where k<sub>0</sub> = 2π/λ<sub>0</sub> is the free-space wavenumber, λ<sub>0</sub> is the free-space wavelength, I<sub>0</sub> is the current on the dipole, and L is the length of the dipole.
The directivity of the dipole antenna is given be the expression:
<math> D_0 \approx \frac{2}{C + \text{ln}(k_0L) - C_i(k_0L) + \frac{1}{2} \text{sin}(k_0L) \left[ S_i(2k_0L) - 2S_i(k_0L) \right] + \frac{1}{2} \text{cos}(k_0L) \left[ C + \text{ln}(k_0L/2) + C_i(2k_0L) - 2C_i(k_0L) \right] }
\left[ \frac{\text{cos} \left( \frac{k_0 L}{2} \text{cos} \theta \right) - \text{cos} \left( \frac{k_0 L}{2} \right) }{\text{sin}\theta} \right]^2 </math>
=== A Note on the Rotation of Antenna Radiation Patterns ===