A frequency tunable microwave bandpass filter comprises a resonator, including: a cavity with conducting wall substantially cylindrical with axis Z having height H, and partially closed at both ends; and a dielectric element inside the cavity. The resonator resonates at two perpendicular polarizations having distributions of electromagnetic field in the cavity deduced from eachother by 90° rotation. The element rotates about an axis substantially perpendicular to axis Z, between a first and second position. The element comprises a first end wherein: in a first position the element is disposed substantially in a plane perpendicular to axis Z and the center of the first end is disposed at a height in the cavity corresponding substantially to an electric field minimum; and in a second position the element is substantially parallel to Z and the first end is disposed in a plane corresponding to an electric field maximum within +/−30%.