thanks for your reply
"efficiency is better measure to characterize how good an antenna is because efficiency is total radiation coming out from an antenna whereas gain is peak radiation coming out from a direction"
my aim is a directional antenna, this antenna is an array of radiating elements.
just thinking out loud correct please shear any....
there in no "amplifying " action in an antenna i.e. I do not get more power then input power but I can get most of the energy to a specific direction so when aiming a dir antenna, gain is more dominant (at the most, efficiency is limited to the value 1) - antenna with bad efficiency can get good radiation & even better then efficient one.
btw the 3D gives a view of rad pattern so you can see magnitude in 3db is good but on that graph (magnitude) I can not show effic issue