Harmonic Suppression in In-line Parallel-Coupled Microstrip Bandpass Filter by Minkowski Fractals

Present paper highlights an in-line third order parallel-coupled microstrip line Chebyshev bandpass filter at 2.5GHz with Minkowski fractals. An in-line configuration provides more than 62% of size reduction compared to conventional coupled-line filter, with a degradation of second harmonic passband. By employing fractals at the edges of each section of the coupled-lines, modal characteristic impedances are modulated to achieve phase velocity compensation, resulting around 42dB suppression of the unwanted second harmonic in the modified in-line structure having 65% of size reduction. Present design with a fractional bandwidth of 15% has been utilized for WLAN application.