A novel quad-band filter using centrally shorted-stub loaded resonator and stepped impedance resonator

This paper presents a quad-band filter using centrally shorted-stub loaded resonators operated at the first and third passbands and stepped impedance resonators fixed at the second and fourth passbands. A special feed structure consisting of two stepped impedance lines is proposed, and a pair of parallel coupling lines is loaded at the center of the shorted-stub loaded resonators to enhance the couple of the first passband without affecting the third one.