A: They are using older, less powerful deflector grids that are a part of the outer hull plating. The are basically sweaping a clear path in all diretions for the ship.

*ahem*

TOS:
First off, in Matt Jeffries' scribblings on the original Enterprise, the big parabolic dish was the "Main Sensor". The three boxes flanking the dish mount are usually unlabeled, but in a couple places they are labelled sensors, and in others labelled deflectors. The dome on the bottom of the saucer was the "Planetary Sensor Dome". As Gene created the terminology for the show, "Deflectors" were part of the navigational system and "shields" were part of the defense system.

TMP:
Still proceeding on Matt Jeffries' original design, Andy Probert made the new main sensor a more powerful enclosed unit and expanded the planetary sensor dome to include portions of the ship's self-illumination system. He also changed the transparant dome on the bridge to a navigational sensor dome. Nothing is really done on the issue of defensive or navigational systems beyond the comment in the wormhole that the deflectors aren't working.

TWOK:
Shows us there's a separate defense field covering the bridge superstructure. Shows us conformal shields as a bridge display, referring specifically to them as such.

TSFS/TVH: Nothing new here.

TNG: A new ship that has presumably integrated the main sensors and navigational deflectors into a single unit. In the pilot, Worf states "shields and deflectors up". Once again, we have reinforcement of the original tenet that shields and deflectors are not the same thing.

Later in the first season, we see the first appearance of bubble shields. No dialogue given to them in any of their appearances.

TFF:
Different graphic for the shield monitor on the bridge. That's about it.

DS9:
Hardly ever see bubble shields any more. Return to conformal shields.

TUC:
Much use of conformal shields. No bubble shields in evidence.

GEN:
Dialogue references main deflector dish. Based on chronological history of ship design to this point, I posit the Excelsior class is the first to integrate the deflector systems with the main sensor dish.

VOY/FC/INS:
Irrelevent to this discussion thus far.

CONCLUSIONS:
There are not, nor ever have been, any such thing in Star Trek as "deflector shields".

The deflectors are a vital part of the navigational systems and are incorporated into every ship, out of necessity. In earlier ships, they were enclosed in discrete hull mountings. In later designs, they were merged with the main long-range sensor dish to mutual benefit of both systems, I am assuming...

Defensive systems seems to have always been of two types. The "shields" are a sort of hard energy projected just beoyond the hull and acting as a sort of ablative layer to the hull itself. "Screens" are more murky, not getting as much screen time or supporting material as shields... The defense fields from TWOK may fall into this category or not. It is unclear how they functioned. The screens are probably the projected bubbles seen through much of TNG and act as a first-line defense of the ship, but are comparatively weaker than shields, and also of only real defensive value against phasers and slow-moving objects. These may be the nested deflector bubbles diagrammed in the TNG TM.

Thoughts?

From the Encyclopedia: deflectors. Energy field used to protect starships and other vessels from harm resulting from natural hazards or enemy attack. SEE: shields.

There are thus two types of deflectors. Navigational deflectors and deflector shields, the former used generally to sweep aside fragmetary debris, and the latter mainly used to defend against weaponry and large objects.

Also excerpted from the Encyclopedia: shields. ...also referred to as deflectors, deflector shields, or screens.