Antennas, simulations,
antennas related projects and information. |
Example
of JPOLE
modeling |
JPole antennas are difficult to model with MININEC
engine based programs because of the close parallel lines, but if we keep
elements spacing above 1 inch and with careful modeling we can
get reasonable results.
First thing to do is increase segmentation to have
segments smaller then the spacing between the parallel wires. There is a limit beyond which
segment increase will not contribute much to model accuracy.
Increasing segments means that you must use the VM version if you go
beyond the 50 segments limit found in the standard version.
Another thing to remember is to keep segment ration between
adjacent wires in a maximum 1 to 2 ratio.
Use the 3D view to verify that wires are connected correctly
The model below was designed for NEC4WIN/VM the VM version.
The NEC4WIN/VM model:
CM JPOLE 146 MHz
CE
GND Reference
UNITS Inches
Height 120
Over Ground 13 5 (Diel. - Cond. µSiemens)
Boundary Circular
F 146.000
GW 0 1 0.000 0.000 0.000 0.000 0.000 1.250 0.125
GW 1 10 0.000 0.000 1.250 0.000 0.000 20.000 0.125
GW 2 4 0.000 0.000 0.000 2.000 0.000 0.000 0.125
GW 3 4 0.000 0.000 1.250 2.000 0.000 1.250 0.125
GW 4 1 2.000 0.000 0.000 2.000 0.000 1.250 0.125
GW 5 30 2.000 0.000 1.250 2.000 0.000 60.000 0.125
S 1 17 100 0
Coax 50
Download
this model here
3D Views
The
picture on the right show how the antenna looks. Click on the
picture for a larger view.
To check connections between wires and wire length
click on the "Wire info" button (4rth from the left) as in
picture below. Small circles show the interconnections between
wires. Note how the source (red dot) is placed on the shorting bar
between the two vertical sections of the J Pole.
Results
If we run the simulation for the antenna at 3 feet
and medium ground we get:
Antenna Height is : 3.04 m (10ft)
Ground Diel. = 13 Cond. = 5
Frequency : 146.000 MHz
Wave Length : 2.053 m (6.737 ft)
IMPEDANCE = 40.51 + j 9.55 Ohms at Source 1
SWR = 1.35
Voltage = 100.00 + j 0.00 at Pulse 45
Current = 2.34 - j 0.55 Amps
Power = 116.92 WATTS
Some frequency sweeps
SWR is minimum for 146 MHz at around 1.25 - 1.3
Max Gain is 5.3 in the direction of the small vertical section.
Front to Back varies from 1.1 to 1.5. The view below show a side
view of the Far Field. The antenna long section in yellow is right
of the invisible small section.
Note:
All graphs and view produced on NEC4WIN/PRO our 'next generation' VM
version with improved graphics. NEC4WIN/PRO is still in development
and not released yet.
