Parallel feed microstrip quasi-elliptic function bandpass filter

This paper presents a new type of microstrip quasi-elliptic function bandpass filter built in parallel feed configuration with a pair of open-loop dual-mode resonators. By employing this new coupling scheme, it is flexible to implement different single- or dual-band filtering characteristics. As an example, a three-pole quasi-elliptic function filter of this type with a finite-frequency transmission zero on each side of the passband is demonstrated experimentally.