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

Document Type : Research Paper


Department of Electrical Engineering, Vali-e-Asr University of Rafsanjan, Rafsanjan, Iran.


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 stubs 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%.