Radome construction - Page 1
Forum section: electronics / projects

author: e100
author_rank: Frequent Contributor
timestamp: October 06, 2019, 02:03:28 pm
content: http://www.adf-gallery.com.au/gallery/albums/F-111-A8-112/F111_A8_112_Birdstrike.jpgThis is the radome on jet after a bird strike. I kind of imagined it would be constructed like the hull of a fibreglass boat, but it's nothing like it.Can anyone explain why it's built this way?

author: MadTux
author_rank: Frequent Contributor
timestamp: October 06, 2019, 02:10:28 pm
content: These are directional fibers, not undirectional fleeces like on fibreglass boats.Undirectional fleece is cheaper, but directional fibers, like on that radome has much better strength to weight ratio, because fibers can be orientated so that the load is applied along the fibers.Can also made thinner this way, so less radar absorbtion/reflection.

author: coppice
author_rank: Super Contributor
timestamp: October 06, 2019, 02:14:29 pm
content: A boat is not a complete circular structure. When you have a complete circular structure and plenty of money to spend on the strongest possible construction you end up with something like that aircraft's nose. I've seen structures like this being assembled. They put a huge number of hours of labour into getting the fibres set up just right in UV curable resin, and when everything has been inspected and accepted the UV light goes on.

author: coppercone2
author_rank: Super Contributor
timestamp: October 06, 2019, 02:16:01 pm
content: can you buy an old radome as military surplus to put on a home roof to guard an antenna?

author: German_EE
author_rank: Super Contributor
timestamp: October 06, 2019, 04:02:21 pm
content: I built a radome once after we lost satellite reception due to snow on the dish. Nothing sophisticated, just a wooden frame covered by a layer of polythene but it was still there when I left six years later.

author: SeanB
author_rank: Super Contributor
timestamp: October 06, 2019, 04:26:00 pm
content: You can, though you might pay a bit for shipping, as they tend to come from aircraft graveyards, and often the cheapest shipping method is airfreight to your local hub airfield, as they are rather big, but internal airline shipping is capable of handling them without damage.Have seen just how strong they are, saw an aircraft where it ran into a wall after the tow connection broke. New guy inside, and they forgot to disconnect nosewheel steering, there was no battery to run aux hydraulics (wouldn't have helped anyway, as there was no engine either, and half the pipes were capped with plastic plugs) so he only was able to put a few strokes in on the emergency pump before the plane hit the wall.Not much damage to the wall, designed to survive pretty much anything short of a nuclear blast, other than a single hole where the tip of the radome crunched in. The pitot assembly in front took the initial impact, sheering off it's mountings and pushing back into the nose. Unfortunately right behind it is a large block, called " Assembly, electrical control", which contains every single electrical circuit, circuit breaker and relay for the aircraft in a single block, and the aluminium alloy tube sliced longitudinally through the central panel that makes up the heart of this box. Good thing there was no battery in, as these is no fuse between the main battery bus and this box, and the cable is rated to survive 8kA of current flow, while only rising 200C above ambient.Luckily there was another airframe at the maintenance centre undergoing a full overhaul, as repair time on this box was estimated at 2 years plus. So, undo 6 bolts, remove 200 electrical connectors, a few dozen hydraulic hoses, the remains of the pitot static system, airconditioning and oxygen systems and nose off, on a pallet and fly away, with the new to the plane serviced nose arriving the next week to be installed.Radome popped up by the shop next door for service and inspection, and aside from scratches from the steel wall, and needing the stainless steel tip filed round again, it survived unscathed with no delaminations in the resin composite. Cleaned up, painted and tested, and back into stores it went.

author: coppercone2
author_rank: Super Contributor
timestamp: October 06, 2019, 04:41:30 pm
content: actually that sounds a bit dangerous to put on a roof because its too tough (it would be nice if it fell apart if it fell off the roof rather then being dragged into the neighbors house by the wind), needs to be weak, that sounds like putting a knife on the roof.

author: duak
author_rank: Super Contributor
timestamp: October 06, 2019, 05:05:16 pm
content: Would most of the damage have come from aerodynamic forces once the radome was breached?

author: coppice
author_rank: Super Contributor
timestamp: October 06, 2019, 05:17:56 pm
content: Quote from: duak on October 06, 2019, 05:05:16 pmThese things are very strong, but once you get to the point of breakage the resin has a tendency to shatter and fall away from the fibres over a large area. From there it doesn't take much to get the whole structure stripped back to bare fibres. The same thing happens with both glass and carbon fibre reinforced structures, although you obviously can't use carbon fibre for a radome. Carbon fibre is often used for lightweight radar dishes underneath the radome.

author: Stray Electron
author_rank: Super Contributor
timestamp: October 07, 2019, 08:34:13 pm
content: Quote from: coppercone2 on October 06, 2019, 02:16:01 pmIf you're anywhere near Florida I can point you to a place that has a PILE of ship RADAR domes. They range in size from about 1 foot in diameter and a foot and a half tall up to about 42 inch diameter and about 5 1/2 foot tall. These are from cruise ships so there is nothing military or classified or controlled about them. The same gimbal inside the dome usually has directional antennas for sat communications (INMARSAT), GPS antennas and other antennas mounted on it. I have a real nice Applied Satellite Engineering antenna housing sitting right next to me at the moment. It's about the shape and size of an American football. None of these have a layered construction such as fiberglass, they appear to be molded in one piece and made of something like HDPE. I've seen many of these that have spent years at sea and the surface is weathered but otherwise they're completely intact.IMO the biggest problem is how to attach a large object like a radom to the roof of the house securely enough to withhold storms and hurricanes and without penetrating the roof any more than absolutely necessary. In my experience, anything that penetrated the roof will eventually leak and usually by the time that you discover the leak significant damage as already occurred.

author: coppercone2
author_rank: Super Contributor
timestamp: October 07, 2019, 09:16:16 pm
content: I would pour tar around it but its not very appealing now that I think about it, it will look like a pimple

author: German_EE
author_rank: Super Contributor
timestamp: October 09, 2019, 05:09:46 pm
content: I should point out that the roof holding my home made radome and the satellite dish was flat and everything was well secured. Yes, it could have blown off in severe winds but it is more likely that the polythene would be ripped away leaving the wooden frame.Actual radomes for radar are much more interesting as they need to avoid heating from the high RF output yet remain RF transparent for reception. In the past I have tested RF construction materials in the microwave, if they warm up after a quick blast then they don't get used.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: October 10, 2019, 07:12:55 am
content: There are two real ways to build radomes: Either you build them as thin as you can, with low dielectric constant materials. This way, you can hope your radome will simply be 'invisible' to passing waves.The trick, to my knowledge, used on aircraft is to not do that at all. Instead, you design your radome to be a 'matching' network, in such a way that the plane wave passing through it at the angle you expect sees 1/4 wavelength of material (that being, of course, 1/4 wavelength given the dielectric constant of the material, no free-space wavelength).If you do this, you can't just replace one radome with a random other radome - they are designed with specific frequencies and phase centers in mind. The designers will also specify a very specific thickness, and making it thinner (even if you could, strength-wise) would hurt performance.Interestingly, there is some research into applying these techniques to bumpers of cars, to integrate the radar modules in a neater way.This adds a requirement to the material properties - you need them to be predictable and repeatable.

author: coppercone2
author_rank: Super Contributor
timestamp: October 10, 2019, 10:06:58 pm
content: is the radome at a far field distance from the antenna in this case?

author: coppice
author_rank: Super Contributor
timestamp: October 10, 2019, 10:11:18 pm
content: Quote from: German_EE on October 09, 2019, 05:09:46 pmAn issue with radomes on the nose of aircraft is the need to have a metal strap across the fibre glass dome for lightning protection, without the strap reflecting too much power back into the receiver, especially when using a continuous transmission type of radar, like FMICW.

author: coppercone2
author_rank: Super Contributor
timestamp: October 10, 2019, 10:42:58 pm
content: I wonder if techniques for the design of lens for horn antenna lens can be used for radomes..