Exact derivation of aperture errors in antenna measurements

Antenna-pattern measurements are generally undertaken by placing the antenna under test (usually the receiving antenna) sufficiently far from the transmitting antenna that the receiving antenna is illuminated with a plane wave. Gain measurements, whether by substitution, paired horns, or integration of the area under the beam pattern, depend upon the same criterion. A true plane wave is only achieved by separating the two antennas by an infinite distance, but it has been shown by Milne (1950) that small departures from a plane wave do not usually seriously degrade the measurement. The authors consider three aspects of the fields across a linear aperture. The finite spacing between the antennas produces a phase deviation and an amplitude taper. If we are only interested in the apparent gain loss, we need to combine both tapers into an illumination efficiency. It is surprising how little the illumination loss is when the phase deviation and amplitude taper are large. The formulation is given in terms of linear apertures, and can be easily extended to circular or rectangular apertures by adjusting the limits of the integrals     

Scattering of a plane electromagnetic wave by a linear array of cylindrical elements

An approximate method for numerically calculating the scattered field of a linear array of center-loaded cylindrical elements illuminated by a plane wave incident in theHplane of the array is described. To illustrate the use of the approximation technique, theH-plane scattered field of an eight-element model array is calculated for various conditions of impedance loading and illumination. From extensive calculations, it is found that theHplane scattered field of the array can be represented approximately by the product of the electric field scattered in the reflected direction and an interference factor. The interference factor is the equivalent of the complex array factor of the model array when excited with uniform amplitude and an element-to-element phase progression proportional to the sine of the angle of incidence of the illumination.     

基于最小二乘法的平面波综合

将最小二乘法引入近场天线测量中,提出了一种新的平面波综合方法。以半波对称振子组成的矩形平面阵作为平面波综合的理论模型,用这一新方法寻求阵列单元的最佳幅相分布,以使所综合出的准平面波质量最好。计算结果表明在待测区域大小一定的条件下,利用本文方法可以实现较传统方法更小的探头阵列要求。良好的仿真结果证实了该方法在天线测量及散射测量应用中的有效性。     

均匀天线阵列的空间相关性函数分析

推导了均匀圆形阵列与均匀线形阵列的空间相关性函数精确表达式和近似表达式。表达式由天线间距、阵列形状以及到达角分布构成。利用均匀角能量分布,分析均匀圆形阵列与均匀线形阵列的空间相关性精确模型和近似模型,并利用Matlab进行仿真。仿真结果表明,近似分析在一定的条件下可替代精确分析,并可减少74%的运算时间。     

基于SIW的多波束CTS阵列天线设计

文中设计了一款基于基片集成波导(SIW)的毫米波高增益多波束连续横向枝节(CTS)阵列天线,它通过切换馈电端口实现多波束功能。该天线整体结构简单,采用印刷电路板工艺实现。天线主要包含馈电喇叭、平面波转换结构以及辐射结构三个部分,由三层基板构成。馈源为基于SIW的馈电喇叭,并在口径处添加匹配结构以提高其辐射性能;平面波转换结构由SIW抛物面和渐变耦合槽组成,可将馈电喇叭辐射出的柱面波转换为幅度服从泰勒分布的平面波进而为CTS阵列馈电,因此天线具有低副瓣的特性;辐射结构为1×8的CTS阵列,通过优化缝隙宽度以保证每个单元辐射出相等的能量。天线工作在30 GHz,通过切换馈电端口可在±20°范围内实现波束切换,天线测试结果与仿真结果吻合,验证了设计的合理性。     

Adaptive processing using real weights based on a direct data domain least squares approach

In traditional, adaptive signal processing algorithms one change both the amplitude and phase of the weight vectors associated with an array at each of the antenna elements. The use of complex weights offers greater control over the array response at the expense of system complexity. However, it is easier if one requires only amplitude variation with a fixed phase for all the weight vectors associated with all the antenna elements. Because one uses only real arithmetic operations to find the amplitude of the weights connected to the antenna, the computational complexity is reduced considerably. Hence, this paper addresses the use of real weights in an adaptive system. In this paper we describe a new direct data domain least squares (D/sup 3/LS) method using real weights, which utilizes only a single snapshot of the data for adaptive processing. This technique may be useful for real time implementation of the D/sup 3/LS method on a chip.     

Pattern Synthesis of Conformal Array Antenna in the Presence of Platform Using Differential Evolution Algorithm

A synthesis method based on differential evolution algorithm is proposed for conformal antenna arrays in the presence of platform. With the desired phase weights determined by the scan angle and array geometry, the amplitude weights of elements are optimized by differential evolution algorithm to drive down the side-lobes. Both the effect of platform on radiation pattern of conformal array and the mutual coupling between the elements are taken into account by calculating the antenna array and platform simultaneously using the method of moment. Application of adaptive integral method reduces the storage and computation time needed by the method of moments.     

A large antenna array for millimeter wave propagation studies

An antenna array has been constructed for reception of line-of-sight, ground-to-ground transmissions at 35 GHz over a 28-km path. It measures, individually, the amplitude and the relative phase of the arriving wave at each of eight antenna elements spaced horizontally over a distance of 24 m transverse to the path. Preliminary observations have shown perturbations in amplitude which appear at one end of the array and progress sequentially in a matter of seconds from element to element across the array. Similar traveling perturbations occur in the phase measurements. Variations in tilt of the wave front are observed, usually amounting from a few to tens of seconds of arc. In addition, changes in wave-front curvature have been measured corresponding to an apparent shrinkage or expansion of path length on the order of ten percent. Other capabilities of the array as a propagation-research tool are mentioned.     

Sidelobes Due to Periodic Amplitude and Phase Errors in the Aperture Field of a Radial Waveguide Pin-Fed Array Antenna

The location and level of the sidelobes of a radial waveguide pin-fed array antenna, which stem from periodic amplitude and phase errors in the actual antenna aperture field, are derived based on a simple model of a line source as well as the pertinent model of a circular aperture. The theoretical results are verified by comparisons with numerical and measured data     

Heating patterns generated by phase modulation of a hexagonal arrayof interstitial antennas

In this paper, we investigate an array of six interstitial microwave antennas used for hyperthermia cancer treatment. The purpose is to generate both uniform and controlled nonuniform heating patterns in biological tissue by phase modulating the signals applied to each antenna. The array consists of six antennas positioned on the corners of a hexagon. The distance between two diagonal antennas is 4 cm. The distributions of absorbed power per unit mass within the array are computed, and then converted into temperature distributions through a thermal conduction simulation. The SAR and temperature patterns are presented in both the lateral plane (perpendicular to the antennas) and the axial plane (parallel with the antennas). By proper phase modulation of microwave signals applied to each antenna, a uniform heating pattern can be produced within the entire array volume. Also, a peripheral heating pattern may be generated around the array; again, by using the proper phase modulation. The modulation schemes for generating both types of heating patterns are discussed.     

Circular array of outward sloping monopoles for vehicular diversityantennas

A circular array of outward-sloping monopoles is analyzed as a diversity antenna for vehicle rooftop mounting. The monopoles are assumed to approximate minimum scattering antennas, have sinusoidal current distributions, and reside on an infinite, perfectly conducting ground plane. The envelopes of the received signals are considered Rayleigh distributed. The advantage of the array configuration is that the feedpoint spacing can be made almost arbitrarily small, even for a large number of branches. A three-element array with element lengths of 0.6 wavelengths and feedpoint spacing 0.1 wavelengths operating at 463 MHz was field-tested and the results are in good agreement with the analysis     

用于船舶自动识别系统的机载阵列天线设计

为了满足船舶自动识别系统抗干扰性能的要求,设计了一种机载阵列天线.天线阵列由5个单极子天线单元组成,整体尺寸为Φ720 mm×306 mm,天线单元沿圆周均匀排列.通过泰勒分布和牛顿优化算法,优化阵列的辐射幅度及相位,得到实测的方位面增益-15 dB抑制范围达到128°,-20 dB抑制范围达到77°;装机后-15 dB抑制范围在114°以上,-20 dB抑制范围在51°以上.该阵列天线结构简单,成本低,满足机载环境的使用要求.     

Spatial signature estimation for uniform linear arrays with unknownreceiver gains and phases

The problem of spatial signature estimation using a uniform linear array (ULA) with unknown receiver gain and phase responses is studied. Sufficient conditions for identifying the spatial signatures are derived, and a closed-form ESPRIT-like estimator is proposed. The performance of the method is investigated by means of simulations and on experimental data collected with an antenna array in a suburban environment. The results show that the absence of receiver calibration is not critical for uplink signal waveform estimation using a plane wave model     

Quasi-optical 150-GHz power combining oscillator

A quasi-optical power combiner for a five-element in-line oscillator array is experimentally investigated at 150 GHz. The combiner consists of a periodic dielectric phase grating (hologram) which transforms the near-field of a rectangular horn antenna array into a pseudo-plane wave. The horn array is excited by IMPATT oscillators operating uniformly in both amplitude and phase. A dual offset reflector set-up transforms the pseudo-plane wave to a Gaussian beam which matches the field pattern of a dual mode receiving antenna. Even though an inter-element spacing of 9.5 /spl lambda/ has been chosen, the passive structure gives a power combining efficiency of 74.1%. The power combining oscillator has been operated in both free-running and injection-locked mode. A CW output power of 78.0 mW and 83.5 mW was measured for the free-running and injection-locked oscillator, respectively, which is corresponding to a power combining efficiency of 66.5% and 71.2%, respectively.     

A multi-objective approach in the linear antenna array design

We show that linear antenna array design can be modeled as a multi-objective optimization problem. A genetic algorithm is proposed for the solution of this problem. This genetic algorithm efficiently computes the trade-off curve between main beam width and side lobe level for linear antenna arrays with uniform and non-uniform separations. For uniform separation, the proposed algorithm is validated against the Chebyshev method for the cases of 6-, 8-, 10-, and 12-element linear arrays. Simulation results for non-uniform spacing with uniform and non-uniform excitations applied across the array indicate that the trade-off curve between main beam width and side lobe level for uniform spacing arrays can be improved by introducing non-uniform spacing.     

Microwave hyperthermia induced by a phased interstitial antennaarray

An interstitial microwave antenna array for hyperthermia cancer treatment is investigated. The purpose is to generate both uniform and controlled nonuniform temperature distributions in biological tissue by modulating the phases of the signals applied to each antenna. The array has four antennas positioned on the corners of a 2 cm square. The distributions of absorbed power within the arrays are computed and then converted into temperature distributions through a heat conduction simulation. The temperature patterns over phantom muscle are presented in both the lateral plane (perpendicular to the antennas) and the axial plane (parallel to the antennas). It is found that by proper phase modulation of radiofrequency signals applied to each antenna, a uniform heating can be produced in the entire array volume     

Antenna Pattern Correction Technique Based on an Adaptive Array Algorithm

An antenna pattern correction technique is presented that is based on an adaptive array algorithm. In the method, the antenna pattern of the antenna under test (AUT) is measured several times at different positions in the quiet-zone. The corrected antenna pattern is obtained by taking a weighted average of the measured patterns. An array synthesis algorithm is employed for obtaining the averaging weights at each rotation angle of the AUT. The weights are adapted specifically for a given AUT. The adaptive array correction technique is demonstrated in a hologram based compact antenna test range (CATR) at 310 GHz with both a synthetic antenna and a physical test antenna. For verification, the accuracy provided by the adaptive array correction technique is compared to that provided by uniform weighting.     

幅相误差对阵列天线相位中心的影响分析

为精确预测阵列天线相位中心的特性, 研究了阵列口径的幅相误差对阵列天线相位中心的影响.对阵列天线相位中心的求解方法进行了简要论述, 得出了阵列天线相位中心的计算方法; 采用该方法对一个算例阵列进行仿真计算, 分别引入均匀分布和正态分布的幅相误差, 计算得出不同类型幅相误差造成的天线相位中心变化.分析计算结果可以得出, 幅相误差对阵列天线相位中心可造成显著影响, 并且该影响与幅相误差分布类型和误差限有关.该研究结论可用于指导高精度阵列天线的设计.     

A Near-Field Array of Yagi-Uda Antennas for Electromagnetic-Susceptibility Testing

In electromagnetic-susceptibility testing of electronic equipment, the ideal incident field is a plane wave. To approximate this condition, a seven-element array of Yagi-Uda antennas has been constructed and tested at a frequency of 500 MHz. The element weightings are determined by a near-field synthesis technique, which optimizes the uniformity of the field throughout a rectangular test volume in the near field of the array. The amplitude and phase of the electric field have been measured throughout the test volume with a short-dipole probe, and the agreement with the theory is excellent.     

平面波谱恢复算法在平面近场测量中的应用

介绍用于天线平面近场测量的一种近远场变换新算法。该法利用被测天线的平面波谱和口径场幅相分布之间的关系,以及天线口面的约束条件,用G-P迭代算法从平面波谱的置信谱域部分恢复出置信谱域外的平面波谱。这种方法减小了较小截断角下有限扫描面对测量精度的影响,并提高了天线近场测量的效率。