SAW Resonator: 1 Port vs. 2 Port Comparison

Introduction

SAW (Surface Acoustic Wave) resonators are crucial components in RF systems and come in 1-port and 2-port configurations. Understanding their differences helps optimize performance for specific applications. This guide explains how these types work and highlights their applications.

In SAW devices, the wave travels on the surface of piezoelectric materials. They typically use wafers made from quartz crystal, LiTaO3, or LiNbO3 as the piezoelectric material. Wave propagation characteristics depend on the cutting angle or propagation direction of the material. There are various types of waves in SAW devices, and each one is used as per the desired application.

SAW generation

Electrical signals are transformed into surface acoustic waves with the help of piezoelectric materials. When an electric field is applied, the piezoelectric material changes shape (i.e., it gets deformed). Hence, by forming comb-shaped electrodes known as IDT (Inter Digital Transducers) and with signal application, SAW waves are generated. The velocity of the acoustic wave usually depends on the substrate type or the wave type (Rayleigh wave, leaky wave, Love wave) used. The variation in the pitch of IDT electrodes will change the frequency of the generated waves.

Similarly, if the pitch of the IDT and SAWs matches, it generates an electrical signal between the IDT electrodes upon the application of SAW waves at the IDT.

SAW reflection

There are two basic components used in SAW devices: IDTs and gratings. To reflect a SAW with wavelength “λ”, a pitch of λ/2 is used between electrodes.

What is a Resonator?

Definition of a resonator: A resonator is a device that naturally oscillates (or resonates) at a certain frequency with a higher magnitude. The frequency at which the maximum amplitude is obtained is known as the resonant frequency or resonance frequency. The oscillations can be either EM (electromagnetic) or acoustic in nature.

Function: The resonator is used to generate a wave at a specific frequency or to select particular frequencies from a signal. The resonator, which uses a structure as shown in the figures below, is known as a SAW resonator.

In SAW devices, resonance is achieved by placing gratings in the propagation direction of the SAW, which is excited by the IDT.

1 Port SAW Resonator

1 port SAW resonator

The figure above depicts a 1-port SAW resonator. It uses one IDT structure.

2 Port SAW Resonator

2 port SAW resonator

The figure above depicts a 2-port SAW resonator. It uses two IDTs: one for input and the other for output between the gratings. The 2-port SAW resonator is often used as a filter due to its propagation characteristics between the IDTs.

Conclusion

Choosing between a 1-port or 2-port SAW resonator depends on the application needs, such as filtering or oscillation. Understanding their unique features ensures optimal performance.