Design of LTCC Bandpass Filter with Broadband External Suppression for 5G Applications

This paper describes a design of Low Temperature Co-fired Ceramic (LTCC) bandpass filter for 5G (the fifth Generation) applications. This design consists of curved parallel coupling lines (CPCLs). The advantage of CPCL is that it can increase the coupling capacitance of the parallel coupled line structure to achieve good impedance matching. More coupling capacitors also make the parasitic passband of the filter farther away from the center frequency of the main passband, so as to have wider out-of-band suppression and better insertion loss. In this article, a curved line structure is proposed for the first time to design LTCC filter, and an equivalent circuit is proposed to describe its working principle. A LTCC filter using CPCLs is designed in the 702-798 MHz band. The test results show that the return loss in the passband of the filter is better than 32 dB and the insertion loss is better than 0.6 dB. Therefore, the proposed design can provide a promising solution for 5G wireless communication system.