They look as if they might be home to families of extra-terrestrials recently arrived on earth from some sort of galactic cataclysm – and they are everywhere and increasing in number. Yet there is no need to call in the air force just yet if you spot one of these on your travels. Your average radome may look like it is from a science fiction novel but its real purpose is much more down to earth: it is a kind of umbrella.
It’s all about the weather. Inside a radome there will be a microwave or radar antenna. If you build a case around something like a radar antenna then ordinarily something called attenuation happens – it is sometimes known as extinction. This is when flux gradually loses intensity through a medium. A simple example is you in the summertime – you wear dark glasses to attenuate sunlight.
In such a way the radomes are built for minimal attenuation. The electromagnetic signal which is received or transmitted by the antenna needs to be as little disturbed as possible while the hardware which emits or collects the signal needs to be protected from the elements. Often a radome also functions as a shelter for those who operate the antenna. Radomes can often be tens of meters in diameter.
The material out of which the radome is constructed is transparent to radio or radar waves. So, a radome protects antenna within from the wind, rain ice, sand and even ultraviolet rays. They are also handy for hiding sophisticated and secret technology from the gaze of the public. When the antenna within are rotating you could also say that they protect people who otherwise might get in the way and get inadvertently sliced and diced.
Radomes are built in a number of shapes; the most popular (to both scientists and the public) are those that are shaped in a spherical or geodesic manner. There is something about the shape which captures the imagination. Typically they are made from fibreglass but they are also constructed from polytetrafluoroethylene or PTFE. That’s teflon to you and me.
An antenna dish situated in a place where it rains a lot is in danger of gathering a great deal of water on its surface. The radome protects it from this – and if in addition the radar dish spins then its rotational mechanism will also be protected from the wind and associated detritus swept along by it.
In cold places like the arctic ice is the problem. If it accumulates on antenna then they can become seriously detuned. It causes something known as VSWR (voltage standing wave ratio) to increase and this power is inevitably fed back to the transmitter. The result, ironically, would be that because of ice the transmitter can overheat. There is such a thing as a foldback circuit which could avoid this but then the range of the station would be dramatically reduced by this.
So, a radome will stop the antenna being damaged or affected by the elements by providing a strong weatherproof cover – more often than not made of teflon or fibreglass, as stated before. Fiberglass was developed as a structural material during the Second World War because of the need for radomes to cover radar dishes on aircraft and ships. Anything you use made out of fiberglass, from a canoes to kit cars have this original need to thank for their existence.
Even when spherical or geodesic in shape in parts of the world where it is rainy, not all the water will naturally run off the surface. A sheet of water, however thin, on the surface of a radome will degrade the performance of the antenna within. The structure of a radome has a trick up its sleeve. When well designed the surface of the radome will be hydrophobic so that the water will bead up and form large droplets which the run off the radome. The newer radomes are made from super-hydrophobic Teflon.
Menwith Hill in the UK (above) is a particularly striking place as it holds a collection of over 30 radomes which, it is thought, intercept satellite communications. Situated in North Yorkshire the base’s true operations are top secret but it is known that it provides support both in terms of communication and intelligence to the UK and the USA. It is considered by many to be the largest electronic observation base on the planet.
To some what goes on inside some radomes may border on the sinister; to others they are simply another method employed by our governments to protect us. Yet the instruments within are not simply used for defense. Many would agree, however, that as constructions designed to pique the curiosity if not the imagination – they are a hard act to beat.
