Compact quadruple-mode UWB bandpass filter using open stub loaded multiple-mode resonator

In this paper, a compact quadruple-mode ultrawideband (UWB) bandpass filter (BPF) is designed by using open stub loaded multiple-mode resonator (MMR). The proposed MMR possesses the advantage that odd-mode resonance frequencies exclusively depend on the traditional MMR; even-mode resonance frequencies can be flexibly controlled by impedance-stepped stub, whereas the odd-mode ones are fixed. By simply adjusting the dimension of the impedance-stepped stub, the fourth resonant mode falls down and works together with the first three modes to form a novel quadruple-mode UWB filter. Two other pairs of open stubs are mainly applied to adjust the high resonant modes and obtain good match, respectively. The filter using open stub loaded MMR is simulated, fabricated and measured. The EM simulated and measured results are presented and excellent agreement between them is obtained.