Dual-mode dual-band microstrip square loop resonators and filters

DMDBFs were proposed for miniaturization and asymmetric frequency characteristic. The consisting of two DMRs based on microstrip square loop resonators was fed by a common T-shaped nonorthogonal I/O feed lines located on the horizontal symmetry axis. It was shown that the TZs can be moved from one side of passband to the other side by adjusting the loading elements used to create degenerate resonant modes. The filters exhibit asymmetric frequency response. The nature of coupling between degenerate modes of the DMRs was changed depending on the size of loading elements. Four microstrip DMDBFs were designed, fabricated, and measured to demonstrate the asymmetric frequency characteristic.