Quadrifilar Helicoidal Antenna for 1090 MHz (ADS-B) by grajohnt

Last crawled date: 3 years ago

This is a remix of the Quadrifilar Helix Antenna by @jhsandell for 1090MHz (ADS-B)
The following updates have been made:
The 'bug' that jhsandell noted where the code was using diameters rather than radii has been fixed
This version makes a left-handed helix for right-handed polarization, rather than a right-handed helix for left-handed polarization*
Settings have been adjusted for ADS-B frequencies (1090 MHz)
There are a variety of pros/cons for a QFH antenna for ADS-B:
Pros:
Using circular polarization, antenna is not sensitive to changes in aircraft orientation
Radiation pattern is more or less omni-directional around a single hemisphere (note that this would be in the direction of the feedpoint!)
Multi-path rejection
It's purty
Cons:
ADS-B is by standard vertically-polarized, so using a circularly-polarized antenna means a 3dB loss
Takes up significantly more space than a simple vertical or J-pole
Construction is more complicated than other antenna types, and care must be taken to attach the feedpoint properly
I have not done rigorous A/B testing with this antenna, but at least in my situation, it seems like a vertical antenna is more suitable for ADSB due to the more annular gain pattern. The QFL has less gain at low angles, so picks up fewer aircraft at distance (but probably picks them REALLY well immediately overhead :) )
The wire used in the photographs is 10awg copper wire - this is equal to the 2.5mm wire diameter suggested by the calculator as an optimum for this frequency. However, for a smaller gauge might be recommended for easier construction.
*The photographs show a left-handed polarized (so right-handed helix), rather than the LHP version in the OpenSCAD file. For ADS-B, polarization-handedness is unimportant.