# An Improved Method to Compute the Mutual Capacitance between Interdigital Transducers in Radio Frequency Surface Acoustic Wave Filters

## TL;DR

This paper introduces a faster and more accurate method to calculate capacitance in radio frequency filters, improving design efficiency.

## Contribution

The novel approach combines boundary element and partial capacitance methods to enhance the COM model for SAW filters.

## Key findings

- The proposed method matches commercial software accuracy but calculates faster.
- It enables precise electrical response prediction for dual-mode SAW filters.
- The method can be integrated into filter design optimization processes.

## Abstract

This paper proposes an improved method to calculate the mutual capacitance between interdigital transducer (IDT) electrodes to enhance the accuracy of the traditional coupling-of-modes (COM) model, which is commonly used to simulate surface acoustic wave (SAW) filters and duplexers. In this method, the boundary element method (BEM) is adopted to obtain the capacitance per unit length in a layered medium, while the partial capacitance (PC) method is used to derive the effective relative permittivity of the multi-layered IDT. Numerical results from commercially available software are provided for comparison with the results calculated using the proposed method. The consistent results verify the validity and accuracy of this method, which also demonstrates significantly faster calculation speed compared to commercially available software. Precise electrical response prediction of a dual-mode SAW (DMS) filter can be achieved by applying this method to the COM model, and this ultra-fast calculation method can also be included in filter design optimization.