In Star Trek Voyager, S6E10, Pathfinder, Lieutenant Barclay is able to create a micro-wormhole in order communicate with Voyager.
Meanwhile, the real Voyager, far in the Delta Quadrant, detects the micro-wormhole and a communication signal which Seven of Nine disbelievingly identifies as Federation in origin on a Starfleet Emergency Channel. The crew attempts to clear up the signal while, back on Earth, the jubilant officers and Barclay assist.
For a few seconds, the team on Earth clear up the return signal, two-way communication is established for 86 seconds before the micro-wormhole collapses. A few words are exchanged and data from Voyager's logs, crew reports, and navigational records are transmitted to Earth.
Barclay sends "data on some new hyper-subspace technology", along with recommended modifications to the ship's communications system, so that Voyager's crew will be able to keep regular contact with home. In the final seconds, the crew hear some moving words from Admiral Paris ending with, "I want you all to know we're doing everything we can to bring you home."
So, the Wormhole collapses after a few seconds / minutes. Why didn't they just "reopen" it, e.g. be placing the array next to the needed anomaly in order to be able to have it open permanently (or at least such that they can contact Voyager on a regular basis)?