The three stalks that hold the feed assembly in front of a radio dish are usually called feed support struts or feed support legs.
Other terms you may encounter are:
Feed support arms – probably the most common term in amateur radio astronomy.
Feed struts – a shortened version.
Feed legs – often used for parabolic dishes with three or four supports.
Quadripod – specifically when there are four support legs.
Tripod feed support – when there are three supports, as on many satellite TV dishes and some radio telescopes.
So, if your dish has three supports holding the feed horn or LNB at the focus, you could accurately describe them as three feed support struts forming a tripod.