Ultra-wideband bandpass filters using broadside-coupled microstrip-coplanar waveguide

Bandpass filters that cover the ultra-wideband (UWB) frequency range (3.1-10.6-GHz) are presented. The filters utilise broadside-coupled microstrip-coplanar waveguide making them suitable for printed circuit board technology. To achieve a wide upper stopband, radial slots and stepped impedance resonators are employed either to suppress or to relocate the harmonic responses outside the band of interest. The presented design procedure relies on a quasi-static analysis and conformal mapping. The simulated and measured results of the proposed filters prove their suitability for UWB. Furthermore, the presented filters have a wide upper stopband that extends above 20-GHz, a compact size and less than 0.12-ns peak-to-peak variation in the group delay across the passband.