P6G-2 Synthesis of Frequency Response for Wideband SAW Ladder Type Filters

Abstract

Numerical synthesis of frequency response is discussed for a ladder type filter consisting of ultra-wideband SAW resonators on Cu-grating/15 • YX-LiNbO3 structure. For the synthesis, two parameters of each resonator, i.e., the static capacitance and resonant frequency were numerically optimised, while the capacitance ratio and figure of merit were fixed at specific values determined by substrates and grating electrodes employed. First, six-stage SAW ladder type filters having the passband width of 7 to 21% were designed. The result showed that the specified bandwidth is successfully synthesised. Next, a six-stage ladder type filter having the passband width of 8% was fabricated on Cugrating/15 • YX-LiNbO3 structure for experimental discussion. It was shown that the measured frequency response of the filter was in good agreement with the design, where some in-band spurious dips were removed by weighted dummy electrodes. By making analysis on the behaviour of resonant and anti-resonant frequencies of each resonator, it is shown that the method can be extended to the synthesis of filters having sophisticated frequency responses. The result suggested that the proposed method could become one of the powerful design tools for SAW ladder type filters with specified passband width.

Single and Multiband Acoustic-Wave-Lumped- Element-Resonator (AWLR) Bandpass Filters With Reconfigurable Transfer Function

“…1(a)-so that wider BWs are obtained for higher Z E values. As such, any FBW can be created without being constrained by the acoustic-wave resonators' k 2 t as opposed to traditional ladder-or lattice-type acoustic-wave resonator filter designs in which the FBW is less than k 2 t , as, for example, in [8]- [11]. Furthermore, as can be seen in the inset of Fig.…”

“…However, their performance is limited by narrow fractional BW (FBW)-often less than 0.4-0.8k 2 t , where k 2 t is the electromechanical coupling coefficient of their piezoelectric substrate-and static transfer-function characteristics [8]. As discussed in [9]- [11], larger BWs can be obtained through the development of high-k 2 t substrates. Nevertheless, they come at the expense of lower Q and unwanted spurious-mode generation.…”

Hybrid Acoustic-Wave-Lumped-Element Resonators (AWLRs) for High-<formula formulatype="inline"><tex Notation="TeX">$Q$</tex> </formula> Bandpass Filters With Quasi-Elliptic Frequency Response

“…However, such bandwidth enlargement comes at the expense of reduced out-of-band isolation as in any traditional all-AW filter [12], [20]. Bandwidth limitations that arise from the multi-mode nature of the AW resonator, which need to be considered for the appropriate modeling and development of these RF filters, are discussed in Section II-F. Fig.…”

“…In particular, the spurious modes that appear in a close proximity to the fundamental mode may introduce undesired ripples or notches within the passband and reduce the out-of-band rejection [12], [13], [29]. While the simplified BVD model of the one-port AW resonator predicts well the expected RF filter performance in the vicinity of the design frequency, it does not include the undesired spurious signal contributions in the RF filter response.…”

“…12(a), the RF measured response agrees well with the EM simulations, thus successfully demonstrating the proposed AWLR concept. It should be noted that the presence of spurious modes in a close proximity to the passband is attributed to the multi-mode nature of the AW resonators as typically observed in all state-of-the-art all-AW resonator filters [10], [12]- [14], [16], [17], [27], [33].…”