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Good morning. I was wondering which is the exact physical reason for why a dipole (e.g. a $\lambda/2$ dipole) has the equal radiation pattern in all directions. I have founded many formulas but I can't get the point in practice. Many thanks.

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    $\begingroup$ Can you show us some of these formulas? A dipole is not an isotropic radiator. $\endgroup$ – garyp Jul 17 '19 at 10:23
  • $\begingroup$ I mean, I know that a dipole (Hertzian dipole) has a very low directivity (0 at all) and if I need more of this parameter I should go for an array config. I am interested about the physical reason of this low directivity property. Many thanks. $\endgroup$ – muserock92 Jul 17 '19 at 10:26
  • $\begingroup$ The directivity of a Hertzian dipole is not zero. It's 1.5-1.76 dBi. Granted, it's lower than basically any other configuration, but it's not zero, because, again, a dipole is not an isotropic radiator. $\endgroup$ – probably_someone Jul 17 '19 at 10:29
  • $\begingroup$ Many thanks. Can you tell me why a dipole has such a low directivity value? I know the directivity depends on the ratio lenght versus $\lambda$, but can I read this by a physical reason? Many thanks again. $\endgroup$ – muserock92 Jul 17 '19 at 10:32
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in free space, a dipole is not isotropic: it radiates in a fat "figure-8" pattern with two lobes. the "null point" where the radiation goes to nearly zero corresponds to the direction along the length of the dipole i.e., very little energy is radiated away from the ends of the dipole.

As a dipole antenna is moved close to the ground, its radiation pattern becomes distorted by currents it sets up in the ground and then the radiation pattern becomes less lobe-like and more isotropic.

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