Microwave beams are used in communications with spacecrafts, which propagate in a straight line as the light and, as well as the light, they can be reflected on smooth surfaces, and focused by lenses or curved reflectors to increase its intensity.
The result of this is the same to that of an optical telescope, in which the glass mirrors have been replaced by other metal ones carrying out the same function. These types of microwave antennas are known by the same names as those of equivalent telescopes.
In the antennas, parabolic surfaces are used as reflectors. These parabolic surfaces have the geometric property of gathering on a point in space the energy waves arriving at its surface parallel to the main axis. That point of concentration is the focus of the paraboloid.
When using large antennas, it is not convenient to install the reception equipment at that theoretical point away from the main mirror structure, so that a second mirror is mounted in order that the energy concentration occurs in a more accessible area.
The most common antenna is the Cassegrain one, which uses as secondary reflector (or subreflector), a hyperboloid, one of its two focuses coincide with the main reflector to ensure that the concentration of energy is directed towards the second focus of the hyperboloid, located much closer to the main structure.
As mentioned earlier, this complex has a total of six antennas (only four of them are working) made up by aluminum panels, and supported by steel and concrete structures. The biggest antenna has a mass of 8500 tons, of which 3500 correspond to the moving part. Its main reflector surface has 70m of diameter. It has 1272 panels of different sizes arranged in 17 rows. The panels of the first 8 interior rows have a solid surface, while those at the outer 9 rows are drilled.
If we want an efficient communication with these large antennas, the reflecting surfaces shouldn’t have deformations higher than 1/40 of the wavelength, which means 0.25 mm for frequencies up to 30 GHz.