Double-resonance SAW filters

Abstract

A novel surface acoustic wave filter on a leakywave substrate is studied. It features a hiccup-type resonance occurring around a distributed gap between two long interdigital transducers. Compared to a classical coupled resonator filter, it enables a relatively narrow passband (1% to 2% of center frequency) with low insertion loss, steep skirts, and improved suppression levels. The structure consists of long transducers having the number of fingers greater than 1=K 2 and 1= , where K 2 is the coupling coefficient of the substrate material and is the reflectivity per wavelength, separated with short transducer sections constituting a distributed gap. A strong, localized resonance is formed in the gap region, in addition to the resonance arising in the long structures-hence, the name doubleresonance filter. The substrate studied here is 42 -rotated lithium tantalite. We show experimental results for both single-ended and unbalanced-to-balanced filters at 1.6 GHz, having a minimum insertion loss of 1.07 dB, suppressions of 30 dB, and absolute ;3-dB bandwidth of 29 MHz (1.9% of the center frequency). For the balanced device, the amplitude imbalance over the passband ranges from ;0.6 dB to 2 dB and the phase imbalance from 1 to 4.5 . Furthermore, we have measured the acoustical power distributions using a scanning laser interferometer, and we compare these results with the profiles simulated using a coupling-of-modes model.

6H-6 High-Suppression SAW Filters Based on Double-Resonance Structure

“…Self-matching of the hiccup resonance, discussed in [1], is important also for the operation of the filter studied in this paper. In the self-matching phenomenon, the synchronous resonance arising in the long input IDT acts as a matching inductance for the hiccup resonance, enabling low loss and symmetric shape of filter PB.…”

“…The structure of a surface acoustic wave (SAW) doubleresonance filter (DRF) [1], depicted in Fig. 1, resembles that of a coupled resonator filter (CRF) [2] with acoustically coupled interdigital transducers (IDTs) placed in the propagation path of the SAW.…”

“…A similar structure was first proposed by Plessky et al [5], but due to losses occurring in metallized gaps, the performance of realized devices was not satisfactory. If the losses in the gap are reduced by replacing the metallized gap with short IDT sections (distributed gap), low-loss, narrow-band filter operation with fast transition to rejection band and high rejection levels can be obtained on strong piezoelectric substrates, such as 42 • -LiTaO 3 [1]. The structure enables a relative passband (PB) width of 1%.…”

Optical Characterization of Phononic Crystals in the Frequency Domain

“…Interferometric measurements can often be used not only to characterize a device but also to confirm its operation principle. Furthermore, correct modeling of the device behavior can be validated, as an example, characterization of a double-resonance SAW filter is presented in [18]. All of the above-mentioned capabilities are expected to apply to the characterization of not only conventional SAW devices, but to SAW interaction with micro-structured acoustic metamaterials as well.…”

Non-synchronous resonators on leaky substrates

“…4(b) showing the series-connection of the resonator, with simulations. Placing the notches can be a useful feature for a 2-port filter configuration (see companion paper in this Proceedings [7]). To observe self-matching, the parameters of the device must be chosen such that the anti-resonance and hiccup resonance frequencies coincide.…”