Selecting the right dish

Solid dishes offer many advantages over mesh or perforated dishes. Solid dishes are sturdier, they hold their shape and they do not flex in the wind. They are more expensive, but have better value for money. Most popular solid dish is the prime focus one, where the feed/LNB assembly is positioned exactly on the focal point of the dish. Expect solid aluminium dishes to have a useful life of 10 to 20 years. Their efficiency ranges from 60% for dishes greater than 3.0 meters to 75% for smaller dishes. Solid segmented dishes are also available; segmentation, however, implies reducing shipping costs during transport from one country to the other. Segmenting a parabolic dish causes typically a 10%-20% reduction in efficiency with increased side lobes. TITOSAT systems use only solid one piece (non-segmented) dishes. We have had satellite dishes installed over 20 years ago which are still fully operational in a satisfactory condition. 

Mesh or perforated dishes are more flexible than solid dishes. They move more in the wind - causing the satellite signal to disappear - and are less durable. Mesh dishes are much less expensive, but need more frequent replacement. Expect mesh or perforated dishes to have a useful life of 3 to 5 years. Other disadvantages of mesh or perforated dishes include poor side lobe rejection of adjacent satellites and the rejection is not consistent from year to year. Furthermore, they have poorer efficiencies, typically 35%, since they are imported segmented. This means that a 2.4 meter solid dish with 70% efficiency performs as good as (if not better than) a 3.4 meter mesh dish!

Offset dishes are another type of dish seen on the market. "Offset" means the feed element is purposely kept outside of the "main beam" between the dish and satellite. Offset dishes reduce terrestrial interference and improve the beam shape slightly, but they are more complex to set up and adjust. They have higher efficiencies than prime-focus solid dishes, typically around 75%. However, they are only available in small sizes typically from 60 cm to 1.8 m. 

Diameter choices come down to one statement: "Bigger is better". Bigger dishes offer higher gain, they have narrower beamwidths that have better side lobe rejection of adjacent satellites and better rejection of terrestrial interference. Of course this terminology applies only within the same type of dishes, i.e a 3.0 meter solid one piece dish outperforms a 2.4 meter solid one piece antenna. So, theoretically, a 2.4 meter solid one piece dish should perform as good as a 3.4 meter mesh segmented dish. Whist this may be true if the antennas were operated at C band, but believe it or not, experience showed that a 2.4m solid dish outperforms a 5.0m mesh dish at Ku band.