Transponder Antenna Ground Planes

A friend forwarded the following study ... has anyone tested
Transponder Antenna output on a graphite ship without an additional
ground plan?

Title:
Performance of graphite epoxy as an antenna ground plane
Authors:
Erickson, J. E.; Graham, O. D.
Affiliation:
Air Force Academy, CO.
Publication:
Final Report Air Force Academy, CO.
Publication Date:
08/1978
Category:
Communications and Radar
Origin:
STI
NASA/STI Keywords:
AIRCRAFT ANTENNAS, GRAPHITE-EPOXY COMPOSITES, GROUND SUPPORT EQUIPMENT,
PLATES, ANTENNA RADIATION PATTERNS, DIPOLE ANTENNAS, IMPEDANCE MEASUREMENT,
MONOPOLE ANTENNAS
Bibl iographic Code:
1978aifo.reptQ....E

Abstract
This final report describes work undertaken by members of the Department of
Electrical Engineering at the USAF Academy, Colorado for the Post Doctoral
Program/Rome Air Development Center/Griffiss AFB, N.Y. This effort involved
a study of graphite epoxy composite material as an antenna ground plane at
the frequencies of 370 and 837 MHz. Five by five foot sheets of graphite
epoxy were provided by the Composites Laboratory of the Air Force Flight
Dynamics Laboratory at Wright-Patterson AFB. Antenna impedance and antenna
pattern measurements were made using these graphite epoxy sheets and also an
identically sized sheet of aluminum. These measurements were made with both
monopole and dipole antennas and also with a UHF blade antenna from an F4
aircraft. Results show that the 50 ply sheet of graphite epoxy behaves
identically with an aluminum ground plane when used with a monopole or
dipole receiving antenna at 370 and 837 MHz

"Ken Kochanski (KK)" wrote in message
oups.com...
A friend forwarded the following study ... has anyone tested
Transponder Antenna output on a graphite ship without an additional
ground plan?

.....Snip....

.... Results show that the 50 ply sheet of graphite epoxy behaves
identically with an aluminum ground plane when used with a monopole or
dipole receiving antenna at 370 and 837 MHz


50 ply! How many layers of graphite are used in the construction of the
average sailplane?

Wayne
HP-14 "6F"
http://www.soaridaho.com/

yeah, understood, hardly that many ... I just want to know if we have
any actual test results.

KK

On Apr 6, 8:07 am, "Ken Kochanski (KK)"
wrote:
yeah, understood, hardly that many ... I just want to know if we have
any actual test results.

Standard practice for Schleicher is to install the antenna on the
ASH-26E, ASW-27, etc... just behind the main wheel. Pretty much looks
like they just drill a hole and install a typical antenna with no
other prep work.

Beyond the lack of complaints of poor performance, I don't know if
there has been any scientific testing performed to prove out the
installation.

-Tom

I have a stub antenna installed on the underside of my Ventus 2cM fuselage
(carbon-fiber / epoxy).
No scientific testing, but it seems to work just fine.
The high frequency electro-magnetic fields generated by transponder antennas
hardly penetrate at all into metal or graphite, so I wouldn't expect 5
layers or 50 layers to make any significant difference.
Ray

"5Z" wrote in message
ups.com...
On Apr 6, 8:07 am, "Ken Kochanski (KK)"
wrote:
yeah, understood, hardly that many ... I just want to know if we have
any actual test results.

Standard practice for Schleicher is to install the antenna on the
ASH-26E, ASW-27, etc... just behind the main wheel. Pretty much looks
like they just drill a hole and install a typical antenna with no
other prep work.

Beyond the lack of complaints of poor performance, I don't know if
there has been any scientific testing performed to prove out the
installation.

-Tom

Notice that they stated for use as a receiving antenna. I haven't done any
studies either, but the stub antenna mounted just forward of my landing gear
on my discus 2b seems to work fine. There is no trouble in the static tests
to get it certified, and local controllers seem to "see" my reply just fine.

Bob Greenblatt

On Apr 6, 6:52 am, "Wayne Paul" wrote:

50 ply! How many layers of graphite are used in the construction of the
average sailplane?

Average, I couldn't say. But when we made Brad's carbon fiber HP-24
fuselage, we used the equivalent of about 5 plies at 0.010" (0.25mm)
per ply. In thickness, weight, and stiffness it came out to be about
like what the European factories do.

Thanks, Bob K.