Surface acoustic wave (SAW) device coverage includes delay lines and filters operating at selected frequencies in the range from about 10 MHz to 11 GHz; modeling with single-crystal piezoelectrics and layered structures; resonators and low-loss filters; comb filters and multiplexers; antenna duplexers; harmonic devices; chirp filters for pulse compression; coding with fixed and programmable transversal filters; Barker and quadraphase coding; adaptive filters; acoustic and acoustoelectric convolvers and correlators for radar, spread spectrum, and packet radio; acoustooptic processors for Bragg modulation and spectrum analysis; real-time Fourier-transform and cepstrum processors for radar and sonar; compressive receivers; Nyquist filters for microwave digital radio; clock-recovery filters for fiber communications; fixed-, tunable-, and multimode oscillators and frequency synthesizers; acoustic charge transport (ACT); and other SAW devices for signal processing on gallium arsenide. Shallow bulk acoustic wave (SBAW) device applications include gigahertz delay lines, surface-transverse-wave resonators employing energy-trapping gratings and oscillators with enhanced performance and capability. >

Applications of surface acoustic and shallow bulk acoustic wave devices

An inexpensive frequency-modulated continuous-wave (FMCW) radar system is presented in this paper, which, nevertheless, meets all industrial requirements. The FMCW radar uses a low-cost nonlinear voltage-controlled oscillator (VCO), operating at an IF of 2.45 GHz to generate the frequency modulation of the radar system. This VCO signal is applied twice, first to generate the radar transmitter signal at 24 GHz, and then it is fed to a surface acoustic wave (SAW) delay line. The SAW delay line generates a fixed delay time, which corresponds with a fixed radar distance. Thus, all systematic nonlinearities and stochastic phase errors of the FMCW system can be monitored and, afterwards, can be compensated for in real time. This linearization technique leads to a significant enhancement in dynamic range for a FMCW radar system. For this FMCW system, SAW delay lines with a linear phase characteristic have been designed using a linear optimization program. The delay line consists of two chirped and weighted interdigital transducers. For high volume, low-cost, and high-yield production of the required SAW structures, with linewidths down to 0.3 /spl mu/m, technological improvements had to be achieved, especially in photolithography. Based on these design and fabrication techniques, delay lines at 2.45 GHz operating at the fundamental and third harmonic with bandwidths up to 800 MHz have been realized.

Design, fabrication, and application of precise SAW delay lines used in an FMCW radar system

In the design of high-performance SAW devices it is nec- essary to analyze and correct for the effect of diffraction. We present a fast and accurate method for the analysis of diffraction applicable to a wide class of highly anisotropic materials. Starting from the angular spectrum representation of the diffracted fields, an asymptotic expan- sion of the diffraction integral is given which proves to be accurate even for the very near-field region. Comparisons of beam profile calcula- tions using the asymptotic expression and those made by direct nu- merical integration of the diffraction integral show accuracies of better than one percent for propagation distances greater than 25 wave- lengths and an increase in computation speed by a factor of 25 or bet- ter. As the propagation distance z is further increased into the truly asymptotic region (z e 100ho), the accuracy of the asymptotic expres- sion further improves and the speed is at least 70 times faster than the numerical routine. This range is typical of the spacing in narrow-band high-rejection filters. Results are given for YZ lithium niobate.

Fast Computation of SAW Diffraction by Asymptotic Techniques

A noniterative algorithm for the design of nonequidistantly sampled interdigital transducers (IDTs) is presented. This method allows the precise design of IDTs with a given impulse response. Deviations according to the impulse model are less than 0.1 dB within the passband. The authors present the design and the compensation of second-order effects of a delay line with two chirped and apodized IDTs and present measurements of this filter. >

Design and compensation of nonequidistantly sampled SAW transducers

A simple and elegant method is presented for the minimization of diffractive effects in SAW filters. It is shown that diffraction effects can be almost completely eliminated by merely increasing the aperture of the receiving unapodized transducer. From the leading terms of the Uniform Asymptotic Expansion (UAE) of the diffraction integrals, we can obtain a physical interpretation of the diffraction process in terms of the Geometric Theory of Diffraction GTD). An explanation of this diffraction minimization tec h nique is obtained using the physically intuitive language of the GTD. A simple formula for the necessary dimension of the receiving aperture which yields a desired level of diffraction error for a given transducer separation is given. The validity of the method is confirmed experimentally for devices fabricated on 128 degree rotated Y-cut X-propagating LiNb03. This technique can be applied to a wide class of highly anisotropic materials.

http://ieeexplore.ieee.org/iel5/10286/32719/01535642.pdf

Minmization of Diffraction Effects in SAW Devices Using a Wide Aperture

Abstruct-The uniform asymptotic expansion (UAE) previously developed for the calculation of the diffracted SAW beam profile is extended to the calculation of diffraction effects in the frequency response of a SAW filter. The method provides a fast and accurate method of calculating the effects of diffraction in the frequency response of SAW filters even in the very near field region (z < 2.5 A,,). Accuracy and speed comparisons between the UAE and a direct numerical integration algorithm are given. For transducer separations greater than 25 X. the relative difference between the two methods is less than 0.1 dB in the frequency range of interest. In addition, the computation speed of the UAE is greater than that of the numerical integration algorithm by at least a factor of 60 and continues to increase with increasing transducer separation. This technique is used in conjunction with well-known wide-band compensation procedures to design diffraction compensated SAW filters. Experimental results of diffraction compensated SAW filters constructed on 128" rotated Y-cut X-propagating LiNbO, are given.

C. Flory

Papers

Compensation of Diffraction Effects in SAW Filters Using the Uniform Asymptotic Expansion