Abstract: Sonar and radar systems not only detect targets but also localize them. The process of localization involves bearing and range estimation. These objectives of bearing and range estimation can be accomplished actively or passively, depending on the situation. In active sonar or radar systems, a pulsed signal is transmitted to the target and the echo is received at the receiver. The range of the target is determined from the time delay obtained from the echo. In passive sonar systems, the target is detected from acoustic signals emitted by the target, and it is localized using time delays obtained from received signals at spacially separated points. Several authors have calculated the variance of the time delay estimate in the neighborhood of true time delays and have presented their results in terms of coherence function and signal and noise autospectra. Here we analyze these derivations and show that they are the same for the case of low signal-to-noise ratio (SNR). We also address a practical problem with a target-generated wide-band signal and present the Cramer-Rao lower bound on the variance of the time delay estimate as a function of commonly understood terms such as SNR, bandwidth, observation time, and center frequency of the band. The analysis shows that in the case of low SNR and when signal and noise autospectra are constants over the band or signal and noise autospectra fall off at the same rate, the minimum standard deviation of the time delay estimate varies inversely to the SNR, to the square root of the product of observation time and bandwidth, and to the center frequency (provided W^{2}/12 f\min{0}\max{2} \ll 1 , where W = bandwidth and f_{0} = center frequency of the band). The only difference in the case of a high SNR is that the standard deviation varies inversely to the square root of the SNR, and all other parameter relationships are the same. We also address the effects of different signal and noise autospectral slopes on the variance of the time delay estimate in passive localization.

Abstract: An analysis of constant envelope digital partial response continuous Phase modulation (CPM) systems is reported. Coherent detection is assumed and the channel is Gaussian. The receiver observes the received signal over more than one symbol interval to make use of the correlative properties of the transmitted signal. The Systems are M -ary, and baseband pulse shaping over several symbol intervals is considered. An optimum receiver based on the Viterbi algorithm is presented. Constant envelope digital modulation schemes with excellent spectral tail properties are given. The spectra have extremely low sidelobes. It is concluded that partial response CPM systems have spectrum compaction properties. Furthermore, at equal or even smaller bandwidth than minimum shift keying (MSK), a considerable gain in transmitter power can be obtained. This gain increases with M . Receiver and transmitter configurations are presented.

Abstract: In a direct-sequence spread-spectrum multiple-access communications system several asynchronous signals simultaneously occupy the same channel. Each of the signals employs a signature sequence which is selected to have certain desirable correlation properties. For multiple-access communications the primary goal is to be able to separate the spread-spectrum signals at the receiver even though they occupy the same bandwidth at the same time. This problem is considered in the sections which follow for various forms of direct-sequence spread-spectrum modulation including binary phase-shift keying, quadriphase-shift keying, and minimum-shift keying. The emphasis is on the analysis of system performance rather than on the selection of signature sequences. Hence this material complements the recent paper of Sarwate and Pursley (1980) which examines in detail the problem of signature sequence selection.

Abstract: A pair of complementary strays-insensitive switched-capacitor (SC) integrator circuits are analyzed to determine the errors in their transfer functions due to the finite gain and finite bandwidth of the op amp. The results are used to predict the transfer function deviation of biquadratic filter sections and LC ladder simulations. It is shown that while the effect of finite op amp gain is similar to that encountered in active-RC filters, SC filters are much more tolerant of the finite op amp bandwidth. However, the relationship between transfer function error and finite op amp bandwidth is an exponential one as contrasted to the linear relationship of active-R C filters. Experimental results are presented.

Abstract: Based on theoretical analysis and laboratory data, we proposed a unified two-parameter wave spectral model as is the mean squared surface elevation, and λ0, n0 are the wavelength and frequency of the waves at the spectral peak This spectral model is independent of local wind Because the spectral model depends only on internal parameters, it contains information about fluid-dynamical processes For example, it maintains a variable bandwidth as a function of the significant slope which measures the nonlinearity of the wave field And it also contains the exact total energy of the true spectrum Comparisons of this spectral model with the JONSWAP model and field data show excellent agreements Thus we established an alternative approach for spectral models Future research efforts should concentrate on relating the internal parameters to the external environmental variables

Abstract: Diclosed is a dual band communication receiver for use in a burst communication sytem. The receiver is capable of esentially simultaneous reception at a first carrier frequency (L), such as L-band and a higher carrier frequency (H), such as S-band, using distinct codes and replying in the frequency band received. A typical system is composed of a transponder and an interrogator. The incoming coded signal is down converted to an i.f. frequency compatible with surface acoustic wave (SAW) convolvers. The i.f. signal is then divided between two SAW convolvers, each having a convolution interval of two times the message symbol length (2T). Reference signals A and B are composite signals comprised of alternate L-band and H-band signals, each having a time period equal to T and each L- or H-band signal operating at a 50% duty cycle. Reference signals A and B are time reversed to the input signals applied to the convolver and are orthogonal to one another. Each of the convolver outputs are processed through log video detection circuits to reduce the dynamic range followed by peak detecting and stretching to reduce the pulse bandwidth. The outputs from each peak detection and stretching circuitry are coupled to a smaple-and-hold circuit which are in turn divided such that one path is to synchronization and interrogation sidelobe suppression (also referred to as sidelobe inhibit, ISLI or control signal) matched filters designed to look for the particular symbol sequences between the two convolver channels characteristic of the preamble and ISLI signals. The synchronization signal and the sidelobe suppression signal are used in order to determine if a valid preamble has been detected by the receiver and if the receiver is in a desired portion of the interrogator radiation pattern; if so, then a timing or address signal and the remaining portion of the message which contains the data is clocked into a memory.

Abstract: The design and fabrication of wide-band bulk acousto-optic modulators (temporal modulation) and beam deflectors (spatial modulation) are described. Optimized device parameters can be obtained systematically for given specifications of the desired modulation bandwidth, throughput efficiency and number of resolvable elements. As the device operating frequency goes beyond a few hundred megahertz, the acoustic transducer response becomes sensitive to the intermediate metal layers between the piezoelectric transducer and the acoustooptic interaction medium. Transducer bandwidth and impedance matching can be optimized using computer modeling programs. Criteria for material selection based on performance requirements and propagation loss are presented. Practical considerations for the fabrication of high performance devices and specific device parameters are discussed.

Abstract: Space diversity (adaptive phased-array antennas) is an effective weapon against the cochannel interference encountered in cellular mobile radio systems. High-order diversity, and hence, strong interference suppression, can be achieved with modest hardware complexity by using time-division retransmission. With this technique, which is especially well-suited to digital modulation methods, the adaptive signal processing required for space diversity can be performed at just one end of the communication link, namely, the base station. At the other end (the mobile unit) only a single-element antenna is needed. Moreover, the use of coherent phase-shift keying in such a system allows simple RF circuity, because the adaptive processing is done at baseband. In the context of cellular mobile radio, the combination of space diversity, time-division retransmission and 120-degree corner illumination of each cell can yield a reliable communication channel even in the presence of intercell interference, Ray leigh fading (both flat and frequency-selective), and shadow fading. The use of these techniques allows approximately 130 two-way channels per cell (at 32 kb/s each) to be accommodated in the 40-MHz bandwidth of the 850-MHz mobile radio band.

Abstract: The acoustoelectric effect (i.e., the interaction of ultrasound with conduction electrons in a piezoelectric semiconductor) provides the basis for the construction of a finite aperture, phase insensitive receiver using a single crystal of cadmium sulfide. In this paper we present a formalism describing the operation of such a receiver. Criteria for the optimization of the device in terms of ultrasonic bandwidth, response time, sensitivity, and electrical and mechanical loading are presented. In an accompanying paper [J. Acoust. Soc. Am. 70, 1377–1386 (1981)], we discuss and demonstrate the merits of using a phase insensitive receiver when measurements of a phase distorted (spatially noncoherent) ultrasonic radiation must be made.

Abstract: In the present invention, analog voice information is sampled at a first sampling rate, during periods when voice information is to be transmitted at a frequency which provides a digitized voice rate equal to the transmission rate capability of the transmission channel. During periods when both voice and data are to be transmitted, the analog voice information is sampled at a second sampling rate less than the first sampling rate, thus allowing the merged voice and data information to have a total digitized transmission rate equal to the transmission rate capability of the transmission channel.

Abstract: An analysis of constant envelope digital partial response continuous phase modulation (CPM) systems is reported. Coherent detection is assumed and .the channel is Gaussian. TPe receiver observes the, received signal over more than one symbol interval to make use of the correlative, properties of the transmitted signal. The systems are M-ary, and baseband pulse shaping over several symbol intervals is considered. An optimum receiver based on the Viterbi algorithm is presented. Constant envelope digital modulation schemes with excellent spectral tail properties are given. The spectra have extremely low sidelobes. .It is concluded that partial response CPM systems have spectrum compaction properties. Furthermore, at equal or even smaller bandwidth than minimum shift keying (MSK), a considerable gain in transmitter power can be obtained. This gain increases with M. Receiver and transmitter configurations are presented.

Abstract: A procedure is presented for calculating the power spectrum of the class of digital continuous-phase signals known as multi- h phase codes. These signals have been shown to have attractive power advantages over other uncoded digital schemes such as QPSK, and represent a bandwidth-efficient alternative to other coding. techniques. The method is general, handling M -ary signaling, various frequency pulse shapes, and arbitrary sets of modulation indices. Numerical results are shown for several specific codes. In addition, the issue of spectral lines is resolved, and simple spectral approximations are developed.

Abstract: The fundamental radiation mechanism occurring at an open-circuit discontinuity is discussed to reveal limitations on bandwidth, efficiency, and sidelobe level control inherent in microstrip antennas, based on resonator action. Extraneous radiation from feed transitions is also assessed and shown to be a problem in some cases. Novel two-dimensional arrays using resonant elements are described which illustrate these performance limitations. In contrast, a nonresonant circularly polarized spiral element has a very wide bandwidth at the expense of lower efficiency. Other designs are then noted to show how a particular parameter or aspect can be optimized for antenna applications demanding choice of polarization, frequency scanning, log periodic behavior, low angle radiation, and integration with circuitry on a common substrate.

Abstract: Dynamic range is a key performance parameter for spectrum analyzers. The dynamic range of a Bragg cell power spectrum analyzer is generally limited by the dynamic range of self-scanned photodetector arrays. Interferometric techniques can be used to increase the dynamic range; but it is at the expense of increasing the number of photodetectors required, when the interference is introduced in the spatial domain, or a large photodetector bandwidth, when the interference is introduced in the temporal domain. In this paper we describe an interferometric approach wherein a second Bragg cell generates a spatially modulated reference waveform to produce an interference term that has a constant temporal frequency for all spatial frequencies. The advantages of this approach are lower photodetector bandwidth, improved dynamic range, improved cross talk suppression, more efficient use of the Bragg cell time–bandwidth product, immunity to scattered noise, and improved short pulse detectability. The chief disadvantage is the need for a discrete element photodetector array; when such arrays become available in hybrid or integrated packages, an additional advantage will be that of parallel postdetection processing.

Abstract: Multi- h phase coding is a bandwidth-efficient modulation which offers substantial performance improvement over conventional digital modulations with little or no bandwidth expansion. This paper examines the demodulation of the multi- h signals, and in particular examines the behavior of a decision-directed carrier loop which utilizes the Viterbi algorithm decoder in the calculation of the loop error signal. Both analytic and simulation results are presented and the agreement between the two is shown to be very close.

Abstract: A microprocessor controlled radio receiver system for switching bandwidths of an intermediate frequency stage from a normally scanning mode using a relatively narrow bandwidth to a second mode using a relatively wide bandwidth automatically when there are no interfering signals from adjacent channels of a channel or station selected for receiving. Upon selection of a channel for listening the microprocessor controlled synthesizer causes the synthesizer to scan up one adjacent channel and down one adjacent channel to determine if there is an interfering signal therefrom and then returns to the selected channel. In the event of no interfering signal from an adjacent channel, switching is effected in the IF stage from a narrow bandwidth to a wide bandwidth to improve the quality of reception. If there is an adjacent channel signal detected of sufficient IF energy next to the selected channel, then the narrow bandwidth mode used during the scan will be maintained.

Abstract: An integrator and a voltage controlled oscillator produce a variable frequency output signal. A primary loop is locked to an input signal and has a narrow bandwidth allowing the output signal to precisely track the input signal. An initialization loop is locked to an internally generated reference signal and has a wide bandwidth for pulling the frequency of the output signal very close to the frequency of the reference signal. Since the frequency of the reference signal is approximately equal to the frequency of the input signal the initialization loop pulls the frequency of the output signal very close to the frequency of the input signal thus assuring locking of the primary loop. A switch selectively connects components of the primary loop to the integrator when the frequency difference between the reference signal and the output signal is small and connects components of the initialization loop to the integrator when the frequency difference between the reference signal and the output signal is large.

Abstract: A privacy communication system digitizes a voice signal and divides the signal into different frequency bands or time segments and shifts the bands or segments in frequency and/or time under control of a continually changing pseudo-random key word to develop an encrypted transmitted signal having the same time/bandwidth product as the voice signal.

Abstract: In an FM demodulation circuit which demodulates an FM signal by the use of a phase-lock loop constructed of a phase comparator, a loop filter and a voltage-controlled oscillator, the loop filter is a variable loop filter whose loop band width is varied in correspondence with the modulation band width and the carrier/noise ratio of the input signal by a base band processing circuit.

Abstract: A simplified approach for the design of low-noise bipolar preamplifiers for optical receivers is presented. Analytical solutions for optimum biasing and minimum equivalent input-noise current are derived. Experimental measurements on 100 MHz bandwidth preamplifiers are in good agreement with both analytical solution and CAD model analysis.

Abstract: A signal transfer and processing system for use with a transmission line includes transmission line interface circuitry (30) and signal processing circuitry (100). The processing circuitry receives a signal to be processed, providing a processed signal for further use. An input bandpass filter (119, SW7) selectively limits bandwidth the input signal. A primary active frequency control (123) selectively controls the relative level of the signal provided from the primary bandpass filter means for selectively controlling the relative level of signal dynamics within different frequency bands for providing a frequency controlled signal, which is compressed by a compressor (127). A secondary active frequency control (135) selectively controls the relative level of the primarily compressed signal within different frequency bands to provide a frequency controlled primarily compressed signal which is further compressed by a secondary compressor (137). A feedback circuit (128, 129, 140) between the primary and secondary compressors limits compression by the primary compressor as a time-delayed function of level increase of the secondarily compressed signal. An output bandpass filter (152, SW8) limits bandwidth of the secondarily compressed signal. Switching circuits (30) interconnect signal input and signal output of the signal processing circuitry with the transmission line for causing signals transmitted by the transmission line to be automatically directed through the signal processing circuitry.

Abstract: This paper reviews high speed analog applications of Josephson switching devices. The design and performance of two different analog sampling circuits is described. A method is proposed for delivering room temperature signals to these samplers with 30 GHz or more of bandwidth. An analog-to-digital converter based on quantum interference comparators is also described. This device has achieved conversion rates of 2 × 109samples per second.

Abstract: In this report a theoretical model is developed that predicts the single-point, two-frequency coherence function for transionospheric radio waves. The theoretical model is compared to measured complex frequency correlation coefficients using data from the seven equispaced, phase-coherent UHF signals transmitted by the Wideband satellite. The theory and data are in excellent agreement. The theory is critically dependent upon the power-law index, and the frequency coherence data clearly favor the comparatively small spectral indices that have been consistently measured from the wideband satellite phase data. A model for estimating the pulse delay jitter induced by the coherence bandwidth loss is also developed and compared with the actual delay jitter observed on synthesized pulses obtained from the Wideband UFH comb. The results are in good agreement with the theory. The results presented in this report, which are based on an asymptotic theory, are compared with the more commonly used quadratic theory. The model developed and validated in this report can be used to predict the effects of coherence bandwidth loss in disturbed nuclear environments. Simple formulas for the resultant pulse delay jitter are derived that can be used in predictive codes.

Abstract: The present invention relates to the improved demodulation system which improves the noise characteristics for the demodulation of a wideband television FM signal. A variable bandpass filter (8), the center frequency and the bandwidth of which are controllable, for improving C/N, is inserted at the output of a reference bandpass filter (7) in an FM signal path. The bandwidth of the variable bandpass filter (8) is controlled so that said bandwidth is wide when the input carrier level is high, and said bandwidth is narrow when the input carrier level is low. The center frequency of the variable bandwidth filter (8) is controlled so that said center frequency follows to the instantaneous frequency of the color sub-carrier component (3.58 MHz). Said color sub-carrier component is derived by a narrow-band bandpass filter (10) coupled with the output of said discriminator (9) for controlling the center frequency of the variable bandpass filter (8).

Abstract: Forward‐masked thresholds for 1‐kHz sinusoidal signals were measured as a function of the bandwidth of a noise masker centered at 1 kHz, using a two‐interval forced‐choice technique. The noise spectrum level was 40 dB SPL/Hz, and noise bandwidth was varied from 50 to 1600 Hz. In experiment I signal duration was varied, with a fixed offset–onset time of 5 ms between masker and signal. For the shortest signal (5 ms) threshold at first increased with increasing bandwidth and then decreased. As signal duration increased, the bandwidth at which maximum masking occurred (the rollover bandwidth) decreased, and for the longest signal (45 ms) maximum masking occurred for the narrowest bandwith tested. In experiment II the silent interval between masker and signal was varied, for a signal of 5‐ms duration. Again threshold at first increased with noise bandwidth, and then decreased. However, the rollover bandwidth decreased with increasing silent interval, and threshold varied less with bandwidth. In experiment III ...

Abstract: We report the first demonstration of a polarization‐independent, integrated‐optic wavelength filter. Polarization‐independent filtering is achieved via wavelength selective TE↔TM conversion between a pair of mismatched Ti‐diffused lithium niobate waveguides. A peak coupling efficiency of ∼75% and 5‐A filter bandwidth have been achieved.