A leaky cavity resonator that includes a waveguide, the waveguide being filled with a dielectric material, and at least two complementary split ring resonators (CSRRs), the CSRRs residing inside the waveguide parallel to each other placed symmetrically both radially and in height, a leaky resonant cavity being formed between the at least two CSRRs and a wall of the waveguide. A frequency band of the leaky cavity resonator is adjustable by varying a distance w between at least one outside perimeter of at least one CSRR and an interior wall of the waveguide. A frequency band of the leaky cavity resonator is also adjustable by varying a size of the leaky resonant cavity. The at least two CSRRs each have at least one stub connecting to a wall of the waveguide. A frequency band of the leaky cavity resonator is also adjustable by varying a size of the stubs.