Microstrip line tunable filters using yttrium iron garnet film substrate

Microstrip line tunable filters with a longitudinally magnetized yttrium iron garnet film have been investigated experimentally and theoretically. A half wavelength microstrip line resonator with L-shaped stubs, longer side of which is parallel to the center strip, has been proposed so that attenuation poles are tunable with applied magnetic bias fields and synchronized with the passband, and the experimental results axe compared with the numerical calculation. In addition, we have proposed the composite structure of the above-mentioned resonator and another microstrip line with the same substrate connected in cascade to suppress the unexpected passband due to magnetostatic waves.