Return loss and phase graph how to interpret

checked return loss and phase of folded Patch antenna. Looks like phase is changing way too fast and efficiency at higher side is not good

Phase: looks like there is some cable length included
Efficiency: how can you evaluate antenna efficiency by looking at S-parameters?

About 0.5 m cable, can be eliminated by shifting the reference plane. S11 phase is irrelevant as long you don't want to design a matching network for the antenna. 10 dB return loss means that 90 percent of the forward power are not reflected. Unfortunately S11 can't tell which part of this power is radiated and which is absorbed in the antenna. But if the antenna can be assumed lossless, the efficiency won't be bad at all.