2-IDT double-mode SAW filters with decreased insertion loss and advanced functionalities
This paper presents new 2-IDT double-mode SAW (DMS) filters with the decreased insertion loss and advanced functionalities: low input and output impedances, balanced operation and impedance conversion on 42º YX LiTaO3, 64º YX and 41º YX LiNbO3. To decrease the input and output impedances and resistive losses of the IDT electrodes the parallel connection of the 2-IDT DMS filters in the different acoustic tracks is used simultaneously reducing the aperture of each track. For an impedance conversion a series connection of the output IDTs in the 2 parallel acoustic tracks of the filters is used. To increase the selectivity of the filters the cascaded connection and phase weighting are employed. The constructional and topological optimization of the SAW filters is provided with a computer simulation using an equivalent circuit model. The 240–367 MHz samples of the balanced SAW filters have shown an insertion loss of about 1 dB, stopband attenuation of about 20 dB, impedance conversion from 50–75 Ω at the input to 200–300 Ω at the output in a wide fractional bandwidth of 2–6%. Two cascaded filter has provided an insertion loss of less than 2 dB and stopband attenuation of about 50 dB. The filters are housed in the 5×5×1.35 mm SMD packages.
Low-Loss and Wide-Band Double-Mode Surface Acoustic Wave Filters Using Pitch-Modulated Interdigital Transducers and Reflectors
This paper proposes use of pitch-modulated interdigital transducers (IDTs) and reflectors for the realization of low-loss and wideband longitudinally coupled double-mode surface acoustic wave (DMS) filters. This technique offers drastic improvement of the device performances through the introduction of a sufficient number of degrees of freedom in the DMS filter design. Namely, the pass-band becomes wide and flat, and insertion loss can be reduced through the suppression of the bulk acoustic wave (BAW) scattering. First, it is shown how the BAW scattering loss can be reduced by the use of the pitch-modulated structure. The DMS filter with this structure is designed so that the frequency response becomes similar to that of the filter with the conventional unmodulated structure, and device performances are compared both theoretically and experimentally. It then is demonstrated how the total device performances are improved by the use of this technology when the device is designed optimally for given specifications. Adding to the reduced bulk wave scattering loss, various distinctive features offer drastic improvement of total device performances.
Optimization of Quartz SAW Resonator Structure with Groove Gratings
Abstruct-A new surface acoustic wave (SAW) resonator optimum design method is proposed to reduce resonator sue. The fundamental design feature is optimization of the interdigital transducer (IDT) electrode period to reflector electrode period ratio, in order to adjust the frequency for the maximum IDT admittance to the maximum reflector reflection point. As a result of the optimized electrode period ratio, both reflector and IDT frequency responses are utilized to advantage, and good resonant Characteristics are obtained with a reduced number of reflector electrode fingers. This design method can be effectively applied for SAW resonators with groove gratings, both on reflectors and transducer, that are formed by a reactive sputter etching process. 145 MHz SAW resonators with groove gratings fabricated on a small 6 mm X 3 mm ST-cut quartz chip have provided good electrical performances, such as high Q values above 2 X lo4 and low resonance resistance in the 20-30 range.