Ben's Antenna Gain Calculator

This calculator helps you measure the gain of your antennas.

Antenna Gain Calc

m
MHz
fspl - dB
dBm
dBm
cl - dB
dB
SA Ref Level - dBm
dBi
dBm
Gain - dB
Instructions
  1. Turn on your Signal Generator (SG) and Spectrum Analyzer (SA). Allow 30 minutes for them to warm up for the most accurate measurements, or just don't care.
  2. Set up your Device Under Test (DUT) and your Reference Antenna (RA). Ensure the RA and DUT are pointed correctly. Also ensure the polarization of both antennas is correct.
  3. Measure the distance between your antennas and note it above. Note that for some antennas this may not be from the end of the antenna. Good RAs will have this point marked. Don't change this distance at any point during the test.
  4. Pick a test frequency. If you're testing with a frequency sweep, put the center frequency above.
  5. Pick a test power. If you're allowed to transmit on this frequency or you have an RF blocking chamber to test in, 0dBm is a good choice. Otherwise, pick something below the legal transmit power limit at that frequency. Make sure the power is below the SA's max input power.
  6. Set the test frequency and power on the SG and note them above
  7. Set the center frequency and reference level on the SA to match the SG. Set the span to be about 1% of the frequency, or about 1% larger than the sweep. You can enable averaging or peak hold, but remember to reset it before each measurement if you do.
  8. Get the cables and adapters you'll need to connect the SG to the RA and the DUT to the SA
  9. Set up your cables and adapters to connect the SG to the RA and the DUT to the SA. Connect the SG and SA, but don't connect the RA or DUT yet.
  10. Using as few adapters as possible, connect the cables together where the RA and DUT would connect. This will connect the SG directly to the SA through the test cables
  11. Verify that the SG is connected to the SA to avoid damaging the SG when you turn it on
  12. Turn on the SG output, measure the incoming power on the SA, and note it above (in Calibration Power). Use the peak search feature of a marker to get the best result. This value should be fairly stable, but you may have to estimate the average from a small.
  13. Estimate your antenna gain and put it above. You'll measure the actual value later, but a good estimation will help set up the test correctly. If you discover that you're way off, you'll change this later. For many antennas, 0dB is a reasonable guess.
  14. Set the reference level on your SA to the calculated value (or pick a different level, I'm not your boss). Setting this too high may reduce your measurement quality, too low won't measure at all.
  15. Ensure that the SG's output is off, then disconnect the cables from eachother and connect them to the RA and DUT.
  16. Verify that the DUT and RA haven't moved since you set them up at the beginning, and reset them if they have.
  17. Turn on the SG, clear the SA trace, and note the measured power in the "Measured Power" box above. Turn the SG back off once you're done taking the measurement. If you see a value close to (within ~1-2db) or at your reference level, increase your gain estimation
  18. If you have more measurements to take, do them now.
    1. If you're changing angle or polarization, change those then repeat the last step. Make sure distance does not change.
    2. If you're testing multiple DUTs, you can swap them out now. Just make sure they are all in the same position.
    3. If you're changing frequency, you'll have to redo most of these steps, so do any angle changes first.
  19. Ensure that the SG's output is off before disconnecting the reference antenna.
  20. When you're done, turn everything off and put everything away so it's ready for next time.
gan = -(txp - cl + ant - fspl - rxp)