System Effectiveness Models: An Annotated Bibliography

A state-of-the-art survey on system effectiveness models is presented. A variety of system effectiveness models dealing with military and space systems have been developed by the US Air Force, Army, and Navy. Each model has different attributes in its definition of system effectiveness. This survey classifies these attributes and definitions and presents their relationship to system effectiveness. Attributes included are reliability, availability, operational readiness, repairability, maintainability, serviceability, design adequacy, capability, dependability, human performance, and environmental effects. The system effectiveness models and their computer codes are also classified and reviewed.     

Distance-measurement error associated with antenna phase-center displacement in time-reference radio positioning systems

This paper presents a tutorial discussion of the effects of antenna phase-center displacement on distance determination in time-correlation radio positioning systems. A technique to determine the antenna phase-center displacement as a function of observation angle is reviewed. A simple method to determine the distance error versus observation angle, derived from the antenna phase-center displacement, is then presented. Numerical distance-error predictions, determined directly from antenna phase-center displacement, are presented for a Yagi and a log-periodic antenna used in a commercial UHF radio distance-measurement system. Finally, the measured distance error versus observation angle for these antennas as determined in several field trials is presented, validating the numerical predictions.     

Looking over the horizon [HF radar]

The history of HF (over-the-horizon) radar and its basic principles are outlined. Advances in signal processing that have made HF radar an operational reality are reviewed. Working units that the US Navy and the US Air force have in place, as well as some units under construction are described. Nondefence applications of HF radar, most notably the interdiction of drug traffickers and the monitoring of wind patterns over vast stretches of the ocean are noted     

基于MIMO系统的天线选择

多天线MIMO（Multiple Input Multiple Output）系统利用多个收、发天线有效地改善无线通信系统性能，提高系统容量，增强系统可靠性。然而，由于使用多天线同时收发，这要求发射机和接收机使用与天线一样多的射频链路，增加了系统成本和复杂度。使用天线选择技术可以降低系统成本和复杂度，同时保留MIMO系统的优越性能。文中首先介绍了MIMO系统的实现方式，然后讨论天线选择的方法及性能，最后提出天线选择技术还存在的问题，并得出相关的结论。     

Antenna selection in MIMO systems

Multiple-antenna systems, also known as multiple-input multiple-output radio, can improve the capacity and reliability of radio communication. However, the multiple RF chains associated with multiple antennas are costly in terms of size, power, and hardware. Antenna selection is a low-cost low-complexity alternative to capture many of the advantages of MIMO systems. This article reviews classic results on selection diversity, followed by a discussion of antenna selection algorithms at the transmit and receive sides. Extensions of classical results to antenna subset selection are presented. Finally, several open problems in this area are pointed out.     

Biological effects of electric and magnetic fields associated with ELF communications systems

The U.S. Navy has proposed a submarine communications system that operates at extremely low frequencies (ELF). The land-based transmitting antenna for this system consists of insulated conductors 50 to 100 km long, grounded at each end, and driven by a generator such that the flow of current would be along the cable, into the ground, deep in the earth, and return to the other grounded end of the cable. It would, in effect, be a large loop antenna in which the earth was part of the loop. Over the last ten years the Navy has sponsored a wide variety of research to evaluate the environmental impact of this system. A discussion of this work can logically fall into three periods: 1968 to 1973, 1973 to 1977, and work still in progress. The work during the first period was reviewed by an Ad Hoc Committee formed in 1973 by the Navy. A second committee was formed in 1976 by the National Academy of Sciences and charged to review all existing data. These committees have reported their findings but they are not readily available in the open literature. This paper does not duplicate the work of these committees but rather summarizes their results and combines them with more recent work some of which is still in progress.     

Spectrum Signature Modeling and Data Reduction Techniques Applicable to Airborne Antennas

Information is presented on a modeling technique and on data reduction techniques applicable to obtaining the spectrum signatures of low-gain, low-frequency airborne antennas. The modeling technique demonstrates the degree of simplicity permissible in the fabrication of aircraft scale models on which test antennas are mounted. It is shown that simple geometric shapes employed to represent an aerodynamically shaped aircraft will yield sufficiently accurate information for antenna signature evaluation, thus allowing far-field antenna characteristics to be obtained at a relatively low cost. A brief discussion of an analog-digital converter unit is also included. This unit is employed in the placing of antenna pattern data in a format that is applicable to the Electromagnetic Compatibility Analysis Center (ECAC) computer facilities.     

Revisiting medium-wave ground-system requirements

The classic 1937 paper by Brown, Lewis, and Epstein [1] outlined the necessity for a proper "imaging screen" or "ground system" for efficient operation of a vertically polarized monopole antenna. While Brown et al. showed the effects of various configurations, they did not exhaustively examine the effects of successive reductions of the number of radials, particularly in systems with radial lengths less than 90". Furthermore, their measurements were made at 3 MHz, and were not corrected for the frequency scaling. Recent experimental work, undertaken for a US Department of the Navy laboratory to optimize the performance of temporary medium-wave antenna installations, showed that for surface-mounted radial systems with radials 90" or shorter, both radial length and the number of radials are significant. Property availability for siting of antennas at medium-wave frequencies often results in truncation or other restrictions on radial length. The results of this study provide a guide to the practical limits on such restrictions, as well as data on the resulting efficiency reductions.     

HF radio in Southwest Asia

The use of an HF propagation mode, called rear-vertical incidence skywave (NVIS), by the US Marine Corps is discussed. In an NVIS system, HF signals are radiated nearly vertically. The signal returned from the ionosphere covers the skip zone with an omnidirectional pattern providing a communications range from the transmitter site out to a radial distance of 0 to 300 miles. The development of HF communication systems by the Marine Corps in the 1980s is outlined. The application of several HF communication systems during Operation Desert Storm is described     

Finite-difference time-domain analysis of HF antennas on helicopterairframes

In this paper, the finite-difference time-domain (FDTD) method with the Berenger perfectly matched layer (PML) absorbing boundary condition (ABC) is used to model the radiation characteristics of high frequency (HF) antennas operating in the 2-30 MHz range on a full-scale helicopter. The computed input impedance of both antennas is compared with actual measurements from an operational full-scale helicopter and also with measurements on a scale model NASA generic advanced attack helicopter (GAAH). To study the coupling effects of the helicopter fuselage on the antenna systems, the S-parameters are computed and compared with measurements on the NASA GAAH scale model. Finally, computed gain patterns are compared with actual in-flight measurements of the antenna systems on an operational full-scale helicopter     

Gain measurements of vertically polarized antennas over imperfect ground

A technique is described for measuring the absolute gain of vertically polarized HF antennas. A horizontal half-wave dipole, located near the antenna being measured (test antenna), is used as a reference in a comparison type of gain measurement. A rotatable, linearly polarized, transmitting antenna is mounted on an airplane and used to illuminate the test-reference antenna location. With the airborne antenna vertical, the response of the test antenna is measured. The airborne antenna is quickly rotated to a horizontal position and the response of the reference dipole is measured. When the airplane is in the main lobe of the test and reference antennas, these two measurements yield the gain of the test antenna relative to that of the reference dipole. The gain of a horizontal half-wave dipole is presented graphically, versus main lobe elevation angle, for various heights above imperfect ground. Mutual impedance variations were considered in the computations for these graphs. Model antenna measurements were made at 400 MHz to verify the principle of the technique. On-site HF measurements could give gain figures accurate to within a few tenths of a dB of their true value.     

2014年美国海军通信装备与技术发展综述

2014年,美国海军在军事通信与数据链领域围绕战场网络系统、先进战术数据链系统、机载通信系统、卫星通信系统以及新型通信技术等热点领域展开了大量研究和装备部署工作。跟踪外军通信装备的发展动态,研究外军通信装备和技术发展趋势对促进我国海军通信和通信电子战能力建设具有重要借鉴意义。概述了2014年美国海军通信装备与技术的发展情况,并分析了海军信息网络、数据链和软件无线电的未来发展趋势。     

The nocturnal service area of MF AM broadcast stations usingvertical arrays

The nocturnal service area, or distortionless area, of MF AM broadcast stations depends on the radiation properties of the transmitting antenna and the physical constants of the ground surrounding the transmitting site. These ground constants limit the maximum antenna height and establish how large the nocturnal service area will be. In some instances the nocturnal service area can be increased by the use of vertical antenna array. In this case it is very important to know the increase of the theoretical nocturnal service area of the station and if the use of more sophisticated radiating systems is justified. Calculations were made to determine the theoretical nocturnal service area of a station using vertical arrays, and curves with maximum distortionless distance are given as a function of frequency and ground physical constants. Measurements on reduced-scale models in HF and VHF bands are described, and improvements in antenna antifading properties and in nocturnal service area are shown     

Radio propagation and anti-multipath techniques in the WINenvironment

The unique characteristics of wireless in-building network (WIN) systems based on microwave radio technology are addressed, focusing on the multipath propagation problem which most distinguishes radio from wired LAN media. This is followed by a discussion of the three principal techniques that have been developed within the radio communication industry to deal with this multipath problem: adaptive equalization, spread spectrum, and antenna diversity. A review of the strengths and weaknesses of each of these techniques reveals that antenna diversity is clearly the preferred choice for use in WIN systems operating in the recently allocated spectrum near 18 GHz. An example of such an antenna system is examined. It is shown how these multiple, directional antenna systems function in three types of environment