Microwave/RF Filters based on Bulk Acoustic Wave Resonators
The exponential growth in wireless communication systems in recent years has been due to the requirements of small high performance microwave/RF devices and filters in particular. The main limitation of microwave devices based on traditional technologies is that these technologies are not compatible with the manufacturing process of standard integrated circuits (IC). Microwave devices based on acoustic resonators, and bulk acoustic wave (BAW) resonators in particular, overcome this limitation since this technology is compatible with standard IC technologies. On the other hand, BAW resonators are excited by means of an acoustic wave with lower propagation velocity than that of electromagnetic waves, leading to the size reduction of the resonator and the microwave device as a consequence. Taking into account the physical characteristics of the acoustic material, the design procedure for basic microwave/RF filters is discussed, and also the way to improve the their electrical performance. Aftewards, new filter topologies are presented to achieve more sophisticated responses, in particular a dual-band transmission response.