用蒙特卡罗计算机模拟法估算振荡源不稳定对信号处理的影响

正 1.引言 一般文献在讨论如脉冲压缩、合成孔径等数字信号处理技术时,都假定系统中的振荡源是理想的,即认为它不存在相位噪声,因此不会对信号处理产生不良影响。这个假定当然与实际情况有出入,因此有必要加以研究和修正。但振荡起伏对信号处理的影响相当复杂,很多情况难以利用经典理论来解决。本文提出用蒙特卡罗计算机模拟法来估算这种影响,并以脉冲压缩为例来阐述这一思想。振荡源的相位噪声谱密度则以常用     

用于毫米波固态源的低通阻抗变换器设计

消除低频不稳是利用雪崩管设计毫米波固态源,特别是大功率源的重要课题.本文设计了一种新型的可调谐式低通阻抗变换器以消除振荡源的低频不稳定性.该变换器不仅能大大地抑制低频不稳,而且由它提供的调谐自由度,加上可移动的短路活塞提供的另一调谐自由度可使振荡源调至最佳状态.本文借助计算机对该变换器进行优化设计,并给出其带通特性的理论曲线.     

Estimation of the effect of oscillator instabilities on signal processing by means of Monte Carlo computer simulation

In this paper, Monte Carlo computer simulation is used to estimate the effect of oscillator instabilities on signal processing. The key link of this method is generating high quality random number sequence simulating the phase noise of the oscillator. The case of the pulse compression performance is discussed as an example in order to clarify: (1) the effect of oscillator instabilities on pulce compression performance, and (2) the requirement of oscillator frequency stability when the tolerance of the system performance is known. Finally, some computer simulation examples are given which will provide as reference data for engineering designers.     

Spontaneous spatiotemporal instabilities in current modulatedmaster oscillator power amplifier lasers

We provide the first comprehensive theoretical evidence for nonlinear space-time dynamical behavior which seriously degrades the performance of a monolithically integrated master oscillator power amplifier laser under direct current modulation of the master oscillator. A host of instabilities, reflecting dynamical behavior of different sections of the device, are possible. These instabilities are due to the combination of weak feedback from the power amplifier section of the device causing leakage into the master oscillator section, from the buildup of unsaturated carriers along the narrow edges of the expanding flare and differential saturation of the passive regions under the distributed Bragg reflector grating sections     

Injection priming of a pulsed molecular-beam maser oscillator

Injection priming of a pulsed ammonia-beam maser oscillator of both the closed and open resonator types is discussed. In both systems, oscillation starting-time jitter can be eliminated, and, in addition, amplitude instabilities prevalent in the latter type can be greatly reduced.     

Short-term frequency stability: Characterization, theory, and measurement

An analysis is first presented of the manner in which oscillator short-term instabilities limit performance in a number of applications. This analysis provides guidelines for theoretical formulations, the definition of "short-term stability" and the development of measurement techniques for characterizing short-term instabilities. The factors that affect short-term stability are then discussed, and basic models for theoretical analysis are formulated. The models are used in investigations of the characteristics of outputs of "stable" sources. Measurement techniques are proposed and compared with techniques employed by other investigators.     

Detection of Digital FSK and PSK Using a First-Order Phase-Locked Loop

A classical problem in digital frequency-shifted keyed (FSK) demodulation is the evaluation of the bit error probability performance when an estimator-correlator that incorporates a phaselocked loop (PLL) is employed. Although some attention has been devoted to this problem in the past, an accurate account of the mechanism which produces decision errors has not yet been advanced. This paper examines a special case, viz., a first-order PLL preceded by a wideband IF filter, of the above problem using a new approach which is based upon the renewal Markov process theory and the Meyr distribution. In particular, the ad hoc approach of invoking the Gaussian assumption on the decision variable and patching it with a correction term based on Rice's click theory is not used. Rather, the effective noise is properly characterized by unfolding the renewal Markov process associated with the loop phase error. As a slight extension of the results, the performance of the above PLL detector operating on low data rate PSK is given and demonstrated to be approximately 3 dB superior to that of FSK reception. The theory and analysis presented herein apply to the special case where the bandwidth of the IF filter preceding the first-order PLL is required to be several times the data rate because of frequency uncertainties due to channel Doppler and oscillator instabilities, but the frequency deviation to data rate ratio may be chosen small (if desired) to optimize system error probability performance. In addition to presenting results for the case where the oscillator instabilities are assumed absent and channel Doppler is prefectly tuned out at the receiver oscillator, the effects of small residual Doppler on bit error probability performance is considered. In all cases tested, excellent agreement was obtained between theory and computer simulation results.     

Dispersion relations in time-space periodic media part II—Unstable interactions

The conditions sufficient to assert the existence of absolute (time-growing) instabilities in distributed parametric structures or media are shown. Treating the simple, linearized, time-space periodic transmission line model, it is shown that time-growing instabilities exist in an unbounded medium whenever the pump modulation velocity is greater then the characteristic velocity of the medium and is in the convergent ("nonsonic") range of operation. The existence of these instabilities is based upon the rigorous calculation of the dispersion relation for the model, accounting for all small-signal frequencies. Proof of the existence of the instability, using the dispersion relation of the active structure, is based upon the method of Briggs, previously used in electron-stream interactions. The waveform of these instabilities is that of the backward-wave oscillator and comparisons with backward-wave oscillator (electron-beam) tubes are made. The predictions of the theory hold only for the transient period, for which the linearized model is valid, before the fields reach the nonlinear regime. The analysis, however, forms the basis for certain simple calculations of oscillation frequency, growth rates, predictions of competing interactions, and identification of wave types--all useful for application. The method of analysis should be useful for application to various other types of parametric interactions involving elastic waves, spin waves, plasma waves, etc., in single or multimode coupling schemes. The frequency range of application of such traveling-wave parametric effects extends from the optical range down to the radio-frequency range.     

High-Power 50-GHz Double-Drift-Region IMPATT Oscillators with Improved Bias Circuits for Eliminating Low-Frequency Instabilities

Low-frequency instabilities in millimeter-wave double-drift-region (DDR) IMPATT diodes are investigated and new oscillator circuits with the improved bias circuits for eliminating the low-frequency instability are developed. DDR IMPATT diodes mounted in these circuits exhibited a maximum free-running oscillation power of 1.6 W at 55.5 GHz with 11.5-percent conversion efficiency. A highly stabilized oscillator was also constructed with the maximum output power of 1 W and the frequency stabflity 0.3 ppm/mA at 51.86 GHz.     

Temporal dynamics and facet coating requirements of monolithic MOPAsemiconductor lasers

Dynamics of temporal instabilities in tapered broad-area InGaAs SQW semiconductor master oscillator/power amplifier lasers are experimentally investigated. Multigigahertz self-pulsations are evident in the optical and temporal spectra along with coupled-cavity modes due to the finite output-facet reflectivity. From a previously developed time-dependent coupled-wave model, it is shown that by adjusting the grating strength in the distributed Bragg reflector (DBR) section of the master oscillator the antireflection facet coating requirements can be relaxed. Increased stable operation at high powers is then possible     

Blind self-noise-free frequency detectors for a subclass ofMSK-type signals

Frequency offset due to Doppler shift and/or oscillator instabilities degrade the receiver performance. A family of frequency detectors for frequency offset estimation and compensation in digital receivers is introduced. The proposed detectors are best suited for frequency offset compensation of a subclass of binary continuous phase modulation with h=1/2 that includes modulation schemes with nonnegative frequency pulses. For the considered modulation schemes, the modulation-induced self-noise term is absent from the variance of the frequency estimate. The estimator is nondata- and nontiming-aided and its estimation range is either half or a quarter of the bit rate (R). With larger frequency offsets, the estimators that have a ±R/2 estimation range introduce a frequency ambiguity of R that is of no relevance to the performance of a differential detection based receiver     

A coherent mechanical submillimeter frequency shifter

Highly correlated transmit and local oscillator signals for use in a narrowband heterodyne system are derived from a single submillimeter source. One component is Doppler shifted in frequency by a mechanically rotating device before transmission. The frequency translation does not lead to significant spectral deterioration. Under the condition of only a small differential delay between transmit and local oscillator paths, most phase and frequency instabilities of the submillimeter source are eliminated at the intermediate frequency. The paper describes the frequency shifter's mode of operation and a practical 637GHz design. Based on this design we simulate the effect of various imperfections in the frequency translation process on the output spectrum. Preliminary measurements at 140GHz are included.     

Observation of regular pulse train in a narrow-band optoelectronic oscillator

We have experimentally observed a new operating state of a regular pulse train in a narrow-band optoelectronic oscillator (OEO) system, where the direct-current (DC) bias of the Mach-Zehnder modulator is set at the maximum value of the transmission transfer function instead of the usual quadrature point. The observed quasi-steady-state pulse train is distinctly periodic, with a period of 10.5 µs and a center frequency of 10 GHz, and resembles a mode-locked OEO in its waveform. The formation of regular pulses here may arise from the dynamic balance of nonlinearity and narrow-band filter effects, with the transient characteristics of the pulses arising mainly from instabilities between the gain and cavity loss. Our results are of great importance for deepening the understanding of the nonlinear dynamical processes in OEO systems.     

Dynamic instabilities in master oscillator power amplifiersemiconductor lasers

We investigate theoretically the master oscillator power amplifier using a semiconductor laser model that is fully time and space (laterally and longitudinally) resolved. We numerically examine the stability of the device and identify the nature of the different instabilities. These can arise from undamped relaxation oscillations, beating between the longitudinal modes of any of the cavities that comprise the device, or lateral filamentation     

Diffusion Brillouin stimulee dans un laser en anneau à fibre optique

A cw-pumped optical fiber ring oscillator leads to pulsed emission by stimulated Brillouin back-scattering (dbs for« diffusion Brillouin stimulee»). Numerical treatment of the three-wave coherent equations allows an interpretation of the process efficiency. Accumulation of stimulated acoustical phonons, which severely limits the coupled pump power and is at the origin of instabilities and broadening of the Brillouin pulses, has been avoided by coupling the pump wave with an acousto-optic deflector driven at the oscillator optical round trip frequency. Taking into account the optical Kerr effect, the numerical results are in good accordance with experiment.     

Time tracking error in direct-sequence spread-spectrum networks dueto coherence among signals

Data are presented which reveal a time synchronization error in CDMA (code division multiple access) spread-spectrum networks where mutual signal phase coherence is high among communicators. The error is not white noise but is, in fact, periodic with an amplitude, phase, and mean offset which appears to be related to a mixture of the carrier frequency, chip rate, and code frame rate. This periodicity is more evident as carrier and code phase coherence increases among participants in a network and high tracking accuracy is the goal. This has implications for future high-rate data communications and navigation networks in which errors may be attributed to local oscillator instabilities more than a transmission link. The data using a commercial modem suggest that improvements in local oscillator stabilities will improve coherence among network participants but will not necessarily reduce time synchronization errors     

Enhanced stability of MFA-MOPA semiconductor lasers using a nonlinear, trumpet-shaped flare

Monolithically integrated flared amplifier master oscillator power amplifier (MFA-MOPA) lasers are studied using a high-resolution computational model that resolves time as well as longitudinal and transverse space dependences and includes Lorentzian gain and dispersion dynamics. By altering the linear flare of the power amplifier into a nonlinear, trumpet-shaped flare to overlap the gain region to the expanding field, the instability threshold of the MOPA is increased by /spl sim/2 for single-longitudinal, single-transverse mode operation and /spl sim/3 for single-transverse mode operation. This enables the MOPA to maintain a stable, near-diffraction limited output beam for higher currents before the onset of transverse instabilities. Thus the trumpet-flared MOPA emits an output beam of significantly higher power and brightness. This increased stability is due to a large reduction in feedback from the output facet of the trumpet shaped MFA-MOPA.     

Nonlinear Theory of Parametric Oscillator: Steady-State Operation and Fluctuation Analysis

Parametric oscillators with a superconducting output cavity are of great interest as sources of very high frequency stability. In this paper, a careful analysis is performed for a parametric oscillator model based on an abrupt junction varactor with fixed-bias voltage and ideal shunt mode operation. Steady-state operation, transfer functions for amplitude and phase fluctuations, and additive noise contributions are examined. An overall estimation of system performance as regards to the phase instabilities shows that although the foreseen characteristics are Iess outstanding than expected from a previously reported analysis, this device compares favorably with the most important available sources based on atomic transitions or on superconducting cavity-stabilized oscillators.     

Free-space optical distribution of local oscillator signals inaperture synthesis radio telescope arrays

An alternative to individually phase-stabilised links for distribution of local oscillator (LO) signals in large arrays of radio telescopes is considered. An array is illuminated from an elevated optical source, intensity modulated at the LO frequency. LO phase feedback from the centre of the illuminated zone counteracts tower and atmospheric instabilities, locking a fixed phase at zone centre, and hence a template of constant phase contours around the zone centre point. Other LO detector planes are aligned to equiphase contours, providing a phase coherent LO to all telescopes aside from differential optical path effects. A local PLL at each site reduces the remaining noise from differential slant path variations     

Fourier series and estimation on the circle with applications to synchronous communication--I: Analysis

A wide variety of continuous- and discrete-time estimation problems on the circleS^1are considered with the aid of Fourier series analysis. Measurement and diffusion update equations are derived for the conditional expectation of certain functions of the parameter to be estimated, and we investigate the use of Fourier series to obtain easily implemented optimal estimation equations. A variety of important examples--phase tracking, frequency demodulation, and phase demodulation in the presence of oscillator instabilities, additive noise, Rayleigh fading, or any combination of these--are considered.