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I am trying to understand this plot of directivity from the following link:

enter image description here
http://www.nicera.co.jp/pro/ut/pdf/T4010B4(ENG).pdf

How do I read this plot? I can say that at 0 degree , the energy would be 0 db, at close to 60 degree , this is close to -10dB. Am I right ?

But then what is the meaning of -6dB Full Angle : 100°, I do not see 100 degree anywhere. Even if I imagined I am not able to visualize how it will go to -6dB. Also why they did not show the energy at 100 degree in this plot.

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    \$\begingroup\$ From the plot, +/- 50 degrees is at -6dB. So it looks like the 100 degrees refers to Angle over which the device is responsive at >-6dB ; i.e. a 100 degree angle. \$\endgroup\$
    – akellyirl
    Dec 10, 2014 at 11:42
  • \$\begingroup\$ You have already 180 degree in the diagram \$\endgroup\$
    – GR Tech
    Dec 10, 2014 at 13:48

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You are correct with your interpretation of the plot, yes.

The "-6dB Full Angle : 100°" refers to the spread angle around 0° at which the radiation is greater that -6dB. That is, ±50° around 0°. You can see from the plot that the radiation line crosses the -6dB mark at 50° either side of 0°, so the full spread at > -6dB is 50*2 = 100°.

enter image description here

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