A set of three portable poles set up around people or objects to strengthen a transporter lock where storms, radiation or other interference would make beaming unsafe.
Pattern enhancers are tall, slim devices used by Starfleet away teams. Three are stood in a triangle around whatever is to be transported, and together they boost the signal so that a transporter can hold a firm lock through interference.
They are used in Power Play, when a shuttle carrying Riker, Troi and Data crashes on a storm-swept moon of Mab-Bu VI. Miles O'Brien takes the risk of beaming down through the storm with a set of enhancers so that the party can be brought back, and they are being set up when the entities that go on to possess three of the officers strike.
In Ship in a Bottle, Picard and Data use enhancers on the holodeck in what seems to be a successful attempt to beam the hologram Moriarty into the real world, though the whole scene proves to be part of a simulation.