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An advanced method of phased-array antennas (PAA) performance monitoring is presented in this paper. It allows receiving more accurate results for PAA with binary phase shifters. The special attention is paid to such practical aspects of design and application of built-in performance monitoring systems, as the algorithm of controlled channel signal isolation, choice of the location of probe antennas and transfer matrix calibration which is necessary for PAA performance monitoring at system level.
We introduce a near-field spherical scanning algorithm for antenna measurements that relaxes the usual condition requiring data points to be on a regular spherical grid. Computational complexity is of the same order as for the standard (ideal-positioning) spherical-scanning technique. The new procedure has been tested extensively with simulated data.
In 2001, the Boeing 9-77 Indoor Compact Range successfully passed the range certification process. In preparation and during the On-Site Review in October 2001, RCS data on a pair of ultraspheres for the dualcalibration were collected. In this paper, we analyzed the data with regard to uncertainty analysis. An empirical approach for compensating the systematic error is presented.
We discuss the mitigation of truncation errors in spherical scanning measurements. The main emphasis is the spherical harmonic representation of probe transmitting and receiving functions; however, our method is applicable to nearfield measurement of electrically small antennas for which fullsphere data are either unreliable or unavailable.
This paper presents an approach to experimental identification and investigation of the higher-order diffraction effects. The proposed technique allows one to determine parameters (particularly coordinates of the attachment and launching points) of the higher-order diffraction centers and can be considered as an extension of the Inverse Synthetic-Aperture Radar (ISAR) imaging technique.
WINDSAT is a satellite system designed to be a demonstration of passive microwave polarimetry to measure ocean surface wind speed and direction. The polarimeter works off the crosspol components of the antenna, necessitating high performance requirements both in the building and testing of the antenna. The calibration of the reflector antenna system will be discussed in this paper, along with various analysis done for the project and verified by range measurement.
This paper shall discuss how to correct for the presence of groundwave propagation on a low frequency (3 MHz
ORBIT/FR-Europe is in the process of finishing a new Compact Antenna Test Range for Ericsson Microwave Systems (EMW) in Sweden. The design was presented at AMTA 2001. Here the progress in the project is presented. Most subsystems are now installed, and system level acceptance will follow in the near future.
When making large scale RCS measurements on a ground bounce range, EPS foam columns are frequently used as target support structures for test bodies and air vehicles. Thus, the design of foam columns is a key part in preparing for a large-scale outdoor test. Range engineers require foam column design methods and tools that are both efficient and reliable. This paper describes effective foam column design methods and shows comparisons of predicted column RCS to column measurements performed at NRTF. These comparisons give credibility to the concept of foam column modeling and ground bounce range scattering simulations, and give range engineers confidence in their foam column design process.
Originally installed in 1992, the Advanced Compact Range (ACR) at Wright-Patterson Air Force Base was completely aligned using a Leica multi-theodolite measurement system. The Coherent Laser Radar (CLR) System provides an automated precision measurement capability which can gather significantly more data permitting a more complete characterization of the range in a relatively unobtrusive manner. This paper presents the process and results of applying Laser Radar Metrology as an optical range re-qualification tool within the Air Force Research Laboratory’s ACR.
Tapered chambers have long been used for far-field antenna and RCS measurements. Conventional taper chambers used commercial antennas such as horns or log-period dipoles as wave launchers. One problem of this approach is the movement of the phase center associated with the antenna design. The positioning of the antenna inside the chamber is also critical. Undesired target-zone amplitude and phase distortion are caused by the scattering from the absorber walls. A novel feed antenna design for a tapered chamber is proposed here to provide broadband and dual polarization capabilities. This design integrates the absorber and the conducting walls behind the absorbers into to ensure a stationary phase center over a wider frequency range. In such a design, the dielectric constant of the absorber is utilized to maintain a clean phase front and a single incident wave at high frequencies. The conductivity of the absorber is also utilized to shape the field distribution at low frequencies. As a result, a wider frequency range can achievable for a given chamber size. One trade-off of this design is its reduced efficiency could be associated with the absorber absorption. Some simulation results from a 3-D FDTD model of a prototype design will be presented.
We present quantitative measurements of the imbalance induced in a broadband, wire-cage biconical antenna situated over a conducting ground plane and fed via a coaxial transmission line. The antenna and feed structure taken together are represented as a 2-port, 3-terminal network which, in turn is represented using a Ð equivalent circuit. A new measurement technique which requires no balancing network for determining the equivalent network component values is presented. The complex, frequencydependent elements of the equivalent network are derived from measured data and presented, clearly showing that the imbalance tendancy is strongest in the vicinity of the series resonances of the effective common mode circuit. Thus, it can be concluded that by avoiding feed arrangements which cause series resonances in the common mode circuit within the operating frequency range of the antenna, balance can be maintained without undue requirements on the balancing network.
Target support pylons and foam columns have been in use since the late 1970’s to provide target support for RCS measurements. Pylons currently limit our low frequency measurement capability due to the moderately high scattering from the pylon edges. Additionally both foam column and pylon support structures interact with the target scattering which can limit our ability to completely subtract the target support scattering from the target signature data. Target suspension using a string support system has the potential to eliminate these limitations. MRC has recently completed a string support technology demonstration program to identify the critical components for implementing an indoor string support system for RCS measurements. Critical components identified and demonstrated under this program included a survey of string materials for RCS measurements, development of low coefficient of friction swivel bearings, structural target to string interfaces, and three different techniques for providing target rotation. This presentation will highlight the results from the demonstration program showing viability of string support systems to provide an enhanced RCS measurement capability for indoor RCS measurement ranges
A compact range was recently constructed at the Applied Physics Laboratory to measure broad-beam, fan-beam, and pencil-beam antennas (max aperture: 1 meters). Chebyshev absorber treatments, lightweight composite reflector, foam column mount for light-weight antennas, automated measurement software, and a novel feed spillover rejection algorithm are the technology elements implemented in this compact range measurement facility. This paper will describe a trade study that APL performed before the compact range antenna facility was built. Solutions to some of problems that were encountered during the construction will be discussed as well as the overall performance of the facility. The measurement of a broad-beam antenna will be compared to calculated pattern. This measurement will highlight the advantages of using a software range gate that was recently developed.
A novel technique for mapping stray signal sources in spherical test ranges is presented. The technique is based on near field focusing. However, instead of the phase information, the time of arrival information is used for focusing. Thus, the technique uses field probe data over a frequency band, and provides good down range resolution. The technique is applied to the field probe data of an experimental outdoor spherical test range. The test range uses R-card fences to suppress ground bounce term in the quiet zone. From the stray signal maps obtained using the proposed technique it is clear that the test range is free of the ground bounce term.
When a dual port probe is used for near-field measurements, the amplitude and phase difference between the two ports must be measured and applied to the probe correction files so that the measurements and calculations will have the same reference. For dual port linear probes, the measurement of this “Port-to-Port” ratio is usually accomplished during the gain or pattern measurements by using a rotating linear source antenna.1 When a dual port linear probe is used to measure a circularly polarized antenna, the uncertainty in this Port-to-Port ratio can have a significant effect on the determination of the cross polarized pattern. Uncertainties of tenths of a dB in amplitude or 1-3 degrees phase can cause changes in the cross polarized pattern of 5-10 dB.2 3 The paper will present a method for measuring the Port-to-Port ratio on the near-field range using a circularly polarized antenna as the AUT (Antenna Under Test). The AUT does not need to be perfectly polarized nor do we need to know its correct polarization. The measurements consist of two separate near-field scans. In the first measurement the probe is in its normal position and in the second it is rotated about the Z-axis by 90 degrees. A script then calculates the Port-to-Port ratio by comparing the crosspolarization results from the two measurements. Uncertainties in the Port-to-Port ratio can be reduced to hundredths of a dB in amplitude and tenths of a degree in phase. Measurements were taken at TRW’s Large Horizontal Near-field Antenna Test Range.
Single-beam and composite-beam performance of a 4-port X-band waveguide Butler matrix was measured on the Georgia Tech Research Institute planar near-field range for wideband frequency performance. The techniques necessary to perform accurate measurements on a broad-beamed antenna in a near-field range will be discussed, and measured far-field pattern data collected at the design frequency of 9.3 GHz are presented and compared with predicted results of the Butler matrix. In cases where the measured data and the expected results do not compare well, aperture amplitude and phase data, transformed from the near-field data, are shown as a diagnostic tool for corrections. After correction, new data at 9.3 GHz are presented for comparison with predicted results, and selected farfield pattern data collected at 8.6 GHz and 11.0 GHz are presented.
This paper describes two methods that can be used to measure the leakage signals in quadrature detectors, predict the effect on the far-field pattern, and correct the measured data for leakage bias errors without additional near-field measurements. One method is an extension and addition to the work previously reported by Rousseau1. An alternative method will be discussed to determine the leakage signal by summing the near-field data at the edges of the scan rather than summing below a threshold level. Examples for both broad-beam horns and narrowbeam antennas will be used to illustrate the techniques.
This paper explores the possibility of constructing the interior field distribution of a Luneburg lens antenna through a brute-force implementation of microwaveholographic imaging. Images of the interior fields are constructed at various depths within the lens. Results from measured data, direct simulation, and the Fourier transform of simulated near-field data are compared in order to perform an in-depth comparative study.
In this paper, techniques are presented for the measurement of element radiation patterns of a belt-like C-band conformal array of microstrip patch elements, which wraps completely around the cross-section of an aircraft wing. The element patterns were measured, in situ, then analyzed in terms of phase and amplitude ripple versus element location around the wing. These results indicated trends in interference due to the experimental environment and the geometry of the wing itself. Experiments were conducted which minimized interference effects due to the environment, resulting in the true element patterns in the presence of wing platform interference. In an effort to identify platform-induced interference, anechoic absorber was used to minimize pattern ripple attributed to the edges of the wing, enabling validation of the measured element patterns against simulated data, which did not include platform interference. Thus, determining whether to include the platform effects in the measured data is dependent on the intended use of the results.