Microstrip filter with multiple transmission zeros using shorted stub loaded resonators

A novel microstrip bandpass filter with multiple transmission zeros is proposed, where two half-wavelength resonators loaded by shortcircuited stubs are implemented into its design. A section of coupled lines and a grounded via-hole are introduced to serve as a capacitor and an inductor, respectively. Then, four controllable transmission zeros can be successfully obtained, and the locations of two outer transmission zeros are controlled by the diameter of the via-hole. A secondorder filter sample with better frequency selectivity and wide stopband was fabricated using standard printed circuit board (PCB) technology, and its measured S-parameters agree well with the simulated ones.