Low-loss, multimode 5-IDT SAW filter

Longitudinally coupled resonator filters provide unbalanced-balanced operation with wide bandwidth, low loss, arid high suppression levels. However, reducing the insertion loss in the 1.8-2.2 GHz range remains a challenging problem because at high frequencies the resistive losses arising from the re...

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Bibliographic Details
Published in:IEEE transactions on ultrasonics, ferroelectrics, and frequency control ferroelectrics, and frequency control, 2005-06, Vol.52 (6), p.1013-1019
Main Authors: Meltaus, J., Plessky, V.P., Harma, S., Salomaa, M.M.
Format: Article
Language:English
Subjects:
Apertures
Baluns
Bandwidth
Degradation
Devices
Frequency
Gaps
Insertion loss
Noise levels
Passband
Performance loss
Resonator filters
Ripples
SAW filters
Transducers
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Summary:Longitudinally coupled resonator filters provide unbalanced-balanced operation with wide bandwidth, low loss, arid high suppression levels. However, reducing the insertion loss in the 1.8-2.2 GHz range remains a challenging problem because at high frequencies the resistive losses arising from the relatively wide aperture of the filter may degrade the performance. A 5-interdigital transducer (IDT) filter has six gaps at which the periodicity of the grating is broken, resulting in additional loss due to scattering into the bulk. In this paper, we show that replacing the gaps between the transducers with short transducer sections having their pitch different from that of the main transducers reduces the insertion loss of the device. We present devices with balun operation at 1842 MHz with wide bandwidth of 4.5% and -40 dB suppression, with a minimum insertion loss less than 1 dB in the best devices, and a maximum insertion loss of -1.2 dB in the passband. The passband is quite flat, with
ISSN:0885-3010
1525-8955
DOI:10.1109/TUFFC.2005.1504023