Design of Compact Wide-Stopband Multiband Bandpass Filter With Star-Like Topology

The design techniques and topologies of multiband bandpass filters (MBPFs) have been investigated in insubstantial amount of literature. However, MBPFs with specific bandwidth and wide-stopband are rarely reported. In this brief, we present a tri-band and quad-band bandpass filter (BPF) by employing the star-like topology to cope with the abovementioned issues. For the miniaturization of filter, the folded half-wavelength microstrip resonators with various shapes are served as bandpass and bandstop resonators in each case. Based on the proposed synthesis approach and filter topology, very good in-band filter responses and also good out-band rejection levels are realized. Furthermore, the design architecture extends the free spurious stopband up to
$3.33f_{0}$
and
$3.35f_{0}$
for tri-band and quad-band BPF, respectively. Good rejection level (better than 17 dB in the wide-stop band) are also achieved for both cases.