Correction to "The Shannon sampling theorem&#8212;Its various extensions and applications: A tutorial review"

This book gives the fundamental principles and device design techniques for surface acoustic wave filters. It covers the devices in widespread use today: bandpass and pulse compression filters, correlators and non-linear convolvers and resonators. The newest technologies for low bandpass filters are fully covered such as unidirectional transducers, resonators in impedance element filters, resonators in double-mode surface acoustic wave filters and transverse-coupled resonators using waveguides.The book covers the theory of acoustic wave physics, the piezoelectric effect, electrostatics at a surface, effective permittivity, piezoelectric SAW excitation and reception, and the SAW element factor. These are the main requirements for developing quasi-static theory, which gives a basis for the non-reflective transducers in transversal bandpass filters and interdigital pulse compression filters. It is also needed for the reflective transducers used in the newer devices. It is a thorough revision of a classic on surface acoustic wave filters first published in 1985 and still in print. It uniquely combines easy-to-understand principles with practical design techniques for all the devices in widespread use today. It includes complete coverage of all the latest devices which are key to mobile phones, TVs and radar systems; and, a new foreword by Sir Eric Albert Ash.

Surface Acoustic Wave Filters: With Applications to Electronic Communications and Signal Processing

Possible improvements in recent work on moment invariants are pointed out. Invariants that correctly take into account the effect of change in scale and illumination are described. An example, using two images with arbitrary shift, rotation, scale and contrast change, is also provided.

Moment invariants

The principles of a wide range of acoustic-surface-wave devices employing acoustoelectric interactions with semiconductors are described. It is shown that acoustoelectric amplifiers can increase the dynamic range of a delay-line filter. Such devices have been operated on a CW basis and are beginning to become practical. The acoustic convolver and its derivative devices, the optical scanner, the acoustic focusing and imaging devices, and the storage correlator are described. Several of the signal processing applications of the convolver are discussed. Various types of constructional techniques, including the air gap convolver and acoustoelectric amplifier, the strip coupled and external diode convolvers, the use of piezoelectric semiconductors, deposition of a semiconductor on a piezoelectric substrate, and deposition of a piezoelectric material on a semiconducting substrate are discussed.

Acoustoelectric interactions in acoustic-surface-wave devices

Interception of frequency-hopping (FH) waveforms is commonly achieved by using a set of radiometers (energy detectors) that individually energy-detect subbands of the total spread bandwidth of the suspected transmission. In this paper, a scheme is analyzed which can improve the detection performance of FH waveforms in wide-band additive Gaussian noise (AWGN) using samples from the autocorrelation domain. It is shown that, under fairly general operational assumptions, an appreciable gain in decision signal-to-noise ratio (SNR) can be achieved over that of the radiometer. This gain is proportional to \gamma_{H}^{2} where \gamma _{H} is the hop SNR. The proposed algorithm, albeit inferior to the optimal likelihood-ratio test, has the advantage of reduced complexity. The overall approach has been motivated by the recent implementational feasibility of large time-bandwidth-product real-time correlators such as surface-acoustic wave devices (SAWD's).

LPI Detection of Frequency-Hopping Signals Using Autocorrelation Techniques

A new type of signal-processing device which employs the parametric interaction between surface or volume acoustic waves passing in opposite directions through an acoustic delay line is described. These devices are capable of giving the real-time convolution of two modulated signals, and the time inversion of an arbitrary signal. As one signal acts as the reference for the other, a virtually infinite range of electronically variable signal-processing functions, such as recognition of digital codes, pulse compression of an FM chirp, and the realization of a fast Fourier transform, is possible. Early devices which employed the nonlinearity of the acoustic medium tended to give outputs of the order of 60 dB less than the input signal. Recent developments, in which a semiconductor placed near the piezoelectric medium interacts with the acoustic wave, have yielded results where the loss from input to output is of the order of 30 dB.

Signal Processing by Parametric Interactions in Delay-Line Devices

A new analog adaptive filter for deconvolving distorted signals is described in this paper. The filter uses a storage correlator which implements a clipped version of the least mean squared (LMS) algorithm and uses a special iterative technique to achieve fast convergence. The new filter has a potential bandwidth of 100 MHz and would eventually handle pulsed signals of 10-µs width. For signals with time-bandwidth products of less than 100, the adaptation time is less than 1 ms, which allows operation in real time for most applications, including resolution of radar signals in a cluttered environment, removal of echoes from television signals, deconvolution of distorted signals in nondestructive evaluation, and also in telephony. The filter is particularly suited for radar and communications, as it processes signals directly in the VHF range. Two experiments related to ghost suppression of a pulse and to the field of NDE are described in this paper. The results are in good agreement with computer simulations and show a ghost suppression of 15 dB for the first example and a sidelobe suppression of 8 dB for a transducer signal. The adaptation time is less than 450 µs.

G.S. Kino

Papers

Signal Processing by Parametric Interactions in Delay-Line Devices

Adaptive Deconvolution Using a SAW Storage Correlator