Near-field Measurement System Research Articles

Conical Near-Field Antenna Measurements [AMTA Corner

A near-field measurement technique for the prediction of asymptotic far-field antenna patterns from data obtained from a modified cylindrical or plane-polar near-field measurement system is presented. This technique utilizes a simple change in facility alignment to enable near-field data to be taken over the surface of a conceptual right cone [1, 2], or right conic frustum [3, 4], thereby allowing existing facilities to characterize wide-angle antenna performance in situations where hitherto they would perhaps have been limited by truncation. This paper aims to introduce the measurement technique, and to describe the novel probe-corrected near-field-to-far-field transform algorithm. The algorithm is based upon a cylindrical-mode expansion of the measured fields. Preliminary results of both computational electromagnetic simulations and actual range measurements are presented. As this paper recounts the progress of ongoing research, it concludes with a discussion of the remaining outstanding issues, and presents an overview of the planned future work.

Near-field beam pattern measurement of qualification model of ALMA band 8 (385–500 GHz) cartridge receiver

We have developed a near-field vector beam measurement system covering the range of frequencies from 385 to 500 GHz. The measurement set-up is capable of measurements with dynamic range exceeding 50 dB and amplitude and phase stability respectively of 0.1 dB/h and 1 degree/5 min at room temperature. Beam patterns of the ALMA band 8 corrugated horns and receiver optics block were measured at room temperature and lately compared with physical optics calculations obtained in the far-field. Both co-polar and cross-polar beam patterns of a qualification model of the ALMA band 8 cartridge cooled in a cartridge-test-cryostat have also been measured in the near-field as a detector of a submillimeter vector network analyzer. The measurements presented in this work refer to the lowest, middle and upper frequencies of band 8. The comparisons between software model and experimental measurements at these frequencies show good agreement down to −30 dB for the main polarization component. The cross-polarization level of the beam propagating through the receiver optics block was also characterized. We found that a cross-polarization level better than −28 dB can be achieved at all measured frequencies. The measured beam pattern of this receiver corresponds to efficiency of greater than 92% at the sub reflector (diameter of 750 mm) of the ALMA 12 m optics.

Conical near-field antenna measurement system

A probe-compensated near-field-to-far-field-transform algorithm has been developed that can generate far-field patterns from near-field measurements made on an arbitrary surface. We present the concept, the algorithm, and computer-simulated and measured test results for measurements on a conical surface. The prototype conical near-field measurements were made in a planar near-field range on a horn antenna under test (AUT), mounted on an azimuth-over-elevation positioner to produce a conical measurement surface. This system is especially applicable for producing full-hemisphere far-field patterns for antennas mounted on vehicles, where other standard measurement systems may not adapt well to the profile, may not provide full-hemisphere coverage, or may require large, mechanically complex systems.

A novel portable bipolar near-field measurement system for millimeter-wave antennas: construction, development, and verification

As new antenna designs require higher frequencies and smaller sizes, traditional large-scale antenna measurement systems become ill-suited for such measurements. External mixing, room-sized chambers, and expensive test equipment add large costs and burdens to antenna measurement systems. A smaller and more cost-effective system is presented in this paper. Using the bipolar planar scanning technique developed at UCLA, a portable millimeter-wave antenna measurement system has recently been constructed. The system was designed to fit on the end of a standard optical table, and enjoys the spacesaving and accuracy inherent to the bipolar planar configuration. Simple construction of the chamber allows for relatively easy assembly and disassembly, and allows movement of the system from one table to another, if needed. Antennas of diameters up to 24 in can be accommodated, and scan planes of up to a diameter of 60 in can be measured. Millimeter-wave frequencies from around 30 GHz to 67 GHz can be measured, with potential extension to higher frequencies. Planar nearfield-to-far-field techniques are used to construct the antenna's far-field patterns from the measured near field. In particular, the post processing follows the OSI/EFT method for pattern reconstruction and diagnostics. The design of the scanner configuration allows the incorporation of the phase-retrieval techniques developed for the bipolar configuration. These phaseless measurements allow the use of scalar millimeter-wave test equipment, with much lower cost than comparable vector test equipment.

The ALMA Front End Optics—System Aspects and European Measurement Results

The Atacama large millimeter/submillimeter array (ALMA) is a radio telescope array with 50 Cassegrain style antennas that is currently being built in the Atacama desert in Chile. The telescopes are designed for a frequency range from 30 to 960 GHz with two orthogonal linear polarizations. Due to the extremely wide range, ten receivers are needed to cover the band, the divisions coinciding with the atmospheric windows. All receivers are built into a common cryostat on separate cartridges. The front end optics include the optical elements between the mixers and the secondary reflector. There are three different generic optical layouts. The two lower frequency bands use lenses that double as vacuum breaks. The next two frequency bands use ambient-temperature mirror systema and the upper six frequency bands have their complete optics cooled to cryogenic temperatures. In addition to the very demanding performance requirements, the optics design needs to take into account the constructional and operational aspects. As a large number of front ends will be built, the design must be robust with respect to mechanical and alignment tolerances. The exchange of receivers must be easy and should require as few alignments as possible. During operation, no mechanical adjustments are allowed. Measurement results are shown for the ALMA baseline bands. These measurements were made for single cartridges with the IRAM near-field measurement system and at SRON. The results of these measurements validate the design approach.

Submillimeter-Wave Phasor Beam-Pattern Measurement Based on Two-Stage Heterodyne Mixing With Unitary Harmonic Difference

A near-field phasor beam measurement system is developed for the characterization of heterodyne receiver optics at submillimeter-wave frequencies. The system synthesizes a pair of submillimeter-wave signals as the RF and local oscillator (LO) sources from common reference sources. The synthesized harmonic numbers of the RF and LO sources are arranged with difference by one, which makes this a new configuration with a unitary harmonic difference. The coherent RF and LO signal are down-converted by the receiver under test, then mixed with the microwave-frequency common reference signal to generate the second-order IF signal around 100 MHz for amplitude and phase comparison. The amplitude and phase fluctuation of the measurement system at 683 GHz is within plusmn0.2 dB and plusmn4deg in a 1-h period, respectively. The system dynamic range at 683 and 250 GHz can be as high as 43 and 47 dB, respectively. The system is then used to measure the receiver beam patterns at 683 and 250 GHz with different RF transmitting probe antennas.

Electromagnetic interference shielding effect of nanocomposites with carbon nanotube and shape memory polymer

The nanocomposites with carbon nanotubes (CNTs) and shape memory polymer (SMP) were developed for electrical applications. The specimens with different CNTs weight fractions were prepared. Their electrical resistivities and electromagnetic interference (EMI) shielding effectiveness (SE) were investigated. The electrical resistivity was examined by four-probe method at different testing temperatures of 25, 35, 45, 55 and 65 °C around glass transfer temperature ( T g). As a result, for the developed nanocomposites, even lower weight fraction of CNTs could achieve a high level of conductivity and a low percolation threshold for CNTs content was confirmed. The electrical resistivity for the developed nanocomposites is dependant obviously on temperature with a linear relation like metals. The interconnected conducting network was formed more easily than other fillers. For the EMI SE measurements, a near-field antenna measurement system was used. The experiments to evaluate EMI SE were carried out in three different frequency bands, 8–26.5 GHz (K band), 33–50 GHz (Q band) and 50–75 GHz (V band). The EMI SE of CNT/SMP nanocomposites have a strong dependence of carbon nanotube content and the specimen thickness at all of three frequency bands. The higher frequency, the larger EMI SE. For the materials with 5.5 wt% VGCFs both experiment and analysis will agree well, and theoretical prediction proposed for EMI SE may be useful.

Truncation Errors Quantitative Analysis For Planar Near-Field Measurement of the Millimeter Wave Antenna

The error analyses on planar near-field measurement system of millimeter wave antenna are described.The effect of the position,shape and area of the truncation planar on the measured errors is proposed,and the error equation of the truncation error is deduced to provide a quantitative analysis.Finally,the related computer simulations are carried out.

Accurate Magnified Near-Field Measurement of Optical Waveguides Using a Calibrated CCD Camera

A fast and accurate magnified near-field (NF) measurement technique that employs a charge-coupled device (CCD) camera is described to measure the two-dimensional (2-D) intensity distributions of optical waveguides with arbitrary refractive-index profiles. Calibration of the InGaAs CCD camera used in the system is essential in terms of correction for bad pixels, linearity, and uniformity in order to obtain accurate results. The magnification factor of the system is obtained using a calibrated optical dimensional standard. The NF measurement system with the calibrated CCD camera is validated from the mode field diameter (MFD) measured for six single-mode fibers with different refractive-index profiles. The MFD results from the magnified NF technique exhibit good agreement with those obtained from the far-field scanning technique to within 2.3%. An error of about 15% in the MFD would result if corrections to the CCD camera were not applied to the raw measured data. The refractive-index profiles computed from the measured data for a single-mode fiber and a Ti:LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> waveguide are also presented. The radial-index profile of the fiber exhibits good agreement with the profile measured from the refracted NF technique

ANTENNA TIME DOMAIN PLANAR NEAR FIELD MEASUREMENT SYSTEM

Antenna time domain planar near field measurement is a new Ultra-WideBand (UWB) technology for getting Antenna Under Test (AUT)'s time or frequency domain radiant characteristics within a wide frequency band. In this paper, besides introducing basic theories and technologies, we have developed an antenna time domain planar near-field measurement system and showed from measurement results, the validity of our theories and the feasibility of our system.

GUEST EDITORIAL: "SPECIAL ISSUE: ULTRA-WIDEBAND ANTENNAS AND PROPAGATION"

In February 2002, the Federal Communications Commission (FCC) released the unlicensed frequency band of 3.1–10.6 GHz for commercial applications. This has greatly spurred the development of commercial ultra-wideband (UWB) communications systems and devices worldwide. Due to the extremely wide spectrum, the UWB-based systems have the potential to achieve high data rate in the order of 500Mbps up to even Gbps. On the other hand, in the low power and low data rate applications, the research and development effort has been focused on high accuracy localization or positioning systems. In UWB technology, to cater for the increase in transmission speed, reduction in power consumption and transceiver cost, a comprehensive investigation of UWB system issues, RF circuitry, antenna design, and propagation characteristics must be carried out. This Special Issue with eight strictly selected papers presents advanced progress in research and development of Antennas and Propagation for promising UWB applications. We have to mention here that the response from the community to this Special Issue is pretty good after the call for paper was announced for only six months, and we received 16 very high quality papers. The contributions cover almost all topics related to UWB antennas and propagation. Unfortunately, due to the limited space available, we have to make a very hard decision to include only eight of them in this Special Issue. Some of them have been recommended for possible publication as regular papers in International Journal of Wireless and Optical Communications in the future. The major content of the eight papers in this Special Issue can be summarized below. The first paper entitled “Antenna Time Domain Planar Near-field Measurement System” by N. Wang et al. reports on the advanced progress in development of time-domain near-field measurement. Such time-domain near-field measurement technology is the key to obtain antenna under test’s (AUT) far-field radiation patterns in frequency domain by Fourier transforming the far-field in time domain which is the outcome of transform of near-field far-field and time domain probe correction. The work started in 1996 and has been focused on developing software for general measurement system design, such as system control, time domain sampling, frequency domain probe correction, near-field far-field transform, results correction and analysis. In 2003, the authors built the first antenna time

Spatial Power Divider/Combiner in&amp;lt;tex&amp;gt;$D$&amp;lt;/tex&amp;gt;-Band

Five-element spatial power divider/combiners have been realized at 150 GHz. Holography is applied to couple the field pattern of an in-line rectangular horn antenna array to a pseudoplane wave. The hologram is realized as periodic phase grating. The transformation of the pseudoplane wave to a Gaussian beam is performed by phase modulation with a dual-offset reflector on the one hand, and a system of Fresnel lenses on the other hand. Both setups have been extensively examined. The analysis has been enhanced by a vector near-field measurement system. The comparison of the simulated and measured efficiencies, as well as field distributions shows good agreement.

The bi-polar near-field antenna measuring system at wroclaw university of technology

This paper presents a near-field antenna measurement system that was developed in-house. The capabilities of our bi-polar system were extended by a backward-projection processing of data. The amplitude and phase distribution within the array elements can thus be reconstructed. Major applications of the presented near-field system are in research on advanced beamforming, and in investigations into large-scale integration of lightweight arrays. The results presented were obtained for planar microstrip arrays, and for a phased array operating between 5 GHz and 12 GHz.

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.

Measurement of the backscatter from two pressure-release spheres using a near-field measurement system

The backscattering of sound by two pressure-release spheres was studied using a near-field measurement system (NFMS) based upon the near-field calibration array (NFCA) concept developed by Trott and Van Buren. The NFMS consists of a planar near-field transmit array (NFTA) consisting of 34 real-shaded line elements comprised of 26 hydrophones and a synthetic cylindrical aperture near-field receive array (SA-NFRA) consisting of a single line element comprised of 26 hydrophones. The line elements of the NFTA were shaded to obtain a volume of plane wave uniformity of 1 m3 in front of the NFTA. The synthetic aperture was formed by moving the single line element with a precision positioning system. The total acoustic pressure field was measured by the SA-NFRA. Since the incident pressure and the scattered overlapped in the time domain, background subtraction was used to obtain the scattered pressure. Far-field scattered beam patterns for the SA-NFRA were formed using the NFCA concept to extrapolate near-field measurements to the far field. Three configurations of pressure-release spheres were studied: a single sphere, two spheres arranged perpendicularly to incident field, and two spheres arranged parallel to the incident field. Experimental and numerical model results will be presented as well as NFTA uniformity measurements.

Evaluation of Bistatic Far-Field Quantities From Near-Field Measurements - Abstract

In this paper the relationship between the range-corrected far fields and the near field measurements is established. We propose methods to obtain far field quantities, including the bistatic RCS, bistatic range profiles, and bistatic images from near field measurements. We show how to obtain the Fourier space data in the Ewald sphere when the object is normally or obliquely illuminated and its scattered fields are received by a probe scanning over a planar aperture. We carry out a simulation of a near-field configuration and calculate near field data. From these data, we derive bistatic range profiles and reconstruct three-dimensional (3-D) bistatic images. We also implement a near-field measurement system and propose a calibration procedure so that the Fourier space data can be accurately obtained. A focused projective image has been reconstructed from near field data measured along one-dimensional scanning. Simulation and experimental results have verified the effectiveness of our algorithms.

Scanning near-field optical microscopy: transfer function and resolution limit

We present scanning near-field optical microscopy as an optical instrument characterized by a transfer function. This approach gives some theoretical guidelines for the design of near-field optical measurement systems. We emphasize that it is important to distinguish between the resolution for the optical field and the resolution for the object. In addition, to solve the general inverse diffraction problem the measurement of phase and amplitude of the electromagnetic field is necessary.

Electromagnetic Noise Measurement System Using a Magnetic Field Sensing Coil Array

We developed a near-field magnetic noise measurement system using a shielded-loop-type 432 coil array. To allow measurement of magnetic noises from 1 MHz to several hundred MHz, we took account of the voltage induced by the magnetic field in the pickup coil, impedance matching at the crossing points of lead lines, and the size of ground plane. High resolution of the measurement position can be obtained by using the XY-stage.

Near-field analysis of a thick lens and horn combination: theory and measurements

At millimeter-waves quasi-optical systems are commonly designed based on the Gaussian beam and thin lens approximation. The accuracy of the Gaussian beam and thin lens approximation was studied in the case of a corrugated horn and a thick Teflon lens (focal length to lens diameter ratio f/D=1.2) combination at 87 GHz. A special near-field measurement system was constructed. A large disagreement between the measured and theoretical values with the approximative method was obtained. The measurements showed that the thin lens approximation breaks down when the distance from the input beam waist to the lens is less than 1.5 D. Theoretical values obtained with a thick lens model based on ray tracing and use of exact Huygens' aperture integration principle agree well with the measurements. >

Near-field qualification methodology

A methodology that is a combination of analysis, computer simulation, component certification, self-tests, and comparison tests is presented for the accuracy qualification of near-field antenna measurement ranges. The analysis uses closed-form equations to establish upper-bound far-field determination errors due to near-field measurement errors. Computer simulation is used to model the specific near-field measurement errors associated with the near-field measurement system components. The closed-form equations and computer simulations are used to form a near-field error budget for each of the near-field measurement system components. A near-field system component certification is undertaken to measure the near-field measurement system component error and establish that they are within the error budget. >