数字信道化的级联设计

在宽带信号侦察中数字信道化是一个极其重要的环节。当侦察的信号带宽非常宽,需要的数字信道化个数很大时,用一级信道化实现非常困难。其中,大点数、高速率的DFT设计和硬件实现是一个最突出的难点。针对这个问题,提出了一种数字信道化的级联实现结构,把实信号的数字信道化与复信号的数字信道化级联起来,能够大大降低设计难度,并且这种基于模块化的设计便于工程实现。仿真结果证明,这种方法能够有效实现实信号的无盲区、抗混叠的频谱恢复。     

A disk-loaded thick cylindrical dipole antenna for validation of anEMC test site from 30 to 300 MHz

We propose a new broad-band, short (80-cm-long) disk-loaded thick cylindrical dipole (DTCD) antenna for validation of an electromagnetic compatibility (EMC) test site for the frequency range between 30-300 MHz. In order to achieve broad-band characteristics, we have chosen a thick dipole as DTCD element. Disk loading has been applied to make this dipole shorter. To eliminate any ambiguity in balun characteristics, a commercially available hybrid junction is used as an antenna balun. Thus, the DTCD proposed in this paper is a very short, simple, and well-defined broad-band antenna that covers the frequency range between 30-300 MHz. The DTCD has an azimuthally symmetrical radiation pattern and, thus, is very well suited for the validation of an EMC test site. This paper presents the DTCD antenna characteristics such as input impedance, antenna gain, antenna factor, and classical site attenuation, which are calculated by use of the method of moments (MoM). These theoretical antenna factors and classical site attenuations of the DTCD are compared with experiments over the frequency range of 30-300 MHz. They agree with each other to within ±1 dB in antenna factor and to within ±2 dB in site attenuation. Our preliminary investigation indicates that an additional DTCD (25 cm long) can cover the frequency range of 300-1000 MHz. Therefore, only two DTCDs will be needed for very accurate calculable classical site attenuation values in order to validate an EMC test site for the entire frequency range between 30-1000 MHz     

解读无线通信设备电磁兼容系列标准通用要求

介绍了无线通信设备电磁兼容性要求和测量方法的通用技术要求,如试验布置、免测频段、窄带响应、性能判据等,并对复合无线电设备、多模终端的电磁兼容测试导则进行了解读。     

VHF波段宽带连续波大功率双通道功放组件的设计

首先针对VHF波段宽带连续波大功率固态功放组件的整体指标要求,分析主要指标间的关系和相互制约性,对指标之间相互制约问题折中考虑,优化设计。既能实现大功率、线性化指标要求,又解决了高热耗下的散热难题,同时满足组件的小型化要求。然后分别从功能模块化设计、电磁兼容设计、热设计等方面进行了分析,从功率放大方式的选择和结构布局安排等方面进行了较为详细的介绍。研制出一种双通道VHF波段宽带连续波大功率固态功放组件,满足机载平台对固态功放组件体积和重量的严格要求。最后给出了功放组件的实际测试结果,表明该组件完全满足总体指标要求。     

An Electromagnetic Compatibility Figure of Merit (EMC FOM) for Single-Channel, Voice-Communications Equipment

An EMC Figure of Merit (FOM) for single-channel voice communications systems, based on the channel-denial concept, was developed by using a building-block approach. This approach assumes a co-site environment and involves the use of relatively simple scoring formulas for selected EMC parameters, which are linearly combined, with appropriate weighting factors, to calculate FOM's for transmitters, receivers, and systems (i. e., transmitter-receiver pairs). The parameters chosen for transmitters included spurious emissions, noise near the carrier (i. e., broadband emissions outside the band containing desired modulation components), and intermodulation products. The parameters chosen for receivers were spurious responses, adjacent-signal interactions, and intermodulation products. The parameter scoring formulas were developed to reflect the frequency spectrum denied by each parameter. A channel was considered denied if (S+N+I)/ (N+I) < 10 dB in a moderately dense co-site environment. The weighting factors for the building-block approach were determined by running a computer program that kept track of the number of channels denied by each parameter. Example calculations for HF, VHF, and UHF systems are given, and the interpretation of the scores is discussed. The procedure developed enables quantification of the EMC characteristics of transmitting and receiving equipment. The EMC FOM provides system planners, design engineers and managers with a tool for making objective, consistent decisions. It also has potential value for those concerned with the formulation of EMC specifications and standards. It does not, however, indicate the absolute probability that compatibility will be obtained; rather, it gives information about the relative chance of obtaining compatibility.     

Low-Complexity Design of Variable Bandedge Linear Phase FIR Filters With Sharp Transition Band

This paper presents a very low-complexity design of variable bandedge linear phase finite-impulse-response (FIR) filters with fixed sharp transition width. The idea is to first decompose the input signal into several channels in the frequency domain. The channel(s) involved with the transition band of the variable filter due to the variation of the bandedge is (are) shaped to produce the required transition band, and then summed up with the channels involved with the passband of the variable filter to produce the required frequency response. The proposed variable filter has extremely low complexity when the transition band is sharp, if compared with other techniques such as the Farrow structure. It is possible that the computational complexity of the variable filter is even lower than that of a corresponding fixed filter with the same transition width and ripple specifications implemented in its direct form.      

New Electromagnetic Compatibility Instrumentation and Measurement Requirements and Techniques

This paper illustrates some fundamental instrumentation and measurment terms and the vague or midlesding manner in which they are frequently used. For example, the subject of accuracy is shown in four different common uses and interpretations. Misuse of the accuracy term is also illustrated in describing the performance of receiver linearity and dynamic range, the synthesis of recorder requirements and specifications, and the development of uncertainties in instrumentation and measurement. The damage results in either incorrect or poor decisions based on erroneous data, or wanton waste of dollars and effort by developing the wrong data, or both. Several examples are set forth on how a better technological communication can be effected. Some new instrumentation and measurement techniques recommended for use by the Electromagnetic Compatibility Community are presented. Regarding new instruments or updating of existing instruments, some examples described include statistical signal level detectors, peak-signal vs frequency plotting units, antenna pattern intercept platforms and equipments, and multi-channel crystal-video receivers with RF preamplification, peak detection and hold, and output sampling for X-Y plotting over 9 decades. Many of the EMC instrumentation techniques are borrowed from the EMW and ELINT Communities. Regarding measurement techniques, shielded enclosure attenuation, antenna pattern measurements using the sun as a signal generator and the conduct of electromagnetic site surveys are reviewed. Clearly, this paper covers only a few of a number of new opportunities awaiting EMC Community action.     

Noise Evaluation and Filter Design in CT Images

Filtering CT images to remove noise, and thereby enhance the signal-to-noise ratio in the images, is a difficult process because CT noise is of a broad-band spatial-frequency character, overlapping frequencies of interest in the signal. We present a measurement of the noise power spectrum of a CT scanner and show that some form of spatially variant filtering of CT images can be beneficial if the filtering process is based upon the differences between the frequency characteristics of the noise and the signal. For evaluating the performance, we used a percentage standard deviation, an index representing contrast, a frequency spectral pattern, and several CT images processed with the filter.     

A new set of linear constraints for broad-band time domain element space processors

A new set of linear constraints for designing broad-band time domain element space antenna array processors is presented. The set of linear constraints is used to ensure that a desired look-direction response of the processor over a frequency band of interest can be closely approximated. The design technique is posed in such a way that three types of presteering can be handled: no presteering, coarse presteering, and exact presteering. The elimination of presteering time delays or the possibility to use coarse presteering is an attractive feature in a digital implementation of antenna array processors. The relationship that the new processor has to other broad-band processors is also established. Furthermore, the approach enables various types of errors and mismatches between signal model and actual scenario to be incorporated in the problem formulation.     

Interaction between test site and amplifier nonlinearities insusceptibility tests

Susceptibility tests performed with nonlinear power amplifiers may give nonrepeatable test results or even show susceptibility levels at the spurious frequencies which may be wrongly related to the frequency characteristics of the specified emitted signal. The control of the emission system can be performed in three different ways: local-field AGC, net-power AGC, and incident-power AGC. The first two modes may interact with the test site forcing the amplifier to work in saturation and therefore to generate a large amount of spurious signals which do not represent the wanted test signal. The test site interacts with the instrumentation because of reflections from the environment (mainly the ground plane) and-the high values of VSWR of the transmitting antenna. The incident-power AGC which is adopted in most recent EMC specifications may overcome these problems but only if the test site is carefully standardized-at least in the same manner as done for emission tests     

VHF/UHF radar Part 2: Operational aspects and applications

For Part 1 see ibid., vol.14, no.2, p.61-72 (April 2002). Low-frequency radars have the potential to counter stealth efforts and detect low-flying targets beyond the horizon. Part 2 of this paper discusses approaches to target classification and the problems of vulnerability to jamming and operation in a densely populated frequency band. The anti-jamming capabilities of VHF radars are analysed based on measurements conducted with the FHR experimental radar LARISSA and it is demonstrated that electromagnetic compatibility (EMC) with other users of the band can be achieved using a spectral signal-shaping technique. The paper is completed by an overview of possible and existing VHF/UHF radar applications     

Verification of background noise in the short wave frequency range according to recommendation ITU-R P.372

The so-called background noise level is a very critical figure in many EMC problems, especially when sensitive radio services are involved. In order to provide a sufficient signal-to-noise ratio (SNR) the minimum signal strength is most commonly calculated on the basis of existing noise levels. On the other hand, if the impact of unwanted emissions on radio services is studied, background noise takes on the function of a reference level. An extensive database of noise levels to be expected is available in the recommendation ITU-R P.372. However, most data concerning man-made noise were already measured in the 1970s. Thus, the significant increase of use of electrical devices with fast digital circuits and various communication systems gives reason to question the validity of the ITU recommendation for today's EMC purposes. This paper deals with different measurement techniques with respect to their suitability for measuring extremely low field strengths in the short wave range and presents measurement results for selected environments. Although the measurements are performed with the constraint of using a mobile measuring setup a considerable sensitivity is reached, leading to the conclusion that the ITU-R P.372 still seems to be valid for estimating noise levels.     

数字T/R组件的电磁兼容设计

介绍了大型预警相控阵雷达的数字T/R组件,阐述了数字T/R组件的电磁兼容设计,对其中产生的电磁干扰问题进行了详尽的分析,并提出具体改进措施,通过试验测试组件最终达到性能指标,实现了电磁兼容。通过应用实例,探讨了数字T/R组件电磁兼容设计的思路和方法,为工程研制提供了非常有益的参考经验。     

A statistical characterization of point-to-point microwave linksusing biased Rayleigh distributions

A multipath fading model has been used to examine the characteristics of a point-to-point microwave radio channel. The new attributes of this model that differ from other multipath models enable the incorporation of the ideas of fading severity and time variability. This is achieved by the use of a biased Rayleigh-distributed second (interfering) ray. The biasing constant determines the fading severity, while the Rayleigh cutoff frequency determines the rate-of-change of the channel. For point-to-point microwave radio channels, this model provides narrow-band fading signal-level distributions that completely replicate the Norton or Nakagami-Rice distributions while at the same time providing signal level distributions that replicate those obtained from broad-band measurements. Thus, this model unifies the narrow-band and broadband multipath fading models. Using this model, nondiversity and diversity system operation is investigated and the concept of a broad-band correlation coefficient introduced. The distributions of notch speed are also investigated. Software simulation results are compared with some hardware simulation results and field measurements     

A methodology for true comparison of analytical and measuredfrequency domain spectra in random PWM converters

The analysis of random pulsewidth modulation (PWM) techniques has matured into a state where analytical expressions have been derived to aid in understanding the frequency domain characteristics. Derivations of the formulae require a lot of algebra, and the expressions must be verified by laboratory measurements. It is shown, however, that factors originating from digital signal processing techniques make the comparison difficult if proper measures against misinterpretation are not taken. A methodology to overcome the problems is presented. Novel expressions for the random lead-lag pulse position technique and the random switching frequency technique are also presented as well as their verifications by laboratory measurements on a full-bridge DC/DC power converter     

超短波跳频电台电磁兼容设计

随着电子设备综合集成应用的不断扩大,电磁兼容性显得日益重要。文中从系统电磁兼容性技术指标要求和整机电磁兼容设计措施这两方面,阐述了超短波电台设计中电磁兼容性问题的解决方法。     

2FSK信号宽带识别算法分析

针对现有算法应用的局限性,提出了一种根据频谱特征和时频特征来识别宽带二进制频移键控(BinaryFrequency Shift Keying,2FSK)信号的新算法。根据二进制频移键控(2FSK)信号调制原理从理论上深入分析了信号特征,据此分析结果,给出了特征参数提取方法和宽带识别算法流程以及调制参数测量方法。通过Matlab仿真验证了算法的工作性能。仿真结果表明,在信噪比大于6 dB情况下该算法能从宽带信号中有效的识别出2FSK信号,并测量出信号中心频率和码速率等调制参数。     

A simple four-port parasitic deembedding methodology for high-frequency scattering parameter and noise characterization of SiGe HBTs

A new four-port scattering parameter (S-parameter) and broad-band noise deembedding methodology is presented. This deembedding technique considers distributed on-wafer parasitics in the millimeter-wave band (f>30GHz). The procedure is based on simple analytical calculations and requires no equivalent circuit modeling or electromagnetic simulations. Detailed four-port system analysis and deembedding expressions are derived. Comparisons between this new method and the industry-standard "open-short" method were made using measured and simulated data on state-of-the-art SiGe HBTs with a maximum cutoff frequency of approximately 180 GHz. The comparison demonstrates that better accuracy is achieved using this new four-port method. Based on a combination of measurements and HP-ADS simulations, we also show that this new technique can be used to accurately extract the S-parameters and broad-band noise characteristics to frequencies above 100 GHz.     

星载AIS信号的带通采样与恢复

针对卫星接收机对模拟器件性能要求较高的问题,提出直接对接收到的射频信号进行采样,将模拟信号转换成数字信号,后续处理用软件模块实现的方法。同时结合自动识别系统（AIS）本身两个载波频率接近以及带宽较窄的特点,根据Nyquist带通抽样定理实现以较低速率采样来获取船舶状态信息,研究了一种星载AIS信号全数字解调方法和信息检测恢复技术。首先介绍了带通采样原理,其次详细研究了多用户AIS信号采样频率的确定、两个频道信号分离方法以及单通道信号如何下变频为基带信号,其中基带信号检测采用简化的基于Viterbi的非相干检测方法,最后结合AIS协议进行信号的恢复,并通过示波器采集实际船台发送的AIS信号进行了实验,验证了该过程的正确性。     

星载AIS信号的带通采样与恢复

针对卫星接收机对模拟器件性能要求较高的问题,提出直接对接收到的射频信号进行采样,将模拟信号转换成数字信号,后续处理用软件模块实现的方法。同时结合自动识别系统( AIS )本身两个载波频率接近以及带宽较窄的特点,根据Nyquist带通抽样定理实现以较低速率采样来获取船舶状态信息,研究了一种星载AIS信号全数字解调方法和信息检测恢复技术。首先介绍了带通采样原理,其次详细研究了多用户AIS信号采样频率的确定、两个频道信号分离方法以及单通道信号如何下变频为基带信号,其中基带信号检测采用简化的基于Viterbi的非相干检测方法,最后结合AIS协议进行信号的恢复,并通过示波器采集实际船台发送的AIS信号进行了实验,验证了该过程的正确性。