Design of Wide-Band, Sharp-Rejection Bandpass Filters With Parallel-Coupled Lines

An edge-coupled quarter wavelength resonator and half-wavelength open stubs are used for designing a highly selective wideband bandpass filter (BPF). A homogeneous medium is considered and the even-odd mode approach is used for filter analysis. Next, a microstrip line implementation procedure is described. The filter has sharp rejection, wide stopband, low insertion loss (IL), and fabrication simplicity. A prototype BPF having 69.5% 3-dB fractional bandwidth (FBW) is fabricated. A simple stub modification extends the upper 20-dB stopband to five times that of the filter upper cutoff frequency. Passband IL is within 1.6dB