Phase Compensation for Widely-Spaced Antenna Systems Employing Coherent Signal Combinations

This paper describes a technique for providing phase compensation to signals received at widely-spaced antennas and processed at a central location. Self-compensation is provided for pathlength variations in reference-signal distribution systems. The technique may be adapted to include the measurement and compensation of signal-channel phase variations. Practical systems which require this type of compensation include interferometric systems used for position and position-rate measurements of missiles and spacecraft, interferometers and arrays of antennas used for radio and radar astronomy, and arrays of large-aperture antennas used for deep-space communications.     

Transformation of the Spectrum of a Signal in Communication between Relativistically Moving Inertial Frames

Future space exploration may involve communications between spacecraft moving at relativistic velocities. One of the significant problems associated with such communication is spectral distortion of signals which are propagated between relativistic frames. This distortion is generated by both changing propagation distances and purely relativistic electromagnetic field transformations. In this paper a linear integral transformation is formulated for relating the Fourier spectra of the source antenna excitation current and the resulting incident electric field at the receiving antenna. The kernel of the transformation is evaluated for the case of a steerable source antenna tracking on the advanced receiver position. The transformation is then applied to the case of an ideal thin-wire half-wave dipole source antenna excited by a narrowband, double-sideband modulated current. The specific distortions of spectral spreading and translation are then related to increased bandwidth and upper cutoff frequency requirements of receiving systems in relativistic applications.     

Measurements of Phase-Front Distortion on an Elevated Line-of-Sight Path

An experimental study has been made of phase-front distortion in microwave signals sent over a slanted path. This distortion is important in systems involving phase measurements between a ground station and a moving upper terminal. To insure path stability, the upper terminal was simulated by a series of mountaintop antenna arrays. Phasefront distortion is analyzed in terms of time variations in radio range on a single path and in terms of first and second range differences between pairs of paths. The cross correslations of pairs of range and range difference records are discussed, and the strong dependence of correlation on fluctuation frequency is emphasized. Mountaintop terrain effects on the spatial homogeneity of the phase front are found to be insignificant. Some of the phase-front statistics are found to be weakly dependent on time of day and on wind velocity at the lower terminal.     

Performance of phased-array antennas with mechanical errors

The performance of planar phase-array antennas with mechanical errors is investigated. Errors in array element positions as a result of structural distortions are considered as deterministic and predictable. Detailed calculations for two assumed modes of distortion reveal that their effects on antenna performance are the loss of peak response in the scan direction and the broadening of the mainlobe, while the far-out sidelobe structure remains relatively intact. For large antennas, performance improvement can be expected by suitable phase compensation. Performance of antennas with random errors in their element positions must be treated statistically. Expressions of average directivity and sidelobe level corresponding to arbitrary error magnitudes in element position, amplitude and phase of excitation as well as finite rate of failure of element modules were derived and verified by direct numerical calculations from the antenna directivity patterns. For a planar phased-array antenna typical for space-based radars, the standard deviation of element position errors must not exceed 1% of the operating wavelength in order to maintain a -10 dBi sidelobe level     

弹载天线旋转对接收信号多普勒偏差的影响

由弹体自旋产生的弹载天线的旋转是引起地面测控站多普勒测速误差的一个重要因素.根据线极化信号接收原理,对弹载天线旋转条件下接收的左旋和右旋信号多普勒偏差进行了理论推导和分析.分析结果表明：左/右旋接收信号将产生幅度相等、极性相反的多普勒偏差,多普勒偏差的均值与弹载天线旋转速率在数值上相等,多普勒偏差的方差随着目标视线与天线转轴之间夹角的增大而增大.为验证理论分析结果,开展了天线转台模拟实验,实验测量得到的多普勒偏差的均值和方差与理论分析结果基本一致.最后,根据理论分析和模拟实验结果,提出在实际任务中,可采用左旋和右旋多普勒偏差均值差的一半分别对左/右旋信号的多普勒进行补偿,以减小弹载天线旋转对测速精度的影响.     

Effects of finite weight resolution and calibration errors on theperformance of adaptive array antennas

Adaptive antennas are now used to increase the spectral efficiency in mobile telecommunication systems. A model of the received carrier-to-interference plus noise ratio (CINR) in the adaptive antenna beamformer output is derived, assuming that the weighting units are implemented in hardware, The finite resolution of weights and calibration is shown to reduce the CINR. When hardware weights are used, the phase or amplitude step size in the weights can be so large that it affects the maximum achievable CINR. It is shown how these errors makes the interfering signals “leak” through the beamformer and we show how the output CINR is dependent on power of the input signals. The derived model is extended to include the limited dynamic range of the receivers, by using a simulation model. The theoretical and simulated results are compared with measurements on an adaptive array antenna testbed receiver, designed for the GSM-1800 system. The theoretical model was used to find the performance limiting part in the testbed as the 1 dB resolution in the weight magnitude. Furthermore, the derived models are used in illustrative examples and can be used for system designers to balance the phase and magnitude resolution and the calibration requirements of future adaptive array antennas     

Limitations of Series-Fed Arrays in Broadband Communications

The purpose of this paper is to investigate the signal distortion which results when long, series-fed arrays are used for communication. It is shown that under certain conditions the antenna array can be considered a linear filter, the response of which is a function of frequency as well as spatial coordinates. The distortion accompanying the transmission as measured by the least mean-square difference between the transmitted and the received signals is derived. This expression is evaluated for the case of a uniformly excited array and a rectangular band-pass signal spectrum. In the absence of noise the transmitted signal can be completely recovered in the receiver by employing the proper linear filter. In the presence of noise the signal cannot, of course, be completely recovered. However, a technique for minimizing the distortion, in this case using a pre-filter and a post-filter, is investigated.     

Artificial Beam Sharpening Technique for Radar Beacon Systems

A method of improving angular discrimination artificially in radar beacon systems, without going to extremely high frequencies of operation or using unreasonably large interrogator antennas, involves the use of a null-type antenna pattern superposed on a normal directional beam. The effective are over which replies are obtained is determined by an amplitude discriminator circuit within the beacon which compares the amplitude of the pulse signals received on the null pattern with those received via the directional beam. Only if the latter exceed the former by a predetermined amount does the beacon produce a reply. The method, which has been tried experimentally and its theory verified, produces an increase in traffic handling capacity, as well as improved angular resolution, by reducing unwanted triggering and, hence, clutter on the display and the over-interrogation of transponder beacons. An antenna is described which eliminates triggering on sidelobes by providing the proper current distribution to the radiating elements to cause the null pattern to cover the sidelobes of the normal beam. Triple-pulse amplitude discriminators have been built and tested in a double-pulse interrogation system. Some theoretical considerations and design curves and equations for use in designing nulltype antennas are given in the Appendix.     

Novel array-feed distortion compensation techniques for reflectorantennas

Degradation of antenna performance by reflector surface distortion, which lowers gain and increases sidelobe levels, is addressed. Distortion compensation concepts based on the applications of properly matched array feeds are presented. Results of conceptual developments, numerical simulations, and measurement verifications are presented in support of this approach, with particular attention to the measurement technique. It is shown that the concept is most useful for overcoming the deterioration effects of slowly varying surface distortions, which would make the method very useful for future large space and ground antennas. It is further shown that for a typical, slowly varying thermal or gravitational surface distortion, a 19-element array feed can improve the reflector performance considerably     

基于VLBI的上行组阵标校技术研究

天线组阵能否完全替代大口径天线有一个关键性难题,就是天线阵是否支持上行链路组阵。深空航天器无法将不同地面天线的上行信号对齐,所以上行链路信号的调整必须在地面完成。针对上行组阵发射机相位调整问题,提出一种基于VLBI(Very Long Baseline Interferometry,甚长基线干涉测量)技术的接收模式天线上行组阵标校方案,并对标校精度进行了简要分析。将上行链路时延分解为几何时延和发射系统时延,建立了几何时延模型,通过标定接收时延和发射时延,便可以得到天线阵元间的相位标校值。理论分析结果表明,该方案具有一定的可行性,对上行组阵相位标校的研究具有一定的借鉴意义。     

A Modified Monopulse Technique for Radar Tracking with Low-Angle Multipath

In this paper a new monopluse technique for reducing radar multipath angle-tracking errors is proposed. The solution is achieved by using two monopulse antennas at different heights. The available signals allow one to control the antenna-height diversity so that the elevation angle control signal is not affected by reflected-wave components. The size of the antenna system may be reduced by properly using phase shifters. A possible configuration of such a system is considered and some practical data on the antenna-height diversity are discussed.     

Measuring satellite antennas with a compact hologram test range

Testing of satellite antennas at high millimeter and submillimeter wavelengths has some specific problems not encountered at lower frequencies. The atmospheric attenuation due to water and oxygen molecule resonances at certain frequency bands can be substantial. Therefore, conventional far-field test methods for electrically large antennas are ruled out by the required far-field distance of kilometers or even tens of kilometers. However, the compact antenna test range (CATR) makes such far-field tests possible within an indoor chamber having a controlled atmosphere. The application and ongoing development of a CATR based on a hologram as the focusing element are outlined     

A Selected Bibliography on Adaptive Antenna Arrays

An adaptive antenna array is defined as an antenna array whose output is the weighted sum of the signals received at the antennas, with signal-dependent automatic adjustment of the weights to optimize some criterion. This open-literature bibliography of papers on the subject is intended to provide a brief overview of the field, and the authors involved, up to the end of 1985. Papers are listed both by subject area and by sole/primary/secondary author.     

On the Perfomance of Air Traffic Control Radar Beacon System

The sidelobe suppression and improved sidelobe suppression mode performance of terminal and enroute air traffic control radar beacon systems using the existing antenna and a typical improved antenna in the presence of perfectly dielectric flat ground are investigated theoretically. Necessary analytical expressions for various quantities characterizing the system performance have been derived. A general purpose computer program has been developed for the computation and tabulation of these quantities as functions of the elevation angle of the observation point and for different combinations of heights of the directional and omnidirectional antennas of the beacon. Although the discussions given here apply to some specific antenna configurations, the theoretical method developed has more general application in evaluating quantitatively the performance of the beacon system in a given situation.     

定向耦合器在天线隔离度测试中的应用

飞机机载天线之间可能会因电磁能量互相耦合而产生电磁干扰,天线隔离度测试是验证机载天线布局设计的重要手段之一。根据定向耦合器性能参数定义,通过测量定向耦合器耦合端口和隔离端口的功率值计算出发射天线的净输入功率和接收天线的净输出功率,从而得到天线隔离度。通过机上测试,这种隔离度测试方法简便快捷、稳定可靠,试验结果准确有效。     

The Polar plasma wave instrument

The Plasma Wave Instrument on the Polar spacecraft is designed to provide measurements of plasma waves in the Earth's polar regions over the frequency range from 0.1 Hz to 800 kHz. Three orthogonal electric dipole antennas are used to detect electric fields, two in the spin plane and one aligned along the spacecraft spin axis. A magnetic loop antenna and a triaxial magnetic search coil antenna are used to detect magnetic fields. Signals from these antennas are processed by five receiver systems: a wideband receiver, a high-frequency waveform receiver, a low-frequency waveform receiver, two multichannel analyzers; and a pair of sweep frequency receivers. Compared to previous plasma wave instruments, the Polar plasma wave instrument has several new capabilities. These include (1) an expanded frequency range to improve coverage of both low- and high-frequency wave phenomena, (2) the ability to simultaneously capture signals from six orthogonal electric and magnetic field sensors, and (3) a digital wideband receiver with up to 8-bit resolution and sample rates as high as 249k samples s^–1.     

空间大型星载抛物面天线研究进展

抛物面天线作为星载天线的重要组成部分,在深空探测、移动通信、国防事业、气象监测等方面均具有广泛应用,近年来随着上述学科的快速发展,抛物面天线的研究也越来越受到人们的重视。针对空间大型星载抛物面天线的发展与需求,首先系统地概括了国外星载抛物球面天线的发展现状,综述了刚性、网状以及充气式星载抛物球面天线,对各类星载抛物球面天线的结构、性能进行了较为详细的描述和分析,对国内在该领域的部分研究成果进行了简述。然后梳理了星载抛物柱面天线的发展,对国内外具有代表性的抛物柱面天线进行了介绍,对抛物球面天线和抛物柱面天线进行了参数对比与分析。接下来对近年来针对星载抛物面天线的相关技术进行了介绍。最后对星载抛物面天线的发展趋势做了简要分析与预测。     

Adaptive Main-Beam Nulling for Narrow-Beam Antenna Arrays

Narrow-beam, low-sidelobe antennas may be used to enhance communication in the presence of sidelobe interferers. Protection against main-beam interferers as well can be obtained through the use of an adaptive multibeam antenna. Such an antenna, suitable for time-multiplexed, multichannel signals is described here. The objective is to permit successful communication and signal direction-of-arrival tracking in the presence of a large number of sidelobe interferers and a small number of main-beam interferers.     

卫星天线极化隔离度在轨测试方法与误差分析

建立卫星天线极化隔离度在轨测试的全程链路模型,分析交叉极化分量产生的机理,给出一种符号表示方法标识由各天线馈源激励产生的各段链路上的信号。分析和实际测试结果表明,主极化和交叉极化接收通道都会在2个相近的频点上产生多个极化分量矢量合成的信号,如果频谱仪分辨率设置不当,则得不到正确的测试结果。由于无法完全分离地面天线和卫星天线产生的交叉极化分量,卫星天线极化隔离度受到地面天线极化隔离度的影响。此外,还描述了高精度测量的卫星天线极化隔离度在轨测试流程和误差分析方法。     

On the Design of a Large Aperture Radar for Target Imaging

This paper describes the design, construction, and performance of an experimental radar, in which an electronically scanned X-band array is employed as the receiving antenna. Backscatter from targets uniformly illuminated from a separate transmitting antenna is intercepted by 128 horn antennas, unequally spaced over a nine-foot circular aperture. The received signals are processed electronically to provide a complete scan of a 30X30 degree field every ten milliseconds. Resulting target images were displayed on a cathode ray tube and recorded on 16-mm motion picture film, for varying conditions of target motion using monochromatic and frequency-modulated X-band illumination. Sequences of motion picture frames obtained from a rotating copper cone are presented, which demonstrate significant changes in the image and side-lobe interference patterns for small changes in target aspect angle. Side-lobe interference effects were reduced by integrating many antenna scans as the target rotated; a clear image of a foil letter R is presented that demonstrated this result. The main objective of this work was to test this radar technique as an approach to target recognition.