Advanced RF filters for wireless communications

This paper provides a comprehensive review of advanced radio frequency (RF) filter technologies available in miniature chip or integrated circuit (IC) form for wireless communication applications. The RF filter technologies were organized according to the timeline of their introduction, in conjunction with each generation of wireless (cellular) communication standards (1G to 5G). This approach enabled a clear explanation of the corresponding invention history, working principles, typical applications and future development trends. The article covered commercially successful acoustic filter technologies, including the widely used surface acoustic wave (SAW) and bulk acoustic wave (BAW) filters, as well as electromagnetic filter technologies based on low-temperature co-fired ceramic (LTCC) and integrated passive device (IPD). Additionally, emerging filter technologies such as IHP-SAW, suspended thin-film lithium niobate (LiNbO₃ or LN) resonant devices and hybrid were also discussed. In order to achieve higher performance, smaller form factor and lower cost for the wireless communication industry, it is believed that fundamental breakthroughs in materials and fabrication techniques are necessary for the future development of RF filters.