If you are on a budget (which I guess you are): Get a cheap NanoVNA or similar device. <50€ straight from China. Or get a used SWR meter / antenna analyzer from the usual places (fellow hams, internet, flea markets). It will save you so much trouble, and it is really handy to have one. If you don’t, you can still do it the old-school way of receiving a known signal and simply looking at the outcome. But for that you need a known signal (or generate one). A friend with a radio, for example. Or a broadcast station. Or some local activity.

I built a mag-loop out of tinfoil and duct tape to try out an idea once, because that was faster than getting CST Studio to accept it. It works, because of course it does, but be warned that contact resistances are a bitch.