I am getting weird results trying to model a small 433 MHz helix antenna similar to this one with 4nec2:
In particular I am not able to obtain a resonable SWR value. This is the antenna an example of the nec file.
CE
SY L=0.0205 'Length of helix
SY S=0.001 'Pitch
SY R=0.0003 'Wire radius
SY N=(L-2*R)/S 'Turns
SY D=0.005 'Helix diameter
SY L1=0.008 'Length of base wire
SY L2=0.0055 'Length wire to be soldered
GW 1 3 0 0 -L1 0 L2 -L1 R
GW 2 1 0 0 0 0 0 -L1 R
GW 3 1 D/2 0 0 0 0 0 R
GH 4 N*12 S L D/2 D/2 D/2 D/2 R
GM 0 0 -90 0 0 0 L1 L2 0
GE 1
GN 1
EK
EX 0 1 2 0 1 0 0
FR 0 0 0 0 433 0
EN
I tried also adding a reflector to the model but still the results waren't right. I think that the problem could be the segments length, near the $0.001\lambda$ limit.
Here an example of the outputs I am getting: