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.


This document is Copyright© 2003 ORION Microsystems