Miniature dual-mode bandpass filter based on meander loop resonator with source-load coupling

The advantages of the dual-mode meander loop resonator are its compact size and low radiation loss. In this letter, a miniature dual-mode microstrip meander loop resonator is proposed. The proposed dual-mode resonator has the advantage that the even-mode resonant frequency can be flexibly shifted whereas the odd-mode resonant frequency is preserved and the size reduction of about 50% compared with the dual-mode bandpass filters such as ring resonator, and square loop filter at the same center frequency. The technique to use capacitive source-load coupling to improve the performance of microstrip dual-mode filters is proposed also. The realized filter response possesses a transmission zero in lower stopband and two transmission zeros in upper stopband which improves the stopband rejection. Both simulated and measured results are presented.