Dual-band filter based on dual-stubs loaded square loop resonator

A novel dual-band filter based on dual-stubs loaded square loop resonator (DSLSLR) is presented in this paper. Firstly, two first- and second-order degenerate resonant modes in a loop resonator are excited through dual-stubs loading outside two opposite corners of the loop, which achieve the fundamental resonances of two bands. Next, two resonators are cascaded with proper coupling to further split the two resonant modes for dual-band operation. Then two patches are added inside the other two opposite corners of the loop in order to improve the return loss of the second band. Such a novel dual-band filter operating at 2.9 GHz and 3.8 GHz is designed and fabricated.