Notes:
The Fan-Dipole Antenna Calculator was developed to predict the characteristics of a fan-dipole antenna with
up-to 5-elements, given physical dimensions entered via slider widgets. It allows you to see what the effects
of additional dipoles will do to the feedpoint impedance (and therefore the VSWR based on 50 ohm feed) for your antenna.
It supports:
- Up-to Five dipole elements
- Estimated effects of changing droop angle
- Metric and Imperial units
It is based on [1] closed-form equations (8-60a) and (8-60b), which solve for the feedpoint resistance (Rin) and inductance (Xin)
of a center-fed wire antenna for a given frequency. These are then used to solve for the parallel impedance of the enabled elements.
It assumes the wire-elements are uncoupled, so ensure you use spreaders to keep the elements well-separated.
The intent is to use this tool to quickly select your dipole lengths. You could then use an electromagnetic solver
such as EZNEC or MMANA-GAL for more accurate modeling including environmental effects such as height-above-ground.
I developed this fan-dipole calculator to take advantage of the
touch-screens and high-speed of modern mobile phones, to allow users to get realtime feedback of the predicted
behaviour of a fan-dipole antenna.
-- 73 de VK3CPU
Inputs via the slider and radio widgets:
- θ : Droop angle in degrees
- D1 : Length of dipole (end-to-end)
- D2 : Length of dipole (end-to-end)
- D3 : Length of dipole (end-to-end)
- D4 : Length of dipole (end-to-end)
- D5 : Length of dipole (end-to-end)
Calculated parameters:
- VSWR : Voltage Standing Wave Ratio [1 - 6]
- |Z| : Feedpoint impedance in Ohms [0 - 500]
- Rin : Feedpoint resistance in Ohms [0 - 500]
- Xin : Feedpoint inductance in Ohms [0 - 500]
Usage hints:
Tap on legend items to disable or enable an output parameter. This can be used to declutter the chart.
Tap on a chart curve to display a tooltip containing calculated output parameters for that frequency.
TODO:
Solve for the relative currents and therefore power per element.
Save the checkbox state in the URL.
Other VK3CPU calculators:
References:
[1]: Constantine A. Balanis,
"Antenna Theory 3rd Ed" , Wiley, 2005, pp. 465.
Change history:
[14-June-25] v0.8
* Modify slider range to allow for 160m to 10m operation.
[14-June-25] v0.7
* Move droop angle text location. Add a line and arc.
[3-June-25] v0.5
* Fix some layout issues.
[3-June-25] v0.4
* Enable angle adjustment factor.
[27-May-25] v0.1
* Draft check-in.