Here is another quadrifilar helix antenna design, this time for ADSB (aircraft mode-S transponder) reception at 1090 MHz. Unlike other antenna types this antenna has a spherical coverage with 120° 3dB beamwidth and estimated peak gain of 4.6dBi at 1090MHz.
The basic design was done using Antenna Magus 5.2 and I just used the calculated dimensions. See report for details.
Return loss and VSWR.
To make things easier you may use the drill template. Glue around a plastic pipe with 20mm outer diameter and drill 1.5mm holes in the circle centers. Then build after the description.
- Lengths of volute 0&1 are the wire lengths from lower to upper stubs.
- This antenna is RH circular polarized while usual ADSB and transponder antennas in airplanes are vertical polarized. Advantage of circular polarization is the multi-path rejection and immunity against polarization mismatch due to antenna installation/position.