Analyzing Three Types of Design Methods for 5G N41 Band Acoustic Wave Filters

This paper presents three design methods for acoustic wave (AW) filters: the direct conversion design method, the slope parameter method, and the band edge fitting method (BEFM). Since the conventional BVD model consists only of lumped elements and has accuracy only near the resonance frequency, an NM-BVD model capable of broadband modeling is proposed in this paper and used to design the filter. In the proposed BEFM, a systematically optimal filter method is used to design the AW filter, and each AW resonator is tuned to the filter prototype value to meet the desired specifications. Thus, the filter design time and the number of resonators can be efficiently improved, and the filter design time can be reduced compared with the direct conversion and slope parameter methods commonly used in filter design. To demonstrate the effectiveness of these design methods, the proposed methods were used to design and fabricate an N41 filter using scandium-doped aluminum nitride (ScAlN) resonators. The broadband capabilities of the filter were verified using BEFM. The design, fabrication, and measurement of a broadband filter that meets the requirements of the 5G N41 frequency band centered at 2.593 GHz with a bandwidth of 196 MHz have verified the filter fabricated using the proposed design method. The insertion loss is less than -3 dB in the target band and more than 30 dB out of band. In summary, the proposed BEFM provides an efficient and accurate method for designing AW filters.