Compact bandpass filters with wide controllable fractional bandwidth

In this letter, complementary split ring resonators (CSRR) are proposed to design bandpass filters (BPFs) having wide controllable 3-dB fractional bandwidth (FBW). FBW can be varied between 10% and 100%. In addition, filters have the advantages of compactness, sharp rejection, low insertion loss (IL), and low cost. Two prototype fabricated filters of FBW 10.8% and 81.6% show a maximum passband IL of 1.2dB. Filter occupying area is less than 0.25lambdagtimes0.15lambdag, where lambdagis the guided wavelength at the midband frequency