Rf Saw Ladder Filters Developed

Surface Acoustic Wave(SAW) Ladder-type Filter is widely used in mobile communications, satellite communications, radio frequency identification system receiver and transmitter, because of its low insertion loss, simple structure, small size, light weight and without matching circuit. In this paper, using the Coupling-of-Modes model(COM) analyze the Ladder-type Filter's element—SAW Resonator. The theory discuss the choice of substrate materials, the characteristics SAW Rayleigh mode and leaky wave mode, inter-digital transducer (IDT) designs, reflective grating design, and write these parameters to the Matlab files, after that, a variety of different types of simulation procedure for single resonator can be used to optimize these parameters to met the targets. In the help of the microelectronic planar processing, finally in the substrate of LiTaO3, we get two different modes of single resonators, with the center frequency of 406MHz and 500MHz respectively.In the next, analyze the theoretical simulation of the SAW Ladder-type filter, and the filter's series arm resonator and the parallel arm resonator. Using the Matlab programming design a Ladder-type simulation software packge, we can quickly and easily give a single series arm resonator and a single parallel arm resonator frequency response equation, and the trapezoidal formula vibration frequency response of the filter. In particular, comparison of various filter parameters on the device performance by optimizing the parameters, we get a conventional 6-order SAW ladder-type filter with the center frequency of 500MHz, insertion loss of 3.7dB, a bandwidth of 25MHz, and the rectangle coefficient is 1.8.Obtained by analysis of 6-order conventional ladder filter pass-band low-end frequency response of subsidence due to the mismatch between the filter stage formed, according to the matching principle in the inter-stage matching unit of production by adding the matching structure of ladder filter, the newly matched filter has a small pass-band ripple by the contrast of conventional 6-order SAW ladder-type filter. Based on the the conventional 6-order filter, by applying the structure of normal m-derived LC filter to the design of ladder-type filter, which contrast with traditional ladder-type filter, has a narrower pass band and more sharpen transition band, without sacrificing the insert loss and out of band rejection. At last, we get a narrow band filters with the pass band of 15MHz, and the rectangle coefficient is 1.2.