Feed to Helix antenna

what are the ways to excite helix antenna?
how to connect helix wire to center conductor of coaxial? with cylinder of radius as same as helix wire or with sheet ?
what is the far field distance for it ?

A helix with a ground plane behind it has impedance 140 Ohms.
This method is to include a 83.6 Ohms quarter wave electrical length line between the 50 ohms input and the helix.

One physical form of this is to make the first quarter-turn be a "Lecher Line", which is a single line set over a ground plane. It becomes a wider tab over for the first quarter-turn. Pictures are of a 2.4GHz prototype test build. It can be tweaked a bit to optimum match by slightly changing the height of the tab. Also, a capacitive adjustment screw of tab from the ground plane to near the end of the Lecher line can tune it a little. Easy, non critical, quite wideband, but if the quarter-turn tab is the wrong length, that is bad!