NEC-LIST: Antenna factors of bicone antennas

Hi,

I have been trying to determine the antenna factors of a bicone
antenna by modelling it as a 3 segment feed wire with 6 extending
elements on each end, each also three segments long. I have tried
these three configurations to determine the antenna factor

1. Modelling another identical antenna 100 m away and finding the AF
from the site attenuation

2. Putting a 1V voltage source on the central segment of the feed
wire and finding the E-field at a distance of 100 m from the antenna

3. Illuminating the bicone with a plane wave of 1 V/m and placing a 50
Ohm load on the central section of the feed wire, and then finding the
AF from the current across this load.

The core file is attached, and the data extracted from the output file
using existing data extractor programs. The problem is that the
antenna factors are different depending on the configuration, with the
figure derived from the SA being exactly between the values from
methods 2 and 3. The variation is only about 0.6 dB, but I cannot see
why there should be this much. Has anyone seen this before, or know
of a reason why I might get different values?

Thanks,

Sara

Sara Fletcher (Ms.)
_______________________________

Sara Fletcher, Research Scientist
CEM, Building 72,
National Physical Laboratory,
Teddington, Middlesex TW11 0LW
http://www.npl.co.uk/

Tel. 0181 943 6058
______________________________
bicone.nec

CM Small bicone model, length 0.3318 m, with six extending
CM elements on each end making an angle of 30 degrees with
CM the feed wire, in the yz plane. EX Plane wave card and
CM NE card must be in the x-direction. This has been checked
CM against MJS's original model and found to be geometrically
CM identical.
CE SHF 17/11/98
GW1 3 00.000 -0.04875 00.000 00.000 0.04875 00.0000 0.003
GW2 3 00.000 -0.04875 00.000 00.000 -0.16590 0.06764 0.003
GW3 3 00.000 -0.04875 00.000 00.000 -0.16590 -0.06764 0.003
GW4 3 00.000 0.04875 00.000 00.000 0.16590 0.06764 0.003
GW5 3 00.000 0.04875 00.000 00.000 0.16590 -0.06764 0.003
GW6 3 00.000 -0.04875 00.000 0.05858 -0.16590 0.03382 0.003
GW7 3 00.000 -0.04875 00.000 0.05858 -0.16590 -0.03382 0.003
GW8 3 00.000 -0.04875 00.000 -0.05858 -0.16590 0.03382 0.003
GW9 3 00.000 -0.04875 00.000 -0.05858 -0.16590 -0.03382 0.003
GW10 3 00.000 0.04875 00.000 0.05858 0.16590 0.03382 0.003
GW11 3 00.000 0.04875 00.000 0.05858 0.16590 -0.03382 0.003
GW12 3 00.000 0.04875 00.000 -0.05858 0.16590 0.03382 0.003
GW13 3 00.000 0.04875 00.000 -0.05858 0.16590 -0.03382 0.003
GE 0
FR 0 2 0 0 100.0 100.0
CE Receiving configuration
LD 4 1 2 2 50.0 0
EX 1 1 1 0 90 0 90 1 1
PT 0 1 2 2
CE Transmitting configuration
EX 0 1 2 01 1.0 0.0
NE 0 1 1 1 100.0 0.0 0.0 0.0 0.0 0.0
XQ
EN
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Received on Wed Nov 18 1998 - 18:14:16 EST