A Novel Compact Ultra-Wideband Bandpass Filter Using Microstrip Stub-Loaded Tri-Mode Resonator

One novel compact ultra-wideband filter is presented by using a tri-mode resonator and coupled-line sections as inverter circuits. Open stub-loaded are used to widen the passband of filter without aperture-enhanced coupled line structure. Five transmission poles in the passband are shown. Two sharp attenuation poles can be located close to either side of the desired pass band. The passband of filter and the locations of attenuation poles can be controlled by the sizes of the open stubs. The simulated results demonstrate that the insertion loss is lower than 0.5 dB in the passband (3.9-10.1GHz); about 90% FBW is achieved; and the group delay variation in the passband is less than 0.5 ns.