  Superconducting circuit quantum electrodynamics experiments with propagating
microwaves require devices acting as beam splitters. Using niobium thin films
on silicon and sapphire substrates, we fabricated superconducting 180{\deg}
microstrip hybrid ring couplers, acting as beam splitters with center
frequencies of about 6GHz. For the magnitude of the coupling and isolation we
find -3.5+/-0.5dB and at least -15dB, respectively, in a bandwidth of 2GHz. We
also investigate the effect of reflections at the superconductor-normal
conductor contact by means of low temperature laser scanning microscopy. Our
measurements show that our hybrid rings are well suited for on-chip
applications in circuit quantum electrodynamics experiments.
