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My cubesat team is working on our design for rolled whip antennas to deploy in a UHF turnstile configuration based on this design: enter image description here

What I would like advice on is the material for the antennas themselves. Spring steel has ideal mechanical properties, but isn't an optimal antenna metal. The material of the one shown is apparently Nitinol shape memory alloy, that will unroll itself when heated. What other metals would you suggest looking into further?

The system characteristics are

  • 435 MHz
  • Under 50kHz BW
  • 4W max power
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  • $\begingroup$ which bands are we talking about? $\endgroup$ – Marcus Müller Oct 17 '16 at 9:19
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    $\begingroup$ Can you tell us more about your reference design? I don't fully understand it; to me, it looks like there's the PCB and potentially critical components with very varying magnetic susceptibility where the magnetic field of the coils would be strongest o.O $\endgroup$ – Marcus Müller Oct 17 '16 at 9:25
  • $\begingroup$ Ahhh I'm stupid; this is a rolled up antenna, prior to being deployed in space :) $\endgroup$ – Marcus Müller Oct 17 '16 at 9:30
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As usual, for antennas, the better your material conducts, the higher your antenna efficiency. Hence, go for copper. It has an excellent conductivity per volume (which might or might not be critical in your application), and there's not many metals that will beat its conductivity at all. Steel really isn't good for that.

If you're using suitable frequencies, steel wire with a copper coating might work for a dipole. The frequency will define your skin depth and the losses that a non-perfectly conducting antenna will incur. Definitely sounds like you'd have to just copper-coat some spring steel and try.

Another thing: I don't know how stiff the deployed antenna will be, but you are in the earth's magnetic field, with long ferromagnetic rods; that will excert a torque on your satellite... I can't calculate how much, though, since I know nothing about your antenna sizes, your orbit, your height or anything about the satellite.

Generally, when asking about "what's the perfect material for my antenna", you should include a lot of factors:

  • frequency (which I find kind of obvious)
  • bandwidth
  • acceptable loss
  • power
  • mechanical forces
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  • $\begingroup$ Sorry for not specifying the critical details! $\endgroup$ – Kontakt Oct 17 '16 at 13:37
  • $\begingroup$ Frequency is UHF in the 435 MHz satellite band, bandwidth would be as much as we are allocated, probably in the range of 9-50kHz. Acceptable losses I would have to really dig into our working link budget. Power <4W. Mechanical forces should be fairly low. I would think the magentorquer effect should be minimal, with no net torque transmitted to the satellite since the signal is sinusoidal. I will need to look into bending, but I would expect negligible amounts. $\endgroup$ – Kontakt Oct 17 '16 at 13:48
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    $\begingroup$ @KontaktKM4REF Please edit that information into your question rather than leaving it in a comment. $\endgroup$ – Kevin Reid AG6YO Oct 17 '16 at 18:02
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I think the mechanical properties for proper deployment are much more important than the electrical properties.

The picture appears to show elements that are flat tapes rather than round wires, which is probably a good idea. I'm thinking that if the tape can be given a slightly U-shaped cross-section (like a steel measuring tape), it will be better able to fully straighten itself after deployment, and may allow you to use thinner (lighter) steel stock.

And as Marcus says, plating the steel with copper and/or silver will improve its electrical characteristics without compromising its mechanical characteristics.

I'm trying to figure out the deployment mechanism, but the picture is a bit fuzzy. There are little plastic doors holding the coiled elements in place, with spring-loaded threads holding the doors closed. Are those pairs of SMD resistors designed to heat up and cut the thread for deployment?

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  • $\begingroup$ The system has coiled antenna elements that load the doors, which are held in place with monofilament. When you heat the resistors, the monofilament plasticly deforms and the antenna springs out. $\endgroup$ – Kontakt Oct 17 '16 at 13:36
  • $\begingroup$ Ah. So you're sure that the monofilament will never reach its "plastic deformation" temperature at any time during the pre-launch or launch procedures, and that the resistors CAN heat it up to that temperature under all ambient conditions after the cubesat has separated from the launch vehicle... $\endgroup$ – Dave Tweed N3AOA Oct 17 '16 at 13:49
  • $\begingroup$ Yes. It's a proven design and the standard for cubesat deployments. $\endgroup$ – Kontakt Oct 17 '16 at 13:50
  • $\begingroup$ OK, but then what is your actual question? Are you proposing to deviate from the standard in some way? Surely the material from which the elements are made is part of that standard. $\endgroup$ – Dave Tweed N3AOA Oct 17 '16 at 13:51
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    $\begingroup$ Please add all this info by editing to your question itself – it's very relevant to the question! $\endgroup$ – Marcus Müller Oct 17 '16 at 18:04

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