Compact Dual-mode Bandpass Filter Using Square Loop Resonator with Both Capacitance and Inductance Stubs Loaded

In this paper, a new miniaturized bandpass filter (BPF) utilizing a novel square loop resonator is presented. For the first time, the square loop resonator is realized by loading both capacitive and inductive stubs. Four identical stubs are loaded as capacitance on the corner outside of the square loop resonator, and four triangular ring stubs are loaded as inductance inside the loop resonator. The outside loaded branches are applied to enhance the self-capacitance. Because of the loaded capacitance the square loop resonator can realize the size reduction. The inside triangular ring stubs are used to increase the resonator perimeter significantly and hence decrease the size of the resonance. To verify this design, a fabricated sample has been tested. Compared to the conventional BPF without capacitance and inductance loaded square loop resonator, the newly designed BPF has a size reduction of 83% and wider stopband. Measurements are in good agreement with simulated results.