A novel ultra-wideband filter with wider stopband employing multiple-mode resonator and low-pass filter

A novel microstrip ultra-wideband (UWB) bandpass filter (BPF) is presented by stub-loaded multiple-mode resonator (MMR) and low-pass filter in this paper. What called Multi-mode resonator filters for UWB is that two or more resonant mode contained in the pass band and with a strong coupling in input and output ports. In this paper the Multi-mode resonators is proposed by a half-wavelength resonator with electrical length 2θ1 and characteristic admittance Y1, and a fan-shape stub-loaded stepped impedance in the center. The length of coupled-line on both sides is confirmed to just one-fourth wave of center frequency, two odd mode frequencies are produced by it, which is the center frequency. Fan-shape line with stepped impedance stub-loaded in the center effects even mode frequency, thus appropriately adjust the length and width of fan-shape and rectangular, which linked between, can make the even-mode frequencies evenly distributed on both sides of the center frequency. At the same time the introduction of fan-shape stepped impedance stubs can produced at least two transmission zeros at the two sides of the pass band. Low pass filter adopted defected ground structure (DGS) and alternating stub-load with triangular and trapezoidal, the narrow gap between triangular and trapezoidal will produce a cross coupling, which resulting in transmission zeros. Cascading simulation of the two filters shows that the filter has not only wider stop band , but better side band selectivity.