try to get an energy shield emitter with some 'high frequency values'
If you put points in electronics, low frequency shields are far better since their very high/high/medium ratings will be high enough to stop pretty much everything except for Snipers Aimed Shot (but that happens like twice in the whole game) while also being very good aganist any slow projectiles (crossbows, spits, psionics, chemical pistols) and melee.
But if you don't have crafting, I agree that high frequency is a better choice. Thresholds on found/bought shields are pretty low so only the high frequency shield will be able to stop anything fully.
BUT, Deep Ceverns are generally full of enemies that use slow projectiles (bio spits, acid spits, tentacle darts and psionics) so I would go with low freq for DC regardless.