Applied methodology for harmonic suppression of microstrip edge coupled bandpass filters using composite circuit materials

A simple composite material structure is proposed which allows suppression of harmonic modes for microstrip edge-coupled bandpass filters. The structure can be employed easily in the printed circuit board (PCB) fabrication process and gives a simple method for equalizing the phase velocity of even- and odd-mode propagation within a given range of frequencies. It is known that equalizing the even- and odd-mode phase velocities supports minimizing harmonic responses of microstrip coupled circuits. An overview of auxiliary concepts will be given, followed by the examination of models using a commercial field solving software to demonstrate the phase velocity equalization as well as filter performance with suppressed harmonics. Finally, measured S parameters from circuit evaluations will be shown and compared to the data from software models.