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AMTA Paper Archive

Deriving Far-Field Performance Parameters from Near-Field Amplitude Measurements of Wireless Devices
P Iversen,S. Gaymay, November 2006

The CTIA (The Wireless Association – www.ctia.org) were the first to publish a widely accepted test plan for antenna performance testing of “live” mobile phones[1]. The test plan describes the use of phantom heads and involves recording transmitted power and receiver sensitivity information over a full sphere to derive parameters such as Total Radiated Power (TRP) and Total Integrated Sensitivity (TIS). The test plan, has until now, assumed that testing is performed in the far-field at test distances greater than 2D2/.. For typical mobile phone frequency and device test diameters (assumed 300mm in the CTIA test plan), this has not been a constraint. However, as such testing evolves to include the various versions of IEEE 802.11 combined with new devices such as larger laptops and other consumer electronics, a far-field test requirement would lead to very large test facilities. Using experiments and rigorous simulations, this paper will show that for the commonly accepted performance criteria, the far-field requirement is unnecessarily strict. A minimum distance requirement based on the geometry and probe pattern is proposed which will ensure that the performance parameters (TRP, TIS, and others) are obtained with insignificant loss of accuracy.

Traditional Antenna Measurements and CTIA OTA Measurements - Merging the Technologies
D. Gray,I. Lin, November 2006

This paper describes traditional antenna measurements and the relationship to the Over-the- Air (OTA) measurements specified by the Cellular Telecommunications & Internet Association (CTIA). It discusses the differences, the likenesses, and the importance of providing a system that can provide both traditional antenna measurements and CTIA OTA measurements. It will address the processes of providing a complete turn-key system – including chamber – that will meet CTIA certifications. Further, this paper shows the unique flexibility and features that the 700S-90 provides for meeting the customer’s needs, for a wide-variety of applications.

Expanding an ISO 17025-based Assessment Program in Wireless Compliance Test Facilities to Incorporate Characterization Measurements
R. Jost, November 2006

This paper proposes an approach for the wireless industry to use in assessing its measurement facilities to help ensure that they are providing measurement results that are accurate and repeatable, with a knowable error and uncertainty. This approach is based upon the successful development of a certification program for US RCS facilities based upon an ISO 17025-like standard. Key pieces of this program include a documentation standard for defining the facility's capabilities and operation, and a Report of Measurement and an accompanying Uncertainty Analysis. This paper will discuss the similarities and differences between an existing RCS certification program and the proposed wireless program, to include technical distinctions between the two programs. These distinctions are based upon such factors as a 1-way instead of 2-way propagation paths, the various modulation schemes in use today and the different types of measurements such as Specific Absorption Rate that are not considered in RCS measurements.

A New Look at Phaseless Planar Near Field Measurements: Limitations, Simulations, Measurements, and a Hybrid Solution
F. Razavi,Y. Rahmat-Samii, November 2006

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 function of not only the independency of different sets of measurements but also the characteristics of the antenna under test (AUT). Features of antenna like its beam direction will have profound effect on the success of phase reconstruction algorithms. The failure of a well known phase retrieval method, Iterative Fourier Transform (IFT), is investigated for a case where the antenna has a scanned beam. It is found that this is due to the non-judiciary choice of the initial guess. To alleviate the deficiency of the IFT a simple but effective initial guess is sought by Differential Evolutionary Algorithm (DEA). DEA tries to find the best initial phase guess which minimizes an error criterion. Subsequently this best guess will be fed to the phase retrieval IFT 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.

On the Impact of Non-Rectangular Two Dimensional Near-field Filter Functions in Planar Near-Field Antenna Measurements
D. Janse van Rensburg, November 2006

In this paper a circular planar near-field scan region is considered as an alternative to the commonly used rectangular boundary. It is shown how the selection of this alternative boundary can reduce test time and also to what extent the alternative truncation boundary will affect far-field accuracy. It is also shown how well known single dimensional filter functions can be applied over a two-dimensional region of test and how these attenuate the truncation effect. The boundary and filter functions are applied to measured data sets, acquisition time reduction is demonstrated and the impact on far-field radiation pattern integrity in assessed.

Comparative Validation Methodology for a Combined Cylindrical and Spherical Near-Field Measurement System
U. Shemer,C. Tse Tong, November 2006

DSO National Laboratories has commissioned a high performance combined near-field and far-field antenna test facility in 2004. This facility supports highly accurate measurement of a wide range of antenna types over 1 – 18 GHz. This combined NF-FF system allows for planar, cylindrical and spherical near-field measurements, as well as far-field measurements. The combined near-field and far-field test facility has undergone meticulous validations making use of a TICRA calibrated “Golden Antenna” (GA). A detailed account of the cylindrical and spherical near-field comparative validation methodology and the test results are the subject of this article. The validation results for planar near-field (PNF), cylindrical near-field (CNF), spherical near-field (SNF) and far-field measurements have clearly shown that the system fulfils all the performance requirements without the use of a calibrated probe. Although dedicated near-field test facilities are generally thought to provide superior measurement accuracies, it will be shown in this article that a well-designed combined NF-FF test facility can deliver highly accurate results without the use of a calibrated probe. This makes the combined NF-FF system a viable and cost-effective antenna measurement solution, without compromising on measurement accuracies.

Pattern Reconstruction from Nonuniformly Distributed Spherical Near-Field Measurements
F. D'Agostino,C. Gennarelli, F. Ferrara, G. Riccio, M. Migliozzi, R. Guerriero, November 2006

ABSTRACT An efficient probe compensated NF–FF transforma­tion technique with spherical scanning requiring a minimum number of irregularly spaced data is pro­posed in this paper. The Singular Value Decompo­sition method is applied for recovering the uniformly distributed samples from the irregularly spaced ones. The positions of the uniform samples are fixed by a nonredundant sampling representation of the electro­magnetic field. It is so possible to efficiently recon­struct the near-field data required by one of the avail­able NF–FF transformation techniques with spherical scanning. Many numerical tests have been performed to assess the effectiveness of the proposed technique.

A Note to Show How an Alternative Spherical Mode Normalization Simplified the Relationship Between Transmitting and Receiving Characteristics
D. Hess, November 2006

In this paper we show how a modification in the choice of mode normalization changes the pair-wise transmitting-receiving conversion to a one-to-one equality for a reciprocal antenna: This change affords us greater simplicity and the opportunity to avoid confusion when manipulating the scattering coefficients. For this relation to hold, there is a useful convention defining two fiducial coordinate systems for the antenna – one a transmitting and the other a receiving coordinate system.

Reduction of Truncation Error in the Near-Field-Far-Field Transformation with Planar Spiral Scanning
F. D'Agostino,C. Gennarelli, C. Rizzo, C. Savarese, F. Ferrara, R. Guerriero, November 2006

ABSTRACT An elaborate and effective strategy for estimating the samples external to the measurement region in the planar spiral scanning is developed in this paper. It relies on the nonredundant sampling representations of the electromagnetic field and on the optimal sam­pling interpolation expansions of central type and uses the singular value decomposition method for extrapolating the outside samples. It is so possible to reduce the inevitable truncation error affecting the near-field reconstruction, thus giving rise to a more accurate far-field prediction. Numerical examples as­sess the effectiveness of the proposed technique.

Low-Cost, High Resolution X-Band Laboratory Radar System for Synthetic Aperture Radar Applications
G. Charvat, November 2006

Using a discarded garage door opener, an old cordless drill, and a collection of surplus microwave parts, a high resolution X-band linear rail synthetic aperture radar (SAR) imaging system was developed for approximately $240 material cost. Entry into the field of radar cross section measurements or SAR algorithm development is often difficult due to the cost of high-end precision pulsed IF or other precision radar test instruments. The low cost system presented in this paper is a frequency modulated continuous wave radar utilizing a homodyne radar architecture. Transmit chirp covers 8 GHz to 12.4 GHz with 15 dBm of transmit power. Due to the fairly wide transmit bandwidth of 4.4 GHz, this radar is capable of approximately 1.4 inches of range resolution. The dynamic range of this system was measured to be 60 dB thus providing high sensitivity. The radar system traverses a 96 inch automated linear rail, acquiring range profiles at any user defined spacing. SAR imaging results prove that this system could easily image objects as small as pushpins and 4.37 mm diameter steel spheres.

A Dual-Linear Polarization UWB Dielectric Rod Probe Design
J-Y. Chung,C-C. Chen, November 2006

A dual-polarization ultrawide bandwidth (UWB) dielectric rod antenna containing two concentric dielectric cylinders was developed for near field probing applications. This antenna features more than 4:1 bandwidth, dual-linear polarization, stable radiation center and symmetric patterns. The antenna begins with a tapered wave-launching section consisting of shaped conducting plates and resistive films. This launcher section is followed by a guided section where the excited HE11 modes are transported to the radiation section. The radiation section contains specially shaped dimensions and materials to generate similar E and H plane patterns with 3-dB beamwidths greater than 55° over 4:1 bandwidth (2 to 8 GHz).

Simulation of a Helical Antenna on a Hemispherical Surface
A. Daya,B. Mitchell, G. Hampton, J. Kemp, November 2006

This paper will present techniques used to simulate semi-hemispherical spiral antennas with measured VSWR and antenna pattern data for performance verification. Previous work on semi-hemispherical spiral antennas has been done by Lobkova, Protsenko, and Molchanov [1]. GTRI researchers have built on this work by developing a MATLAB computer model to create a general semi-hemispherical spiral antenna pattern model. Parameters that can be adjusted include the radius of the sphere, the number of turns of the spiral, the creation of a 1-arm or 2-arm spiral, and the inclusion of dielectric material between the spiral and ground plane. In creating the MATLAB computer model, GTRI researchers found errors in the notation of the elliptical integral in [1] and added additional details for the calculation of the antenna pattern. The paper will then present the characterization of a specific example of a semi-hemispherical spiral antenna. First, the VSWR of a single antenna was measured using a standard HP8510 Network Analyzer setup. Next, antenna pattern data was measured for a single spiral antenna and a pair of spiral antennas on both the GTRI planar near-field range and the GTRI anechoic chamber. The paper will conclude with the presentation of the modeled and measured antenna pattern data for the single antenna case.

Spiral Antenna Miniaturization using Volumetric Inductive Loading
B. Kramer,C-C. Chen, J. Volakis, M. Lee, T. Ping, November 2006

This paper describes the miniaturization of a spiral antenna using inductive loading. The inductive loading of the spiral is implemented using a two dimensional approach (meandering) and a volumetric or three dimensional approach. It is shown that the volumetric approach can achieve greater miniaturization than the two dimensional approach. In addition, the simulation results for the volumetric approach are validated by the fabrication and measurement of one of the volumetric designs.

Microwave Frequency Antennas Printed on Flexible Substrates
K. Whites,K. Kirschenmann, T. Amert, November 2006

Direct-write deposition is a low temperature method of printing electrical devices with fine features (25 µm and smaller) without the use of masks, resist chemicals, or lithographic processing. In this paper, we present a brief survey of the three predominate direct-write methods, all of which are found in the Direct Write Laboratory at the South Dakota School of Mines and Technology (SDSMT). We also describe our efforts employing these machines to successfully construct microwave frequency antennas on flexible substrates using a highly conductive ink developed at SDSMT. This silver ink has an electrical conductivity approximately 85% of bulk silver, which we have found to be sufficiently large even for high Q circuits and antennas operating at 5 GHz and higher.

Cross-Polarization Parameters in the Presence of Drift in Radar Cross Section Measurements
L. Muth, November 2006

We use a rotating dihedral to determine the cross-polarization ratios of radar cross section measurement systems. Even a small amplitude drift can severely degrade the calibration accuracy, since the calibration relies on accurate determination of polarimetric data over a large dynamic range. We show analytically how drift introduces errors into the system parame­ters, and outline an analytic procedure to minimize the in.uence of drift to estimate system parameters with greater accuracy. We show that only very lim­ited information about the drift is needed to provide measured system parameters accurate to second order in the error-free parameters. Higher-order accuracies can be achieved by using more detailed information about the drift. We use simulations to explain and illustrate the analytic development of this theory. We also show that, using cross-polarimetric measurements on a cylinder, we can recover the exact system param­eters. These .ndings show that we can now calibrate polarimetric radar cross section systems without the large uncertainties that can be introduced by drift.

Comparison of RCS Measurement of a NASA Almond Using Classical Compact Indoor Facility and a new Phased Array Antenna
J. De Kat, November 2006

CEA-Cesta has developed a new phased array antenna for RCS dual polarization wide bandwidth measurement in V/UHF bands. This array enables us to enhance signal to noise ratio especially at low frequencies. It is composed of 3 sub arrays dedicated each to one frequency band. The innovative design allows installing it in one of CEA/CESTA RCS facilities called “CAMELIA”. In order to validate this array in the highest sub-band [700 to 2000MHz], we measured in both HH and VV polarizations the near field RCS of a 2.5m long NASA almond target. This canonical object has been made of polystyrene coated with conducting nickel varnish. It has been hung on an eight wires rotating positionner. The results are compared with the data acquired in a classical RCS compact range and with the output of the 3D finite element code called ODYSSEE developed at CEA.

Surface Wave Contributions in the RCS of a Squat Cylinder
S. Wei, November 2006

While using squat cylinders for calibrations, we study the MoM-simulated data in terms of surface waves. We have found that the fine structures in both the amplitude and the phase are related to the target geometry. Key Words: RCS calibration, simulation, polarization

Applications of Interferoceiver for RCS Measurement and RF Imaging
M-C. Li, November 2006

It is widely known to radar engineers that the best radar receiver is a correlation receiver, which correlates the originally transmitted radar pulse with received pulses from the reflection. But the true correlation receiver could not yet be realized in past. The advancement of fiber optical technology changes that. The new and true correlation receiver, which has been referred to as interferoceiver, revolutionizes the technical foundation of radar and electronic warfare. The present talk discusses the use of the interferoceiver in advancing techniques of RCS measurement and RF imaging.

A Partial Rotation Formulation of the Circular Near Field-to-Far Field Transformation (CNFFFT)
S. Rice,I. LaHaie, November 2006

For many years now, General Dynamics has described the development, characterization, and performance of an image-based circular near-field-to-far-field transformation (CNFFFT) for predicting far-field radar cross-section (RCS) from near-field measurements collected on a circular path around the target. In this paper, we consider the CNFFFT algorithm as an azimuthal filtering process and develop a formulation capable of transforming data that is not measured over a full 360º. Such a formulation has applications in measurement scenarios where collection of a complete rotation is not practical. As part of the development, we provide guidelines for the near-field data support required to achieve a desired accuracy in the sub-360º CNFFFT result. Numerical simulations are provided to demonstrate that the results of this partial-rotation formulation are consistent with the full-circle CNFFFT results presented in past papers.







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