How would I calculate aperture efficiency for an antenna?

Question

How to calculate aperture efficiency for an antenna with the following parameters:

• Big reflector diameter= 24 mm
• Gain= 9.265 dbi
• Frequency= 11.60 GHz

Answer 1

For any antenna, also for wire antennas, you can calculate so called effective area with $A_{eff} = \frac{\lambda^2}{(4\pi)}G$. An ideal antenna with surface area of $A_{eff}$ absorbs the same amount of power from the plane wave as that antenna. Aperture efficiency is defined as ratio of effective and physical surface area $\eta_{ap} = A_{eff}/A_{phys}$. For a circular reflector antenna the physical size is the area of your antenna facing the incoming plane wave $ A_{phys} = \pi(d/2)^2$.