A microwave device of the slot-line type with a photonic band gap structure, including at least: a first substrate in a dielectric material having a first permittivity ∈r1, a second substrate in a dielectric material having a second permittivity ∈r2, and between the two substrates, a conductive layer in which at least one slot-line is engraved, with, on the face of the first and second substrates opposite the face in contact with the conductive layer, facing the slot-line, periodic metal patterns. A compact filtering structure is realized.