A Compact Microstrip Lowpass Filter Possessing Sharp Roll-off and Ultra Wide Stopband

A novel microstrip lowpass filter possessing sharp roll-off rate and attaining ultra wide stopband is demonstrated in this article. An interdigital structure placed between the symmetric double stepped high-low impedance resonators offers enhanced transition characteristics along with the creation of finite attenuation poles in high frequency region. With the inclusion of symmetric series combination of coupled inductive stubs and tapered patch capacitors in the proposed design, miniaturized size, sharp transition characteristics from passband to stopband, minimal insertion loss in the passband and suppression of undesired harmonics. The filter has been designed, fabricated and measured successfully.