Ultra-Compact Ultra-Wideband Bandpass Filter Based on Multi Mode Resonator Concept

An ultra-compact ultra-wide band (UWB) bandpass filter (BPF) with a very sharp rejection for the high-speed wireless communication applications is proposed. The functional basis of the proposed structure is based on the multi-mode resonator (MMR) technique. The suggested ultra-wideband filter is realized by using two doublet parallel coupling lines, two symmetrical open stubs and tri-section step-impedance open stubs which are located at the center of the configuration. In order to analyze the suggested configuration, the even-mode and odd-mode methods have been utilized because of the proposed UWB BPF is a symmetrical structure. Five modes which are including three even modes and two odd modes have been placed within the UWB band. By changing the dimensions of the tri-section step-impedance open stub and two symmetrical open stubs, the resonant modes of the constructed MMR can be tuned. These two parts have been mainly applied to adjust the resonant modes into desired passband. Changing the dimensions of the two symmetrical open stubs affects both the even and odd modes. But the tri-section step-impedance open stubs can only specially control the even-mode resonant frequencies, whereas the odd-mode ones are fixed. Consequently, the center frequency and the bandwidth of the proposed configuration can be simply adjusted. Experimental verification is provided and a reasonable agreement between simulated and measured results has been achieved. The proposed UWB BPF has a passband covers 3.55 to 10.65 GHz and the measured 3 dB fractional bandwidth (FBW) is about 100%. The total size of the suggested UWB BPF is about 0.76 × 0.34 λg2.