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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.
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.
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).
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.
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.
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.
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.
This is part three of a series of talks on the development of a new type of near field antenna range. The range is designed to measure the VHF and UHF antenna characteristics of a vehicle over a realistic ground. This means that the spherical symmetry has been lost and the classical spherical mode expansions are not appropriate. We have previously demonstrated a plane wave synthesis approach to the far field transformation, including the lossy dielectric half-space representing the ground. This third yearly presentation will discuss the compensation needed for realistic probe antenna, probe arm and turntable imperfections. Results for actual experimental measurement data with sample space and probe antenna time dispersion compensation will be shown. Comparisons with the theoretical far field computations and the spherical mode expansion results will be included.
This paper discusses the process of optimization of a spherical near-field range for measurement of large UHF antennas used in space applications. Results of a study undertaken to understand and optimize range performance in presence of multi-path errors and mutual coupling are presented. Data is presented showing variation in measured patterns of a generic UHF antenna as a function various parameters such as a) use of probes of different gains, b) separation distance between the probe and the antenna and c) absorber rearrangement. Use and effectiveness of software post processing approaches such as spherical mode filtering, time domain gating and use of proprietary algorithms (e.g. “MARS processing” developed by NSI Inc.) is illustrated. Practical implementation of these approaches and corresponding impact on data density, test duration and computational effort are also discussed.
In a FF antenna range the DUT mechanical Boresight can be aligned with the Range Boresight simply by using a Boresight scope to transfer the DUT mechanical Boresight to the Range coordinate system. This is not applicable to a PNF Range; hence, another transfer device and different transfer methods are required. This paper describes the development, testing and referencing of an existing PNF range to a reference optical cube that serves as the coordinate system transfer device. The optical measurement system employs an automated total station Theodolite system, incorporating true 3D positioning of the NF probe along defined axes of movement. The data collected is processed to best fit a straight line defining the vector representing the axis. The scanning PNF plane is defined with high accuracy, by a geometrical representation of two (or more) axes in that plane. Thus, the scan plane coordinate system was transferred by auto collimation methods to the reference optical cube. A second optical cube must be placed on the AUT to be used as a reference for its mechanical Boresight. When the AUT is set up for testing, the coordinate systems are transferred from each cube to the other by means of co-collimation using a temporarily positioned Theodolite combination.
Dual polarized probes for modern high precision near field measurement systems have stringent performance requirements in terms of pattern shape, on-axis and off-axis polarization purity, return loss and port-to-port isolation. A further requirement to the probe is that the useable bandwidth should exceed the antenna under test. As a consequence, the probe design is often a trade-off between performance requirements and the usable bandwidth of the probe. Current high performance designs are based on corrugated horns with balanced capacitive orthogonal excitation achieving close to 25% bandwidth [1]. This technology is well suited for near field probes in the L to Ka band range. Although attractive for compactness, simplicity and excellent performance, probes with external balanced feeding require high precision couplers and manual tuning that impact the overall complexity and manufacturing cost of the final probe. A reduction in cost and complexity can be achieved while maintaining the high performance standards. SATIMO has developed an innovative near field probe with self-balanced feeding maintaining high performance on a wide bandwidth. The overall simplicity makes the new technology very attractive for probe designs in the L to Ka band range.
Dual polarized probes for modern high precision near field measurement systems have stringent performance requirements in terms of pattern shape, on-axis and off-axis polarization purity, return loss and port-to-port isolation. A further requirement to the probe is that the useable bandwidth should exceed the antenna under test. As a consequence, the probe design is often a trade-off between performance requirements and the usable bandwidth of the probe. Current high performance designs are based on corrugated horns with balanced capacitive orthogonal excitation achieving close to 25% bandwidth [1]. This technology is well suited for near field probes in the L to Ka band range. Although attractive for compactness, simplicity and excellent performance, probes with external balanced feeding require high precision couplers and manual tuning that impact the overall complexity and manufacturing cost of the final probe. A reduction in cost and complexity can be achieved while maintaining the high performance standards. SATIMO has developed an innovative near field probe with self-balanced feeding maintaining high performance on a wide bandwidth. The overall simplicity makes the new technology very attractive for probe designs in the L to Ka band range.
Typically radome tests are performed on outdoor far field ranges or compact ranges. ORBIT/FR has designed, build and qualified a unique spherical near-field radome test facility for the nose-mounted radomes of commercial traffic aircraft for the so-called “after repair” tests according to the international standard RTCA/DO-213, as well as the aircraft manufacturers Component Maintenance Manuals. The facility is extremely compact (chamber size 5.7 m x 5.2 m x 3.2 + 0.7 m, L x W x H), can handle radomes as small as used on the Canadair and as large as used on the Airbus-380 and can be installed directly in the repair workshop for such radomes. The tests performed are transmission efficiency and side lobe level increase. The system is completely automated, so that a workshop technician can operate the facility. Utmost attention has been paid to operational aspects and both operator and equipment safety. After the measurements are done, a test report is fully automatically generated according to RTCA requirements and classifications. The facility is equipped to test all standard Airbus, Boeing, Canadair and Dash nose radomes.
Typically radome tests are performed on outdoor far field ranges or compact ranges. ORBIT/FR has designed, build and qualified a unique spherical near-field radome test facility for the nose-mounted radomes of commercial traffic aircraft for the so-called “after repair” tests according to the international standard RTCA/DO-213, as well as the aircraft manufacturers Component Maintenance Manuals. The facility is extremely compact (chamber size 5.7 m x 5.2 m x 3.2 + 0.7 m, L x W x H), can handle radomes as small as used on the Canadair and as large as used on the Airbus-380 and can be installed directly in the repair workshop for such radomes. The tests performed are transmission efficiency and side lobe level increase. The system is completely automated, so that a workshop technician can operate the facility. Utmost attention has been paid to operational aspects and both operator and equipment safety. After the measurements are done, a test report is fully automatically generated according to RTCA requirements and classifications. The facility is equipped to test all standard Airbus, Boeing, Canadair and Dash nose radomes.
Satellite TV reflectors for home use, provided to the public by service companies such as DIRECTV, have many features which must be adequately characterized prior to design release, including: • Multiple Beam Frequency Re-use • FCC Sidelobe Envelope Verification • Circular Polarization Isolation These features must be adequately tested at frequencies up to Ku band and beyond. The use of a far-field range is impractical, as some of the reflectors measure several feet in diameter, and thus requires a range length of several hundred feet at Ku band. Near-field testing requires a full scan to determine a single cut for evaluation of FCC compliant sidelobe performance. Thus, a compact range is a logical alternative for measurement of this class of antennas. The compact range can provide a quick assessment of multiple beam coverage performance and pass/fail analysis against FCC sidelobe curve specifications. In addition, the feeds for these antennas often use Low Noise Block (LNB) Downconverters that are built in as part of the feed assembly. Measuring the output of an LNB does not yield the phase information required to determine all polarization parameters. A spinning linear measurement with some unique processing was implemented on this range to determine the full polarization characterization, using some elementary assumptions about polarization sense. This paper describes the implementation of a compact range based measurement facility for satellite antenna testing, with emphasis on the circular polarization measurement of the LNB assembly, capability for comparison against FCC sidelobe levels, and measurement of offset beams featuring frequency re-use capability.
A computational technique based on near-field to far field transformation is presented. This can be more versatile and accurate than the conventional modal expansions. The established method for near-field to far-field transformation has been the modal expansion method. The primary drawback of the technique is that when a Fourier transform is used, the fields outside the measurement region area is assumed to be zero, particularly in the planar and cylindrical case. Consequently the far-fields are accurately determined only over a particular angular sector which is dependent on the measurement configuration. A simple and accurate integral equation solution which represents an alternate method for computing far-fields from measured near-fields is presented. The basic idea is to replace the radiating antenna by equivalent electric and/or magnetic currents which reside on a fictitious surface and encompasses the antenna. These equivalent currents are assumed to radiate identical fields as the original antenna in the region of interest. Using the surface equivalence principle different types of the E-field integral equation (EFIE) have been developed. The method of moments (MoM) has been utilized to transform the integral equation into a matrix one and the conjugate gradient (CG) procedure has been applied to solve it numerically. Hence, this procedure is not limited by the Nyquist sampling criteria nor by the presence of evanescent waves which may make source reconstruction using current procedures unstable. Accurate far-fields over large elevation and azimuthal ranges have been calculated from simple measurements based on planar and spherical scanning.
Nowadays near-field measurement techniques are widely used for detecting the characteristics of the radiated pattern for a large variety of antennas. The core of any near-field measurement is the near-field to far-field transformation. Such transformations use different coordinate systems, like planar, cylindrical, or spherical, and may utilize special solutions. They are already well known for many years. The common feature of all mentioned near- to far-field transformations is the usage of regular measurement grids on planar, cylindrical, or, respectively, spherical surfaces. Future applications, like the Airborne Near-Field Test Facility (ANTF) are expected to lack this characteristic of regular measurement grids, since the flying or floating probe platform cannot be guided sufficiently accurate. This requires the utilization of advanced data processing methods for interpolating measured data on an arbitrary irregular grid to a nearby regular grid, or direct transformation to the far-field. It will be shown that this data processing can be performed by using the Stratton-Chu representation formula utilizing equivalent currents on a well-chosen artificial surface or the classical mode expansion method with additional pre-processing. This paper describes briefly the principles of the ANTF, discusses the application of the equivalent current method and compares it with the widely used mode expansion method. Measured and processed data examples will be presented.
NSI has developed a novel technique for automating antenna range configurations. Although automation has shown to dramatically improve range productivity, most of today’s antenna ranges are reconfigured manually. Today’s automated ranges use electromechanical RF switches to control the RF signal path, which is contained primarily in a central rack, thereby limiting automation to ranges that are relatively small in size. Larger ranges, however, tend to locate many of the RF components such as mixers, couplers, amplifiers and multipliers remotely near the probe or AUT, sometimes 100 ft (30 m) or more from the rack, making the remote RF components more difficult to access and control. To address this problem, NSI has developed the Range Transition Manager (RTM) for automating large antenna ranges. The RTM uses modular packaging with a LAN interface and embedded processor to provide commonality and flexibility in automating various range sizes and types. The RTM family of modules provide a full range of automation capability for 0.5 to 18 GHz and higher frequencies. This paper will describe the capabilities of the Range Transition Manager developed for a large near-field scanner and describe how the RTM improves overall range productivity.
Spherical near-field measurements have become a common way to assess performance of a wide variety of antennas. Published reports on range error assessments for spherical near-field ranges however are not very common. This is likely due to the perceived additional complexity of the spherical near-field measurement process as compared to planar or cylindrical measurement techniques. This paper will establish and demonstrate a simple procedure for characterizing the performance of a spherical near-field range. The measurement steps and reporting can be largely automated with careful attention to the test process. We will summarize the process and document the accuracy of a spherical near-field test range at NSI using the same NIST 18 terms commonly used for planar near-field measurements.
This paper describes the new NIST tabletop millimeter-wave extrapolation range that will provide on-axis gain services up to 110 GHz. A discussion of the extrapolation measurement method, as presented at the Antenna Measurements Techniques Association (AMTA) in 1999, is the basis for much this paper. The extrapolation method for determining gain of directive antennas at quasi-near-field distances is based on a generalized three-antenna approach. It has been used at NIST for more than twenty years to calibrate antenna gain standards up to 20 GHz to within 0.1 dB and up to 50 GHz to within 0.15 dB. The basic theory, description of the measurement system, data acquisition procedure, and measurement results for three antennas at 94 GHz will be presented.