Hello Physics Forums!
I'm not an engineer/scientist but I work with antennas and I'm having trouble deciphering the above antenna radiation pattern diagram.
I am used to seeing radiation patterns expressed in polar plots. Usually the scale is set to dBi (where the isotropic antenna = 0dBi), or it is set to main beam bore sight power (where the peak of the main beam is 0 dB). The diagram above is scaled differently.
As you can see, the isotropic level is '7 dB'. The bore sight of the main beam is at about 2 dB. The half-power points (5 dB) occur at roughly +/- 35 degrees off bore sight.
I have some questions:
1) Why is the diagram scaled this way? What does it mean to say that the bore sight of the main beam is at 2 dB? 2 dB less than what?
2) Shouldn't all of these measurements be in negative dB? e.g. shouldn't the isotropic level be -7 dB?
3) Could I go ahead and 'convert' this diagram to isotropic scale? So the bore sight is at 5 dBi, the power at 90 / 270 degrees is roughly -9 dbi, etc.?