Need info on antenna reflector spacing

[drone]

I have a 6 element collinear 1365 MHZ. I want to install
a reflector, how do you compute the spacing between the
antenna and reflector?

 

It gets complicated. The reflector will affect the tune of the antenna and who knows where that will end up (without analysis or experimentation).

Simple answer would be a bit less than a quarter wavelength (0.2 to 0.25 lambda) or roughly 5 cm (for your frequency).

If you really want some serious gain, use a Corner Reflector.

 

[jbartos]

Suggestion: Visit

http://www.guerrilla.net/reference/antennas/2ghz_collinear_omni

http://www.guerrilla.net/reference/antennas/2ghz_collinear_omni_lowpwr/

http://www.rason.org/Projects/collant/collant.htm

http://www.repeater-builder.com/rbtip/wa6svt.html

http://www.indiamart.com/starantenna/collinear-antenna.html

http://www.cushcraft.com/comm/comm_data_sheets/S8243B.pdf

etc. for more info.