飞行器共形天线新型制造工艺及应用研究进展

共形天线具有小型化、低剖面、大孔径等特点,是未来天线重点发展趋势之一,以气动一体化天线、超宽带窄波束天线为代表的共形天线成为目前飞行器天线领域的研究热点。当前共形天线的制作工艺主要包括打印、转印、激光加工等,采用合适的工艺能够实现天线的大面积共形制造。讨论了共形天线在不同飞行器载体上的优势,如打印制作的低剖面机载天线可实现战机的气动隐身一体化需求,也可满足弹载天线小型超宽带需求,柔性天线可应用于星载充气可展开天线等。在此基础上对当前共形天线存在的关键技术问题进行了阐述,并对共形天线在航空航天领域的未来发展做出了展望。     

对均匀直线阵列天线的方向性的估值

本文对均匀直线阵列天线在相控扫描过程中的主瓣宽度和方向性系数进行了估算。     

Interferometer Design for Elevation Angle Estimation

Radars that are developed for the purpose of monitoring aircraft landings in the terminal air traffic control system can be designed to exploit the relatively high signal-to-noise ratio that characterizes the power budgets calculated for such a link. An interferometer using a pair of low gain antennas can be used to obtain passive coverage over a targe azimuth and elevation sector. A large baseline can be used to obtain the desired elevation angle estimation accuracy. In this paper an optimal tradeoff between the width of the subarray aperture and the width of the interferometer baseline is performed that achieves a specified elevation angle estimation error while minimizing the overall height of the interferometer configuration. The algorithm searches through the class of antenna patterns that can be synthesized from so-called finite impulse response, linear phase digital filters. For the specific problem of designing an elevation sensor for monitoring landing aircraft on final approach, the elevation angle can be estimated with no more than 1-mrad rms error when the aircraft is within ± 60° azimuth, 2.5° to 40° elevation, using two 7-wavelength subarray antennas spaced 8 wave-lengths apart. The design of a separate sensor for resolving the interferometer ambiguities is formulated as a hypothesis testing problem and solved using statistical decision theory. A bound on the probability of an ambiguity error is derived that accounts for the effects of ground reflection multipath and receiver noise.     

Polarization Mismatch Errors in Radio Phase Interferometers

An analysis is presented which deals with the effects of polarization mismatch errors on the accuracy of a phase interferometer used for position location of unknown emitters relative to known calibration emitters. Closed-form expressions for the induced phase difference between interferometer antennas are derived for several combinations of receiving and transmitting antenna polarizations. Errors contributed by mechanical misalignment between antennas, as well as effects of power loss attributable to polarization mismatch, are also considered. The analysis leads to the conclusion that circularly polarized interferometer and transmitter antennas are best suited for the position location application, if it is assumed that polarization tracking of the interferometer antennas is not available. It is shown that a reasonable amount of ellipticity can be tolerated before the phase error becomes significant.     

圆柱共形缝隙阵列的相位补偿方法研究

对圆柱共形缝隙阵列的相位补偿方法进行了研究。首先根据对偶原理,给出了任意方向放置的缝隙单元的远场计算公式。然后根据叠加原理推导出圆柱共形缝隙阵列的远区场计算公式,并通过相位补偿方法使共形阵列的电磁特性接近于平面阵列。最后对9×9圆柱共形缝隙阵列、其对应的平面阵列以及相位补偿后阵列的远区场实际算例进行验证分析。结果表明,通过相位补偿可以对共形阵列的电磁特性进行改善。     

The Radio Plasma Imager investigation on the IMAGE spacecraft

Radio plasma imaging uses total reflection of electromagnetic waves from plasmas whose plasma frequencies equal the radio sounding frequency and whose electron density gradients are parallel to the wave normals. The Radio Plasma Imager (RPI) has two orthogonal 500-m long dipole antennas in the spin plane for near omni-directional transmission. The third antenna is a 20-m dipole along the spin axis. Echoes from the magnetopause, plasmasphere and cusp will be received with the three orthogonal antennas, allowing the determination of their angle-of-arrival. Thus it will be possible to create image fragments of the reflecting density structures. The instrument can execute a large variety of programmable measuring options at frequencies between 3 kHz and 3 MHz. Tuning of the transmit antennas provides optimum power transfer from the 10 W transmitter to the antennas. The instrument can operate in three active sounding modes: (1) remote sounding to probe magnetospheric boundaries, (2) local (relaxation) sounding to probe the local plasma frequency and scalar magnetic field, and (3) whistler stimulation sounding. In addition, there is a passive mode to record natural emissions, and to determine the local electron density, the scalar magnetic field, and temperature by using a thermal noise spectroscopy technique.     

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     

Optimized RF test range for educational purposes

Both the design and construction of a composite scale airframe and the equipment for an anechoic test range plus the in-house production of absorptive wall covering-all for engineering education-are briefly described. It is shown, that low cost home-made absorbing material with an attenuation of 30 dB or more can be designed. Waveguide and ground plane antennas for test purposes can be constructed from surplus materials. In this case the design and measurements of a 3 GHz antenna pair are shown. Finally, as a test object, a cheap yet effective scale model of a modern fighter aircraft is used for measurements of radar cross section and antenna installations. As a demonstration of the total system capabilities, the measurement of installed F-18 antennas is shown     

用矩量法研究直升机高频天线电磁特性的旋翼调制效应

 基于面元模型的矩量法与快速多极子方法结合分析了直升机机载高频通信天线电磁特性的旋翼调制效应。通过三维计算机辅助实体建模技术,建立了一个尺度与真实直升机相当的仿真模型,实现了机体表面网格的自动剖分。应用准静态法和FFT技术,计算分析了旋转桨叶对天线辐射场幅度和频率的调制效应,还分析了桨叶旋转对天线输入导纳和互导纳的影响。计算结果表明,旋转桨叶对直升机机载天线辐射场产生了显著的影响。本方法亦适用于其它类型的直升机和其它具有旋转桨叶的载体上天线电磁特性的分析。     

Some Effects of Hard Limiting in Adaptive Antenna Systems

Adaptive antennas are often implemented with the Applebaum-Howells-type adaptive processor usually include a hard limiter between each antenna port and its correlation mixer, primarily for dynamic range compression. Brennan and Reed [3] analyzed the effects of hard limiting, and their conclusions suggest that it does not degrade the steady-state performance of the adaptive processor. Standard and hard-limited processors are compared and it is shown that when the two types of processor have the same sensitivity threshold, the hard-limited one can fail to provide sufficient interference cancellation when the correlation matrix of input signals has two or more eigenvalues of differing magnitudes. The consequence of hard limiting is that (depending on the processor design parameters) the larger of two or more signals can capture the hard limiter, allowing the smaller signals to pass through the processor essentially unattenuated. It is also shown that when a hard-limited processor is designed to provide the same cancellation as a standard one, it must have essentially as large a dynamic range as the standard, processor; therefore, it offers no advantage of dynamic range compression. Moreover, the hard-limited processor lacks a constant sensitivity threshold, which can be a desirable feature of a standard processor. Specific examples are presented for identical-element array antennas and for multiple-beam antennas.     

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。     

Superconducting antennas

The applicability of superconductors to antennas is examined with emphasis on the roles of external and internal fields. Six potential implementations have resulted. These are superdirective arrays, millimeter-wavelength arrays, electrically small antennas, matching of antennas, phasers for electronic scanning, and traveling-wave array feeds. Most superdirective arrays are still impractical, because of high Q and strict tolerances. Large millimeter arrays appear feasible, due to a major reduction in feed losses. For electrically small antennas, high Q again limits applicability. However, matching of small superdirective arrays and all electrically small antennas, including large transmit antennas, is very attractive, as matching network losses are greatly reduced. Switched-line phasers offer a major size reduction; phase control by means of temperature of a single line poses some problems. Traveling-wave array beam steering by means of temperature also appears possible. The last two utilize the kinetic inductance provided by thin films     

Some properties of retrodirective beam of multiple sidelobecanceler

The retrodirective or perturbation beam concept is often used to aid in explaining the nulling of interference sources. The classical explanation for cancellation of a single-zero-bandwidth source is that of a perturbation beam steered to and peaking at that interferer angle. The subtraction of this perturbation beam from the main beam causes the nulling. It is shown that, for discrete point main and auxiliary antennas, this explanation can be generalized to non-zero bandwidth sources. It is demonstrated that if the main and auxiliary antennas are spatial points, then the retrodirective beam is nonuniformly weighted, steered to the interference source, and peaks at the interferer angle. For the more realistic assumption of a nonpoint main antenna, the retrodirective beam does not peak at the interferer angle for any bandwidth     

机载天线隔离度的分析计算与仿真

机载天线间的隔离度是飞机系统电磁兼容性的主要参数之一,用来表征天线间的耦合强弱程度.在实际工程中,飞机上集中了大量天线,使得周围空间电磁环境很复杂.在研究机载天线电磁兼容性时,采用计算天线间的隔离度数值的方法来实现.本文先通过对配置在圆柱体模型上的两个天线的隔离度进行理论分析和计算,然后采用HFSS仿真软件对所需频带内的两个天线隔离度进行了仿真,并将其两者的结果进行了比较,从而实现对整个频带内的天线的电磁兼容性的正确预测和评估.     

Orbital Inclination Effects on Communications Satellite System Design

Starting from the analysis of recommendations and technical reports of the International Telecommunications Union on the stationkeeping and pointing accuracy requirements of quasi-geostationary communications satellites, the following effects of orbital inclination and yaw control error on the system design are discussed: (1) the excursion in longitude during a 24 h period; (2) the efficiency of the geostationary orbit utilization for systems with frequency reuse using linear orthogonal polarizations; (3) the angular tracking requirements of Earth station antennas; and (4) the performance of TDMA systems.     

Textile antennas: effects of antenna bending on input matching and impedance bandwidth

How the performance of wearable textile antennas is affected on the antenna bending is described herein. The authors focus on the resonance frequency fluctuation and input-match bandwidth variation due to the antenna bending. The results are given for three different antennas, namely, a conventional patch, EBG, and dual-band U-slot antennas     

A computing model and its experimental testing for an evaluation of electromagnetic interferences created by interfering circuits on transmission or high-voltage lines above a dissipative ground

In this paper we present useful calculations for a prediction of the electromagnetic field created by interfering circuits on a linear horizontal transmission line over an imperfectly conducting ground. The interfering circuits are assimilated to antennas and treated by using the dipole-radiation theory. The current distribution is determinated by the transmission-line theory. We present here the computational procedure allowing a fast and accurate calculation of the electromagnetic fields components of a series of dipoles. We give the linear characteristics Z, Y of the transmission line by incorporating the ground effects. The response of a terminated one-wire transmission line set over the ground and excited by a non-uniform field is given. A comparison between computed results given by the model and experimental measurements is provided.     

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     

Radio interferometer for geosynchronous-satellite direction finding

A radio interferometer capable of azimuth-elevation direction finding for geosynchronous satellites has been developed. The interferometer has two small-diameter antennas and four movable planar mirrors. The movable mirrors reflect the microwaves from the satellite and guide them to the fixed receiving antennas. Two of the movable mirrors are mounted on a rotary arm, so that the baseline of the interferometer can rotate in the horizontal plane. This configuration enables the interferometer to eliminate phase-ambiguity problems and cable-phase errors, resulting in a direction finding accuracy of better than 0.01 deg in the Ku band.     

基于非全向天线的无人机MIMO信道模型研究

为研究无人机信道特性,针对地面控制站( GCS)环境特点和非全向多天线系统,建立并分析了基于散射体三维几何分布的单跳同心圆筒散射(GBSBCCS)宽带传播模型,根据方位角非全向散射和俯仰角非对称分布的特性,结合无人机实际飞行参数特点,推导出简洁的空时频联合相关函数.通过仿真进行了验证,并对相关特性影响因素进行分析,结果...