  We investigate one-dimensional Josephson junction arrays with generalized
unit cells as a circuit approach to engineer microwave band gaps. An array
described by a lattice with a basis can be designed to have a gap in the
electromagnetic spectrum, in full analogy to electronic band gaps in diatomic
or many-atomic crystals. We derive the dependence of this gap on the array
parameters in the linear regime, and suggest experimentally feasible designs to
bring the gap below the single junction plasma frequency. The gap can be tuned
in a wide frequency range by applying external flux, and it persists in the
presence of small imperfections.
