A Modified Coaxical Low-Pass Filter with Miniaturized Size and Broad Stopband Using Loading Dielectric Substrates Technology

A miniaturized broad stopband low-pass filter loaded with multiple dielectric substrates is proposed in this article. The filter mainly adopts a SIR like structure with multiple dielectric substrates loaded at both ends. The loading of multiple dielectric substrates is to increase the ground capacitance within a finite size to reduce the cutoff frequency of the low-pass filter and achieve miniaturization of the low-pass filter size. In addition, by controlling the impedance of the transmission lines in the coaxical cavity, the cutoff frequency can be changed while maintaining the first harmonic frequency unchanged. Finally, a low-pass filter with a cutoff frequency of 2 GHz and a first harmonic frequency of 18.7 GHz was designed. This filter structure can be used in highly miniaturized mobile communication systems sub-6 GHz.