[time-nuts] GPS antenna in silicon/RTV encapsulation
jimlux at earthlink.net
Mon Apr 14 23:32:27 EDT 2014
On 4/14/14, 12:11 PM, EWKehren at aol.com wrote:
> Am experimenting with small low cost GPS antennas and am considering as an
> alternative RTV/silicon. Any information on RF attenuation of RTV/silicon
> at 1.6 GHz ?
Are you potting the antenna in a solid mass of silicone? Or using it to
seal an enclosure or what?
pure silicone is very low loss, and it probably has an epsilon around 3.
It can be loaded with silica (which is also low loss) to adjust the
mechanical properties and electrical properties. It can also be loaded
with other things (TiO2) which will increase the epsilon, but also the
the plastics that are notorious for loss are ones that have metal or
carbon loading or that are hygroscopic so they pick up water.
In the clear plastics world, Polypropylene, polyethylene and polystrene
are pretty good. Polycarbonate isn't as good, neither are various
acetals (Delrin) and acetates
Here's a chart
or another chart
here's a whole report from Dow on silcone rubbers as dielectrics
They give quite low loss tangents at 10^9 cps (which I looked up on my
cps to Hz conversion chart.. That's in your frequency range) 0.0059 loss
tangent for Silastic 80.
The trick for you will be knowing what else is in your particular
silicone resin, and controlling the water content.
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