Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
Antenna systems are increasing in complexity at a rapid pace as advances are made in electronics, signal processing, communication, and navigation technologies. In the past, antenna design requirements have focused on parameters such as gain, efficiency, input impedance, and radiation pattern (e.g., beamwidth and sidelobe level). For some new systems, the group delay characteristics of the antenna are important, where the group delay is proportional to the derivative of the insertion phase as a function of frequency. The group delay is required to stay within certain bounds as a function of frequency and pattern angle. Unfortunately, there are not well established methods or standards for calibrating antenna group delay like the standard methods used for gain and input impedance. This paper presents a method for calibrating the group delay of three antennas based on an extension of the widely used three-antenna gain and polarization calibration methods. No prior knowledge of the gain or group delay of the three antennas is required. The method is demonstrated by a measurement example where it is shown that multipath errors and time gating can be critical for calibrating the group delay.
We propose a novel microwave measurement system that consists of transmitting and receiving optical-fiber link systems. The system can measure parameters of S11 and S21 of an antenna under test (AUT) by the procedure of OSLT 1-pass and 2-port calibration, due to the simultaneous measurement of its relevant signals going into, reflected and transmitted from the AUT. It is shown by some experiments that the S11 and S21 of the two log-periodic antennas measured by the optical link system agree very well with those by a conventional system using metal coaxial cables. It is proved that the optical system can be used to evaluate the S11 and S21 of the AUT in broad frequency range without using coaxial cable.
Inversion of the material parameters for a sample usually requires that the sample fill the waveguide cross-section. Alternative methods require that a non-filling sample be aligned along the center-line of the waveguide. However, it is not known how errors in placement impact the accuracy of the inversion. Hence, a numerical simulation to assess these errors is beneficial to the community. The extraction of the S-parameters from a rectangulardielectric-filled waveguide is conducted numerically by means of the Finite Element Method (FEM) and the Thru-Reflect-Line (TRL) calibration technique. Three different ratios of dielectric sample width (d) to waveguide width (a) are primarily studied. The results are then validated with experimental data on the X-band. An assessment of error with respect to position will be presented at the meeting.
Direction Finding (DF) systems have long been an area of intense research within the Air Force Research Laboratory. There are presently two types of existing DF systems: wideband multi-mode antennas and interferometers. Wideband multi-mode DF systems allow for a large bandwidth but present a low resolution and high variance. Interferometers provide high accuracy and low variance but are narrow band and require a large number of single aperture antenna elements. An effort has commenced to incorporate a broadband DF system with high resolution using two multi-mode spiral antennas. Using an interferometer of multi-mode elements, we can provide high resolution and wideband operation without using numerous antennas. This paper presents the results of extensive wideband measurements carried out on a four-arm spiral antenna and the associated modeformer. These measurements are used to assess and validate the angle estimation capability of the multi-arm spiral antenna.
Standard Gain Horns (SGH) are normally used as reference antennas in antenna measurements. Gain charts for SGH are provided by the supplier. These charts give the gain of the SGH in dBi versus frequency but do not provide any information on the phase variations versus frequency. For complete antenna calibration, one needs the phase as well as gain data for SGH over the frequency band of interest. To obtain the gain and phase data, one can use the three-antenna method which requires three independent measurements and, therefore, is more susceptible to measurement errors. Note that if one has access to two identical antennas, the three-antenna method reduces to a single measurement which is more desirable. In practice, however, one does not have access to two identical antennas. In this paper, a novel method which mimics measurements with two identical antennas is described. In the method, one performs S11 type measurements on the antenna of interest by placing the antenna in front of a large conductive flat plate. The late term in the S11 measurements is then used to obtain the boresight gain and phase of the antenna under test. The measured gain and phase data of several antennas obtained using the proposed method is presented and compared with the results obtained using the three-antenna method as well as with analytical results.
Operating frequencies in the gigahertz range is creating an increased need for electromagnetic compatibility (EMC) testing. In the United States, FCC regulations require conformance to radiated and conducted emissions specifications. An EMC laboratory was established at Cal Poly San Luis Obispo (screen room, test instrumentation, and software) and an experiment was developed to explore conducted emissions effects. This paper will describe the test configuration, explain the calibration procedure needed to acquire accurate measurements, and illustrate measurement techniques applied to two example systems. In addition, the data collection process is illustrated through software donated by CKC Laboratories (EMC specialists). To verify the functionality of the laboratory and to assess measurement accuracy, two 12V/15W switching power supplies are characterized for conducted emissions performance; one as supplied by the vendor (KGCOMP) and a second unit with the EMC filters removed. The noise spectrum for both units are plotted against frequency and compared to FCC specifications. The unaltered unit is shown to be in compliance, thus verifying the accuracy of the test procedure and instrumentation.
Co-polarized and cross-polarized radar cross sections (RCS) are required to completely characterize a complex target. However, it is common for a RCS range to measure only the co-polarized RCS. This practice is primarily due to the inability to produce accurate cross-polarization analysis data for the calibration targets. The most commonly used calibration targets, spheres and cylinders, cannot be used to calibrate cross-polarized RCS due to lack of cross-polarized returns. In this paper, we consider objects that can potentially be used as calibration targets for cross-polarization measurements. Specifically, we numerically study the cross-polarized responses of the Tungsten rod, the grooved cylinder, and triangular dihedrals. Co-polarized measurement data are also included in this initial assessment. From this initial study, we find the counter-balanced dihedral to be a suitable calibration target for cross-polarized measurements.
RCS data from 8 to 18 GHz on an ensemble of aluminum spheres (dia. 14", 8", 6". and 3.22x) and stainless steel ball bearings (dia. 1.25", 1.0", and 0.75"), as supported by strings in the 9-77 Range, have been collected. For inter-range comparison, the same spheres as supported separately by strings and by a foam tower have been measured in the Millimeter Wave Range (MMWR). By taking selected dual calibration pairs, the uncertainty analyses on the three sets of data show general consistency between the two Ranges, as well as between the two methods of support. In addition, the results allow us to sort out the good spheres for calibration from the bad ones.
There is a trend within the RCS community to use squatty cylinders in place of spheres for calibration. A higher degree of accuracy can be achieved; however, cylinder calibrations require much more precision in the alignment procedures. This effort is doubled when the dual calibration target is also a cylinder. The dual calibration test article could be a sphere thus reducing calibration efforts as long as good correlation exists between theory and measurement sphere data. A series of measurements were collected at the NASA Langley Research Center Compact Range Pilot Facility to study measurement errors of spheres atop foam columns to determine their feasibility for dual calibration use.
In recent years the need for higher quality RCS calibrations has lead to several different calibration technique investigations, such as squat cylinders, bi-cones and hybrids of both. A desirable calibration technique requires: easy implementation, a known theoretical or calculable solution and minimal interaction. The sphere as a calibration target satisfies two of the three requirements. It has no alignment issues and can be easily calculated, but the sphere-holder interaction introduces several dB of error. To reduce this interaction error, a 3D string-reel support system has been developed and demonstrated that significantly improves sphere calibration accuracy. The string-reel sphere positioning system utilizes low dielectric and highly swept strings to achieve minimal calibration error. An additional benefit of this technique allows for field probing and quick quiet zone evaluations.
Rapid characterization and pre-qualification measurements are becoming more and more important for the ever-growing number of small antennas, mobile phones and other wireless terminals. There is a need driven by the wireless industries for a smart test set-up with reduced dimensions and capable of measuring radiating devices. Satimo has developed a compact, mobile and cost-effective test station called StarLab which is able to perform rapid 3D measurements of the pattern radiated by wireless devices. The StarLab equipment is derived from Satimo’s StarGate systems which are now well established spherical near field test ranges. StarLab uses a circular probe array to allow for real time full elevation cuts and volumetric 3D radiation pattern measurement within a few minutes. It is operating between 400MHz and 6GHz and can be configured for passive measurements and also cable less-active measurements. This paper describes in detail the multi-probe antenna test station and its different configurations for passive and active measurements. The accuracies for gain and power measurements are also presented as well as considerations on the total radiated power measured by the equipment. Additionally, calibration issues are discussed. Finally, measurements performed with the StarLab test station at Satimo are shown and illustrate the capabilities of the system. The measurement results are validated by comparison to the results obtained in other test ranges.
This paper describes the development, testing and evaluation of a new, automated system for calibration and AUT alignment of a planar near-field scanner that allows the calibration system to remain in place during AUT measurement and which can be used to support AUT alignment to the scan plane. During scanner calibration, probe aperture position measurements are made using a tracking laser interferometer, a fixture that positions the interferometer retro reflector at a precise location relative to the probe aperture and a probe roll axis that maintains the proper orientation between the retro reflector and the interferometer as the probe position is moved. Aperture scan path information is used to construct a best-fit scan plane and to define a Cartesian, scanner-based coordinate system. Scan path data is then used to build a probe position error map for each of the three Cartesian coordinates as a function of the nominal position in the scan plane. These error maps can be used to implement software-based corrections (K-corrections) or they may be used for active Z-axis correction during measurements. By using a set of tooling points on the antenna mount, an AUT coordinate system is measured with the interferometer. The system then directs an operator through a set of AUT adjustments that align the AUT with the planar near-field scanner to a desired accuracy. This paper describes the implementation and testing of the system on an actual planar scanner and AUT test environment, showing the improvement in effective scanner planarity.
Accurate near-field calibration of a large 60 ft. diameter reflector can be accomplished with a minimal sampling technique. Near-field amplitude and phase is collected as the reflector scans across a receiving calibration tower. The near-field data is then transformed to a far-field pattern using a Fourier transform technique. Information on far-field EIRP, directivity, pointing, axial ratio and tilt, as well as encoder timing is obtained with accuracies comparable to anechoic chamber measurement techniques. The system was analyzed for sampling and multipath effects, as well as the effects of phase and amplitude stability. A spherical wave expansion technique was compared to a straight-forward summation technique for the Fourier transform.
We present a first-order analysis of the RCS errors resulting from non-uniform ground-bounce illumination in mobile, ground-to-ground, diagnostic RCS measurements of aircraft. For the case of a non-planar ground surface, these errors are a function of both aspect angle and position on the target. We quantify the errors in terms of their impact on the sector mean RCS as a function of position on the target. For typical targets, we show that the mean RCS error increases significantly for points displaced (either horizontally or vertically) from the calibration point. Conversely, the sector mean RCS is relatively insensitive to small-scale variations in the height of the ground, even though the errors at a single frequency and aspect angle can be quite large.
The National RCS Test Facility (NRTF) has measured radar cross section (RCS) of fixed wing aircraft for many years. In order to expand our testing options at the NRTF Mainsite test facility, the NRTF has developed a rotorcraft measurement capability. The design is compatible for use with our 50-foot pylon, but unlike existing rotators, allows for RCS measurement of test articles that require significant forward and aft target pitches. Target mounting and positioning was not the only challenge. Our new capability required the control and collection of rotor blade position information, in addition to the control and collection of traditional target azimuth and elevation data. Modification of our existing acquisition software and command and control systems was also required. In order to maintain the integrity of the NRTF’s calibration processes and enable the use of existing calibration devices, hardware was constructed to enable mounting of these devices to the spindle system. Other important considerations that influenced the design and implementation of the spindle mount capability include cost effective mounting/dismounting of test articles (to include the targets and calibration devices) safety of the test articles and personnel, and the effective determination of backgrounds.
In general, the RF test setups of antenna test facilities are designed and optimized for antenna pattern and gain measurements. However, the operation of test facilities, especially the here considered 'Double Reflector Compact Ranges', can be extended, so that they can also be used for RCS testing. A simple and very practical expansion of the RF antenna test setup - while maintaining the real-time capability - can be achieved with the aid of a hardware gating system. With this type of setup, RCS measurements have successfully been performed in the Compensated Compact Ranges of EADS Astrium. The applied gating system was the high resolution Hard- gating System HG2000 of EADS Astrium, developed together with the Munich Univ. of App. Sciences. Within this paper, the applied facility and the gating system will be described firstly. Subsequently, the modified test setup and the test results obtained by calibration measurements will be shown. They will give an indication of the achievable resolution for the extended test system w.r.t. object size detection and resulting amplitude dynamic range.
Satimo’s STARGATE probe array systems are now well established as an efficient tool for testing radiated performances of wireless devices and antennas. Since 1998, about forty STARGATE measurement systems have been successfully installed worldwide. Recently, a range of new applications have also demonstrated the suitability of probe arrays for large radiating structures and directive antennas. These new generation of measurement set-ups present innovative aspects regarding their rapidity, dynamic range, and accuracy. This paper will describe several novel antenna testing concepts based on probe arrays that cover automotive, aerospace, and military applications and a wide range of frequencies. The basic difference between traditional approaches using single probe and the STARGATE approach using an array of probes will be explained along with probe array calibration procedures. An error analysis budget using the conventional NIST error terms will be presented including the specific terms related to the use of probe arrays. Also a discussion will be made on some of the key technical challenges to making large probe arrays including such issues as dynamic range, mechanical tolerances, and data truncation effects.
New results are presented on using small spheres mounted on a foam tower for calibration. Subtraction of the foam tower response is found to be necessary and sufficient for the dual-calibration method to work.
A calibration uncertainty analysis was conducted for the Air Force Research Laboratory’s (AFRL) Advanced Compact Range (ACR) in 2000. This analysis was a key component of the Radar Cross Section (RCS) ISO-25 (ANSI-Z-540) Range Certification Demonstration Project. In this analysis many of the uncertainty components were argued to be small or negligible. These arguments were accepted as being reasonable based on engineering experience. Since 2000 the ACR radar has been replaced with an Aeroflex Lintek Elan radar system. A new measurement uncertainty analysis was conducted for the ACR using the Elan radar and for a general (non-calibration) target. We present results comparing the previous results to the current analysis results.
We have been developing an uncertainty analysis of RCS calibrations and measurements in the 2 – 18 GHz range at the Etcheron Valley RCS outdoor ground-bounce facility. In this study we report on the results of the uncertainty analysis primarily at 11.3 GHz, but results at some other frequencies are also discussed. We plan to address all components of uncertainty, and present here in some detail the procedures used to determine the uncertainties due to nonplanar illumination, drift, noise-background and nonlinearity. We use a measurement-based approach to obtain upper-bound estimates for the component uncertainties, which are combined using root-sumsquares (RSS) to obtain the overall uncertainty. The uncertainties at any frequency can be determined using these measurement procedures.