A frequency-tunable microwave bandpass filter including a wave guide having a rectangular cross-section and including a stationary first conductive portion I and a movable second conductive portion II. The first portion includes first conductive partitions having one or more conductive obstacles related to complementary openings in the section of the guide that forms capacitive irises. The first partitions are transversely mounted, at the propagation of the wave in the guide, define cavities in the longitudinal direction of the guide, are rigidly connected to the first portion and the second conductive partitions that have one or more openings defining capacitive irises, and, in combination with the adjacent guide lengths, form immitance inverters. The first partitions form a series of resonating cavities coupled by the immitance inverters. A means ensures electrical contact between the conductive portions I and II.