Antenna Under Test Research Articles

A Nonredundant Near-Field to Far-Field Transformation with Spherical Spiral Scanning for Nonspherical Antennas

A Nonredundant Near-Field to Far-Field Transformation with Spherical Spiral Scanning for Nonspherical Antennas

Antenna pattern corrections using a space diversity of the antenna under test (AUT) on top of the turntable

Antenna pattern corrections using a space diversity of the antenna under test (AUT) on top of the turntable

Phaseless Antenna Characterization by Effective Aperture Field and Data Representations

The problem of antenna characterization from phaseless near-field data is addressed by appropriate use of the available information on the Antenna Under Test (AUT) and on the scanning geometry to provide efficient representations for both the unknowns and the data. Such a strategy allows improving the reliability and the accuracy of the proposed characterization algorithm and, at the same time, shortens the overall measurement process. An extensive numerical and experimental analysis, together with a comparison with existing approaches, endorses the algorithm reliability and accuracy and confirms its usefulness for antennas having a general radiating (vector) behavior, i.e., either focusing or non-focusing.

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 2–40 GHz Probe Station Based Setup for On-Wafer Antenna Measurements

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <?Pub Dtl=""?>A probe station based setup for on-wafer antenna measurements is presented. The setup allows for measurement of return loss and radiation patterns of an on-wafer antenna—henceforth referred to as the antenna under test (AUT), radiating at broadside and fed through a coplanar waveguide (CPW). It eliminates the need for wafer dicing and custom-built test fixtures with coaxial connectors or waveguide flanges by contacting the AUT with a coplanar microwave probe. In addition, the AUT is probed exactly where it will be connected to a transceiver IC later on, obviating de-embedding of the measured data. Sources of measurement errors are related to calibration, insufficient dynamic range, misalignment, forward scattering from nearby objects, and vibrations. The performance of the setup is demonstrated from 2 to 40 GHz through measurement of an on-wafer electrically small slot antenna <formula formulatype="inline"><tex>$(\lambda _{0}/{35}\times \lambda _{0}/{35}, {3.5} \times 3.5~{\rm mm}^{2})$</tex></formula> radiating at 2.45 GHz and an aperture coupled microstrip antenna <formula formulatype="inline"><tex>$({2.4} \times {1.7}~{\rm mm}^{2})$</tex></formula> radiating at 38 GHz. </para>

On the Comparison Between the Spherical Wave Expansion and the Sources Reconstruction Method

A comparison between two well-known near field to far field (NF-FF) transformation methods is presented: the spherical wave expansion (SWE) and the sources reconstruction method (SRM). The goal of this paper is to show the methods performance for NF-FF transformation pointing out the advantages and limitations of each one. First, the computational cost is studied, showing its dependence with the antenna under test (AUT) electric size. Second, the NF-FF transformation accuracy of each method is compared for a fixed AUT electric size, analyzing also the influence of the main parameters that affect the SRM and SWE accuracy. Third, the SRM capabilities are presented, with focus on the NF-NF transformation inside the minimum sphere. Practical applications of the SWE and SRM are illustrated by means of an example of NF-FF transformation and antenna diagnostics problem using measured NF data.

Application of the SWE-to-PWE antenna diagnostics technique to an offset reflector antenna

A new antenna diagnostics technique has been developed for the DTU-ESA Spherical Near-Field Antenna Test Facility, which is operated by the Technical University of Denmark (DTU) for the European Space Agency (ESA). The technique is based on the transformation of the spherical-wave expansion (SWE) of the radiated field, obtained from a spherical near-field measurement, to the plane-wave expansion (PWE). It allows an accurate reconstruction of the field in the extreme near-field region of the antenna under test (AUT), including the aperture field. The fundamental properties of the SWE-to-PWE transformation, as well as the influence of finite measurement accuracy, have been reported previously. We validate here the new antenna diagnostics technique through an experimental investigation of a commercially available offset reflector antenna, where a tilt of the feed horn and surface distortions were intentionally introduced. The effects of these errors were detected inthe antenna's far-field pattern, and the accuracy and ability of the diagnostic technique to subsequently identify them were investigated. Real measurement data were employed for each test case.

Double $\phi$-Step $\theta$-Scanning Technique for Spherical Near-Field Antenna Measurements

Probe-corrected spherical near-field antenna measurements with an arbitrary probe set certain requirements on an applicable scanning technique. The computational complexity of the general high-order probe correction technique for an arbitrary probe, that is based on the Phi scanning, is O(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> ), where N is proportional to the radius of the antenna under test (AUT) minimum sphere in wavelengths. With the present knowledge, the computational complexity of the probe correction for arbitrary probes in the case of the thetas scanning is O(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> ), which is typically not acceptable. This paper documents a specific double Phi-step thetas scanning technique for spherical near-field antenna measurements. This technique not only constitutes an alternative spherical scanning technique, but it also enables formulating an associated probe correction technique for arbitrary probes with the computational complexity of 0(N4) while the possibility for the exploitation of the advantages of the thetas scanning are maintained.

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.

An Accurate Equivalent Behavioral Model of Antenna Radiation Using a Mode-Matching Technique Based on Spherical Near Field Measurements

A new and simple method for modeling an antenna under test (AUT) from spherical near-field (NF) measurements is presented. This method utilizes NF data to determine an equivalent behavioral model composed of magnetic and electric dipoles placed over a fictitious sphere surrounding the AUT. A spherical wave expansion (SWE) of the measured NF is developed to derive a linear relation between the transmission coefficients of the AUT and the transmission coefficients of each dipole. Dipole transmission coefficients are determined using the translational and rotational addition theorems. Finally, a least square method is employed to compute the excitation of each current source. Once the equivalent model is obtained, it can be used to study the behavior of the original AUT in different environments. Computations with electromagnetic simulation data illustrate the accuracy of the proposed method and the reliability of the derived model.

Antenna Measurement Method in Fresnel Region by $\phi$-Variation Scanning

The far-field pattern and gain obtained using the far-field measurement method can be highly accurate when the distance between the source antenna and the antenna under test (AUT) satisfies the Rayleigh far-field criterion. In this letter, we propose an improved Fresnel region measurement method that can be applied in a shortened distance between two antennas. The many Fresnel fields required are captured by changing angle phi of the scanning plane. This scanning involves rotating the roll positioners of the source antenna and the AUT in the same direction and by the same amount, and rotating the azimuth positioner in the horizontal plane. The radiation pattern and gain from the simulation and experimental measurements agreed closely with the reference far-field pattern and gain. The proposed antenna measurement method in Fresnel region by phi-variation scanning can be easily applied to most popular far-field measurement systems without any additional cost.

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.

A comparison of software- and hardware-gating techniques applied to near-field antenna measurements

Abstract. It is well-known that antenna measurements are error prone with respect to reflections within an antenna measurements test facility. The influence on near-field (NF) measurements with subsequent NF to far-field (FF) transformation can be significantly reduced applying soft- or hard-gating techniques. Hard-gating systems are often used in compact range facilities employing fast PIN-diode switches (Hartmann, 2000) whereas soft-gating systems utilize a network analyzer to gather frequency samples and eliminate objectionable distortions in the time-domain by means of Fourier-transformation techniques. Near-field (NF) antenna measurements are known to be sensitive to various errors concerning the measurement setup as there have to be mentioned the accuracy of the positioner, the measurement instruments or the quality of the anechoic chamber itself. Two different approaches employing soft- and hard-gating techniques are discussed with respect to practical applications. Signal generation for the antenna under test (AUT) is implemented using a newly developed hard-gating system based on digital signal synthesis allowing gate-widths of 250 ps to 10 ns. Measurement results obtained from a Yagi-Uda antenna under test (AUT) and a dual polarized open-ended waveguide used as probe antenna are presented for the GSM 1800 frequency range.

A new look at phaseless planar near-field measurements: limitations, simulations, measurements, and a hybrid solution

In this paper, we have revisited the phase-retrieval problem for planar near-field antenna measurements. It will be shown that the complexity of retrieval procedures is a function not only of the independency of different sets of measurements, but also of the characteristics of the antenna under test (AUT). Antenna-pattern features, such as its beam direction, will have a profound effect on the success of phase-reconstruction algorithms. The failure of a well-known phase-retrieval method, the iterative Fourier technique, is investigated for a case where the antenna has a scanned beam. It is found that this is due to a less-than-optimum choice of the initial guess. To alleviate the deficiency of the iterative Fourier technique, a simple but effective initial guess is sought by the use of the differential evolutionary algorithm. This global search technique tries to find the best initial phase guess that minimizes an error criterion. Subsequently, this best guess is fed to the iterative Fourier phase-retrieval routine for further phase refinements. Having done this, the far-field can subsequently be constructed. The improvement in the phase-reconstruction algorithm is examined through a series of simulations and measurements.

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.

Measured patterns of a resistive V‐dipole fed with a double‐Y balun

AbstractThe performance of a double‐Y balun feeding a resistive V‐dipole is evaluated via antenna‐pattern measurements. An optical link is constructed for containing the feedline radiation to a laser receiver unit and the antenna under test (AUT), hence avoiding the uncertainty caused by cable radiation in a conventional antenna pattern‐measurement setup. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 380–383, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21356

A feed scanning based APC technique for compact antenna test ranges

The measurement accuracy of a compact antenna test range (CATR) depends on the level of spurious signals. To improve the measurement accuracy, several error compensation methods have been developed, but most of them are not feasible at submillimeter wavelengths. This paper introduces an error compensation technique for compact antenna test ranges, which is especially suitable at submillimeter wavelengths. The method is based on antenna pattern comparison (APC). In the original APC technique the antenna pattern is recorded several times at different positions of the quiet-zone field, and the corrected pattern is obtained by averaging the measured patterns. In the proposed method, the lightweight transmitter is moved instead of moving the heavy combination of the antenna under test (AUT) and the rotation stage. The feasibility of the method is studied and the method is tested with measurements in a hologram based compact antenna test range at 310 GHz. The accuracy provided by the proposed method is compared to the accuracy provided by the conventional APC. The accuracies provided by both methods are practically equal.

Particle-swarm optimization and its application to antenna far-field-pattern prediction from planar scanning

Particle-swarm optimization (PSO) is a high-performance optimizer, recently introduced to the electromagnetics community, which seems to be an attractive alternative to other stochastic optimization methods such as genetic algorithms. An overview of the main characteristics and schemes related to the PSO technique available in the literature are presented and discussed. Furthermore, in this paper, equivalent magnetic-surface currents and PSO are used together to model the radiation of an antenna under test (AUT) from planar near-field data. The results of a comparison of the performance of both global and local PSOs with synchronous and asynchronous updates, as well as the results of reconstructed far-field patterns from near-field samples, are included in order to demonstrate the usefulness of the method. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 398–403, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20648

Antenna far‐field pattern reconstruction using equivalent currents and genetic algorithms

AbstractA method for computing the far‐field pattern of an antenna under test (AUT) from near‐field data is presented. Based on the equivalence principle, the AUT is replaced by equivalent magnetic surface currents, whose components are optimized using microgenetic algorithms. Results of reconstructed far‐field patterns from synthetic near‐field samples, a comparison to the approach using classical methods, and an analysis of the method's performance and limitations are included. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 21–25, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20195

Use of Balun Chokes in Small-Antenna Radiation Measurements

Measurements of the free-space radiation characteristics of small antennas, such as in mobile communications handsets, typically suffer from the influence of the attached radio frequency (RF) feed. A sleeve-like balun choke placed on the feed cable close to the antenna under test (AUT) prevents surface currents of the AUT from propagating onto the outer shield of the RF feed cable. Therefore, measurement results with the balun correspond well to those of an isolated AUT, much better than without any measures against cable effects. The balun can typically be used at a 10% relative bandwidth. A dual-frequency balun minimizes the cable-related effects at two separate frequency bands. This is useful in the measurements of dual-frequency antennas. The results of both simulations and measurements for a dual-band balun are presented in this paper, proving the usefulness of the proposed balun and its advantages over alternative means to decrease the cable-related effects.