New synthesis features and nonlinear modelling of electroacoustic filters for cellular and space applications

Abstract

Electroacoustic filters, also known as acoustic wave (AW) filters, are very helpful in space missions since they can operate reliably under the harsh conditions of space at very high frequencies. The performance of electrical components can be harmed by the intense radiation, extreme temperatures, and other environmental stressors that spacecraft and satellites are exposed to. However, these situations can be handled by electroacoustic materials. Additionally, tuneable electroacoustic filters, which have seen a growing market in recent decades, introduce several advantages over fixed-frequency filters since they are able to operate over different frequency ranges. The fact of being able to adjust the operation band of the filter offers great flexibility as regards communication applications. Furthermore, miniaturization is another key feature for the use of electroacoustic filters in space applications as it leads to volume and mass savings. The first aim of the present thesis is to further develop the software tool for the synthesis of electroacoustic filters, FILTRAW®, in order to increase the flexibility of the design process, as well as to reduce the derived fabrication costs. The current project is embedded in the framework of a European Space Agency project to design tuneable electroacoustic filters, which aim to advance in flexible payloads. As the need for more adaptable and economical space missions grows, flexible payloads are becoming more and more crucial. Furthermore, the project is conducted within the collaborative framework between UPC and Qorvo¿, as an integral aspect of their ongoing partnership. The tool will introduce the capability to synthesize filters in transversal configuration in addition to the conventional ladder configuration. This topology was created and proved through a previous ESA project and an initial prototype for space application was manufactured. Moreover, the tool will enable the adjustment of the ladder filter synthesis outcome to conform to established manufacturing restrictions, such as the necessity for establishing a specific electroacoustic coupling at the resonators or the avoidance of external lumped components in the filter. These synthesis functionalities have been requested by Qorvo¿, a leading company in the electroacoustic filter industry, which is currently collaborating with the Universitat Politècnica de Catalunya (UPC). The second aim of the project is to model the nonlinear behaviour of the individual resonators composing the AW filter in order to predict the nonlinear behaviour of a whole ladder filter structure. By performing this analysis, it becomes feasible to ascertain the primary resonators that are contributing to the network's nonlinear response at both the harmonics and intermodulation products and asses the influence of the physical and nonlinear parameters of the resonators on the nonlinear response of the AW filter. Nonlinear effects can introduce unwanted distortion and intermodulation products in signals, degrading the quality of communication and data transmission in space systems. Furthermore, it is important to consider that space components often have stringent performance specifications and requirements. Therefore, evaluating the nonlinear behaviour ensures that the AW filter meets the specified performance criteria.