The most commonly quoted and usable parameter in regards to antennas is S11. S11 (return loss) represents how much power is reflected from the antenna, and hence is known as the reflection coefficient (sometimes written as gamma: or return loss. If S11=0 dB, then all the power is reflected from the antenna and nothing is radiated. As well as using this, insertion loss could also be calculated.
Follow C. A. Balanis or J.D. Cross book for Antenna.