Re: NEC-LIST: Modeling of Simple Dipole

Takahiro Tamae asked:
>
> I calculated gain of Dipole antenna by two programs. One is modeling
> an antenna by only one wire,but another is by three wires,as below.
> As a result,I obtained different answers. The first's was 2.12dBi,the
> other's was 4.24dBi. In addition,Impedances were 72.533+j3.471,
> 44.458+j1.389.
>
> Could you tell me the reasons or my mistakes?

Takahiro,

When modeling a dipole using the voltage-source excitation, the
segments on either side of the excited segment have to be the same
length as the the excited segment. You can check the accuracy of the
computed input impedance by requesting, on the RP line, that NEC
compute the average power gain. For an antenna in free space, the
value should be 1.0. For your 1-wire model, the average gain was
0.9957, and for your 3-wire model, it was 1.62. You also have to set
the theta and phi angles on this line to compute a three-dimensional
pattern. With the following input data set, the impedance came out to
be 73.1 + j5.4, the maximum gain was 2.15 dBi, and the average gain
was 1.0016 (I didn't bother to optimize the model ). If 95 segments
is too many, you can use multiple wires that get increasingly
longer. You can experiment with the lengths, but a 1.5:1 ratio between
adjacent segments ought to work.

CM Simple dipole antenna in Free Space
CM 3-wires, ***95 segments***
CE
GW 1,47, 0,0.5,0, 0,48,0, 0.1
GW 2,47, 0,-0.5,0, 0,-48,0, 0.1
GW 3,1, 0,-0.5,0, 0,0.5,0, 0.1
GS 0 0 .01
GE 0
EX 0 3 1 00 1 0
FR 0 1 0 0 150 1
RP 0 61 121 1001 0 0 3 3
EN

Bill Klocko
IIT Research Institute
Annapolis, MD
Received on Mon Oct 20 1997 - 09:48:59 EDT