I would say that if all you are designing are passive non-resonant antennas then a VNA may not be all that useful.
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However, if you are designing resonant antennas or any sort of filter then a VNA is essential. For resonant antennas the best way to tell where they are resonant is with a VNA. Filters, especially ones where you are winding toroids for inductors need to be tweaked to get best performance, and a VNA is the best tool for that.
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For active antennas it could be argued that a spectrum analyzer is better. It is if you want to do IMD measurements.
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As inexpensive as the NanoVNA and TinySA I would get both if you can afford them. Make sure you buy the "real" versions and not clones if you do. There are groups for both and resources to find a source for the "real' units.
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Mike M
