有源相控阵天线发射方向图测试简易方法

有源相控阵天线需要对接收和发射两种状态的天线方向图进行测试。现有天线测试远场只能进行接收态的方向图测试,介绍了在远场进行发射态方向图测试的一种简易方法。利用远场的测试转台和发射喇叭,使用频谱分析仪接收有源相控阵天线发射的数据,编制测试软件采集处理数据,即能实现有源相控阵天线发射方向图的测试。该测试方法简单易行。     

Fields of horizontal currents located above the Earth

The plane-wave spectrum technique is used to derive the field of horizontal currents located in a horizontal plane above the Earth. The far field is derived asymptotically, and the near field is computed by a two-dimensional fast Fourier transform. Specific numerical results are presented for a pair of oppositely directed dipoles, and the results have application to detection of buried objects. When the antenna is located at low heights, the field is enhanced in the Earth and decreased in the air     

Estimating the coordinates of a moving target from the doppler data measured by forward-scatter radar systems

The feasibility of the estimation of a target’s coordinates solely from the Doppler data measured by forward-scatter radar systems (RSs) is analyzed. It is shown that the coordinates’ ambiguity is inherent in a bistatic RS with one transmitting antenna and one receiving antenna. This ambiguity is eliminated in a system with one transmitting antenna and two receiving antennas located close to each other. Algorithms for determining the target’s coordinates in this system are proposed. The accuracy of estimating the target’s coordinates is evaluated and compared to that obtained with a bistatic RS that measures the Doppler frequency and a signal’s direction of arrival.     

Coupling between Two Antennas Separated by a Planar Interface

The plane-wave spectrum technique is used to analyze the coupling between a pair of antennas separated by a planar interface. Multiple reflections between the antennas or between either antenna and the interface are included in the formulation. The formulation is used to model detection of buried objects, and a low-frequency metal detector example is analyzed in detail. For a transmitting loop and a buried oblate spheroid, the plane wave spectrum technique is shown to agree with well-known quasi-static approximations. Some experimental results from a 3-kHz metal detector are also shown.     

Quadratic antenna systems and noise excited antennas

A quadratic receiving antenna system is defined as a multiport antenna whose outputs are passed through square-law detectors, or, in pair, through correlators (product detectors). These detected signals are then linearly combined with different weights to give the output or response of the receiving system. A reciprocity relation is derived which relates the electromagnetic field radiated by a multiport transmitting antenna excited by quasi-monochromatic noise sources to the response of a quadratic receiving antenna system. The noise sources exciting the transmitting antenna may be independent or they may be correlated. In general, the radiated field is partially polarized. The weights used in combining the signals from the square-law detectors and the correlators in the associated receiving system are determined by the intensities of, and the correlations between, the noise sources exciting the transmitting antennas. Practical use has been made of the derived reciprocity relation. The radiation properties of noise-excited multiport antennas have been determined by measurements made on the associated quadratic receiving system.     

On the equivalent circuit of a receiving antenna

The equivalent circuit of a receiving antenna consists of a current generator and two admittances: one for the load, and one for the antenna. The short-circuit current, I_g - receiving property - may be expressed in terms of the transmitting properties of the antenna. The article gives a derivation for the value of I_g. It is assumed, to simplify matters, that the antenna is located in free space, and that its feeding line is a monomode waveguide (a coaxial cable, for example). The extension to multimode lines, or to spatial regions containing linear media (possibly anisotropic, and/or non-reciprocal) is fairly straightforward     

UWB系统中天线性能对脉冲波形的影响

分析了超宽带无线系统中,天线在发射和接收过程中对基带脉冲信号波形的失真影响.采用了天线系统传递函数描述天线的辐射和接收特性,在暗室中对典型的超宽带印刷天线进行频域特性和时域特性的测量,给出了脉冲信号的辐射和接收过程.研究表明结合天线系统传递函数,可以设计出更符合FCC辐射功率掩蔽的脉冲信号,以及选取出波形保真系数最佳的本地模板信号,从而获得全局性能最优的超宽带系统.     

Transmission of Circular Polarized Waves Between Elevated Antenna

Transmission of circularly polarized signals between elevated antenna over lossy earth is discussed for a frequency of 100 MHz. By decomposing the circularly polarized signals into vertical and horizontal components and considering only direct and ground-reflected waves, it is shown that for fixed transmitting antenna height and horizontal separation, the field intensity at the receiving antenna varies sinusoidally with receiving antenna height. Reference curves of field strength versus height are included for typical tower heights, separations, and soil conditions. Comments on FCC power height curves are also included.     

Considerations for source pulses and antennas in UWB radio systems

This paper addresses two vital design considerations in ultrawide-band radio systems. One is that radiated power density spectrum shaping must comply with certain emission limit mask for coexistence with other electronic systems. Another is that the design of source pulses and transmitting/receiving antennas should be optimal for the performance of overall systems. The design of source pulses and transmitting/receiving antennas under the two considerations is discussed. First, the characteristics of transmitting/receiving antenna systems are described by a system transfer function. Then, the design of source pulses and transmitting antennas are studied based on the considerations for emission limits. Finally, the design of transmitting and receiving antennas are investigated in terms of pulse fidelity and system transmission efficiency. In the studies, thin wire dipoles with narrow bandwidths and planar dipoles with broad bandwidths are exemplified.     

An analytical solution to the diffraction problem of diagnosing the position and size of a sphere

A method for determining the position and dimensions of a body from the scattered field is described. The body (a metal solid sphere) is situated in the near-field zone of a transmitting antenna, and the receiving antenna is situated in the near zone of the body. The parameters of the body are calculated from the measured wave amplitudes in the dielectric waveguide of the receiving antenna. For calibration of the antenna, the body is replaced by a metal mirror.     

Linear array characteristics with one-dimensional reactive-regionnear-field scanning: simulations and measurements

A model for simulating the performance of a phased-array antenna with one-dimensional near-field scanning is addressed. Measurements and simulations in the reactive near-field region for a linear array with monopole elements are described. The array and near-field probe characteristics are simulated by using the method of moments. Measurements and simulations of the array near-zone received voltage, plane-wave spectrum, and far-field data, using centerline scanning at less than one wavelength distance from the antenna, are shown to be in good agreement. The presence of evanescent grating lobes in the plane-wave spectrum is observed. It is shown that a V-dipole theoretical probe antenna can accurately model a practical near-field measurement probe     

Range distance requirements for large antenna measurements

The dependence of the radiation patterns and antenna gains on the measurement distance when both transmitting antenna and receiving antenna have the same order of large dimensions is discussed. The antenna under test is the transmitting antenna. The near-zone radiation patterns (Fresnel pattern) and the antenna gains of various kinds of circular aperture distributions vs the measurement distances are calculated for an arbitrary size of the receiving probe antenna. It is found both theoretically and experimentally that the near-zone measurement error of the radiation patterns introduced when the receiving antenna is of comparable or the same dimension as the transmitting antenna is smaller than the error introduced when the receiving antenna is very small. Thus, it is concluded that as a range criterion 2D²_a/λ is more appropriate than 2(D_a+D_b)² /λ for pattern measurements (D_a and D_b are linear dimensions of the transmitting and receiving antennas, and D_a⩾D_b is assumed). It is shown that the gain error for any aperture distribution obtained by using a large receiving probe antenna is greater at any range distance than the error obtained by using a small antenna such as a dipole     

大气激光通信中传输能量损耗分析的应用研究

对大气激光通信中的光传输能量损耗进行分析,着重讨论了造成接收端光功率损耗的几个主要影响因素,并做了综合性的计算机仿真,得到发射功率一定的情况下发射天线轴向偏焦和收发天线系统间横向偏移取不同量值时接收端光功率的变化。在损耗分析的基础上,文章探讨了接收端满足最低光功率条件下,偏焦和偏轴相互间的关系,提出通过调节发射天线偏焦来改善远距离接收端天线捕获的方法。在发射功率为10000 mW,距离为10 km,接收端光功率阈值为50 mW的情况下,发射天线未偏焦时收发天线系统间的允许最大偏轴量为495.9 mm;当焦点偏移6.69 mm,允许最大偏轴量达到最大值为628.5 mm,与未偏焦的情况相比增加了26.74%,满足接收端光功率要求下收发天线系统间允许横向偏移区域的面积增加了60.63%,这有效地降低了大气激光通信中远距离接收端捕获的难度。     

平面火山烟雾形天线的脉冲辐射特性

设计了一种火山烟雾形平面印刷超宽带天线.研究显示其阻抗带宽低频端可达0.8GHz,在加载电阻回路后带宽低频端可扩展至0.5GHz,在1ns宽的高斯微分脉冲激励下,双锥天线作为发射天线,比较了加载电阻和未加载电阻天线的接收波形,由结果可知,加载天线可以进一步减小脉冲信号波形失真。     

地下磁感应通信阵列天线传播特性分析

针对地下磁感应通信系统中单个磁性天线路径损耗大、通信效率低、传输距离短的问题,研究了双线圈天线与3D天线两种协同式天线的电磁传播特性.基于Matlab对根据天线数学模型得到的磁感应强度进行了仿真和分析,并将两种天线的传输性能与单一磁性天线进行了比较.研究表明,两种天线的磁场强度都有很大提高,并具有方向性和对称性,双线圈...     

Multifunction single-package antenna system for spin-stabilized near-synchronous satellite

An antenna system is described for a spin-stabilized satellite with its axis normal to the orbital plane. Three antennas in a compact lightweight package comprise the antenna system: a switched-beamX-band transmitting antenna, an omnidirectionalX-band receiving antenna and an omnidirectional VHF telemetry antenna. The first is a cluster of eight circularly polarized horns pointed radially outward every 45 degrees about the spin axis. An eight-throw solid-state waveguide switch turns on that horn currently pointing most nearly to earth. This is accomplished by providing the switch with electrical signals from a logic circuit operating on information from earth sensors. The second antenna is a circularly polarized biconical horn located above the cluster of transmitting horns. Its sense of polarization is opposite that of the transmitting antenna, and a filter in the transmission line to the receiver insures the required isolation. The third antenna is obtained by feeding across the gap between the twoX-band antennas and exciting the external surfaces to radiate in a linearly polarized mode. Total weight of the three-antenna package is less than4frac{1}{2}pounds; it occupies a volume less than 10 inches square by 8 inches high above the top panel of the satellite.     

Near-field scattering by physical theory of diffraction andshooting and bouncing rays

This paper proposes a method to compute the near-field RCS and Doppler spectrum of a target when the distances to the antennas are comparable to the target size. By dealing with a small piece of the target surface at a time, the transmitting antenna, and the receiving antenna are in the far-field zone of the small piece of the induced currents. The electromagnetic field produced by this small piece of induced currents can be written as a spherical wave. Sum up all spherical waves produced by every small piece of induced currents and we can obtain the total scattered field at the receiving antenna. The physical theory of diffraction (PTD) and the method of shooting and bouncing rays (SBR) are modified to evaluate the received signals. Numerical results based on these techniques are obtained and discussed. The formulation applies the simple concepts of “equivalent” image and vector effective height, which are believed to be novel     

Short low loss AM antenna

An exploration is made of ways to improve the performance of a relatively small transmitting or receiving AM antenna system. Short vertical towers can be top-loaded to increase the radiation resistance and lower the base input capacitive reactance. An insulated counterpoise is connected to the coupling unit and to ground through an inductance which is tuned so as to maximize the field strength radiated in the far field     

A multiview microwave imaging system for two-dimensional penetrableobjects

A microwave imaging system is based on a multiview numerical solution to the integral equation of 2D transverse magnetic (TM) scattering is proposed. This solution is achieved by the moment method, and a pseudoinversion transformation is used to face ill-conditioning problems. All experimental setup is described that uses a scanning subsystem for measuring the values of the scattered electric field inside an observation domain located outside the investigation one (i.e., the area containing the cross sections of cylindrical dielectric scatters). Rotations of the investigation domain with respect to the scanning subsystem and the transmitting antenna allow a multiview imaging process. The imaging system does not require plane-wave illumination and does not use any first-order approximations; hence, it may be used even in the case of strong scatterers. The offline and once-and-for-all computation of the pseudoinverse matrix allows an inexpensive reconstruction in terms of computer resources. Some tests of the system were carried out, and the results are reported