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

The theory of a new type of bandstop-to-all-pass reconfigurable filter is developed in this work. A bandstop filter structure with both source-to-load and inter-resonator coupling is implemented. The synthesis equations are manipulated such that the signals in the filter's resonators and source-to-load transmission line can be made to constructively or destructively interfere at the output port through tuning of the resonant frequency of the filter's resonators. The relationship between resonator quality factor, filter bandwidth, and the all-pass response state is shown for the first time. The theory is proven through fabrication of a bandstop-to-all-pass filter with resonator unloaded quality factors greater than 500. Measured results show that the filter can continuously tune from insertion loss of 2.1 dB in the all-pass state to insertion loss of 69 dB in the bandstop state at the center frequency of the filter. Analog tuning of the attenuation level is also shown. The capability to switch from an all-pass to a variable-attenuation bandstop response enables a spectrally aware system to operate over wide bandwidths when interference levels are low and to dynamically add bandstop responses when interference affects its performance or signal equalization is required.

Switchless Tunable Bandstop-to-All-Pass Reconfigurable Filter

This paper gives a historical account of the development of Rayleigh-wave, or surface acoustic wave (SAW), devices for applications in electronics. The subject was spurred on initially by the requirements of pulse compression radar, and became a practical reality with the planar interdigital transducer, dating from 1965. The accessibility of the propagation path gave rise to substantial versatility, and a huge variety of devices were developed. Passive SAW devices are now ubiquitous, with applications ranging from professional radar and communications systems to consumer areas such as TV, pagers and mobile phones. The paper describes the extensive work, particularly in the 1970s, to investigate SAW propagation in crystalline media, including piezoelectric coupling diffraction and temperature effects. This led to identification of many suitable materials. Concurrently, many devices began development, including pulse compression filters, bandpass filters, resonators, oscillators, convolvers and matched filters for spread spectrum. In the 1970s, many of these became established in professional systems, and the SAW bandpass filter became a standard component for domestic TV. In the 1980s and 9Os, SAW responded to the new call for low-loss filters, particularly for mobile phones. With losses as low as 2 dB required (and subsequently achieved) at RF frequencies around 900 MHz, a raft of new technologies was developed. Additionally, for IF filters special techniques were evolved to reduce the physical size needed for narrow bandwidths. Such devices are now manufactured in very large quantities. In order to satisfy these needs, new types of surface wave, particularly transverse leaky waves, were investigated, and materials using such waves now have their place alongside more traditional materials.

History of SAW devices

Pressure sensing diaphragms comprise a cylindrical or spherical crystalline member in which an internal cylindrical or spherical chamber is provided. In the internally loaded embodiments, a fluid is introduced into the chamber and the pressure exerted by the fluid causes generally tensile stress in the region of the diaphragm generally about the chamber. In the externally loaded embodiments, the diaphragm is immersed within the fluid and the pressure exerted by the fluid causes generally compressive stress in the region of the diaphragm generally about the chamber. For each of the embodiments, the stresses arising cause certain mechanical and electrical properties of the crystalline material to change. The change in these properties is detected by observing the frequency behavior of one or more oscillators whose frequencies of operation are controlled by respective surface acoustic wave devices provided in the regions of elastic deformation. Many diaphragm arrangements are capable of providing temperature compensated pressure measurements. Two particularly useful orientations for the temperature compensated embodiments are the SST and ST orientations.

Surface acoustic wave sensors

An introduction to Surface-Acoustic-Wave (SAW) devices-their operation, advantages, and applications--is presented. The process of design and realization of high-performance SAW filters is examined from initial specifications to final device operation. Several techniques drawn from a variety of disciplines illustrate the implementation of finite impulse response SAW frequency functions. Material properties, transducer weighting, and computer-aided design are treated. An example of the design and testing of a 321-MHz 0.35-percent bandwidth, 65-dB sidelobe, 15-dB insertion loss filter is presented.

Miniature surface-acoustic-wave filters

http://ieeexplore.ieee.org/iel5/10281/32714/01534535.pdf

A Digitally Compensated SAW Oscillator

: In order to avoid frequency spurious signals in bandpass filtering applications, low out-of-band sidelobes are necessary. The purpose of the present paper is to describe in detail the techniques necessary to achieve 60-70 dB sidelobe SAW filters operating in the UHF Region. These techniques include the use of withdrawal weighted (WW) transducers either as both input and output of the filter or in combination with overlap apodized transducers plus a thorough understanding and control of second order effects. The utility of these procedures will be illustrated by a description of the design, fabrication and testing of a 335 MHz, 0.34 percent bandwidth, 15 dB insertion loss, SAW filter on ST quartz having sidelobes and all other spurious (electromagnetic feedthru and 'bulk' mode interference) at least 63 dB below the output. In addition, experimental examples of design parameter variations and second order effects will be presented and correlated with theory where appropriate.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA052703&Location=U2&doc=GetTRDoc.pdf

Low Sidelobe SAW Filters Using Overlap and Withdrawal Weighted Transducers

The design and testing of two high-performance 9channel switchable SAW fiiter banks are described. Bank #l covers 360-468 MHz in 12-MHz steps (no Titer at 420 MHz) with each channel consist- ing of a length apodized and a withdrawal weighted transducer. Input multiplexing is achieved by the parallel interconnection of three induc- tively tuned sets of three series connected transducers. This scheme re- sults in both low and uniform insertion loss between channels. A mean value of 25.8 dB with a standard deviation of 0.75 dB was achieved. The highest spurious signals in the frequency domain are approximately 57 dB down and are due to electromagnetic feedthrough. The individ- ual high-frequency SAW fiiters themselves are capable of 63-65dB spurious suppression with approximately 19dB insertion loss. If needed, low-loss narrow-band matching techniques can be used and are de- scribed. Bank #2 covers 321-345 MHz in 3-MHz steps with a mean channel insertion loss of 19.8 dB. This includes l .S dB of output switch (a 9 X 1 switch used to select the desired frequency channel) insertion loss and can be compared to an individual Titer value of 14 dB. Sub- stantial improvement over power division is achieved. For this bank the strongest frequency spurious was approximately 61 dB.

Switchable SAW Filter Banks at UHF

SAW Filters for Frequency Synthesis Applications

http://ieeexplore.ieee.org/iel5/10275/32708/01533486.pdf

G.A. Roberts

Papers

A Digitally Compensated SAW Oscillator

Low Sidelobe SAW Filters Using Overlap and Withdrawal Weighted Transducers

Switchable SAW Filter Banks at UHF

SAW Filters for Frequency Synthesis Applications

A Minimal Diffraction Lithium Tantalate Substrate for Contiguous SAW Butterworth Filters