Performance Evaluation and Design of Stacked Crystal Filters

When very small size, microwave frequency and high quality factor resonators are required, bulk acoustic wave (BAW) resonators are generally used. However, in devices such as oscillators, the use of two stacked BAW resonators, a structure known as stacked crystal filter, can help to overcome the fundamental trade-off between tunability and phase-noise performance. For that reason, this paper evaluates the performance of this type of resonators, and it presents a collection of closed-form expressions for its primary design.