Design and Simulation of GPS(1.56-1.61GHz) RF Lattice and Ladder Type SAW Filter

In this paper, different structures of Lattice and Ladder type GPS surface acoustic wave (SAW) filter for a band of 1.56GHz to 1.61GHz are designed and simulated. Here we optimized and simulated lattice and ladder-type structures with proper variation in design to achieve high selectivity, small size, low insertion loss (<1.8dB in passband), high rejection (>35dB in out of band), more return loss (>10dB) and low cost. The SAW devices give high reliability, good stability, high power handling capability and they are extensively used in high-frequency telecommunication systems such as mobile handsets and TV sets. An electrical equivalent of a resonator is designed using Butterworth-van-dyke (BVD) model. The ladder-type design is obtained by connecting those resonators in series and parallel by choosing proper stages to get the desired response and a lattice-type filter is designed by connecting resonators in series and crossed arms with a cascade structure. The obtained electrical equivalent model was then converted to physical inter-digital transducer (IDT) parameters like wavelength, aperture, pitch, number of IDTs, the width of the IDT, and number of reflectors. With the help of physical parameters, we have designed a resonator (i.e., IDT and reflectors) layout. The whole design of the filter will be fabricated on lithium tantalate (LiTiO3) substrate which gives high physical strength, better power handling capacity, good reflection coefficient, a large electromechanical coupling coefficient
$(\mathrm{K}_{\mathrm{t}}^{2}$
, and is unaffected by pyroelectricity.