Originally field tested aboard the prototype USS Sovereign, these shields make use of redundant shield generators which alternate coverage on a specific area when integrity drops below a predetermined percentage. In practice, this allows the active shield generator to bare the brunt of incoming fire while the redundant generator remains on hot standby. As the primary generator drops in integrity, power is then increased to the redundant generator which seamlessly takes over the burden of shielding that portion of the ship, allowing the other generator to once again recharge on standby.
The purpose of this type of shielding is to provide effective protection for a starship while at the same time preserving the shield generators in question. The tried and tested tactic of targeting shields could allow an enemy to disable or destroy a Starfleet vessel’s protection with a disproportionately small attack. Regenerative shielding, on the other hand, actively deconcentrates all incoming fire over the entire shield grid network. While this actually lowers overall shielding capacity, it protects the active generator and allows it to recharge unhindered while the redundant generator system continues providing the ship with shielding.
Advances in this type of shielding have allowed Starfleet to incorporate the entire active-redundant set-up in single generators without any shortfall in effectiveness. General increases in shield power also means incoming fire does not need to be spread over the entire shield grid, only relevant sections.