radiation plot

I measured dB levels for a given antenna every 5.0 degrees. I would like to know if any one can help me understand how to make a graphical plot of the radiation pattern using a polar circular graph.

I was told that I had to "normalize" the data. Is this necessary? If so how do I do this?

I attached the measurements I obtained

Well, a critical part of the data is the calibration. You need another antenna with known gain, like a horn or a dipole, and you measure that 2nd antenna on the original setup with the same power levels, etc. That way you can take your "raw" data, and convert it to something meaningful, like data in dBi. You do not have to rotate that antenna in azimuth, but you would want to position it to measure horizontal, and then vertical, polarization gain (i.e. a different cal number for the two polarizations).

After that, it is just a quick trip to the excel plotting wizard.

Thanks biff44 but can you "dumb it down" for a novice to understand? I used a horn antenna ets 3160-3. You said that I dont have to rotate the antenna azimuth but can I obtain the radiation plot with the data i have shown you already? If so how?
From what you have written it appears that the data I provided to you is not useful when plotting the data in excel. Its not clear what you are saying.

You should indeed calibrate the measurement data. This is easily done by replacing your antenna under test by an antenna with known antenna gain. With this, you should be able to determine the offset between your readout and the actual antenna gain. When you apply this same offset to your measurement number, you have the "calibrated data". You can then tabulate this in excel and use a radar plot to display the radiation pattern.

Yeah, what he said.

Lets say in your antenna under test, for one orientation you measured a received power of -40 dBm. You then walk over to the test antenna, disconnect it, and replace it with an antenna of known gain, say + 2 dBi gain. You remeasure the received power and note that it is now, say -30 dBm. The original antenna gain would be:

+2 dBi + (-40 dBm) - (-30 dBm) = -8 dBi

Or, in other words, your test antenna had 10 dB less gain than a reference antenna with +2 dBi of known gain.

you only need to do this test at one azimuth, the one where the test antenna is "pointing" at your source antenna.

If you are interested in measuring both antenna polarizations, then you reference antenna might have to be spun on its axis to measure first horizontal gain, and then vertical gain, and then you do 2 calibration corrections.