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We have developed the spherical near-field measurement system using a photonic sensor as the probe of the spherical scanning. Because the photonic sensor is a few gram of weight and a few mm in length, the measurement system can be compact and simple. The probe compensation is not needed because the photonic sensor can be considered as an ideal infinitesimal electric dipole antenna in the spherical near-field measurements as well as the planar near-field measurements as shown before. To demonstrate the validity of the system, we have measured the antenna patterns of a microstrip antenna on a finite printed board at 5.85 GHz. The measurements by the photonic sensor agreed with the one by the far-field method.
This paper will discuss the application of alignment techniques and tools in a near-field testfacility. Standard alignment telescopes are not directly applicable in a general purpose near-field set-up because of limited dimensions of such a facility, where a direct target is not available and is often to close to the antenna to be in the focus region of the telescope itself. Self-made optical tools will be presented to overcome this problem, including some estimates about the required and obtained accuracies. Using these tools is demonstrated as a fast and accurate way to align an antenna to the measurement set-up.
This paper describes the installation and implementation of a Cylindrical Near-field Test Facility at Chelton Radomes Ltd, Stevenage, (formerly British Aerospace Systems and Equipment Ltd.), in the UK for the testing of large radome/antenna combinations. Test site commissioning and validation activities to determine measurement accuracy & repeatability for the radome performance parameters of transmission loss and boresight error, are discussed. Test data from actual measurements are presented.
While probe arrays are now recognized to allow rapid and accurate near-field measurements, the interaction with the Antenna Under Test (AUT) is still sometimes considered as a potential limitation, especially for electrically large directive antennas [1]. Based on numerical simulations, this paper reports the results of a thorough investigation of the interaction mechanism and analyses its impact on the far-field pattern accuracy. The most often, interaction effects can be maintained at an acceptable level, thanks to an appropriate design of the probe array element and structure. However, the efficiency of a posteriori compensation schemes has also been investigated. The Pattern Coherent Averaging Technique (PCAT) [2], which is well known for compensating plane wave deviations in the quiet zone of antenna far-field test ranges or interactions from single probe near-field facilities, also proved very efficient to reduce the interaction effects with a probe array.
In this paper I demonstrate how our current technology now very readily permits a standard of accuracy and utility to be realized, that was formerly available only in research laboratories. This is accomplished with standardly available positioning equipment and standardly available software. Accurate alignment of the range is enabled by a tracking laser interferometer. This composite nearfield scanning antenna range has afforded us the opportunity to compare readily, far-field results from the classic planar, cylindrical and spherical coodinate systems. Comparison data are presented.
This work is part of the UK Ministry of Defence initiative to examine causes of uncertainties in RCS measurements and to establish a network of certified facilities. Having developed a ‘best practice’ guide where causes of uncertainty were listed, the effect of polar diagram was selected as a priority topic. Correction algorithms for RCS measurements require knowledge of the beam shape and resolution in crossrange of the significant scatterers. Accordingly, the accuracy of polar diagram measurement, the effect of amplitude ripple and the applicability of the correction algorithms to near-field data were addressed. Measurements were made on two targets, a long cylinder and a small aircraft. Two antennas and two ranges were used to achieve 1dB, 3dB and 6dB illumination tapers across the cylinder. The 6dB taper situation was modelled for three different numbers of points. The work demonstrated that polar diagram effects are significant for point scatterers or simple targets, like the cylinder; however, for the small aircraft with a large number of distributed scatterers, the overall effect is less significant.
In this paper, the use of a low cost compact RCS measurement system is described, aimed at the characterisation of superstructure details. This system has been installed in a large room available within a shipyard, so that the measurement process is quite simple and efficient, even though under near-field conditions. Results are relevant to radar images and RCS, and can be used for the selection of details, for the optimisation of their backscattering and/or their installation process, and for the improvement of simulation codes. Comparison with simulations is also reported.
SOLANGE is a large RCS indoor measurement facility operated at SHF and V/UHF frequencies. In the V/UHF band, couplings between the target and the walls can be exhibited. These perturbations due to non-directive transmitting/receiving antenna, and non-absorbing walls must be eliminated to derive the intrinsic response of the target. To reduce their levels CELAR introduced smart methods («SAV »: Site Altitude Variable and « EAV »: Environnement Altitude Variable): the transmitting/receiving antenna (and also the target in the EAV method) is translated along the elevation axis, and the acquired data are averaged. CELAR and CEA collaborated to qualify the chamber in the U/VHF band. The aim of the study is to identify and quantify the error sources, and to suggest some improvements. The analysis, based on RCS measurements of canonical targets, includes data processing (clutter reduction) and evaluation of the effects of SAV and EAV on the couplings. A theoretical algorithm is used to assess the performances of the processing, and to optimize measurement altitudes. It introduces an analytical model for the antenna and its images with respect to the walls, and calculates the scattered near field. This study enabled us to suggest improvements in the parameters of the processing, as well as in the RCS facility configuration.
Undesirable antenna to antenna coupling has caused EMI problems between the WSC-6 SATCOM system and various systems in many shipboard installations. Long term solutions are currently being explored to resolve this EMI problem, which include adaptive interference cancellers and redesign of the WSC-6 feed and subreflector. However, these solutions are expensive and require several years to develop. An intermediate solution using RAM shrouds around the main reflector and subreflector edges of the WSC- 6 antenna has been proposed. The RAM shrouds were designed to reduce the spillover and diffraction of the antenna while having minimal impact on the antenna performances. A lightweight RAM was chosen to minimize the weight increase of the antenna. A prototype unit with the proposed modifications has been fabricated, assembled and tested in a tapered anechoic chamber, a near-field range, and a compact range. Significant reductions in the WSC-6 antenna sidelobes and backlobe have been verified via these measurements. Highlights of these modifications are described. Measured data (near field, compact range, tapered chamber, and shipboard) are presented.
Undesirable antenna to antenna coupling has caused EMI problems between the WSC-6 SATCOM system and various systems in many shipboard installations. Long term solutions are currently being explored to resolve this EMI problem, which include adaptive interference cancellers and redesign of the WSC-6 feed and subreflector. However, these solutions are expensive and require several years to develop. An intermediate solution using RAM shrouds around the main reflector and subreflector edges of the WSC- 6 antenna has been proposed. The RAM shrouds were designed to reduce the spillover and diffraction of the antenna while having minimal impact on the antenna performances. A lightweight RAM was chosen to minimize the weight increase of the antenna. A prototype unit with the proposed modifications has been fabricated, assembled and tested in a tapered anechoic chamber, a near-field range, and a compact range. Significant reductions in the WSC-6 antenna sidelobes and backlobe have been verified via these measurements. Highlights of these modifications are described. Measured data (near field, compact range, tapered chamber, and shipboard) are presented.
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.
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.
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.
The possibility of launching satellites with increasing volume and weight leads to a higher economy and costefficiency for the service of future communication satellites, which are equipped with platforms up to 12 m in width for a variety of different antennas. For testing the radiation characteristics of the antennas of such large antenna farms, new test facilities are required to be designed and built up. Besides near-field test facilities, compact ranges exist, which provide additionally short test campaigns according to its real time measurement capability. Usually, for communication satellite testing, the highly accurate CCR 75/60 of Astrium GmbH, Germany, was used until now. For the future large satellites, Astrium newly designed the CCR 120/100, which provides a test zone of more than 8 m in diameter. The paper shows the requirements for testing of the large satellite antennas. Further, the design criteria, the range geometry and first simulation results of the CCR 120/100 are shown.
Active and multimode antenna measurements for the ever-growing number of wireless applications are becoming more and more important. There is a need driven by the mobile phone and Bluetooth industries among others to develop a test set-up capable of measuring active radiating devices under real operating conditions. For example, it is of great interest to measure the radiation characteristics of a mobile phone integrating the full communication system. The implementation of such measurements involves aspects of control, synchronization and receivers dedicated to multi-mode test configurations.
A Wideband Optically Multiplexed Beamformer Architecture (WOMBAt) was developed and characterized at the Crane Naval Surface Warfare Center Active Array Measurement Test Bed (AAMTB) facility. The project included development and integration of the WOMBAt photonic beamformer with the Active Array Measurement Test Vehicle (AAMTV). The AAMTV is a 64-channel transmit-receive (TR) module based phased array beamformer that is integrated with the AAMTB facility 12’x9’ planar near-field scanner. The AAMTV provided phase trimming and a small amount of electrical delay while the WOMBAt provided longer optical delays using commercial-off-the-shelf (COTS) components typically manufactured for the telecommunication industry. By integrating the WOMBAt with the AAMTV, a highly flexible test environment was achieved that included system calibration, multi-frequency scanning, and antenna pattern analysis. This paper presents antenna pattern results showing less than 0.7 dB of amplitude variation over the frequency range from 9 to 10 GHz at each of the measured nominal steering angles. The beamformer was steered to greater than ±69 degrees with an observed beam squint from 9 to 10 GHz of less than 1 degree.