# Reference for Harmonic Analysis?

I'm looking primarily for references for Harmonic Analysis. I'm mostly considering Doran&Fell or Deitmar, but I have access to lectures using Stein as well. The important thing is covering Unitary representation theory of locally compact groups, in particular Abelian and compact groups, and the Gelfand transformation.

I'd also like to ask for the prerequisites of the recomended references (in particular, I have not studied spectral theory, so if that is a necessity I'd appreciate references on that to prepare the ground for Harmonic Analysis).

On the other hand, the non-compact non-abelian case is extremely difficult. Honestly, I wouldn't bother trying to learn anything going into the proofs at all -- just the statement of the Plancherel theorem should be fine. The only proof that I've seen the proof of this written down is in Dixmier's books on $C^*$ and von Neumann algebras, both of which are extremely difficult books, and it requires pretty much all of the both of them. As long as you're happy to learn statements, Deitmar's book has a nice enough chapter on this.