Narrow-band Band-pass Filter With Harmonics Suppression

Abstract

This paper presents a narrow-band band-pass filter with high selectivity and low insertion loss. The filter has a good characteristics of narrow-band filtering and harmonic suppression. Its harmonic suppression ability is realized by Transmission zeros which result from loading open stub coupling line. The center frequency and bandwidth is determined by the length of coupling line. Based on even-odd mode analysis and transmission line theory, the filter is analyzed and the formula is deduced. The central frequency of the filter is 6.63GHz, and its 3dB bandwidth is 290MHz. The minimum insertion loss in the pass-band is 0.44dB. The proposed filter has a suppression of -31dB in the two harmonic frequency points. In order to verify the theory and confirm the simulation results, the filter is fabricated and tested. And the measured results are in good agreement with the simulation results.