SAW filters based on parallel-connected coupled resonator filters with offset frequencies

Area of Science:

• Acoustic wave devices
• Filter synthesis
• Microwave engineering

Background:

• Surface acoustic wave (SAW) filters are crucial components in radio frequency (RF) systems.
• Traditional SAW filter designs face limitations in achieving wide passbands with low insertion loss and precise rejection control.
• The concept of coupled resonators offers a potential avenue for advanced filter synthesis.

Purpose of the Study:

• To develop and demonstrate a novel two-track surface acoustic wave (SAW) filter architecture.
• To achieve wide passbands with low insertion loss and well-controlled signal rejections.
• To validate the performance of this new design on quartz and 42° LiTaO3 substrates.

Main Methods:

• Utilized the concept of coupled resonators with two parallel-connected filter tracks, incorporating a frequency shift between them.
• Employed the coupling-of-modes (COM) model and the transmission-matrix approach for device design and optimization.
• Fabricated and tested prototype devices with varying transducer configurations and output types.

Main Results:

• Demonstrated a wide passband with low insertion loss and controlled rejections through mutual interaction of transfer functions.
• Achieved a minimum insertion loss of 4 dB and 0.23% bandwidth at 868 MHz on quartz.
• Attained a 1.3 dB minimum insertion loss and 4.1% bandwidth at 1960 MHz on 42° LiTaO3, featuring remarkably flat passbands.

Conclusions:

• The two-track coupled resonator approach is effective for synthesizing advanced SAW filters.
• The fabricated devices show promising performance, particularly on 42° LiTaO3, offering wide bandwidths and low loss.
• Precise material parameter control and reliable fabrication are critical for achieving desired rejection frequencies.