Dr.Yaqeen Sabah Mezaal, so the impact of the body will certainly shift the resonance of the antenna. If you have HFSS you can probably set the material around the antenna to model that of human tissue or what ever you'd like to sense. What i've done in the past is measure the antenna in ambient environment where nothing interacts with it and then measure it in the test environment. Once you know the shift in return loss you can then design it to be somewhere in the middle to handle both cases if need be.

-Adam

Conference Paper Effects of human body on antenna performance: A quantitative study

Dr.Yaqeen Sabah Mezaal In terms of the VNA, once you insure you have a good calibration, typically short, open, load, through, to calibrate out the electrical length of the cables you should get a good return loss measurement. Just ensure the fixture or what ever you use to mount/handle the antenna does not change resonance.

Many thanks for your advantageous comments. Adam weidling