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     

FFT applications to plane-polar near-field antenna measurements

The four-point bivariate Lagrange interpolation algorithm was applied to near-field antenna data measured in a plane-polar facility. The results were sufficiently accurate to permit the use of the FFT (fast Fourier transform) algorithm to calculate the far-field patterns of the antenna. Good agreement was obtained between the far-field patterns as calculated by the Jacobi-Bessel and the FFT algorithms. The significant advantage in using the FFT is in the calculation of the principal plane cuts, which may be made very quickly. Also, the application of the FFT algorithm directly to the near-field data was used to perform surface holographic diagnosis of a reflector antenna. The effects due to the focusing of the emergent beam from the reflector, as well as the effects of the information in the wide-angle regions, are shown. The use of the plane-polar near-field antenna test range has therefore been expanded to include these useful FFT applications     

Recent experimental results in near-field antenna measurements

Recent experimental results on determination of antenna pattern and power gain from near-field measurements are described. Two new antenna measurement theorems were applied. Measurements were made on an electrically large horn lens, a standard-gain horn and a nominal duplicate of the measuring antenna. Some comparisons with direct far-field measurement results were made.     

Determination of far-field antenna patterns from near-field measurements

In many cases, it is impractical or impossible to make antenna pattern measurements on a conventional far-field range; the distance to the radiating far field may be too long, it may be impractical to move the antenna from its operating environment to an antenna range, or the desired amount of pattern data may require too much time on a far-field range. For these and other reasons, it is often desirable or necessary to determine far-field antenna patterns from measurements made in the radiating near-field region; three basic techniques for accomplishing this have proven to be successful. In the first technique, the aperture phase and amplitude distributions are sampled by a scanning field probe, and then the measured distributions are transformed to the far field. In the second technique, a plane wave that is approximately uniform in amplitude is created by a feed and large reflector in the immediate vicinity of the test antenna. And in the third technique, the test antenna is focused within the radiating near-field region, patterns are measured at the reduced range, and then the antenna is refocused to infinity. Each of these techniques is discussed, and the various advantages and limitations of each technique are presented.     

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.     

An offset dual-reflector antenna shaped from near-field measurements of the feed horn: Theoretical calculations and measurements

A synthesizing procedure for shaping dual-reflector offset antennas is described. The synthesis is based on geometrical optics and near-field measurements of amplitude and phase from the feed element. The procedure preserves good symmetry in mapping from feed to aperture which results in minimal distortions of the electrical characteristics of the antenna. A 1.8 m antenna has been manufactured and measured at 12 GHz. The radiation pattern is characterized by low sidelobes and cross polarization introduced by the offset geometry below -50 dB.     

Correction of near-field antenna measurements made with an arbitrary but known measuring antenna

We describe a technique for rigorously correcting for the effects of an arbitrary but known measuring antenna (or `probe?) in determination of vectorial far-field antenna pattern and power-gain function from near-field measurements.     

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.     

Displacement errors in antenna near-field measurements and theireffect on the far field

The effects of probe displacement errors in the near-field measurement procedure on the far-field spectrum are studied. Expressions are derived for the displacement error functions that maximize the fractional error in the spectrum for both the on-axis and off-axis directions. The x- y- and z-displacement error in planar scanning are studied and the results are generalized to errors in spherical scanning. Some simple near-field models are used to obtain order-of-magnitude estimates for the fractional error as a function of relevant scale lengths of the near-field, defined as the lengths over which significant variations occur     

Control of scattering from probes for near-field antenna measurements by use of skirt

A novel approach to reducing the multiple reflections between the test antenna and the probe in near-field antenna measurements is proposed. Instead of absorbers, this approach makes use of a skirt on the probe to shield against the mounting structure behind the probe.     

An overview of fractal antenna engineering research

Recent efforts by several researchers around the world to combine fractal geometry with electromagnetic theory have led to a plethora of new and innovative antenna designs. In this report, we provide a comprehensive overview of recent developments in the rapidly growing field of fractal antenna engineering. Fractal antenna engineering research has been primarily focused in two areas: the first deals with the analysis and design of fractal antenna elements, and the second concerns the application of fractal concepts to the design of antenna arrays. Fractals have no characteristic size, and are generally composed of many copies of themselves at different scales. These unique properties of fractals have been exploited in order to develop a new class of antenna-element designs that are multi-band and/or compact in size. On the other hand, fractal arrays are a subset of thinned arrays, and have been shown to possess several highly desirable properties, including multi-band performance, low sidelobe levels, and the ability to develop rapid beamforming algorithms based on the recursive nature of fractals. Fractal elements and arrays are also ideal candidates for use in reconfigurable systems. Finally, we provide a brief summary of recent work in the related area of fractal frequency-selective surfaces.     

扫描波束天线无相位近场测量技术

以寻找高频扫描波束天线近场测量方法为目的, 提出了一种结合差分进化算法和迭代傅里叶变换算法的双平面无相位近场测量方法.首先用线极化探头在近区采集正交方向切向场幅值信息; 其次使用差分进化算法寻找合适的初始迭代相位; 再利用迭代傅里叶变换算法对一扫描面上的相位进行还原; 最后使用采样幅值和还原相位结合近远场变换理论求得天线远场方向图.为验证方法可行性, 以对称振子天线阵为模型, 对不同扫描角时的测量过程进行仿真, 均获得良好结果.     

Applications of probe-compensated near-field measurements

The theory of near-field measurements for antenna practitioners is summarized, and the measurement procedures in three coordinate systems, namely rectangular, cylindrical, and spherical are outlined. Specific topics include probe characterization, measurement systems, data reduction, and attendant accuracies. The results of recent studies are also summarized, and some brief remarks on future applications of near-field measurements in the laboratory, the production line, and in field testing and evaluation conclude the paper.     

High-precision outdoor cylindrical near-field antenna test facility

A new antenna test range is described. Although the facility is located outdoors, it allows precision probing of the cylindrical near-field of large and very complex antenna systems, with turning diameters up to 20 m and frequencies up to 20 GHz. The facility includes a 36 m high concrete scanner tower with low radar cross-section. Other significant features of the facility are the comprehensive air-conditioning system for all accuracy-dependent components, a permanent auto-alignment system, which ensures precision cylindrical measurements, and an interleaved high-speed data collection system, which delivers high-speed data collection within a minimum time frame. Test results, including a comparison with the patterns of a reference antenna measured on two other ranges, demonstrate the measurement integrity of the new facility     

An approximate expression to estimate signal-to-noise ratioimprovement in cylindrical near-field measurements

A very simple approximate expression for the process gain (PG) for the cylindrical case is derived. The different approximations and assumptions required to obtain this expression are shown. This expression might be useful for most practical cylindrical near-field measurements, providing a very simple mean to assess the near-field dynamic range requirements to obtain a desired far-field signal-to-noise ratio (SNR)     

Basic theory of probe-compensated near-field measurements

The general problem concerning the interaction of a probe antenna with the near field of an arbitrary antenna is considered. The application of the Lorentz reciprocity theorem to the problem of determining antenna characteristics, including the far-field pattern, is presented. The data required to correct for the directional effects of the probe, the effect of probe correction on the measured data, and the attendant mathematical computations in rectangular systems are described. Extensions to cylindrical and spherical systems are discussed.     

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.     

Segmented loop antenna for UHF near-field RFID applications

A segmented loop antenna is presented for ultra-high frequency (UHF) near-field radio frequency identification (RFID) applications. The proposed segmented configuration makes the current along the loop remain in-phase even though the perimeter of the loop is comparable to the operating wavelength, so that a strong and uniform magnetic field is generated in the region surrounding the antenna. The antenna printed on a FR4 printed circuit board (PCB) with an overall size of 160 x 180 x 0.5 mm achieves good impedance matching and uniform magnetic field distribution over an operating bandwidth of 800?1040 MHz, which is desirable for UHF near-field RFID reader applications.