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 42^o YX LiTaO₃, 64^o YX and 41^o 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.