|MadSci Network: Astronomy|
Hi Noe, That's a great question! In the case of a dish antenna, the effective area is more or less the physical area of the dish. In the case of wire antennas, the effective area can be calculated given the directive gain. The directive gain is well known for any number of antenna geometries and widely published by manufacturers. The effective area given the directive gain is: A = L^2 * G / 4*pi Where A is the effective area, L is the wavelength of incident radiation, and G is the directive gain. For a half wave dipole antenna, the directive gain is approximately 1.64, substituting that value for G simplifies the equation to: A = 0.131 * L^2 If you have 100 such antennas and their power is collected coherently (in phase), the total effective area is simply 100 times the area of one antenna. This is just like 100 parabolic mirrors concentrating their power on one spot. The total area is the sum of all individual areas. There are some issues to be concerned about. If the antenna power is not added in phase, power will be re-radiated and lost. Also, the antennas must be more than a wavelength apart. If not, each antenna will not operate independently and you will have created a single, more complex antenna with different directive gain and effective area. Your antennas spread a mile apart should not cause any trouble unless you plan to measure wavelengths a mile long! Here are some links to dipole antennas and effective area: http://en.wikipedia.org/wiki/Dipole_antenna http://en.wikipedia.org/wiki/Antenna_effective_area Good luck! http://madhu.com - http://madhu.com/blog
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