Compact quad-mode single band/dual-mode dualband bandpass filters using two coupled loop resonators

In this letter, a quad-mode single band bandpass filter and a dual-mode dualband bandpass filter are designed and fabricated by the same structure (two coupled dual-mode loop resonators), which consist of an outer loop resonator with square-patch perturbation at the corner and a inner loop resonator with corner-cut perturbation at the corner. Four transmission zeros are realized in the stopbands to improve the selectivity of the two proposed bandpass filters. Good agreement is observed between simulated and measured performances.