I use with my colleagues the Ansys HFSS. I think that CST is similar for use. In any case, the simulation of new designs of antennas, microstrips, Frequency Selective Surfaces, and metamaterials is an art and requires skill.
I agree with the colleagues that the most simulation software for the microstrip components is CST. W used it many times in analyzing and designing microstrip devices and circuits. You can see these circuits by referring to my publications list at the link: https://www.researchgate.net/profile/Abdelhalim-Zekry/research