Miniaturized lowpass filter with wide band rejection using modified stepped‐impedance hairpin resonator

A novel lowpass filter with a miniaturized size of 0.069 λ g × 0.087 λ g (where λ g is the guided wavelength at 0.9 GHz) is presented in this letter. Based on modified stepped‐impedance hairpin resonator cell, a compound resonator structure is proposed by properly arranging two different resonator cells. As a result, miniaturization performance of lowpass filter can be achieved and multiple resonances can be formed in the stopband. Moreover, to further improve its band rejection performance, a pair of compound resonators is symmetrically loaded on the main transmission line, together with an open stub located at its center. Finally, a wide stopband of 13th harmonic suppression can be achieved with 3 dB cutoff frequency at 0.9 GHz. Experiment results show that a relative stopband bandwidth of 158.2% can be realized with a criterion of better than 17 dB suppression degree, which reveal good agreement with simulation ones. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1313–1317, 2017