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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.
A new strategy to filter the environmental clutter in the measured near/far zone field data due to reflections and diffractions from objects in the measurement zone is presented. The approach is based on the new concepts of Point Source Spectral Content and Local Spectral Content of the reduced field detected on the observation domain. The effectiveness and the performances of the approach has been evaluated by processing synthetic as well as real world data.
An error detection technique was developed for culling large masses of measured antenna pattern data by first removing information that is likely to be associated with the antenna. Since the maximum spatial frequency of radiation from the antenna can be determined by its electrical size, any energy outside that spatial band is not considered to be valid and may be used to flag suspicious data. This analysis can be accomplished rapidly and can be used to cull patterns containing such anomalies as spikes, notches, non-closures and multipath effects. This paper describes the method with examples from simulated and measured patterns.
We present and analyze a procedure for performing relative, ultra-wideband antenna pattern measurements in a non-ideal EM facility. Ultra-wideband, shortimpulse, TEM horn transmission measurements were performed and compared with computer-modeled radiation pattern results. These measurements allowed us to analyze radiation lobes and nulls in both boresight and off-axis antenna positions. The results show that the measurements performed in this testing environment agreed well with computer models.
This paper presents a method for correcting RCS data obtained from objects extending beyond the boundaries of the test zone into the transition region of a large compact range collimator. The technique, exploiting the non-zero irradiation in the transition regions, uses results of calculated or measured field probes in conjunction with an image-based decomposition of the target angular response to correct for the field taper. The taper correction is developed as a weighting function applied to the spatial distribution with frequency-dependent coefficients derived from the field probes; the corrected RCS response is then obtained by an inverse operation. The paper addresses the conceptual notions of the approach and the limitations inherent to the underlying assumptions. Results of tests on canonical and actual targets are shown to demonstrate the applicability of the technique.
Waveguide simulators are widely used for low cost validation of periodic microwave designs and to perform antenna measurements. We have used measurement results of a waveguide simulator to predict both Frequency Selective Surface (FSS) and reflectarray responses. For scan angles close to normal, a suitable waveguide simulator is relatively wide and measurement results are often corrupted. This is often caused by uncontrolled multi-mode operation. The work presented here describes a waveguide simulator, which solves this problem for triple-mode operation. The triple-mode waveguide simulator has three standard waveguide ports and one triple-mode port. This device can be excited on the three standard ports. It produces each of the three propagating modes at the triple-mode port separately. Simulations and measurements on a prototype show good agreement. With our current set-up, three scan angles can be predicted instantaneously and grating lobes can be studied as well.
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.
From the earliest days of antenna development, the need for measurement of performance and function has been present. Some characteristics of antennas, such as radiation pattern, are measured by moving one antenna with respect to another. In early antenna testing, outdoor ranges were used to provide a close approximation to the pattern. However, due to the challenges of weather and other environmental effects, antenna testing moved indoors with a number of methods used to compensate for the lack of available space. This paper presents an overview of the history of testing at BATC, from the early days of outdoor testing to the transition to conventional anechoic chambers and nearfield probe facilities. During this time, a variety of techniques have been used to augment standard methods for special requirements, and this paper seeks to communicate some of these methods to the testing community as well as providing a general history of antenna measurement.
A system has been developed for acquiring an antenna’s complete (3D) radiation pattern and radar cross-section (RCS) measurements. The system consists of a motion controller, a network analyser and tower assembly. The tower assembly is in an anechoic chamber. The tower has a novel design. It uses three motors in a special configuration, thereby allowing 2 ½ degrees of freedom. This freedom gives the ability to run complete antenna or RCS measurements automatically. Another advantage stemming from the degrees of freedom is expansion of the range of measurements. This is enabled by a variety of possible positions inside the chamber. Tests have also been carried out on system performance. The data acquisition rate becomes crucial when dealing with 3D pattern measurements. The performance of an HP 8720 or 8753 network analyser series can be dramatically increased by using the power sweep mode for data acquisition. Together with the “external trigger-on-point” mode, this gives the best positioning accuracy. The six-month experience has demonstrated the flexibility and reliability of the set up and ideas.
We discuss progress in developing a new broadband (10 MHz to 40 GHz) RF field standard to be used for calibrating small electromagnetic field probes. The technique generates a well-defined and uniform TEM mode field between the conductors of an air-filled coaxial transmission line of conical geometry (termed a “co-conical” line) that is terminated in a well-matched, high-power, distributed load. We show that generation of higher-order mode fields will be minimal due to the line’s circular and symmetrical crosssection. Internal field levels equivalent to power density levels in excess of 10 mW/cm2 can be generated using broadband power sources of only 20 watts output. The new system will be capable of rapid, automated and accurate calibration of small field probes and can realize significant savings in both equipment/facility expenses and operational costs.
In June 2001, the DoD Range Commanders Council Signature Measurement and Standards Group (RCC/SMSG) certified that the Helendale Measurement Facility (HMF) outdoor radar cross section (RCS) measurement Range Book met the ANSI-Z-540 documentation standards established by the DoD demonstration project. This paper describes how Lockheed Martin Aeronautics (LM Aero) applied the ANSI Z-540 [1,2,3] standard to obtain National Certification of the HMF RCS range. The dual calibration results for Pit #1 and Pit #3 are presented showing upper and lower uncertainty error bounds established by this process. Schedule, cost, range book format, and “lessons learned” from the LM Aero experience are also discussed.
This paper reviews the Helendale Measurement Facility (HMF) ground plane range uncertainty analysis and associated data collection. Range uncertainty analysis is a requirement for ISO-25/ANSI-Z-540 range certification and is a priority one section in the Helendale Range Book. Targets used for the analysis were two sets of right circular “squat” calibration cylinders. These cylinders are the dual calibration cylinders for HMF. Calibration measurement uncertainties are established statistically from a large number of repeated measurements at S, C, X, and Ku bands. Each measurement was taken at two target support locations down range. The field data collected included monostatic scattering from two calibration cylinders, backgrounds with no target and support, and drift data for quality control. I and Q imbalance, frequency stability, range accuracy, linearity, and field uniformity at target locations were considered in the analysis. The uncertainty analysis is based on RSS addition of errors and assumes all errors are additive and that targets are not LO. The statistical approach used to perform the uncertainty analysis reported in this paper was developed cooperatively at AFRL and Mission Research Corporation.
It is a very common practice to over specify the Quiet Zone performance requirements for an anechoic chamber. Very often what is done is a person who is in need of a chamber contacts someone with a similar facility, often a supplier or a customer, and simply patterns their performance requirement after what the other guy has done. This often results in a chamber, which is specified to a tighter performance requirement than is actually needed to perform the particular measurements required and can cost thousands of dollars more than is necessary. Qualcomm had a requirement to build a chamber for the evaluation of various antenna designs for mobile communication equipment. Due to building and space limitations the “ideal” size for a chamber operating in the 800 Mhz to 6.0 Ghz was not available. Qualcomm worked with AEMI to define the performance parameters to provide them with the best performing chamber that could be built within the restricted space available. Once the design parameters were defined adequately the chamber deign was developed and the chamber was built. Once the chamber was built Qualcomm went about defining the best test methods and parameters that could be achieved given the performance limitations that were evident in the design due to the compromises that had to be made in the limited space available to accommodate the chamber. This paper will discuss the design process, the design limitations and the methods used to overcome the performance compromises made in the development of the chamber and its intended purpose.
A new measurement technique based on an electromagnetic parametric scattering model has been described. The technique makes it possible to measure antenna gain and the newly defined radiation center by performing two wideband scattering measurements. This approach allows the measurement of the in-situ installed antenna performance. The dispersive nature of the wideband antennas is demonstrated. This dispersive nature of the antenna has significant impact on its use in imaging systems.
While there are standard test methods to characterize the performance of passive antennas, active antennas (with integrated amplifiers) and more complex systems with adaptive functionality create new testing challenges, both in definition and approach. Active antenna gain is a combination of the antenna gain and the embedded amplifier gain. Since these amplifiers may be distributed throughout the array with gain variations between amplifiers, there is a challenge in performing measurements that separate the two gain components. For adaptive antennas, the pattern changes with the incident angle of the test signal, so the adaptive function is often disabled to provide a snapshot of the system, like antenna patterns, for a particular set of conditions. In other cases of adaptive antennas, the composite system performance is measured for angular changes while the system adapts. This paper presents an overview of the testing of both active antennas and adaptive antenna combining systems. Examples of the types of test metrics and errors will be given.
A usual way of performing pattern-measurements on circularly polarized antennas is by measuring the linear components of the field and mathematically converting those to the left-hand and right-hand circular components. These synthesized circular components are sensitive for a number of factors: The exact orthogonality of the measured linear components, the measurement-accuracy of both phase and amplitude of the measured linear components, the polarization-pureness (or the accuracy of the description of the polarization-characteristics) of the probe, etc. This paper analyzes these factors, using a computer-model. An indication on the requirements to be imposed on the measurement-equipment is provided.
Two of NASA’s Deep Space Network (DSN) 70-meter reflectors are measured using a Leica TDM-5000 theodolite. The main reflector surface was measured at five elevation angles so that a gravity deformation model could be derived that described the main reflector distortions over the entire range of elevation angles. The report describes the measurement equipment and accuracy and the results derived from the data.