Miniaturized high-order UWB bandpass filter using third-order E-shape microstrip structure

Recently a new systematic design rule was proposed to realize high-order UWB bandpass filters using cascaded E-shape microstrip structures. The responses of these miniaturized filters show one transmission zero at the upper stop-band. In order to improve the selectivity at the lower stop-band, this paper proposes a new generation of miniaturized high-order UWB bandpass filters having an attenuation pole in the lower stopband. The filters, employing the E-shape microstrip structure, are the cascade of third-order UWB bandpass filters electromagnetically coupled through λ/4 microstrip lines realised on the dielectric superstrate of the structure. A high selectivity sixth-order UWB bandpass filter is designed, simulated, fabricated and measured. The dimension of the filter is about 4 mm × 6 mm × 0.5 mm excluding the feeding ports. The results from the simulation and measurement show good agreement. It is observed that this filter has attenuation better than 40 dB immediately after the passband, and over a large frequency range in the lower and upper stop bands.