I have been designing a micro strip patch antenna with inset feed and I have a few HFSS simulation questions
What is the application for which the design is carried out?
For a single element patch antenna system, a farfield gain of 5 to 7 dB is usually common. 8.5 dB gain is possible and is good. You are achieving a return loss of nearly about 10 dB (or, -10 dB as shown in most simulation environments). More improvement on return loss will be better and the same can be achieved by tuning the dimensions of the radiating patch. This however, depends on the application for which the design is carried out. The requirements of the application largely determine the design. From your design, good gain is achieved but return loss is not that good. Something around 15 dB will be better for any application.
The designed antenna also exhibits multi-band operation as can be seen from the return loss plot.