NEC-LIST: about the convergence of the nec2

Hi,all

I am a rookie in using the nec2. Recently I try to use the free release
of the 4nec2 to analyze an antenna with complex structure. The input
model is described in the cards below. I keep the gap between the voltage
source unchanged and reduce the segment length gradually, however, neither
 the input impedance nor the pattern converges.

I think there may be some possible reasons:
1. The exciting gap of the voltage source is too short.
2. The segments of the wire connected to the same joint differ a lot.
3. Several wires are too close to the perfect electric ground

But I cannot see any convergence after considering the factors above.

Well, Would you please help me analyze the problem in my model?
Thanks a lot

the card in my model:

CE
GW 1 30 0 0 20 36.201 0 0.7517 0.01
GW 2 30 0 0 20 18.1 31.351 0.7517 0.01
GW 3 30 0 0 20 -18.1 31.351 0.7517 0.01
GW 4 30 0 0 20 -36.2 0 0.7517 0.01
GW 5 30 0 0 20 -18.1 -31.35 0.7517 0.01
GW 6 30 0 0 20 18.1 -31.35 0.7517 0.01
GW 7 18 0 0 16 18.385 0 0.5731 0.01
GW 8 18 0 0 16 9.1925 15.922 0.5731 0.01
GW 9 18 0 0 16 -9.193 15.922 0.5731 0.01
GW 10 18 0 0 16 -18.39 0 0.5731 0.01
GW 11 18 0 0 16 -9.193 -15.92 0.5713 0.01
GW 12 18 0 0 16 9.1925 -15.92 0.5731 0.01
GW 13 4 0 0 16 0 0 20 0.01
GW 14 1 0 0 0 0 0 0.3 0.01
GW 15 24 0 0 0.3 0 0 16 0.01
GE 1
EX 0 14 1 0 1 0
GN 1
FR 0 1 0 0 2 0
EN

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