Inspired by the "How does target shields work?" thread, I thought I'd try a rough, preliminary summary of a possible timeline for deflector shield tech development:
late 2150's - The Daedalus class prototype is the first to test shield generator elements. These are circular ringways of superconducting charged plasma (or even some solid conductor) accelerated to very high speeds and passing through a series of verterium cortenide "lenses" which convert the very high em flux to an outwardly directed subspace deflection effect. The large, prototype ring elements actually dictated the simple spherical and cylindrical hull forms of this "plain jane" ship and even inspired a somewhat optimistic and quickly reversed deletion of the forward deflector dish. The mechanism described here is my idea of something that would require the recharge delay inferred by the percentage power losses described while under fire. I see use of these first shields as akin to a turtle drawing into it's shell, with no frequency windows for sensors or comms and probable interference with subspace based drive systems.
Late 22nd Century - I seem to recall several references to this being the period when the ubiquitous "transtator" makes it's debut, possibly leading to things like tuneable shields which allow concurrent use of sensors, comms and drives, etc.. I wonder if using shield feedback as a sort of sensor field might make more sense than trying to tune the shields to allow sensors to read through them. If you're going to let feedback rip through bridge consoles and the like in battle, surely you must be trying to put it to some use.
2271 - The "new shields" on the 1701 refit use warp amplification based (at least in part) on the subspace field based romulan cloaking device "acquired" a few years earlier. This system is the first to pick up the individual, local deflector screen blisters and lift them off the hull into the first TNG style continuous field bubble. This would be a "second stage" shield mode, dropping back to the individual screens when the drive is off line or "stage one" shields are deemed adequate for the situation.
2360's - Shield frequency auto-rotation control algorithms become common in the face of the borg threat. I have to say I've always been leary of the reference to a characteristic shield operating frequency for the 1701D in ST:Generations. You'd think a high energy field generation system with a characteristic operating frequency would be radiating it like a quasar.
2370's - I'll assume the "regenerative" shields on the Prometheus are more evolutionary than revolutionary and represent a significant increase in the recovery rate of existing shield systems.
Post TNG - Interphasic or transphasic systems come into general use (with the appropriate diplomatic kissing-up to the romulans I suppose).
Crits, additions and revisions to the above are most welcome. Hit me with the good stuff people.

late 2150's - The Daedalus class prototype is the first to test shield generator elements. These are circular ringways of superconducting charged plasma (or even some solid conductor) accelerated to very high speeds and passing through a series of verterium cortenide "lenses" which convert the very high em flux to an outwardly directed subspace deflection effect. The large, prototype ring elements actually dictated the simple spherical and cylindrical hull forms of this "plain jane" ship and even inspired a somewhat optimistic and quickly reversed deletion of the forward deflector dish. The mechanism described here is my idea of something that would require the recharge delay inferred by the percentage power losses described while under fire. I see use of these first shields as akin to a turtle drawing into it's shell, with no frequency windows for sensors or comms and probable interference with subspace based drive systems.
Late 22nd Century - I seem to recall several references to this being the period when the ubiquitous "transtator" makes it's debut, possibly leading to things like tuneable shields which allow concurrent use of sensors, comms and drives, etc.. I wonder if using shield feedback as a sort of sensor field might make more sense than trying to tune the shields to allow sensors to read through them. If you're going to let feedback rip through bridge consoles and the like in battle, surely you must be trying to put it to some use.
2271 - The "new shields" on the 1701 refit use warp amplification based (at least in part) on the subspace field based romulan cloaking device "acquired" a few years earlier. This system is the first to pick up the individual, local deflector screen blisters and lift them off the hull into the first TNG style continuous field bubble. This would be a "second stage" shield mode, dropping back to the individual screens when the drive is off line or "stage one" shields are deemed adequate for the situation.
2360's - Shield frequency auto-rotation control algorithms become common in the face of the borg threat. I have to say I've always been leary of the reference to a characteristic shield operating frequency for the 1701D in ST:Generations. You'd think a high energy field generation system with a characteristic operating frequency would be radiating it like a quasar.
2370's - I'll assume the "regenerative" shields on the Prometheus are more evolutionary than revolutionary and represent a significant increase in the recovery rate of existing shield systems.
Post TNG - Interphasic or transphasic systems come into general use (with the appropriate diplomatic kissing-up to the romulans I suppose).
Crits, additions and revisions to the above are most welcome. Hit me with the good stuff people.
