Just remember that the more nervous you are, the more nervous he'll be. All he knows is that you're dropping him off some place new and you're upset about it. If you drop him off and you're happy and excited, he'll think he's getting something great and the whole experience will be better. Also, the more he goes, the more he'll realize that you ARE coming back.
and don't think of it as being behind bars, he's just chilling out in a kennel watching what's going on till it's his turn.
but even saying all that, I know exactly how you feel. I had to drop my dog off at a boarding place once and it was horrible watching her try to get back to me after they took her. But, I knew she'd be fine and they'd take great care of her.
Even though I'm a groomer, when I get my spoo I'm planning on dropping him off at work so someone else can groom him sometimes and just to get us both used to it. The thought makes me panic a little, and that's with knowing I can 100% trust my salon and coworkers.
don't worry, it'll get easier with time!