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Abstract
This paper presents a novel lowpass-bandpass multiplexer consisting of one lowpass channel and four bandpass channels. Dumb-bell defected ground structures and stepped impedance resonators are employed to extend the stopband of the lowpass filter and bandpass filters, respectively. Stepped impedance stubs are used to bring a sharp selectivity in the lowpass channel design. Good isolation between channels is obtained by careful design of the input signal splitting structure, which is realized by utilizing four shunt open stubs with electric length of quarter-wavelength at the center frequency of the four bandpass channels, respectively. To verify the above concept, a lowpass-bandpass quintuplexer is designed, fabricated, and measured. The cut-off frequency of the lowpass filter is selected to be 1 GHz. The central passband frequencies are chosen to be 2.4, 3.5, 4.6, 5.8 GHz. Experimental measurements are in good agreement with simulations.
Funding
This work is supported by the National Natural Science Foundation of China [grant number 61571194], the Foundation for Distinguished Young Talents in Higher Education of Guangdong, the Science and Technology Planning Project of Guangdong Province [grant number 2014A010103013], Natural Science Foundation of Guangdong Province [grant number 2015A030313203], the Fundamental Research Funds for the Central Universities [grant numbers 2015ZZ093 and 2015ZM066], and the Pearl River Nova Program of Guangzhou [grant number 201610010095].