________________________________
From: [email protected] [mailto:[email protected]] On Behalf Of Price,
Andrew
(SELEX GALILEO, UK)
Sent: Wednesday, December 03, 2008 11:56 PM
To: [email protected]
Subject: High frequency Antennas for EM surveys
Hi everyone
I am looking for an Antenna 1GHz to 18GHz that can be used for em survey
work. This antenna is required for measureing EM fields inside vehicles as
well as outside. The standard double ridge horn has too much directivity.
I have already identified an antenna to cover the frequency range 30MHz
to
1GHz this is an active dipole by Credence Technologies.
Can anybody advise???
Regards
Andy
Andrew P. Price
Principle Hardware Engineer, EMC Specialist
Andy:
Fields inside a vehicle are going to be influenced considerably by reflections
>from the many nearby surfaces. You might want to consider measuring power
density and converting to a field strength.
If you still want to use an antenna, then the very old Polarad CA-B comes to
mind. This antenna was a vertically polarized discone, so it was omni in the
horizontal axis. Antenna factor was about 40 dB from 1 GHz to 10 GHz, so I
don't know if it degraded gracefully up to 18 GHz or what. Still, the design
is valid, if you want to build your own discone. Essentially, a coax
penetration of a 12" diameter ground plane, with the center conductor blended
into a cone that extends maybe 6" to a 6" diameter. Build it solid and get a
traceable calibration, and you're ready to go.
It might be advisable to think about using a couple of stirrers to maximize
you detection probabilities within the vehicle.
Regards,
Ed Price
[email protected] <blocked::mailto:[email protected]> WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780
Military & Avionics EMC Is Our Specialty
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