Quite a few field types don't work, user selector and date ranges i know about, wouldn't be surprised if radio buttons were also not "supported".
customsearchjs="1" and do the search you want. The URL should change to something like:
example.tiki/search#type=pdf (not sure what radio buttons will look like)
Note, you need to give your input an id, here it would be
id="type" - you can then use that url to preset the field (hopefully?)