High-power tunable microwave filters can be made with ferrimagnetic materials by using coupled spin wave, electromagnetic wave modes of propagation which are decoupled from the processes that limit the power handling capability of conventional YIG filters. These novel filters can be used for spectral containment of transmitter emissions, or as feedback elements with microwave amplifiers, so as to create high-power tunable oscillators. Measurements have been made at X- and S-bands on one implementation of this technique, namely a pair of waveguides coupled via a polycrystalline YIG disc. Linear operation to 20 kW has been achieved.