"No parabolic antennas were found to be used in actual activities." – This is incorrect. Parabolic antennas are actually quite suitable for activities at frequencies of 430 MHz and below. In microwave and higher amateur radio bands, the parabolic antenna is almost the only option (along with horn antennas, etc.).
1. Gain from parabolic surfaces, considering:
It can be seen that the gain depends on D and λ. Therefore, for the same gain, lower frequencies (longer wavelengths) require larger parabolic areas; for the same area, higher frequencies result in greater gain. Of course, beam width also needs to be considered. Thus, in amateur applications, a minimum of 430MHz with 7 is required.A parabolic antenna with a diameter of 10 meters, paired with a 144 MHz band (which is already quite extreme), would be impractical to use at even lower frequencies.
2. When selecting a feed, the primary considerations are: 1) whether it can effectively illuminate the entire parabolic reflecting surface, and 2) its polarization characteristics. A poorly designed feed that illuminates only part of the surface is inefficient (e.g., using a 4DP feed with poor directivity). Conversely, a feed that's too small wastes the surface area. Furthermore, factors like obstruction need to be considered. For example, an OK1DFC feed mounted on a parabolic dish with a 1.5:1 direct-to-feed ratio is ideal in terms of performance, but its ring shape obstructs 1/4 of the dish, which is undesirable. Finally, it's important to note that for lunar reflection and satellite communication, circular polarization is generally preferred because it minimizes interference from different polarization modes.
3. Used satellite TV antennas can be reused, but not in this way. They can be used for local microwave communication testing, EME reception and transmission, deep-space satellite reception and radio astronomy experiments, WX satellite reception, etc. Suitable feed lines and receiving links need to be created. Details are not elaborated here.
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