Miniaturized Dual-Band Differential Filter Based on CSRR-Loaded Dual-Mode SIW Cavity

In this letter, a miniaturized differential substrate-integrated waveguide (SIW) bandpass filter with dual-band response has been illustrated. Two complementary split-ring resonators are etched on the top metal layer. According to the theory of evanescent-mode propagation, a differential-mode (DM) passband below the waveguide cutoff can be obtained. Next, the fundamental frequency of the SIW cavity can be tuned closely to the second harmonic by partially removing the dielectric material inside the SIW cavity which constructs another DM passband. With the proper positions of the feeding lines, the third harmonic can also be well suppressed. Moreover, good common-mode suppression has been achieved for the employment of the proposed balanced structure and the center frequencies of the two DM passbands can be flexibly controlled. A differential filter operating at 6.22 and 8.24 GHz has been realized and fabricated to validate the design idea.