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Near Field

A Portable Near-Field Scanner for Calibrating the AN/SPS-48E Antennas on LPD-17 Ships
D. Woollen,F. Closser, W. Slowey, November 2006

The AN/SPS-48E antenna is a three dimensional air search antenna that is currently installed on 27 US ships. Currently the 48E antenna is removed from the ship after five to seven years to be overhauled at NSWC Crane Division. The new San Antonio Class ships (LPD 17 – 25) have a new enclosed mast design, the Advanced Electromagnetic Mast/Sensor (AEM/S), in which the 48E antenna and others are installed inside the enclosed mast. The cost of removing the enclosed mast led to the decision that the 48E antenna systems (antennas and pedestals) will not be removed for overhaul and maintenance on these ships as is currently done for all other installations. As a result, new fixtures and procedures need to be developed to allow maintenance inside of the mast. The most challenging of the new fixtures is a near-field scanner, which will be used to re-tune the antenna and characterize the RF performance parameters. This paper discusses the design and development effort currently underway for this Enclosed Mast Antenna Calibration System (EMACS), most notably the mechanical design constraints placed on the scanner by the enclosed mast regarding equipment movement, installation, alignment and testing.

Evaluation of Low-Cost Phased Array Antenna Design
J. Kemp,B. Mitchell, L. Corey, R. Cotton, November 2006

In the early 1990's, Georgia Tech Research Institute (GTRI) was able to acquire an unclassified phased-array antenna from the former Soviet Union. Since that time, GTRI personnel have analyzed the antenna for design features that enabled the production of low-cost phased-array antennas. Antenna pattern data collected on the GTRI planar near-field range of a working and errored antenna will be presented. Also, modeled antenna pattern data will be presented as a comparison to show the particular effects of the low-cost design versus an ideal antenna. Finally, the original control mechanism of the phased-array antenna will be analyzed and compared with a modern control mechanism developed by GTRI researchers. Control data for the original and new control systems was captured with a logic analyzer and will be presented for comparison.

Time domain Planar Near-Field Measurement Simulation
X. Shen,X. Chen, November 2006

The UWB radar operates simultaneously over large bandwidth and the antenna parameters must refer to simultaneous performance over the whole of the bandwidth. Conventional frequency domain (FD) parameters like pattern, gain, etc. are not adequate for UWB antenna. This paper describes an UWB radar antenna planar near field (PNF) measurement system under construction to get the impulse response or transient characteristic of the UWB antenna. Unlike the conventional antenna or RCS time domain test system, the UWB radar signal instead of the carrier-free short time pulse was used to excite the antenna that can avoid the decrease of the dynamic range and satisfy the needs of SAR and the other UWB radar antennas measurement. In order to demonstrate the data analysis program, FDTD simulation software was used to calculate the E-field of M×N points in a fictitious plane at different times just like the actual oscilloscope’s sampling signals in the time domain planar near field (TDPNF) measurement. The calculated results can be considered the actual oscilloscope’s sampling output signals. Through non-direct frequency domain near field to far field transform and direct time domain near field to far field transform, we get the almost same radiation patterns comparing to the FD measurements and software simulation results. At last, varied time windows were used to remove the influences of the non-ideal measurement environment.

Time domain Planar Near-Field Measurement Simulation
X. Shen,X. Chen, November 2006

The UWB radar operates simultaneously over large bandwidth and the antenna parameters must refer to simultaneous performance over the whole of the bandwidth. Conventional frequency domain (FD) parameters like pattern, gain, etc. are not adequate for UWB antenna. This paper describes an UWB radar antenna planar near field (PNF) measurement system under construction to get the impulse response or transient characteristic of the UWB antenna. Unlike the conventional antenna or RCS time domain test system, the UWB radar signal instead of the carrier-free short time pulse was used to excite the antenna that can avoid the decrease of the dynamic range and satisfy the needs of SAR and the other UWB radar antennas measurement. In order to demonstrate the data analysis program, FDTD simulation software was used to calculate the E-field of M×N points in a fictitious plane at different times just like the actual oscilloscope’s sampling signals in the time domain planar near field (TDPNF) measurement. The calculated results can be considered the actual oscilloscope’s sampling output signals. Through non-direct frequency domain near field to far field transform and direct time domain near field to far field transform, we get the almost same radiation patterns comparing to the FD measurements and software simulation results. At last, varied time windows were used to remove the influences of the non-ideal measurement environment.

Full Sphere Far-Field Antenna Patterns Obtained Using a Small Planar Scanner and a Poly-Planar Measurement Technique
S. Gregson,C. Parini, J. McCormick, November 2006

This paper presents an overview of work carried out in developing the probe-corrected, poly-planar near-field antenna measurement technique [1, 2, 3, 4, 5]. The poly-planar method essentially entails a very general technique for deriving asymptotic far-field antenna patterns from near-field measurements taken over faceted surfaces. The probe-corrected, poly-planar near-field to far-field transformation, consisting of an innovative hybrid physical optics (PO) [6] plane wave spectrum (PWS) [7] formulation, is summarised, and the importance of correctly reconstructing the normal electric field component for each of the discrete partial scans to the success of this process is highlighted. As an illustration, in this paper the poly-planar technique is deployed to provide coverage over the entire far-field sphere by utilising a small planar facility to acquire two orthogonal tangential near electric field components over the surface of a conceptual cube centred about the antenna under test (AUT). The success of the poly-planar technique is demonstrated through numerical simulation and experimental measurement. A discussion into the limitations of the partial scan technique is also presented.

Hemispherical Near-Field Antenna Measurements in an EMC Chamber Environment
G. Pinchuk,E. Katz, R. Braun, T. Kozan, November 2006

Hemispherical Near-Field (NF) antenna measurement technique has been applied for automotive antenna testing within a chamber dedicated to EMC tests. An existing turntable was used for azimuth rotation of a vehicle and a new portable 90°arch was added for elevation scanning of the radiated NF of the Device Under Test (DUT - vehicle with the antenna). Two antenna types were tested during chamber commissioning, one for GPS and another for XM satellite radio applications at frequencies 1.57 and 2.33 GHz respectively. Test results have shown that the EMC chamber can be successfully used for automotive antenna measurements as well, with accuracies acceptable for automotive applications. For higher operating frequencies, the EMC absorbers must be changed to less reflective material. In the paper, the measurement system is described, and the test results are presented, as well as some considerations on far-field pattern restoration based on measured hemispherical NF data.

Planar Near-field Measurement Results at 94 GHz Using Probe Position Correction
J. Guerrieri,D. Tamura, K. MacReynolds, M. Francis, R. Wittmann, November 2005

This paper presents results of planar near-field measurements at 16, 35 and 94 GHz using probe position correction algorithms. The algorithms correct for position errors of the probe near the scan plane. The probe’s actual position is measured using a laser tracker integrated into the planar-near-field scanning system at NIST. The laser tracker simultaneously obtains probe-position information at each point where amplitude and phase data are acquired during planar near-field antenna measurements.

Using a Chirp Z-transform on Planar Near-Field Data to Expand a Portion of the Far-Field with Increased Resolution and No Interpolation
D. Thompson, November 2005

This paper describes the use of a two-dimensional chirp z-transform (2D-CZT) to efficiently concentrate a large number of sample points in a single portion of the far zone without interpolation. This work presents the equivalence of transforms calculated from measured near-field data using both the 2D-CZT and 2D-fast Fourier transform (FFT). The paper also shows that the 2D-CZT is computationally more efficient than a zero-padded FFT when one requires a high resolution over a small area of the pattern.

On the Application of Range of the Iterative Probe Correction Technique in Spherical Near-Field Antenna Measurements
T. Laitinen,O. Breinbjerg, S. Pivnenko, November 2005

ABSTRACT An iterative probe correction technique for spherical near-field antenna measurements is examined. This technique has previously been shown to be ideally-suited for non-ideal first-order probes. In this paper its performance for other probes is examined.

Development of a Hemispherical Near-Field Range with a Realistic Ground - Part 2
E. Walton,C. Buxton, G.F. Paynter, J. Snow, T-H. Lee, November 2005

This paper will discuss the development of a VHF/UHF near field test range for the case where there are reflections from a realistic ground surface. We will show the results of a direct computation algorithm where a far field pattern is computed using plane wave synthesis. The performance of a C++ program that implements this algorithm will be discussed.

Development of a Hemispherical Near-Field Range with a Realistic Ground - Part 2
E. Walton,C. Buxton, G.F. Paynter, J. Snow, T-H. Lee, November 2005

This paper will discuss the development of a VHF/UHF near field test range for the case where there are reflections from a realistic ground surface. We will show the results of a direct computation algorithm where a far field pattern is computed using plane wave synthesis. The performance of a C++ program that implements this algorithm will be discussed.

Efficient Near-Field to Far-Field Transformation on Strategic Scanning Geometries
S. Costanzo,G. Di Massa, November 2005

Direct far-field transformation is developed from bi-polar near-field samples. As compared to conventional interpolation and expansion methods, a significant reduction in the computation time is obtained by the efficient use of the Fast Fourier Transform and the related shift theorem. Numerical simulations on array of Huyghens sources are considered as validations.

V-Band Planar Near-Field Antenna Test Facility and KRISS
J-S. Kang,H-K. Choi, J-H. Kim, N-W. Kang, November 2005

Planar near-field antenna measurement facility at KRISS has been upgraded to V-band (50 GHz – 75 GHz). This paper describes the planar near-field antenna measurement facility that consists of a planar near-field scanner, a microwave subsystem and an extrapolation range, and shows the measurement results of a V-band near-field probe and a Cassegrain antenna.

Measurements of the CloudSat Collimating Antenna Assembly Experiences at 94 GHz on Two Antenna Ranges
J. Harrell,A. Prata, C. Lee-Yow, C. Stubenrauch, L.R. Amaro, R. Beckon, T.A. Cariveau, November 2005

This paper presents measurements of the CloudSat Collimating Antenna (CA) as fabricated for the 94.05 GHz CloudSat radar, which is to be used to measure moisture profiles in the atmosphere. The CloudSat CA is a 3 reflector system consisting of the 3 "final" (relative to the transmitted energy) reflecting surfaces of the CloudSat instrument. This assembly was fed by a horn designed to approximate the illumination from a Quasi-Optical Transmission Line (QOTL). This same horn was employed as a "standard" for measurement of the CA gain via substitution, and its patterns were also measured (this substitution represents a departure from the standard insertion loss technique in the near field range). The CloudSat CA presented a substantial measurement challenge because of the frequency and the electrical size of the aperture is approximately 600 wavelengths in diameter, with a nominal beamwidth of 0.11 degrees. In addition, very high accuracy was needed to characterize the lower sidelobe levels of this antenna. The CA measurements were performed on a 3122-ft outdoor range (this distance was 41% of the far field requirement), which were immediately followed by measurements in an indoor cylindrical Near Field (NF) range. The instrumentation challenges, electrical, mechanical, and environmental are described. Comparison of the outdoor vs. indoor pattern data is presented, as well as the effect of the application of tie-scans to the near field data.

A Feasibility Study of Phase Retrieval Algorithms at Sub-Millimeter Wavelengths
A. Von Lerber,A. Lisno, A.V. Räisänen, J. Ala-Laurinaho, V. Viikari, November 2005

The applicability of phase retrieval algorithms for near-field measurements was studied at sub-millimeter wavelengths. Two different phase retrieval algorithms were implemented according to the existing scientific literature and they were both tested and compared at 310 GHz using a planar near-field measurement data. The chosen algorithms were Plane-to-Plane Diffraction algorithm (PPD) and Conjugate-Gradient Method (CGM). A lens antenna with diameter of 60 mm was used in the measurement experiment and the distance between the measurement planes was 50 mm. With this distance both of these algorithms could retrieve the phase that agreed well with the measured phase. We also implemented a combined algorithm for improved convergence.

A High Performance Combined NF-FF Antenna Test Facility
U. Shemer,C.T. Tong, November 2005

DSO National Laboratories (DSO) has commissioned a state-of-the-art 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. The overall system accuracy allows for future extensions to 40GHz and higher. The 11.0m x 5.5m x 4.0m (L x W x H) shielded facility houses the anechoic chamber and the control room. As the proffered location for this indoor facility is on top of an existing complex instead of the ground floor, antenna pick­up is facilitated by a specialized loading platform accompanied by a heavy-duty state of the art fully automated 2.0m x 3.0m (W x H) sliding door, as well as an overhead crane that spans the entire chamber width. Absorber layout comprises 8-inch, 12-inch, 18-inch and 24-inch pyramidal absorbers. The positioning system is a heavy-duty high precision 3.6m x 2.9m (W x H) T-type planar scanner and AUT positioner. The AUT positioner system is configured as roll over upper slide over azimuth over lower slide system. This positioning system configuration allows for planar, cylindrical and spherical near-field measurements. A rapidly rotating roll positioner is mounted on a specialized alignment fixture behind the scanner to facilitate far-field measurements. Instrumentation is based on an Agilent PNA E8362B. Software is based on the MiDAS 4.0 package. A Real-Time Controller (RTC), accompanied by an 8-port RF switch, facilitates multi-port antenna measurements, with the possibility of interfacing to an active antenna.

A Simple Probe Calibration Method of a New Compact Spherical Near-Field Measurement System for Antennas from 1 GHz to 10 GHz
M. Hirose,K. Komiyama, S. Kurokawa, November 2005

ABSTRACT We have developed a new compact spherical near-field measurement system using a photonic sensor as a probe and successfully measured the 3D antenna patterns of a double-ridged horn antenna from 1 GHz to 10 GHz. This system consists of a compact spherical scanner and a photonic sensor that is used for the probe of the spherical near-field measurements. In our system, only one probe can be used for the wide frequency range measurements and the probe compensation is not needed in the measurements. For the system, we propose a simple calibration method using a double-ridged horn antenna for our system. We calibrate the system by measuring the double-ridged horn antenna on the reasonable assumption that the antenna efficiency is 100 %. Comparing the absolute gain obtained by the proposed calibration method with the one decided by using three-antenna method at far-field range, we show that the agreement is good within 1 dB over the whole frequency range.

An Apparent Discrepancy Between Impedance Mismatch Factors for Near-Field and Far-Field Measurements
D. Hess, November 2005

In making accurate measurements of antenna gain one must correct for the impedance mismatches between (1) the signal generator and transmitting antenna, (2) between the receiving power sensor and the receiving antenna and (3) between the signal generator and receiving power sensor. This is true for both far-field gain measurements and near-field gain measurements. It has recently come to our attention that there is a lack of clarity as to the form the mismatch factor should take when correcting near-field measured data. We show that a different form of impedance mismatch factor is to be used with the voltage domain equations of near-field than has been used with the power domain Friis transmission equation.

Low Cost and High Accuracy Alignment Methods for Cylindrical and Spherical Near-Field Measurement Systems
J. Demas, November 2005

Precise mechanical alignment of motion axes of both cylindrical and spherical near-field systems is critical to producing accurate data. Until recently the only way to align these types of systems was to employ traditional optical tooling (i.e. jig transits, theodolites). Alignment by these methods is difficult, time consuming, and requires specialized training. More recently, laser trackers have been used for this type of alignment. Unfortunately, these devices are expensive and demand an even higher level of operator training. This paper describes the use of low cost alignment tools and techniques that have been developed by Nearfield Systems, Inc. (NSI) that greatly simplify the alignment process. Setup and alignment can be performed in a very short period of time by technicians that have been given minimal training. Suitable optical alignment procedures when followed by the use of electrical alignment techniques [7] yield sufficient alignment accuracy to permit testing up to Ku-band.

Spherical Near-Field Arch Range Upgrade
j. Aubin,A. Kipple, C. Arnold, J. Puri, November 2005

An upgrade to the large 75 foot radius spherical arch range at the U.S. Army Electronic Proving Ground at Ft. Huachuca, AZ has presented a complex design challenge in order to accommodate multiple test requirements, including both far-field and near-field measurements, as well as antenna under test (AUT) mode switching, over a wide frequency range. The range features a 60 foot diameter turntable (capable of supporting 80 tons) for azimuth positioning of large vehicles. The large arch/turntable positioning system combination presents a number of design issues in the implementation of a high performance, wideband RF subsystem. In addition, a significant requirement for this range is to allow either the probe mounted on the arch or the AUT mounted on the vehicle to transmit. The RF subsystem design utilizes the Agilent PNA in conjunction with the Agilent 85310 Distributed Downconverter system. Location of all the primary RF components are key issues in achieving sufficient transmit power, LO power, and receive sensitivity. Moreover, the selection and placement of the long RF cable runs has a significant impact on system level performance, and required thorough investigation. A unique utilization of available synthesizers provides a compact physical configuration and also provides an increase in speed over other multiple source configurations. This paper examines the design considerations for the RF subsystem and the configuration for achieving both near-field and far-field measurements for the case of the AUT transmitting as well as receiving.







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