "the ratio of the power density at a distant point due to the passive repeater to the power density which would exist at the same point" if the repeater were replaced by a matched antenna (or basically nothing at all).

So basically it's a measure of how much better the signal is when you add the reflector, and that's why it can achieve such high gains: because the signals traveling so far are already being atmospherically attenuated by hundreds of dB. Maybe that's not new information to others.

Anyways, cool stuff. Sometimes the best solutions are the simplest.

http://www.gbppr.net/splat/Passive-Repeater-Engineering.pdf#...

jauntywundrkind

Very topical item, with NISAR unfurling to it's full 39 foot deployment up in space.

https://www.jpl.nasa.gov/news/giant-radar-antenna-reflector-...

ziofill

“The mission scans nearly all the planet’s land and ice surfaces twice every 12 days.” What was wrong with saying once every 6 days?