Re: NEC-LIST:Out of band response of a GHz ant...

How far out of band?

A typical horn is pretty broadband, although the antenna gain (referenced
to an isotrope) does change with frequency. How much waveguide is there
between the transition and the horn? are you below cutoff?

Is the horn corrugated, or smooth walled? (the former is better...)

There are creeping modes that propagate around the edge and back along the
sides. Some loaded absorber helps a lot (the thin sheet stuff loaded with
ferrite). Sticking the horn through a panel of absorber also helps
(although it will screw up the noise temperature, so don't do this for a
radiometer...)
In any case, isolation is "pretty good" between two horns, side by
side. Say, 40-60 dB. The big thing will be reflections off stuff in the
foreground (speaking photographically)... A housefly a meter away will
provide a very noticeable reflection.

In any case, I have seen folks build a "stepped frequency radar" using a
network analyzer and two horns, then using the analyzer's frequency->time
domain function.

At 10:50 AM 3/27/2002 -0600, Richeson, Peter D wrote:
>I am trying to get the isolation between antennas operating in the GHz.
>Does anyone know what the out of band response of say a horn antenna would
>be? My systems are separated by several GHz but are close together.
>

Jim Lux
Spacecraft Telecommunications Equipment Section
Jet Propulsion Laboratory
4800 Oak Grove Road, Mail Stop 161-213
Pasadena CA 91109

818/354-2075, fax 818/393-6875

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