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A tapped wiggly-coupled technique is applied to parallel-coupled microstrip bandpass filters for multi-octave out-of-band spurious suppression. The coupled edges of tapped microstrip resonators are wiggled to equalise the odd-mode and even-mode phase velocities such that the nearest two spurious harmonics can be eliminated. The simulation and experiment show that both the second and the third spurious level are reduced below 42 dB up to 9 GHz for a 2.45 GHz and 5.7% bandwidth bandpass filter. [ABSTRACT FROM AUTHOR]