insertion loss of balun for antenna

hi,
what is mean by insertion loss ? and if i am designing a balun for antenna for impedance matching then what should be vallue of insrtion loss?if i have S21 -10db from 25GHZ -40 GHz then is it bad insertion loss?please guide me about it

well, yes that is a little high, but you have a very high frequency range. Here is a 36 ghz balun with 6 db loss:
http://www.markimicrowave.com/BAL-00...alun-P731.aspx

How are you making the measurement....it is actually difficult measurement to do since the output is balanced two ports. If you do the measurement wrong, you get an apparent 3 dB higher loss.

thanks biff for reply,i have not fabricate it now i am just simulating it now.i have used stripline to microstrip line transition as balun structure,its S11 AND S22 are good but insertion loss S21 IS strange. so if i understand bu your answer if i have insertion loss curve below 1 db then it will be ok? why it is so?insertion loss is loss in transmitted signal so if its value is lower then it will be good?then why we want value to be higher than -6 db? its my first time to deal with balun therefore i am unable to understand insertion loss concept