A miniaturized multi-layer lowpass filter for microwave application

This paper presents a miniaturized multi-layer lowpass filter with sharp roll off suppression rate beyond the passband realized by low temperature co-fired ceramic (LTCC) technology for microwave application. By improving the prototype filter structure, three transmission zeros can be introduced to achieve sharp suppression rate. The proposed filter is designed with a cut-off frequency of 1.40GHz and the measured insertion loss is less than 0.6dB. The attenuation is less than -40 dB above 1.6GHz, and the bandwidth between the cutoff frequency and 1.6 GHz is only 200MHz. The three transmission zeros are obtained at 1.63GHz, 1.86GHz, 2.6GHz respectively. Due to the multi-layer structure, the size of this miniaturized filter is 3.2mm*2mm*1.41mm. This paper proves that the proposed filter is suitable for microwave application.