Design of a UHF low-loss Leaky SAW Impedance Element filter unit section

Surface Acoustic Wave (SAW) filters form key components in RF and IF stages of many of today´s wireless communication systems. Their small size and rugged construction make them an obvious choice in designs where size and weight are at a premium. IF SAW filters provide excellent design flexibility and shape factors but are limited by the high insertion losses offered. On the contrary, resonator based low loss RF SAW filters offer low losses and a remarkable degree of miniaturization. This paper discusses the design and realization of a unit section of low loss resonator based Impedance Element (IE) SAW filter in a ladder construction. The design centre frequency is chosen to be 790 MHz. This corresponds to a critical line dimension of 1.25 μm on 42°Y-X LiTaO₃ Leaky SAW (LSAW) substrate and is well within the lithographic capabilities of most contemporary micro-lithographic systems. To extract the material constants of various SAW/LSAW substrates, a program is written in MATLAB. A Finite Element Method (FEM) simulation tool is utilized to characterize the resonance characteristics of SAW resonators. This tool uses the derived constants as inputs. An equivalent circuit approach is used to carry out filter simulation in ADS. Results are presented for a fabricated unit filter section and compared with simulation.