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ghb
Joined: 15 Jul 2002
Posts: 82
Helped: 5
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 11 Mar 2003 17:15 determining dielectric constant of unknown material |
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with only a scalar network analyzer
and an anechoic chamber with pattern recorder
currently deciding on an approach
but was wondering if anyone else might have some thoughts on this
thanx in advance
gb
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flatulent
Joined: 19 Jul 2002
Posts: 4856
Helped: 292
Location: Middle Earth
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| 11 Mar 2003 17:32 bulk or PC |
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Is your material in bulk form or is it a printed circuit card? If bulk you could use your chamber to measure the transmission of a plane wave through the material. When it is a half wave thick there is no reflection and the transmission has a local maximum.
For printed circuit material, you can use it as a capacitor. After finding the capacitance you work backwards from the formula to get e-sub-r.
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ghb
Joined: 15 Jul 2002
Posts: 82
Helped: 5
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| 11 Mar 2003 17:49 |
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the material will be used for printed circuit style design
housing a patch antenna and its feeding network
material was chosen by customer however
this material is not a typically used in microwave applications
ie there is no dielectric constant data taken for microwave frequencies
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ghb
Joined: 15 Jul 2002
Posts: 82
Helped: 5
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| 11 Mar 2003 17:52 |
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sorry forgot to mention
that i have the material in bulk form
i was thinking along the plane wave idea
however the capacitive approach sounds reasonable also
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flatulent
Joined: 19 Jul 2002
Posts: 4856
Helped: 292
Location: Middle Earth
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| 11 Mar 2003 18:03 one possible probem |
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| One possible problem you may face in the antenna use is that the material may have a high loss which will drastically reduce the antenna efficiency. Try it out. Your customer may want to change the material once they find the extra cost of higher power amplifiers to get the same radiation field as from a good antenna is more than the cost of using good microwave material.
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g86
Joined: 21 Jan 2003
Posts: 208
Helped: 4
Location: On top of antenna :))
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| 11 Mar 2003 18:04 Re: determining dielectric constant of unknown material |
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I normally use waveguide for a chunk of dielectric and see the refraction.
This technique dose not need a network analyzer.
And one of my friend uses horn antennas to mesure the permittivity of a sheet dielectric with a ground plane (suitable for patch antenna and high frequency). May be you are also interested in this method.
Scalar network analyzer may not give you the imaginary component.
  
| ghb wrote: |
with only a scalar network analyzer
and an anechoic chamber with pattern recorder
currently deciding on an approach
but was wondering if anyone else might have some thoughts on this
thanx in advance
gb |
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Timelord
Joined: 04 Aug 2001
Posts: 32
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| 11 Mar 2003 18:56 Re Dielectric Measurement |
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Here is a link which I posted some time ago. You may find what you are looking for there
http://www.boulder.nist.gov/div813/rfelec/properties/Pages/publications.html
Timelord
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