Design and implementation of a compact quarter-wavelength stepped-impedance resonator bandpass filter with good harmonic suppression performance

In this paper, a bandpass filter with good suppression of both the second and third harmonic is designed and implemented. To reduce the size of the filter, quarter-wavelength stepped-impedance resonator (SIR) is used, the filter consists of four SIR resonators and a narrow line between the two resonators in the middle. One transmission zero is introduced in the upper stopband by mixed electric and magnetic coupling. Good agreement between simulation and measurement is achieved. Both simulated and measured results shows that, the second harmonic suppression is over 45dB, and the third harmonic suppression is over 35dB. Wide passband, low insertion loss and compact size have also been realized in this design.