phase center horn antenna

Can somebody tell me is the phase center of horn antenna is at the same location from where feeding to horn is provided. i am using horn as a feeder for parabolic reflector, which portion of horn should be place at the focal point.

The horn antennas hasn't real phase ceneter (read Balanis). The point of 'relative' or 'virtual' phase center usually lies near the aperture slightly deep into the horn(on my calculation and measurements) for small angles horns, but the precise location of this point defined individually for any concrete horn and concrete distance.

Best regards,
Kit-the-great

if youre rely interested in learning about horn antennas make a google search with "can antenna" it is home made for wireles networksand there are tons of article to read , or serach for ATV (amateur television).

I agree with the answer of Kit-the-great.
I add some considerations.
If the feed is placed on primary focus, i.e the illumintion angle is "large" (F/D= 0.3...0.4), so the phase center is pratically placed on the aperture, and the usually accepdet tollerance is +/- 0.5 Lambda.
If the feed is placed on Cassegrain (or Gregorian) focus, you must know the position of phase centre, but fortunally the tollerance is mutliplied by magnification factor (tipically 10 for F/D=0.32) so the tollerance became +/-5Lambda.
As rule of thumb, for a 25 dB gain horn, the phase center is L/3 deep (where L is the distance Mouth-Thoat).

you can see hand book of antenna written by yee

The phase center is problem. You can find it in EM software (for example CST MWS) or experimentally - change position feed - set feed, that the center of aperture horn is in the focus parabola and change this position + or - and watch gain of parabolic antenna. You can find optimal position. (but the better than gain is first minimum on the radiations pattern - it must be
"deep")