RE: NEC-LIST:Proper Antenna Patterns

You are somewhat correct. Because an antenna has it own characteristic
impedance, the current distribution on the antenna is altered by the
"source" impedance whether it is a receive or transmit antenna. Altering the
current distribution in turn alters the pattern. This may not be noticeable
on a simple dipole but becomes quit noticeable in complex scattering
environments (even on simple Yagis).

-----Original Message-----
From: ROSSI Giuseppe [mailto:giuseppe.rossi_at_fiat.com]
Sent: Thursday, October 11, 2001 9:08 AM
To: 'KLysiak'
Subject: R: NEC-LIST:Proper Antenna Patterns

altough I'm not a pure scientist on antenna
as an engineer, i believe that antenna pattern do not depend on
antenna input impedance.
The radiation pattern is completely due to the flow of the current on the
antenna.
So as long as there is current flowing on the antenna i.e.
the input impedance is not completely reactive every antenna produces
its own antenna pattern.

In other word the field emitted by the antenna do not rely on input
impedance
but only on the current and geometrical property of the antenna

Sincerely

Ing. Giuseppe Rossi

-----Messaggio originale-----
Da: KLysiak [mailto:KLysiak_at_swri.edu]
Inviato: giovedì 11 ottobre 2001 15:37
A: nec-list_at_gweep.ca
Oggetto: NEC-LIST:Proper Antenna Patterns

Colleagues,
        The complex (real and imaginary parts or amplitude and phase)
antenna
patterns for transmit and receive antennas change with termination
impedance. Normally NEC uses an ideal conjugate matched source on transmit
antennas. If the antenna is fed with something other than an ideal conjugate
load (i.e. 50 ohm coax) its pattern will change.
        How can this be properly modeled in NEC? In particular, if we want
to model
a LPDA that has internal transmission lines which we want to feed with a 50
ohm source. How do we a 50 ohm source to a segment that has an internal
transmission line on it?

Keith A. Lysiak, Ph.D.
Southwest Research Institute

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