超低副瓣天线平面近场测量取样方式的新准则

采用实验的方法给出了用平面近场技术测量超低副瓣天线时收发天线之间的近区测试距离以及取样密度的选取准则 ,提出了超低副瓣天线测量对测试系统温度漂移的要求 ,并给出了满足系统温度漂移要求的测试方式。依据新的选取准则 ,实测了最佳角锥喇叭和波纹喇叭天线的 E面方向图。测试结果说明 ,该选取准则具有良好的重复性 ,且重复精度为 60 d B± 2 d B     

Aperture sampling requirements in planar near-field and patterncalculations

The paper covers a simple idea. If we sample an aperture, we can obtain valid patterns over a limited angular region about the normal to the aperture. The same expression can be used with near-field measurements. I reduced the expression to a nomograph. A nomograph allows one to rapidly test various choices. In the second half of the paper, I answer questions caused by the February column which discussed polarization (Milligan, IEEE Antennas. Propag. Mag., vol.38, no.1, p.56-8, 1996)     

模式滤波技术在平面近场天线测量中的应用

为了修正平面近场测量中的多次反射误差,介绍了模式滤波修正技术在平面近场测量中的应用,提出了一种合适的模式滤波函数.推导出模式滤波修正技术的相关公式并进行了数值仿真,仿真结果表明通过利用模式滤波技术对平面近场天线测量结果进行后处理能够有效地改善测量结果.     

Alignment procedures for planar near-field positioners

The alignment of a planar near-field scanner is important for achieving low phase error in measurements and, hence, good pattern data. Non-planarity phase errors can be measured and removed in the data-collection software. However, better mechanical alignment translates into better sidelobe measurements and a higher frequency of operation. This paper describes a procedure for installation and alignment of a planar-scanner positioner, and illustrates the procedure using a box-frame-type scanner. Alignment of the scan plane is independent of the drive system used, since the positional errors associated with the drive system are defined as positional errors     

Error analysis techniques for planar near-field measurements

A combination of techniques is described for reliably estimating the magnitude of each error arising in planar near-field measurements. They include mathematical analysis, computer simulation, and measurement tests. There are three primary applications for these tests: in designing a measurement facility, the requirements of each part of the measurement system can be specified to meet a given level of accuracy; during actual measurements, the experimenter can identify, and reduce where necessary, potential sources of error in the measurement; and when a measurement has been completed, the estimated uncertainty in the measurement can be obtained with confidence and ease. The latter application has been used in many measurements to verify that the planar near-field technique produces high-accuracy results competitive with any other measurement technique     

The bi-polar planar near-field measurement technique, part II:near-field to far-field transformation and holographic imaging methods

A novel customized bi-polar planar near-field measurement technique is presented in a two-part paper. This bipolar technique offers a large scan plane size with minimal “real-estate” requirements and a simple mechanical implementation, requiring only rotational motions, resulting in a highly accurate and cost-effective antenna measurement and diagnostic system. Part I of this two-part paper introduced the bi-polar planar near-field measurement concept, discussed the implementation of this technique at the University of California, Los Angeles (UCLA), and provided a comparative survey of measured results. This paper examines the data processing algorithms that have been developed and customized to exploit the unique features of the bi-polar planar near-field measurement technique. Near-field to far-field transformation algorithms investigated include both interpolatory and non-interpolatory algorithms due to the a typical arrangement of the bi-polar near-field samples. The algorithms which have been tailored for the bi-polar configuration include the optimal sampling interpolation (OSI)/fast Fourier transform (FFT), Jacobi-Bessel transform, and Fourier-Bessel transform. Additionally, holographic imaging for determination of antenna aperture fields has been incorporated to facilitate antenna diagnostics. Results for a simulated measurement of an array of infinitesimal dipoles and a measured waveguide-fed slot array antenna are included. Appropriate guidelines with respect to the advantages and disadvantages of the various processing algorithms are provided     

Numerical beam alignment procedure for planar near-field phaseretrieval

The authors demonstrate mathematically that the direction of an antenna beam (antenna pointing) can be determined by the centre-of-gravity of its beam intensity. The technique is validated using measurements on a 1.118 m 94 GHz Cassegrain reflector and is seen as pivotal in the future application of the phase retrieval technique for near-field/far-field prediction     

Scan-plane reduction techniques for planar near-field antenna measurements

In this work, two planar near-field scan-plane reduction techniques are considered and results are presented. It is shown how truncation based on field-intensity contours, instead of simple geometric truncation, can in some cases improve the efficiency of the truncation process. Both techniques are applied to measured data sets, and it is shown how these methods can be used to reduce data-acquisition times, while also assessing the impact of the total acquisition surface reduction on the far-field radiation-pattern integrity.     

Electro-optic near-field mapping of planar resonators

A comprehensive experimental and theoretical study for the determination of the electric near-field above planar resonators is presented. The transverse component of the electric field is mapped by external electro-optic (EO) sampling technique with high spatial and temporal resolution. The evolution of the near-field radiation pattern of the investigated 7-GHz planar resonator to the onset of the far-field pattern is traced by measurements at various heights above the sample. Frequency-dependent measurements allow to characterize the field pattern changes when the frequency is swept through the main resonance. Additional undesired resonances are identified by the detected mode pattern. The experimental data are reproduced by simulations based upon an electric field integral equation (EFIE) method     

Simple accurate expressions for planar spiral inductances

We present several new simple and accurate expressions for the DC inductance of square, hexagonal, octagonal, and circular spiral inductors. We evaluate the accuracy of our expressions, as well as several previously published inductance expressions, in two ways: by comparison with three-dimensional field solver predictions and by comparison with our own measurements, and also previously published measurements. Our simple expression matches the field solver inductance values typically within around 3%, about an order of magnitude better than the previously published expressions, which have typical errors ground 20% (or more). Comparison with measured values gives similar results: our expressions (and, indeed, the field solver results) match within around 5%, compared to errors of around 20% for the previously published expressions. (We believe most of the additional errors in the comparison to published measured values is due to the variety of experimental conditions under which the inductance was measured.) Our simple expressions are accurate enough for design and optimization of inductors or of circuits incorporating inductors. Indeed, since inductor tolerance is typically on the order of several percent, “more accurate” expressions are not really needed in practice     

平面近远场变换的快速算法

基于考虑探头补偿的平面近远场变换理论 ,根据实际需要 ,提出了一种工程实用的平面近远场变换快速算法。通过该算法由近场测量数据变换得到的天线远场方向图 ,既能达到任意分辨率 ,又能节约计算内存和提高计算速度。     

Spatial sampling and filtering in near-field measurements

A sample spacing criterion and a data minimization technique for measurements made over the surface of a plane in the near field of an antenna are presented. The sample spacing is shown to depend on the distance from the antenna to the measurement plane, and on the extent to which evanescent waves can be neglected. The near-field data minimization technique utilizes two-dimensional spatial filtering to effect a significant reduction in computational effort required to calculate selected portions of the far-field pattern. Far-field patterns of anXband antenna calculated from near-field measurements are presented and compared with those measured on a standard far-field range. The far-field calculations are repeated for several near-field sample spacings and for various post-filter sample rates.     

A new planar feed for slot spiral antennas

A new planar, wideband feed for a slot spiral antenna is presented and tested at VHF frequencies. Radiation pattern measurements are presented to demonstrate the performance and usefulness of this feed. In contrast to most traditional printed spiral antenna designs, the one presented here incorporates a completely planar balun and feed, making it more attractive for conformal applications     

Effect of random errors in planar near-field measurement

Expressions that relate the signal-to-noise ratio in the near field to the signal-to-noise ratio in the far field are developed. The expressions are then used to predict errors in far-field patterns obtained from near-field data. A technique for measuring the noise in the calculated far-field pattern by calculating the spectrum in the evanescent region from a single-dimensional oversampled scan is also described     

近场测量相控阵天线的全息成像方法

研究了一种利用近场测量技术全息成像相控阵天线口径幅相的方法。该方法是把近场测量获得的方向图函数与由单元形式及幅相分布表示的方向图函数进行比较,采用FFT算法和空间域的Fourier重构法,可以快速、精确地成像出相控阵天线口径的“全息图”,进而诊断出阵中单元幅相的奇异程度。通过仿真实验,检验了该方法的成像分辨率和精度,并考察了不同口径区域的成像误差对辐射方向图的影响程度,说明该具有非常好的应用前景。     

Antenna coupling and near-field sampling in plane-polar coordinates

A probe-corrected vector transmission formula and a rigorous sampling-reconstruction theorem for near-field antenna measurements in plane-polar coordinates are derived from three fundamental theorems of antenna theory: the mutual coupling function between two antennas satisfies the homogeneous wave equation; a receiving antenna can be represented as a differentiator of the incident field; and the mutual coupling function is virtually bandlimited. The rigorous sampling equations are applied to compute the far fields of a circular-aperture antenna sampled in the near field at half-wavelength radial spacing     

一种修正平面近场测量中探头位置误差的有效算法

该文提出了一种修正平面近场测量中探头位置误差的算法,并进行了计算机模拟。计算结果表明,所提出的修正算法收敛速度快、数值稳定性好、计算精度高,是一种实用而有效的修正平面近场测量中探头位置误差的方法。     

Phaseless bi-polar planar near-field measurements and diagnosticsof array antennas

Antenna near-field measurements typically require very accurate measurement of the near-field phase. There are applications where an accurate phase measurement may not be practically achievable. Phaseless measurements are beginning to emerge as an alternative microwave antenna measurements technique when phase cannot be directly measured. There are many important aspects for successful implementation of a phaseless measurement algorithm. This paper presents appropriate phaseless measurement requirements and a phase retrieval algorithm tailored for the bi-polar planar near-field antenna measurement technique. Two amplitude measurements and a squared amplitude optimal sampling interpolation method are integrated with an iterative Fourier procedure to first retrieve the phase information and then construct both the far-field pattern and diagnostic characteristics of the antenna under test. In order to critically examine the methodologies developed in this paper, phaseless measurement results for two different array antennas are presented and compared to results obtained when the near-field amplitude and phase are directly measured     

Prediction of far-field from uniform and non-uniform under-sampled near-field data in planar near-field antenna measurements

In near-field antenna measurements various forms of uniform and non-uniform sampling techniques have been widely deployed. Considering the fact that the near-field pattern of any antenna is a spatially quasi-band-width-limited function of space coordinates, Shannon's theorem simply defines the sampling frequency. Based on the sampling theorem, in order to precisely reconstruct a band-limited signal from its samples, the sampling frequency must be at least twice as much as the signal's bandwidth. Through the simulations and theoretical evaluations this research shows that if the near-field pattern is either uniformly or non-uniformly under-sampled due to any practical reasons, yet a good estimation of far-field pattern can be obtained especially if the antenna under test (AUT) is a directive high-gain or super high-gain antenna. Also the time efficiency of far-field prediction from under-sampled near-field data is discussed and the advantages and disadvantages are highlighted.