Radome Material Question
Radome Material Question
(OP)
The system is a cylindrical phased array. The antenna elements are dipoles at DC ground potential.
The problem:
1) Due to weight and packaging constraints, must use a flexible, lightweight material as a weather-resistant radome.
2) Due to flexibility requirement, the radome contact with the array elements is intermittant, especially in windy conditions.
3) In low-humidity windy conditions, static charge builds up on the surface of the radome, and can cause catastrophic failure to sensitive LNA components located on the antenna PCB assembly.
Question:
Does anyone know of a radome material (currently using nylon) that has decent surface charge mobility properties as well as decent dielectric loss properties at L-band? I have talked to Gore-Tex about their microwave material, but cannot get anyone except sales folks to return my calls.
Any informatiion is greatly appreciated.
The problem:
1) Due to weight and packaging constraints, must use a flexible, lightweight material as a weather-resistant radome.
2) Due to flexibility requirement, the radome contact with the array elements is intermittant, especially in windy conditions.
3) In low-humidity windy conditions, static charge builds up on the surface of the radome, and can cause catastrophic failure to sensitive LNA components located on the antenna PCB assembly.
Question:
Does anyone know of a radome material (currently using nylon) that has decent surface charge mobility properties as well as decent dielectric loss properties at L-band? I have talked to Gore-Tex about their microwave material, but cannot get anyone except sales folks to return my calls.
Any informatiion is greatly appreciated.
RE: Radome Material Question
At least it can be treated as a thin wall design which simplifies things but I would try the radome people like Norton.
RE: Radome Material Question
See this site:
http://www.syrres.com/stc/products_lcmr.htm
RE: Radome Material Question
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Radome Material Question
RE: Radome Material Question
Or the same with something like Tyvek?
TTFN
RE: Radome Material Question
I'd also investigate why the DC-grounded antennas aren't protecting the LNA inputs from the static. I would have thought that they would...
RE: Radome Material Question
We thought the same thing. The inputs are pretty well protected by grounded stub input filters and limiter diodes, but the outputs of the LNAs are vulnerable to the overvoltage of the discharge. These antenna columns have approximately 5' of cabling between them and the primary power supplies, so there is some impedance between the local ground and system ground, thus allowing ground plane charging. I have had success putting 1N5907s across the bias supply filter caps for the LNAs, but would like to find a non-electronic solution until we can re-spin the board.
RE: Radome Material Question
I do not understand the loose wire grid in the cover material. Would that still be radiolucent?
RE: Radome Material Question
If the static discharge is getting into the LNAs through the power supply (as you've indicated), then fixing it should be fairly easy.
If you're not perfectly clear on the exact failure mode, then it might be well worth doing a detailed analysis to see how the 'sparks' are getting in.
If it is getting into the device via the power supply, then you can fix that (easily), then you don't have to worry about the radome any more...
RE: Radome Material Question
You could try buying an ESD labcoat with embedded wiring just to test it out:
http://
http://www.vidaro.com/StaticControlESD/index.html
http:/
TTFN
RE: Radome Material Question
The static is definitely coming from the radome. The reason it causes the ground-to-power bus voltage to exceed the absolute maximum for the LNA device is that the impedance of the twisted pair back to the power supply system ground has some finite inductance which resists the dissipation of the many coulombs of charge injected onto the antenna elements (local ground plane) for several hundred nanoseconds while it flows through the output pin lead wire of the LNAs. I can short the power supply connector and inject charge onto the ground plane and the charge dissipation time is reduced to several nanoseconds. We first encountered this phenomenon out at Fort Huachuca Az during MIL 810F sand tests,which are performed in 40 MPH winds. The local humidity was a whopping 7% that day, and if it had been dark, I'll bet we could have seen the little lightening bolts going off inside the radome.
RE: Radome Material Question
But, you might also want to think about the 'RF Noise' issue of all these static discharges. Will your system still work with all this static occuring right at the input?
It seems like you've got the worst possible radome material when it comes to static. How about tossing it into the dryer with a sheet of 'Bounce' or similar consumer static control product? It seems like anything would help.
RE: Radome Material Question
Nylon just seems like the worst way to go in a dry environment with a lot of ionising-particulate circulation.
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Radome Material Question
RE: Radome Material Question
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Radome Material Question
This is the prime reason why I suggest always using grounded center conductor antennas. You could switch to a folded dipole antenna which has typically wider bandwidth and the two arms are connected, i.e. center conductor to ground.
also, the famous quarter wave short = open circuit.
If your antenna is a printed circuit, you could add a quarter wave short on the distribution systems to short out the center conductor.
kch
RE: Radome Material Question
As I mentioned in the original post, the elements are an integral part of the ground plane. The problem is that the small impedance between the local antenna system ground and the main system ground causes ground charging when massive charge dump onto the plane occurs. We have actually observed this phenomon an oscilloscope attached between the power and ground pins during the sand tests.
RE: Radome Material Question
...lack of voltage protection ACROSS the victim device (locally). Distant grounds, and the associated inductance to get there, are not 'the problem' - they're just a real world given. It's a red herring to even mention it.
Once the radome is sorted, then you'll probably find that human static discharge during set-up and take-down handling will be the next problem... You might as well respin the PCB to add the protection diodes. And just be glad that the susceptibility is - apparently - just on the power supply side and not in the RF side where adding protection might be much more difficult.
RE: Radome Material Question
If your antenna is not circularly polarized, and is linear polarization, then following IRstuff's suggestion you can metallize your radome in the opposite linear polarization. It's possible to metallize about 75% of the radome surface and still have great rf transmission properties in your primary linear polarization. Normally you'd think to add thin wires as suggested by IRstuff, oriented cross polarized covering 1-5% of the radome surface, but a recent analysis by a co-worker showed that having much more metal, or just the right thickness metal to non metal ratio can provide minimal thru loss over a pretty wide bandwidth. I was very surprised at this result, but I believe it.
Is your antenna linear polarization? If so, you could try a metal tape experiment, or wire experiment with very little effort.
Actually, what is your plan? Is this a very high priority item with funding requiring detailed analysis and a 9 month project with modifications of 462 pieces of hardware? Just trying out my psychic thoughts.
kch
PS: Has anyone noticed that the word your is often typed you, must be a human factors natural oops, I do it alot.
RE: Radome Material Question
P.S. I often type "woudl" instead of "would"... no matter how carefully I try to type, I always default back to 'dl'. Very frustrating, especially when other words like "told", "sold", and "should" seem to come out OK the first time around. <shrug>
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Radome Material Question
This system is vertical pol in the orientation of the array cylinder. If you follow the link in the 3rd post, you will see a picture of the system. If you go further and follow the Army link in that piece, you will see a picture of the system without the radome, and if you look carefully, you can see the outline of the individual dipole elements through the PC board material. That is an interesting experiment with the cross-poled wire. We may try that ourselves.
Our next test is scheduled in early August, and we are going to try to "bungee" the radome axially between the individual columns, and if old Dan Bernoulli is kind, hopefully we can maintain intimate contact between the sides of the radome and the antenna elements, keeping the charging to a minimum. Just in case, however, I am taking along an extra set of columns with 1N5907's back-soldered across all the LNA bias filter capacitors.
RE: Radome Material Question
RE: Radome Material Question
I saw the photo's. The wires should work unless dissipated static is a localized point source and not globally connected, which is probably is since current doesn't move on an insulator. Hence, I'd guess that individual sections of your radome make static that's isolated from the other areas of your radome. Maybe you'll need this anti-static paint http://ww
Slight concern using wires that you keep them crosspole if your radome material droops or can change orientation. I'm curious about the rain and it's affects with a wet radome. Normally, you'd want the rain to ball up and roll down the surface, seems like it would wick down and cause problems. A smooth surface can have hydrophobic coatings added to minimize loss due to sheeting. At 2-3 ghz, expect 5-10 dB loss due to a sheet of water, plus pointing error accuracy degradation.
Raytheon Raymarine makes a marine radome 19" diam. x 19" high, although your unit looks larger than that. There are other larger sized and low cost lightweight radomes from Andrew Corp available.
kchiggins
RE: Radome Material Question
I think I will order a sample of the staticide and try it. The problem I see with it is if it stiffens the material when it dries. This system has to be taken down and moved frequently, so the radome gets folded up into a small volume and crunched into a carrying case. If the paint tended to crack, I can forsee problems. Perhaps a thin coat applied in the field in arid locations would work.
RE: Radome Material Question
I haven't used the material shown, just found it on the web. I'd do an S21 from antenna to antenna with a sample to make sure it's not too lossy.
I realize from your statement why the array looks so odd, cuz it folds small. Interesting mechanical arrangement.
Maybe a secondary anti-static bag or cloth painted with anti-static coating fitted over the array first may be friendlier than spraying your radome material? At least you won't have to tell your co-workers that you ruined a radome with the anti-static paint until you know it works.
Maybe if you add a plastic disk to the top surface that hangs over 3 inches or so, it might keep the radome from touching the antenna surface and keep the rain off better. The bird poop would miss the radome too if the top disk is large enough. Maybe funnel water collected down thru pipes between your elements. Lots of useless ideas to consider I know.
Let us know how your experiments come out.
I hope your system can be attached to an audio warning system for inbound projectiles to give people a few seconds to take cover. Add some pits or sandbags for more protection. Good luck.
kchiggins
www.toyon.com
RE: Radome Material Question
RE: Radome Material Question
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Radome Material Question
RE: Radome Material Question
"Radome must be washed on spin cycle using Woolite at least once a week during normal use."
I've seen army use procedure manuals that actually listed things like "Do not handle board with taco sauce in vicinity." (Gotta love our government). A board was fried because some moron tech handled the boar while eating a taco... sauce spilled on it, shorted it out, magically creating a new caution line in the manual. When the board came back, the taco sauce had dried in place, the tech didn't even worry about cleaning up the evidence.
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Radome Material Question
RE: Radome Material Question
http://www.mystaticguard.com/products.cfm
which, apparently, you can also make yourself:
http://www.recipegoldmine.com/house/house17.html
TTFN
RE: Radome Material Question
just saw this in the Plastics solutions newsletter and thought of vous. Maybe they have a thin sheet you could use to dissipate your static.
Mike Oliveto,
Quadrant Engineering Plastics Products
Statically dissipative plastics reduce losses during the handling of electro-sensitive devices and improve safety and reliability of packaging equipment.
Kevin
RE: Radome Material Question
RE: Radome Material Question
The fabric listed in this url might be what you want:
h
RE: Radome Material Question
kch
RE: Radome Material Question
http
We are also looking for a combination polyester-nylon fabric, which should have pretty good anti-static properties, since these materials have complementary work functions. So far, we are trying to buy COTS without getting involved in a big R&D effort with a supplier, but have not had any great success as yet.
RE: Radome Material Question
Thanks, Brian.