Parallel coupled microstrip filters with suppression of harmonic response

Corrugated coupled microstrip lines are proposed to design planar microwave filters with suppression of spurious response at twice the center frequency (2f/sub o/). The corrugated structure is designed to equalize the phase velocities of the two eigenmodes in the propagation direction. The designed bandpass filters have a wide upper stopband with satisfactory attenuation levels. In addition, the symmetry of the passband response is improved. Measured results of two fabricated circuits show that the idea works very well.