Fig.3. The equivalent transmission line model for the proposed three-band BPF in Filter 2
The variation in frequency with different L 1 andL s1 is shown in Fig. 4 (a) and Fig. 4 (b), respectively. It shows that with the increase of the parameterL 1, the center frequencyf 1 of the first passband is basically unchanged, while the center frequencies f 2 andf 3 of the second and third passbands move to the lower frequency, and the variation speed of f 3 is obvious faster than f 2.