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I'm working on a radio module that is made to transmit from a rocket to a ground station for a homemade project. The airframe is made of carbon, therefore I cannot place the antenna(s) inside the rocket (carbon is not RF transparent). However, placing the antenna on the outside of the rocket proves to be an issue as the carbon attenuates the RF, and quite a bit of power is lossed.

Are there any dielectric materials that I can build from household items to insulate the antenna from the carbon? I've tried teflon, mica, and aluminum foil, which seem to work well, but are not quite up to my standard.

Thanks in advance

EDIT: Photo of antenna on airframe

SECOND EDIT:

After testing S parameters, the most intriguing result was that of S11. The VNA documented a reflected power of -12dB when using mica as an insulator 10mm off of the airframe. This 10mm of separation was done with foam that we had lying around. Using the solely foam to separate the antenna from the carbon resulted in a reflected power of -7dB at 10mm and -4.3dB at 7mm. The mica sheet alone gave a reflected power of -3.4dB. These numbers are all on top of the -0.3dB that is reflected when the patch is placed directly onto the airframe, which is a significant distance.

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  • \$\begingroup\$ I don't think a dielectric will help. The conductive body is going to affect your antenna no matter what you do. Aluminum foil is not a dielectric, by the way. \$\endgroup\$ – mkeith May 6 '18 at 18:12
  • \$\begingroup\$ When I use a simple power meter on the receiving side, the gain is quite a bit higher with one of the dielectric materials, and progressively increases with the addition of layers. Also, I'm a bit confused as to why a dielectric wouldn't help (or perhaps I should use a different type of insulation). My understanding is that the proximity of the carbon, and permeability of the material in between directly affects how much power is reflected by an antenna (S11). \$\endgroup\$ – Sandy Beach May 6 '18 at 21:30
  • \$\begingroup\$ Can you post a picture of the rocket and antenna? Basically, any time you put a large conductive body in the nearfield of an antenna, you are going to see some major affect on radiation pattern and VSWR. However, I do believe you regarding your experimental results. However, it doesn't sound like you are looking at the antenna pattern. You are only measuring power at one angle, right? Depending on your application, it may be important to look for nulls in the pattern. \$\endgroup\$ – mkeith May 7 '18 at 0:13
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    \$\begingroup\$ Some dielectrics can be very lossy at some frequencies. \$\endgroup\$ – analogsystemsrf May 7 '18 at 2:40
  • \$\begingroup\$ I can provide you with a photo of the antenna on a piece of the airframe, but that's about all that I have (check post edit). And that's a good note on testing. I completely overlooked testing the signal at different angles, whereas I was simply orienting my receiving monopole in different ways. \$\endgroup\$ – Sandy Beach May 7 '18 at 3:14
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Design your antenna to be a patch antenna and use the carbon-fibre as a ground plane. I've successfully done that when collecting data on from a device mounted on the shaft of an aero engine with the receive antenna on the inside of the carbon-fibre engine cowling. Something like this but not this particular engine: -

enter image description here

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  • \$\begingroup\$ I don't follow when you say to use the CFC as a ground plane. How would I do this? \$\endgroup\$ – Sandy Beach May 7 '18 at 14:11
  • \$\begingroup\$ You don't have to do anything - it will act like a ground plane because it is a reasonable conductor and the patch antenna will utilize this. \$\endgroup\$ – Andy aka May 7 '18 at 14:25
  • \$\begingroup\$ Ok, so how would I get around the fact that the transmitted power significantly decreases when placed on the carbon? \$\endgroup\$ – Sandy Beach May 7 '18 at 14:42
  • \$\begingroup\$ Is that using a proper patch antenna? \$\endgroup\$ – Andy aka May 7 '18 at 16:53
  • \$\begingroup\$ Yes, using the patch antenna in the photo in the post. \$\endgroup\$ – Sandy Beach May 7 '18 at 18:01

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