Probe correction of spherical near-field measurements

Probe correction has been implemented in a computer program which calculates antenna far fields from spherical nearfield measurements. The computer program has been applied to near-field measurements on a satellite model, and the accuracy of the computed far field is significantly improved, compared with the results obtained without probe correction.     

一种减小相控阵天线球面近场测量截断误差的方法

在相控阵天线球面近场测量中,有限扫描面和相控阵天线波束扫描将会引起较大的截断误差.为了解决这一问题,提出利用基于遗传算法参数优化的余弦窗函数对近场数据进行加权处理的方法来有效减小截断误差.以半波振子组成的矩形平面阵作为待测天线,对相控阵天线球面近场测量进行了计算机模拟.模拟结果表明,通过对近场数据进行加余弦窗的处理并用遗传算法对参数进行优化能够大大减小相控阵天线波束扫描时的有限扫描面截断误差,从而证实了文中所提出方法的正确性和有效性.     

Real-time spherical near-field handset antenna measurements

A new spherical near-field measurement system, dedicated to personal-communications applications, has been installed at e-tenna Corporation. The system, sold by Satimo, uses an electronically scanned probe array, and offers a dramatic reduction of the measurement time (by a factor ranging from 60 to 1,000) with respect to conventional mechanical scanners. This test range has undergone extensive acceptance testing, which has verified the specified measurement accuracy. The speed of the system, combined with the availability of full-sphere measurement data, enables rapid measurement of antenna efficiency. The system also enables the measurement of other parameters, such as the percentage of radiated power dissipated into the body of a human test subject operating a cellular telephone     

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。     

Far-field patterns of spaceborne antennas from plane-polar near-field measurements

Certain unique features of a recently constructed plane-polar near-field measurement facility for determining the far-field patterns of large and fragile spaceborne antennas are described. In this facility, the horizontally positioned antenna rotates about its axis while the measuring probe is advanced incrementally in a fixed radial direction. The near-field measured data is then processed using a Jacobi-Bessel expansion to obtain the antenna far fields. A summary of the measurement and computational steps is given. Comparisons between the outdoor far-field measurements and the constructed far-field patterns from the near-field measured data are provided for different antenna sizes and frequencies. Application of the substitution method for the absolute gain measurement is discussed. In particular, results are shown for the 4.8-m mesh-deployable high-gain antenna of the Galileo spacecraft which has the mission of orbiting Jupiter in 1988.     

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     

Suppression of reflections by directive probes in spherical near-field measurements

The influence of probe correction in spherical near-field measurements on signals from outside the test volume is investigated theoretically and experimentally. It is found that the suppression of reflections obtained by a directive probe is not disturbed by the probe correction. A geometric relation between the antenna "minimum sphere" and the probe pattern beamwidth is established, whose satisfaction guarantees the absence of numerical instabilities in the far-field computation. The condition is sufficient, but not necessary if the "minimum sphere" of the antenna is in the near field of the probe.     

Solutions to spherical anisotropic antennas

An exact solution is found for the fields of a spherical antenna with an anisotropic surface. The surface, for which a rather simple solution is found, conducts perfectly only along spiral lines which go from pole to pole, and is otherwise nonconducting. The antenna is either excited by fields at a gap around the equator or at low frequencies between adjacent spirals. The method of solution is described, and results of several representative cases are presented.     

A brief history of near-field measurements of antennas at theNational Bureau of Standards

The US National Bureau of Standards (NBS) played a pioneering role in the development of practical planar near-field antenna measurement techniques. A brief history is presented of that role, which began with theoretical studies to determine corrections for diffraction in a microwave measurement of the speed of light. NBS contributions to the development of nonplanar near-field measurement theory and practice are also described     

随机误差对超低副瓣天线平面近场测量的影响

导出了平面近场测量中近场幅相随机误差所引起的误差谱的解析表达式。利用计算机模拟和统计平均的方法研究了近场幅相随机误差对超低副瓣天线平面近场测量结果的影响 ,并给出不同口径尺寸的超低副瓣天线的平面近场测量 ,为保证- 5 5 d B副瓣± 5 d B的测试精度 ,所能允许的近场幅相随机误差的最大起伏度     

Simplified approach to probe-corrected spherical near-field scanning

A multipole representation for the response of an arbitrary receiving antenna is derived that allows the formulation of probe-corrected spherical near-field scanning simply in terms of conventional vector spherical harmonics. Both the representation and formulation are free of rotational and translational addition theorems. A sampling theorem derived for Legendre functions is used to evaluate the resulting orthogonality integrals by direct summation in a computer time proportional to (ka)3.     

墙壁散射对超低副瓣天线平面近场测量的影响

以二维问题为例，基于平面波谱展开理论和几何光学近似，利用计算机模拟的方法研究了暗室墙壁散射对超低副瓣天线平面近场测量的影响，得到了一些基本的规律和有用的结果。     

The efficiency of near-field Cassegrainian antennas

The aperture efficiency of a near-field Cassegrainian antenna is approximated with a Fresnel field analysis. Curves are presented which give the efficiency of the system in terms of the amplitude distribution on the feed aperture and the Raleigh distance to the subreflector. It is found that separation between feed aperture and subreflector can be as great asfrac{1}{2}d^{2}/lambdawithout excessive loss.     

窗函数在相控阵天线平面近场测量中的应用

有限扫描面截断是影响天线平面近场测量精度的主要误差源之一，尤其是对于波束扫描的相控阵天线的平面近场测量更是如此。为了减小相控阵天线平面近场测量中的有限扫描面截断误差，介绍了余弦窗函数并将其应用到相控阵天线平面近场测量中。计算机模拟结果表明，通过对近场进行加余弦窗的数据处理能够有效地减小有限扫描面截断误差。提出了对近场数据进行加余弦窗处理的适用条件。     

Waveguide-fed spherical dielectric antennas

The results of an experimental investigation into the radiation properties of circular waveguide excited dielectric sphere antennas are reported. The input waveguide had a plain end without a flange or ground plane. The input voltage standing-wave ratio varied from about 1.1 to 2.5 for the sphere sizes used but can usually be reduced to about 1.25 over the 8-12 GHz band by separating the sphere from the waveguide. Separation increases the on-axis gain by 1-3 dB and produces nearly equal beamwidths in bothE- andH- planes. Phase front measurements located a fixed phase center near the end of the waveguide.     

Truncated spherical helical antennas

The truncated spherical helix is presented as a compact circularly polarised antenna with relatively high gain and moderate bandwidth. A numerical investigation into the radiation properties of this antenna is also presented. The antenna provides a directivity of >9 dB and an axial ratio of <3 dB over a 10% bandwidth. The radiation pattern has a broad main beam and better than 20 dB front-to-back ratio     

Evaluating near-field radiation patterns of commercial antennas

A source reconstruction technique from the measured near fields is proposed to obtain a set of equivalent currents that will characterize the forward and backward radiation patterns of an antenna. Once the equivalent sources are determined, the electromagnetic field at any aspect angle and distance from the antenna can be calculated. In this paper, the method is applied to the evaluation of the radiation from commercial antennas at any observation point. The electric field patterns of a DCS base station antenna at 1800 MHz and a horn antenna at 2500 MHz have been calculated and plotted at several distances from the antenna. This method can be used in characterizing the "reference volumes" or exclusion zones for transmitting antennas dealing with the maximum levels of electromagnetic radiation safe for human exposure, as stated in many national and international regulations.     

Waveguide-fed dielectric spherical antennas

A theoretical method is presented for obtaining the far-field patterns of a feed structure consisting of a homogeneous dielectric sphere placed in front of, but displaced from, the open end of a circular waveguide carrying the TE11 mode. Such a feed, for an optimum value of the sphere offset, has a reduced input v.s.w.r., as indicated experimentally elsewhere. Theoretical expressions are derived for the radiated far-field components of this type of a feed and the results are compared with the experimental data obtained from the test feeds