The RSGB amateur radio handbook of some years back had a design where the wire from the helix to the feed coax was routed a special way and the feed coax connector was 50+j0 ohms. No stub was required.
Yes, and the same design has been in ARRL books for decades.
Essentially, the last turn of the helix closest to the ground-screen is used as a tapered-line impedance-transformer.
It's brought close to the screen -before- it gets around the circle to where it will connect to the coax-connector pin. You adjust the length that's 'close' to the screen, and the rate of decrease of spacing, to match the helix to 50+j0.