A folded hybrid coupled-line microstrip bandpass filter with multiple harmonics suppression and wide stopband bandwidth is proposed in this research. A simple design rule together with the usage of an over- and an under-coupled structure is adopted in this filter to eliminate the first two spurious responses from using circuit's zeros. Then, the coupled straight lines are transformed to a folded-line layout to save the circuit space and to tune the third transmission zero for the removal of an extra spurious response. An experiment is conducted for validation and good agreement between simulation and measurement is observed.
Microwave and Optical Technology Lett., 48(9): 1812-1816