A high-selectivity multistage combline filter with wide stop-band

This paper demonstrates a compact combline filter based on multilayer Low Temperature Co-fired Ceramic (LTCC) technology. According to the combline theory and full-wave electro-magnetic (EM) comparing simulation, a filter operates at 2.3GHz-2.75GHz with dimension of chip-size 1812(4.5mm × 3.2mm × 1.5mm) is designed and fabricated. It generates a wide stop-band with three transmission zeros at the high-side skirt at 3.3GHz, 5.2GHz, 5.7GHz respectively to reject interferential frequencies. The passband insertion loss is less than 2dB. The measured results evidence the feasibility of the proposed design.