Miniature Harmonic-Suppressed Microstrip Bandpass Filter Using a Triple-Mode Stub-Loaded Resonator and Spur Lines

A miniature harmonic-suppressed microstrip band pass filter (BPF) with a new triple-mode stub-loaded resonator is presented in this letter. Four distinct mechanisms are utilized to create five transmission zeros (TZs), leading to sharp skirts and wide stopband. Both simulation and measurement results are presented. The simulated/measured minimum passband insertion loss is 0.66 dB/0.78 dB and the 20 dB rejection bandwidth is extended up to 4/0. The size of the filter is about 0.23 λ_g × 0.17 λ_g, where λ_g is the guided wavelength at the center frequency.