Discussion
Using \( A_{e} = D\lambda^{2}/4\pi \), what is a dipole's effective aperture at 3 m wavelength?
Answer: D
With a directivity of 1.64 and a wavelength of three metres:
\[ A_{e} = \tfrac{1.64 \times 9}{4\pi} \approx 1.17 \]
giving about 1.2 square metres for a wire a metre and a half long. The collecting area is far larger than anything the physical wire suggests, and it shrinks as the square of the frequency, which is why the same dipole gathers so much less power at microwave frequencies.
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