A Compact Coaxial Cavity Filter for Broadband Harmonic Suppression

In this paper, a coaxial cavity filter with a wide rejection band and high suppression is proposed. The proposed coaxial cavity filter uses a cylindrical Step Impedance Resonator Structure (SIRs), and the coupling between the four cylindrical resonators results in a fourth-order cavity filter with improved out-of-band suppression and a more compact structure. Experimental results show that the proposed coaxial cavity filter has a central frequency of 1995 MHz, a 3 dB passband range of 1970~2020 MHz (relative bandwidth of 2.506 %) and an insertion loss of less than 0.8 dB. In addition, the cavity filter achieves a suppression of 75 dB in the frequency band (2.19~13.86 GHz) (upper stopband suppression to 6.95f
0
). The filter has the advantage of wide rejection band and compact structure, which makes it a promising application in harmonic suppression and miniaturization systems.