DMSLR-Based Bandpass Filter With Hilbert-Curve Perturbation for Multiple Resonances and Wideband Applications

The dual-mode square loop resonator with Hilbert-curve perturbation is introduced for multiple resonances and wideband filters in this letter. To obtain low insertion loss (0.5 dB), high out-of-band rejection level (${-}49.51$ dB) and wider band (BW 65%) filters, iterative Hilbert-curve perturbation and space-filling technique are proposed. Multiple resonances that included dual modes, third, fourth, and fifth order resonances are presented with resonance splitting plots. Surface current distributions with multiple resonances and transmission zeros are presented and discussed.