A UWB bandpass filter with wide stopband performance using cross-shaped coupled lines

A novel coupling structure is presented for the design of an ultra-wideband (UWB) bandpass filter (BPF) with wide stopband performance. The proposed coupled structure is constructed by modifying the conventional one quarter-wavelength parallel coupled lines into cross-shaped coupled lines (CCLs), which results in size miniaturization as well as wide upper-stopband performance. The CCLs can be properly designed so that the unwanted passband is rejected and the transmission zeros can be assigned toward the harmonic resonances of the triple-mode resonator. By cooperating the proposed CCLs and the triple-mode resonator, a UWB BPF with sharp roll-off and improved out-of-band performance is then constructed. Both simulated and measured results are in good agreement to verify the predicted results.