Phased-array testing and diagnostics using planar near-field scanning
The Antenna Metrology group of the National Institute of Standards and Technology (NIST), working in cooperation with McClellan Air Force Base (MAFB), Sacramento, CA, have examined-measurement techniques to test a large phased-array antenna using planar near-field (PNF) scanning. It was necessary to find methods that would be useful in both field and production testing and could provide gain and diagnostic information in a simple and timely manner. This paper will discuss several aspects of the PNF measurement cycle that impact effective testing of the antenna array. These aspects include the use of a polarization-matched probe, the effect of scan truncation both on the transform to the far field and the transform to the aperture plane, and use of gain prediction curves as a diagnostic tool.
Near-field to far-field transformation using an equivalent magnetic current approach
An alternate method is presented for computing far-field antenna patterns from planar near-field measurements. The method utilizes near-field data to determine equivalent magnetic current sources over a fictitious planar surface which encompasses the antenna, and these currents are used to ascertain the far-fields. An electric field integral equation (EFIE) is developed to relate the near-fields to the equivalent magnetic currents. Method of moments (MOM) procedure is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient method (CGM), and in the case of a rectangular matrix, a least squares solution for the currents is found without explicitly computing the normal form of the operation. Near-field to far-field transformation for planar scanning may be efficiently performed under certain conditions by exploiting the block Toeplitz structure of the matrix and using CGM and Fast Fourier Transform (CGFFT) thereby drastically reducing comparison and storage requirements. Numerical results are presented by extrapolating the far-fields using experimental near-field data.
Theoretical comparison of modal expansion and integral equation methods for near-field to far-field transformation
A theoretical comparison for the application and derivation of modal expansion and integral equation methods is presented. It is shown that one formulation can be transformed into the other one using Fourier transform. From this point of view it can be stated that both method solves the same integral equation but for the modal expansion approach the integral equation is solved in the spectral domain while for the integral equation method the same equation is solved in the space domain. It is shown that for most of the practical antenna types the integral equation method gives more accurate far-field estimation than the modal expansion method, particularly in the planar scanning case.
A Practical technique for near field antenna testing
In recent years different techniques have been developed for measuring large aperture antennas on smaller ranges. Problems still exist with these techniques, though, such as impracticality and size restrictions. This paper presents a new method for measuring a phased-array antenna at approximately one tenth the far-field distance. This method involves focusing the test array to a probe a certain distance away, then moving the probe along an elliptical path. Since different elliptical paths can be easily generated with the same test hardware, this new method promises to yield a measurement technique that can be readily adapted to different sized antennas. This paper also presents the results of computer simulations showing the validity and limitations of this technique.
Accurate planar near-field probe correcion using dual-port circularly-polarized probes
When the planar near-field method is used for antenna characterization, two probes are required to measure an antenna under test (AUT). The receiving patterns (both amplitude and phase) of these probes, obtained from planar near-field measurements, must be utilized to accurately determine the far field of the AUT. This process is commonly called planar near field probe correction. When the AUT is nominally circularly polarized (CP), the measurements are more accurate and efficient if nominally circularly-polarized probes are used. Further efficiency is obtained when only one probe which is dual-polarized is used to allow for simultaneous measurements of both components. However, when using dual-port CP probes to measure the antenna, we must apply the probe correction even for on-axis measurements.
Validation testing of the planar near-field range facility at SPAR Aerospace Limited
A series of measurements to validate the performance of a Planar Near-Field (PNF) Antenna Test Range located at the Satellite and Aerospace Systems Division at Spar Aerospace Limited were made by Scientific-Atlanta during the month of February 1992. These measurements were made as a part of a contract to provide Spar with a Model 2095 Microwave Measurement System with planar near-field software options and related instrumentation and hardware. The range validation consisted of a series of self-tests and far-field pattern comparison tests using a planar array antenna provided by Spar that had been independently calibrated at another range facility. This paper describes the range validation tests and presents some of the results. Comparisons of far-field patterns measured on the validation antenna at both the Spar PNF facility and another antenna range are presented.
The UCLA bi-polar near-field range: processing techniques and measurement comparisons
A novel planar near-field antenna measurement and diagnostic system is described. This bi-polar near-field system offers a large scan plane size with reduced "real estate" requirements and a simple mechanical implementation resulting in a highly cost effective antenna measurement system. A brief description of the bi-polar near-field range and its associated data processing methods are given. Measured results are compared with those obtained on a far-field range and a plane rectangular planar near-field range. It is shown that the UCLA facility produces highly accurate results which rival those of modern production antenna measurement facilities. Holographic images produced from measured data are provided to demonstrate the diagnostic capabilities of the antenna range and to provide electromagnetic field visualization for educational purposes.
Quasi real time antenna testing by means of a 2D modulated scattering array in the focal plane of a compact range
This paper presents the feasability (sic) to explore the Focal Plane (FP) of a Compact Antenna Test Range (CATR). We first introduce the interest of getting very fast the Far Field Pattern of an antenna with a 2D modulated scattering array located at the focus of a CATR. Then, we discuss the geometric, electrical and optical constraints involved when using this technique. A comparison with a classical measurement performed at ESA-ESTEC is shown and we conclude by emphasizing the potentialities of this technique.
Error simulation, estimation and correction in probe corrected planar near field antenna measurements
A Planar Near Field to Far Field (PNF/FF) Transformation Program has been developed. This PNF/FF package includes probe correction, spectral filtering, position errors correction and sampled data expansion. In order to evaluate how measurement system errors affect PNF/FF transformation results, a whole set of simulation routines have also been implemented. In this paper, main modules of the PNF/FF package are discussed and error simulation models together with correction routines are described.
Refurbishment of the TUD-ESA spherical near field antenna test facility
The anechoic chamber housing the TUD-ESA Spherical Near Field Far Field Antenna Test Facility at the Technical University of Denmark dates back to 1967 while the present RF and data collection and control systems were designed and installed in several stages between 1978 and 1985. This paper undertakes to describe the definition and realization of a refurbished and upgraded radio anechoic facility for antenna measurements given as a starting point the already existing facility. In a parallel effort, both the RF and data collection and control subsystems are being renewed and upgraded.
A High Speed Fiber Optic Remote Receiver Link for Improved Antenna Measurements
The remote capability of the ORBIT AL-8000-5 Microwave Receiver is described. The use of a high speed fiber optic link between the remote receiver and the control room unit allows range distances of up to 19,000 feet. With repeaters, the range distance limitation is removed. This eliminates many of the distance cable and EMI problems associated with receivers which use a remote LO.
The small size and weight of the remote unit, allow the system to be mounted on the probe carriage of near-field scanner systems. This eliminates the high frequency phase errors as well as the phase error due to cable bending and temperature variation during the measurement. The result is a lower cost and more accurate measurement system. The advantages of this type of remote system are discussed for both near-field and far-field applications. Measurement data which show the performance of the fiber-optic system are presented. A description and pictures of recent installations are to be provided.
Portable RCS diagnostic system
This paper describes the most recent version of the Model 200 portable RCS diagnostic radar. The Model 200 was designed to provide high-resolution RCS measurements in unprepared rooms indoors as well as on outdoor ranges. The system can provide real aperture measurements, ISAR measurements, or SAR measurements without changing system configuration.
Ground-to-air RCS diagnostic system
The initial phase of METRATEK's new Model 300 Radar System has been installed at the Navy's Chesapeake Tests Range (CTR) at Patuxent River, MD. This ground-to-air Multimode, Multifrequency Instrumentation Radar System (MMIRS) is a high-throughput frequency-and-polarization agile radar that is designed to drastically reduce the cost of measuring the radar cross section of airborne targets by allowing simultaneous measurements to be made at VHF through Ku Band.
High duty instrumentation radar transmitters
Today's requirements for dynamic Radar Cross Section (RCS) test data set new demands upon instrumentation Radar systems. Transmitters must deliver high power and operate at high data rates. Additionally, noise floor reduction of coherent spurious signals improves raw data and minimizes the need for manipulation of data.
High speed antenna measurement systems for S.A.R. applications.
Data collection for Synthetic Aperture Radar (SAR) antenna measurements is increasingly making measurement stages very time consuming. This paper presents the capabilities of fast Planar Near Field (PNF) instruments using a linear modulated probe array. It demonstrates the possibilities to decrease the classical near field mechanical scan time by a factor ranging from 100 to 1000. Emphasis is given to the advantages of this technique for multi parameter antenna measurements.
Polarization grids for applications in compact antenna test ranges
In polarimetric RCS measurements, the cross-polarization levels which are required in the test zone, correspond closely to those which are realizable with most Compact Antenna Test Ranges (CATR). On the other hand, such a performance may not satisfy the accuracy requirements in cross-polarization measurements of high performance microwave antennas. These applications include spacecraft antennas, ground stations for satellite communications or microwave antennas for terrestrial applications, where two polarizations are used simultaneously.
Dual-frequency,dual-polarized millimeter wave antenna characterization
The radiation characteristics for a dual-frequency, dual-polarized millimeter wave antenna for a radar operating at 33 and 95-GHz were measured at the Ipswich Research Facility. On-pole and cross-pole radiation patterns were measured using the 2600 foot far field range. In this paper we'll discuss the general design of the antenna feed system and the instrumentation ensemble used to perform the far field characterization of this high performance large aperture dielectric lens antenna.
Demonstration of bistatic electromagnetic scattering measurements by spherical near-field scanning, A
The far-field radar cross section (RCS) of a conducting sphere is obtained by transforming scattered near-fields measured on a spherical surface. A simple and convenient calibration procedure is described that involves measuring the incident field directly at the target location. Although a non probe-corrected transmission formula was used in this study the importance of prove correction in practice is demonstrated.
Analytic spherical near field to near/far field transformation, An
An efficient and accurate spherical near field to far field transformation without probe correction is presented. The indices m of the Legendre polynomials is summed up analytically, thereby reducing the computation time. Computations with both synthetic and experimental data illustrate the accuracy of this technique.
High-speed, pulsed antenna measurements using the Scientific-Atlanta Model 1795P
Characterizing antennas under pulsed RF conditions has focused attention on a class of measurement challenges not normally encountered in CW measurements. The primary problems often include high transmit power, thermal management of the AUT, and a close interaction between the antenna and its transmitting circuitry. This paper presents instrumentation techniques for pulsed RF antenna measurements using the Scientific-Atlanta 1795P Pulsed Microwave Receiver as an example of a commercially available solution applicable to both active and passive apertures. Emphasis is given to measurement speed, dynamic range, linearity, single pulse versus multiple pulse measurements, pulse width, pulse repetition frequency (PRF), frequency coverage, system integration and automation, and suitability of equipment for antenna range applications.