Currently I have that for a X-Band High Gain Antenna functioning at 8 Ghz, diameter of 3 meters, and a power transmission of 13.1dBW (20 watts) at a distance of about 8.5 AU has a Gain of 52.44 dBi, free path loss of 292.59dBi, and a total received power from transmitter of -152.13dBw.

I am trying to figure out what battery I would need for my mission and I need to figure out how much power this antenna will draw. I've tried looking at research papers pertaining to antennas, but I have had no luck thus far. Any help will be greatly appreciated!


Your question seems to answer itself in some respects: '...a power transmission of 13.1dBW (20 watts)...'

But an antenna doesn't really draw power, it gets fed power (energy) from a source and radiates it into space.

I think the question you really are asking is: "How much power will my amplifier need to power my 20 $W_{RF}$ communications system?"

I had to do a similar exercise a year ago and I was confused by a lot of the terminology but I think I have the following figured out (please correct me if I'm wrong):

  • The transmit sequence goes like this:
    1. Transmitter/transponder/transceiver generates the data signal
    2. Radio Frequency (RF) amplifier amplifies the signal and sends to antenna
    3. the antenna radiates that energy (hopefully towards something)
  • RF power is different from electrical power (in terms of resource allocation)
  • Amplifiers can't make power from nothing and are not 100% efficient

I know the last point seems obvious but in a sea of Watts and dBs, dBms in textbooks and specification sheets its easy to get lost (it was for me).

So you are now looking for an X-band power amplifier (or a transponder with built in amplifier, but at 20 $W_{RF}$ I think you're exclusively in the range of external amplifiers) that will output 20 $W_{RF}$. From a product's specification sheet you can find the input power required in Watts. Then use this power and the time needed to transmit to find how many W-hrs (capacity, Watts x hours) your battery needs. If you don't want to reference a specific product I would assume an amplifier efficiency ($P_{out,RF}/P_{in}$) of about 25% (based on first link below)

Some helpful links (I hope):


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