I believe that MMANA is a MININEC-based program. If that's correct, then
there will be an error wherever wires connect at an angle, as they do in
the ground plane antenna. The error can be minimized by making the
segments of both wires very short near the connection point, either by
greatly increasing the number of segments or by "tapering" the segment
length. A capability to do the "tapering" automatically might be built
into MMANA -- it was a feature of MININEC-based ELNEC 15 years ago. I
don't know if that's the reason for your results, but that's where I'd
start looking.

Roy Lewallen, W7EL

André wrote:
Hello,

(pse excuse my english)

I have some questions about GPA and vertical dipole
(vertical quarter wave with four horizontal radials and half wave center
feed vertical)

With a modelling software (MMANA) and antennas calculated in free space
conditions, at resonance,I get 72 Ohms for the dipole (correct), but only 22
Ohms for the GPA as I expected 36;

does anybody know the reason ?


Another question, The radiation patterns seem to be identical for both
antennas, so I expected the same gain with GPA or dipole, but the soft give
2.13 dBi for the dipole (correct) but only 1.57 dBi for the GPA.

Not due to the fact that the currents are greater in the GPA, as the soft
was working in 'no loss' conditions for the wires.

Tnx if you have solutions,

73

André
F5AD
--------------------------
http://f5ad.free.fr/