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AMTA Paper Archive

THE SOFTWARE DEFINED ANTENNA; PROTOTYPE AND PROGRAMMING
ERIC WALTON (The Ohio State University),J. Young (The Ohio State University), C. Bryant (The Ohio State University), C. Harton (The Ohio State University), D. Crowe (Syntonics LLC ), E. Lee (Syntonics LLC ), J. Dule (The Ohio State University), S. Gemeny (Syntonics LLC), November 2008

The goal of this research is to develop an unconstrained reconfigurable programmable array antenna that we call the Software Defined Antenna™. We create patch arrays using individual controllable pixels. The aperture of the array is made up of a large group of small (<1/10 ?) pixels. Each computer controlled pixel is a small piston made up of a metal top, a dielectric shaft, and a metal base. When a line of pixels is raised into the up position, a microstrip transmission line is created. A patch antenna is created when multiple pixels are raised into the up position to form a larger rectangle or other shape. In the final design, a set of feed lines and antennas can be created to form an antenna array within 1 millisecond. Under computer control, it is possible to change the beam direction, the beamwidth, the polarization, and the frequency of operation of the array. Theoretical results, experimental results and the implementation of a working prototype will be shown.

GENERIC DESIGN OF SPARSE ANTENNA ARRAYS WITH THE CROSS-ENTROPY STOCHASTIC OPTIMISATION METHOD
Pierre Minvielle (CEA/CESTA), November 2008

Recently, there has been a growing interest in sparse antenna arrays. Formally, it can be shown that their design can be expressed as a constrained multi-dimensional nonlinear optimization problem. Generally, through lack of convex property, such a multi-extrema problem is very tricky to solve by usual deterministic optimization methods. In this paper, a recent stochastic approach, called “Cross-Entropy method”, is applied to the continuous constrained design problem. The method is able to construct a random sequence of solutions which converges probabilistically to the optimal or the near-optimal solution. Roughly speaking, it performs adaptive changes to probability density functions according to the Kullback-Leibler cross-entropy. The approach efficiency is illustrated in the design of a sparse antenna array with various requirements. The results indicate the obtained solution relevance. Furthermore, the software versatility to deal with any design requirements is highlighted.

ANALYSIS, DESIGN, OPTIMIZATION AND IMPLEMENTATION OF A CIRCULARLY POLARIZED, X-BAND MICROSTRIP 2 X 2 SEQUENTIALLY ROTATED PHASED ANTENNA ARRAY
Kamran ul Haq Malik (Satellite Research &Development Center-Karachi) ,Uzma Afsheen (NED University of Engineering & Technology), November 2008

Paper discusses the design, optimization and implementation of a Circularly Polarized (CP) microstrip 2 x 2 sequentially rotated phased antenna array for an X-band onboard satellite transceiver. In the final design, CP radiation is constructed by using CP elements, having unique sequential rotation along with sequential phase shift feeding–giving wider 3dB Axial Ratio (AR) Bandwidth. CP in each patch element is achieved by a perturbation segment, in this case a pair of truncated corners and with a single point feed–reducing complexity, weight and RF loss of the array feed. First analysis based on cavity model approach for the single CP patch is carried out, which is used to determine the normalized perturbation parameter. The initial dimensions are calculated using perturbation analysis. Optimization initially for individual patch and then for the array is performed using full wave analysis tools based on Method of Moments (MoM), and verified using Finite Difference Time Domain (FDTD). Finally, the measured input impedance and radiation patterns are correlated with the calculated results. It is observed that the measured Gain and 3db Beamwidth agrees well with the simulated results of the array optimized using MoM, while the measured results of Axial Ratio, VSWR and reflection coefficients Sxx follows closely the results from the simulations based on FDTD.

A Compact 6-Element Tri-band GPS Array
Yijun Zhou (The Ohio State University),Chi-Chih Chen (The Ohio State University), John Volakis (The Ohio State University), November 2008

Small GPS antenna elements and arrays are of great interest for future smaller vehicles. The need to cover the lower L5 band presents an additional challenge. To that end, a compact 6-element GPS array is proposed to cover all three GPS bands, namely, L1 (1575 MHz), L2 (1227 MHz) and L5 (1176 MHz). This GPS array consists of six proximity-fed stacked patches (PFSP), each having 1.2’’ in aperture size (?/8 at L5). The overall GPS array has a diameter of 4.5’’, nearly 90% smaller in area size as compared to the standard 14’’ GPS array. A key feature of the GPS element is its single feed to realize the right-hand circularly polarized polarization (RHCP) via a quadrature phase microstrip line splitter. As a result, only 6 coax cables are needed to feed the entire GPS array. Design concepts and procedures are presented, followed by measurements and a performance assessment.

Recent Developments in Miniaturized Planar Harmonic Radar Antennas
Michael Volz (Michigan State University),Benjamin Crowgey (Michigan State University), Gregory Charvat (Michigan State University), Edward Rothwell (Michigan State University), Leo Kempel (Michigan State University), Eugene Liening (The Dow Chemical Company), Malcolm Warren (The Dow Chemical Company), November 2008

Harmonic radar has recently been shown useful for remote state sensing in high clutter environments. This new application of harmonic radar with chemically sensitive "tags" allows long-range state sensing of individual low-cost passive (battery-less) sensors, such as corrosion indicators for industrial storage tanks. The "tag" response is sensed at the second harmonic of the radar transmitter, eliminating clutter from undesired objects. A new miniaturized planar harmonic radar tag design has been developed from a low-cost switching diode and low-cost laminate, without the use of shorting vias. An 85% cost reduction over the previous tag design has been achieved while maintaining similar performance. Data are presented from field testing and the laboratory environment comparing the new tag design to the old tag design as well as a basic wire dipole.

Radiation by Reactively Loaded Leaky-wave Antennas
Michael Archbold (Michigan State University),Leo Kempel (Michigan State University), Stephen Schneider (Air Force Research Laboratory), November 2008

Microstrip leaky-wave antennas offer a potential low-profile aperture for use over a relatively large bandwidth compared to resonant microstrip patch antennas. The radiation properties of a leakywave antenna can be characterize through the longitudinal wavenumber consisting of attenuation and phase coefficients. Specifically, either the physical length of the antenna or the distance from the feed can define the extent of the aperture such that significant power is transported by the leaky-wave mode (this is primarily determined by the attenuation coefficient), whichever is shorter. The angle of the main radiation lobe can be determined by the normalized phase coefficient. In this work, the longitudinal wavenumber is controlled through the use of reactive edge loads on the antenna. Specifically, the reactive load alters the transverse wavenumber, as dictated by continuity conditions, and consequently the longitudinal wavenumber is also altered from the unloaded state. An approximate theory is presented along with both computational and measured results.

RCS Measurement Facilities Certification Program Update
Roger Davis (RSBP, LLC), November 2008

The National Radar Cross Section Measurement Facilities Certification Program seeks to raise collectively the quality bar across the community. A program to accomplish this goal was initiated in 1995. It continues with facilities joining the program every year. The program has now entered the recertification phase for facilities that achieved certification five or more years ago. This paper will briefly cover the history of the program, the participants, the certification process and criteria, the recertification process, status, and the way ahead.

Approaches for Signature Measurement Uncertainty Analysis
Gregory Wilson (BerrieHill Research Corporation) ,William Muller (ATK Aerospace Structures – Military), Byron Welsh (Air Force Research Laboratory), November 2008

Over the last few years, we have implemented several methodologies pertaining to uncertainty analysis of RF and Optical measurements. These methodologies are currently in use within the radar cross-section, electro-optic/infrared, and material measurement laboratories at the Air Force Research Laboratory. In this paper we discuss from a top level some of the approaches we have implemented, and identify some important issues one needs to address before beginning an uncertainty analysis. We illustrate one such approach as it applies to the estimation of radar cross-section uncertainty.

PROCEDURE AND PROCESS OPTIMIZATION FOR REDUCTION OF MEASUREMENT UNCERTAINTIES IN RF TEST FACILITIES
Juergen Habersack (Astrium GmbH – Satellites, Measurement Technology), November 2008

The measurement accuracy of state-of-the-art RF test facilities like near-field or compact test ranges is influenced due to applied system hardware as well as operational facts which are influenced by human errors. The measurement errors of near-field test facilities were analyzed and published in the past times and are based on the 18-term error model of Newell [1]. For compact test ranges and especially for the cross-polar free compensated compact range a similar error model was established at Astrium GmbH within a study for the satellite service provider INTELSAT [2] in order to define possible facility performance improvements and maximum achievable values for the measurement accuracy. It has to be remarked, that test programs for space applications require very stringent adherence to procedures and documentation of process steps during a test campaign. Within this paper, recommendations for process optimizations and procedures will be presented to guarantee the adherence to the valid error budgets and to minimize the Human Factor. A description of main error contributions in the Compensated Compact Range (CCR) of Astrium GmbH will be performed. Furthermore, the error budgets for pattern and gain measurements and achievable performance improvements will be given.

Dedicated measurement campaign for definition of accurate reference pattern of the VAST12 antenna
Sergey Pivnenko (Technical University of Denmark ),Hakan Eriksson (SAAB Microwave Systems), Manuel Sierra Castaner (Universidad Politécnica de Madrid.), Olav Breinbjerg (Technical University of Denmark), Sara Burgos (Universidad Politécnica de Madrid.), November 2008

In this paper, three possible approaches for definition of a highly accurate reference pattern of a reference antenna are described and their pros and contras are discussed. Following the most reliable approach, a dedicated measurement campaign was planned and carried out in 2007-2008 for definition of the highly accurate reference pattern of the VAST12 antenna. In planning the campaign, conclusions from the first comparison campaign with the VAST12 carried out within the ACE network in 2004-2005 were taken into account and these are also presented and discussed. Some typical measurement errors and uncertainties are listed and briefly discussed.

Characterization of measurement systems through extensive measurement campaigns
Sara Burgos (Universidad Politécnica de Madrid.),Manuel Sierra-Castañer (Universidad Politécnica de Madrid), H. Eriksson (SAAB Microwave Systems), O. Breinbjerg (Technical University of Denmark), S. Pivnenko (Technical University of Denmark), November 2008

Within the European Union network "Antenna Center of Excellence" – ACE (2004-2007), a first intercomparison campaign among different European measurement systems, using the 12 GHz Validation Standard (VAST12) antenna, were carried out during 2004 and 2005. One of the challenges of that campaign was the definition of the accurate reference pattern. This was the reason why a dedicated measurement campaign for definition of the accurate reference pattern was hold during 2007 and beginning of 2008. This second campaign is described in the companion paper “Dedicated measurement campaign for definition of accurate reference pattern of the VAST12 antenna”. This dedicated measurement campaign was performed by Technical University of Denmark (DTU) in Denmark, SAAB Microwave Systems (SAAB) in Sweden and Technical University of Madrid (UPM) in Spain. This campaign consisted of a large number of measurements with slightly different configurations in each of the three institutions (2 spherical near field systems and one compact range). The purpose of this paper is to show the process to achieve the reference pattern from each institution and the evaluation of the accuracy. The acquisitions were performed systematically varying in applied scanning scheme, measurement distances, signal level and so on. The results are analyzed by each institution combining the measurement results in near or far field and extracting from these measurements: a “best” pattern, an evaluation of possible sources of errors (i.e. reflections, mechanical and electrical uncertainties) and an estimation of the items of the uncertainty budget.

COMPENSATION TECHNIQUE FOR OFF-AXIS CP ANTENNA TEST IN COMPACT RANGE
Xian Zhong Zhang (DSO National Laboratories), November 2008

Some compact ranges use two orthogonal linear polarized feed horns for circular polarized antenna measurement. These two feed horns are symmetrically located along the vertical plane through the longitudinal axis (VPTLA). For accurate axial ratio measurement, the CP antenna under test (AUT) should also lie on the VPTLA. However, for some applications, the AUT has to be offset from the VPTLA during measurement. When this happens, rays from two feed horns reaching the AUT are out of phase. This extra phase error causes unwanted test error for the axial ratio measurement. This paper presents an analysis on the error cause, and provides a method to compute and correct the phase error, when the AUT is offset from the VPTLA. The method computes the extra phase difference from two feed horns to the AUT using geometrical optics method. This phase difference is then used to correct the tested data. This paper also shows a successful measurement example using this correction technique.

Equivalences between MIMO and physical/synthetic radar arrays and its implications in the selection of imaging algorithms
Joaquim Fortuny-Guasch (European Commission Joint Research Centre),Alberto Martinez-Vazquez (European Commission Joint Research Centre), Elias Mendez-Dominguez (European Commission Joint Research Centre), November 2008

A first analysis of the equivalences between Multiple Input Multiple Output (MIMO) and physical/synthetic radar arrays is presented. The establishment of these equivalences is addressed to make use of efficient radar imaging algorithms, which were originally conceived for SAR systems, with MIMO arrays. The main advantage of MIMO arrays is that, with a reduced cost and complexity of the antenna feeding network, they offer imaging capabilities very close to those of SAR and physical radar arrays. This makes MIMO radar a very interesting option in real-time imaging applications (e.g., surveillance of small areas). The paper will present some numerical simulations using some reference scenarios where the imaging capabilities of MIMO arrays will be assessed. A comparative analysis with the well-known SAR and uniformly spaced radar arrays will be presented. Here the study is made with one-dimensional radar apertures, and subsequently will be extended to two-dimensional radar apertures. The analysis of the performance of the MIMO arrays is based on a Matlab simulation tool that is used to optimize the array topology and also to form the radar images of a synthetic scenario. The optimization technique is based on a genetic algorithm, using a fitness function measuring the degree of uniformness and uniqueness of the loci of the phase centers of the tx/rx pairs of the MIMO array. Results show that the found topologies show a performance close to uniformly spaced physical radar arrays.

A LOW-POWER, REAL-TIME, S-BAND RADAR IMAGING SYSTEM
Gregory L. Charvat (Michigan State University),Leo C. Kempel (Michigan State University), Edward J. Rothwell (Michigan State University), Chris Coleman (Integrity Applications Incorporated), November 2008

A real-time S-band radar imaging system will be shown in this paper that uses a spatially diverse antenna array connected to a highly sensitive linear FM radar system and uses a synthetic aperture radar (SAR) imaging algorithm to produce real-time radar imagery. The core of this radar system is a high-sensitivity, range gated, radar architecture. Previous work has demonstrated the effectiveness of this radar architecture for applications requiring low-power and high sensitivity for imaging through lossy dielectric slabs at S-band and in free space at both S and X bands. From these results it was decided to develop a real-time S-band SAR imaging system. This is achieved by constructing a spatially diverse antenna array that plugs directly into a pair of S-band transmit and receive radar front ends; thereby providing the ability for real-time SAR imaging of objects. The radar system chirps from approximately 2 GHz to 4 GHz at various rates from 700 microseconds to 10 milliseconds. Transmit power is adjustable from approximately 1 milliwatt or less. The image update rate is approximately one image every 1.9 seconds when operating at a chirp rate of 2.5 milliseconds. This system is capable of producing imagery of target scenes made up of objects as small as 1.25 inch tall nails in free space without the use of coherent integration. Previous applications for this radar system include imaging through dielectric slabs. It will be shown in this paper that this radar system could also be useful for real-time radar imaging of low RCS targets at S-band.

Rapid RADAR Test Range Development Using Lean Engineering Techniques Case Study for the Dynamic Advanced Radar Test (DART) Facility
Bill Richardson (The Boeing Company) ,Mark Bellman (Chamber Services), November 2008

This paper describes how the Dynamic Advanced Radar Test (DART) facility was designed, constructed, integrated and validated within budget in a 12-month time frame using lean engineering techniques. The facility is a world-class Radar seeker test facility. These techniques allowed the DART team to enhance capabilities without adding cost or complexity. The purpose of this paper is to identify a new paradigm in Radio Frequency (RF) range development, whereby all variables are accounted for early in the process, thus preventing and avoiding time consuming and costly mistakes. This process relies on lean engineering Accelerated Improvement Workshops (AIW) and Production, Preparation, Process (3P) workshops to guide the design process. Allowing all stakeholders to be owners through these intense workshops is vital. Additionally since formal evaluation tools and methodologies guide the workshops, improvement opportunities are maximized while minimizing risk.

PERFORMANCE IMPROVEMENT WITH AN R-CARD FENCE
Raul Miravet (ATK Missile Systems),Gabriel A. Sanchez (Advanced ElectroMagnetics, Inc.), Dave Steinberger (Precision Fabrications), Teh-Hong Lee (The Ohio State University), November 2008

Hardware-In-The-Loop chambers provide the chamber designer with many difficult obstacles to overcome in order to establish a high performance environment for the measurement of missile seeker systems. One of the most difficult challenges is to overcome the low performance of absorbing materials at low grazing angles. To solve this problem Tapered R-Card Fences have been used in conjunction with Chebyshev absorbers. Last year we reported on the ATK chamber built in Woodland Hills which showed preliminary test results well within the system requirements. This paper will make a direct comparison of chamber performance with and without Tapered R-Card Fences. The establishment of a sister chamber built in the ATK Alliant Techsystems Inc. ABL facility has provided us with the unique opportunity to test the chamber prior to the installation of the R-Cards and then to test it again with the installation of the R-Cards. This unique opportunity has allowed us a direct comparison of an advanced chamber deign with Chebyshev absorbers as would be utilized in a conventional chamber and the performance increase directly attributable to the introduction of the Tapered R-Cards in the anechoic chamber. The chamber evaluation is carried out utilizing The Ohio State developed TDOA measurement method utilizing their proprietary measurement and analysis software.

EVALUATION OF ISOFILTER™ FIDELITY IN SELECTED APPLICATIONS
Doren W. Hess (MI Technologies),Scott McBride (MI Technologies), November 2008

The IsoFilterTM technique was originally demonstrated to operate by rejecting secondary signals that derive from reflections off of a nearby metallic object – namely, the ground plane surface supporting a small pyramidal horn.[1,2] The aperture of the horn was located several wavelengths above the ground plane and the sidelobes and backlobes of the horn illuminated the ground plane itself. The success of this demonstration has been sufficient to encourage us to pursue further the question of how well the IsoFilterTM technique will work to suppress other types of secondary signals– such as signals coming from other elements of an array antenna or another individual first-order primary radiator nearby. Here we report on some of the results of that investigation. We have calculated the far-field patterns of a sparsely populated array and applied the IsoFilterTM technique. The goodness of the suppression is judged by how well the “IsoFiltered” result agrees with the calculated pattern of the individual radiator.

CONICAL NEAR-FIELD ANTENNA MEASUREMENTS
Stuart F. Gregson (Nearfield Systems Inc.),Greg E. Hindman (Nearfield Systems Inc.), November 2008

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 utilises 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 characterise wide-angle antenna performance in situations where hitherto they would perhaps have been limited by truncation. This paper aims to introduce the measurement technique, describe the novel probe-corrected near-field to far-field transform algorithm which is based upon a cylindrical mode expansion of the measured fields before presenting preliminary results of both computational electromagnetic simulations and actual range measurements. 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.

EXPERIMENTAL VALIDATION OF THE NF-FF TRANSFORMATION WITH HELICOIDAL SCANNING SUITABLE FOR ELONGATED ANTENNAS
Francesco D'Agostino (University of Salerno),Carlo Rizzo (MI Technologies Europe), Claudio Gennarelli (University of Salerno), Flaminio Ferrara (University of Salerno), Jeff Fordham (MI Technologies), Massimo Migliozzi (University of Salerno ), Rocco Guerriero (University of Salerno), November 2008

In this work an experimental validation of the nearfield – far-field transformation technique with helicoidal scanning tailored for elongated antennas is provided. Such a transformation relies on the theoretical results relevant to the nonredundant sampling representations of the electromagnetic fields and makes use of an optimal sampling interpolation algorithm, which allows the reconstruction of the near-field data needed by the near-field – far-field transformation with cylindrical scan. In such a case, a prolate ellipsoid is employed to model an elongated antenna, instead of the sphere adopted in the previous approach. It is so possible to consider measurement cylinders with a diameter smaller than the source height, thus reducing the error related to the truncation of the scanning surface. The comparison of the reconstructions obtained from the data directly measured on the classical cylindrical grid with those recovered from the nonredundant measurements on the helix assesses the validity of this innovative scanning technique.

On the Robustness of Planar Phaseless Near-field Measurements to Probe Positioning Errors
Farhad Razavi (University of California, Los Angeles),Yahya Rahmat-Samii (University of California, Los Angeles), November 2008

The Phaseless techniques have gained considerable attention during the past two decades in the antenna measurements community. The removal of the phase measurements has some immediate advantages over the common vectorial measurements. They are cost effective, well-adapted for higher frequencies and insensitive to phase instabilities. The phaseless techniques have been discussed in the antenna measurements community and the theories behind these techniques are well explained in the literature. Unfortunately the issue of the noise and the presence of measurement errors are not investigated in details to provide strong impetus to the importance of phaseless measurements. In this paper the near field of a number of different types of antennas with high, medium and low side lobes is simulated to create as realistic case as possible. The effects of the probe positioning errors are investigated by injecting random errors in the position of the probe samples along x-, y- and z-axis. It is also illustrated how the positioning errors can distort the phase distributions. Through detailed characterizations of the constructed far field patterns, robustness of the Iterative Fourier technique even at the presence of very high probe positioning errors is demonstrated. It is shown how the utilization of the phaseless techniques will significantly reduce the probe positioning error effects when it is compared to the commonly used amplitude and phase near field measurement techniques.







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