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.)
The maintenance, test, and repair workload for the Air Force's AN/MSQ-118 satellite ground-based receiving communication system has been transferred from the closing McClellan Air Force Repair Facility in Sacramento, California to Tobyhanna Army Depot located in Tobyhanna, Pennsylvania. The workload requires the support of four maintenance shops and two planar near-field ranges. The shops are the antenna repair, power supply repair, low-noise amplifier (LNA) repair, and radome repair shops. The near-field ranges are a 4' x 4' planar scanner used for antenna diagnostics and an 8' x 8' planar scanner used for certification of the repaired antenna-under-test (AUT). This paper will bring the AMTA community up to date on the status of the new Tobyhanna Antenna Repair Facility, focusing on the techniques and methods used to quantify the alignment and performance characteristics of the planar near-field antenna measurement system used for certification. With the relocation complete, test data obtained at both locations will be analyzed and compared to show differences between the baseline measurements taken at McClellan Air Force Base versus those taken at Tobyhanna Army Depot.
Airborne Doppler Velocity Sensors require precise boresight information in determining a Doppler solution. Far-field ranges have been extensively used to provide this boresighting capability. This paper discusses an empirical investigation to determine the feasibility of using near-field techniques to fulfill the boresighting requirement.
A microwave holographic technique based on equivalent magnetic sources reconstruction is presented. This technique, initially used as a main plane near-field to far-field (NF-FF) transformation, can also be used to detect defective elements in arrays as well as to detect irregularities in the surface of reflector antennas.
A microwave holographic technique based on equivalent magnetic sources reconstruction is presented. This technique, initially used as a main plane near-field to far-field (NF-FF) transformation, can also be used to detect defective elements in arrays as well as to detect irregularities in the surface of reflector antennas.
Electromagnetic field measurement systems based on the Advanced Modulated Scattering Technique (A MST) permit fast and accurate diagnostic testing to be performed in the near-field (NF) or the far-field (FF) of antennas and scattering objects. A-MST probe arrays are particularly effective for rapid diagnostic testing applications where it is desired to obtain overall measurement duration reductions of 80% to 98% compared to conventional single-probe measurement times.
The accuracy of the probe antenna pettern used for the probe-corrected near-field measurements is critical for maintaining high accuracy results. The probe correction is applied differently in the three standard near-field techniques - planar, cylindrical, and spherical. This paper will review the differences in sensitivity to probe correction for the three techniques and discuss practical of probe correction models and measurements.
A simulation tool used during the design of near-field ranges for phased array antenna testing is presented. This tool allows the accurate determination of scanner size for testing phased array antennas under steered beam conditions. Estimates can be formed of measured antenna pointing accuracy, side lobe levels, polarization purity, and pattern performance for a chosen rectangular phased array of specified size and aperture distribution. This tool further allows for the accurate testing of software holographic capabilities.
Motorola Cellular Subscriber Research Laboratory has developed and installed new hardware and software for measuring the performance of cellular and satellite phones. The hardware facilities consist of twin 16' cubical, near-field, anechoic chambers. Each has a spherical-scan system custom designed for cellular phone testing. The software consists of data collection, data presentation and database management software running under Windows NT 4.0™. Accurate testing of cellular phones requires that the measurements be made with a human phantom consisting of a human-shaped, liquid-filled fiberglass shell. These phantoms are fragile and must remain vertical. This required that an arm be implemented for the theta axis while a typical azimuth only positioner is used for the phi axis. The Theta axis arm is shaped like a "U" and is mechanically driven from both ends allowing the cross-piece of the "U" to be of a lightweight dielectric material so as to have minimum scattering.
This paper describes an antenna measurement system which combines three types of measurements into one integrated range operating from 45 MHz through 18 GHz. A vehicle can be measured at short ranges inside a protective enclosure at various elevation angles for both low frequency Far Field (FF) measurements and higher frequency Near Field (NF) measurements. The vehicle can also be measured on an extended FF 120m range by radiating through the transparent enclosure. The vehicle enters a 12m radius radome and is mounted on a 6m diameter turntable which enables continuous rotation of the vehicle at a maximum speed of 3 rpm. An elevation positioner moves a lOm arm equipped with linear and roll axes at the top, which provide the NF probe movement. Azimuth rotation of the vehicle and elevation movement of the arm provide a complete hemispherical scan. During FF measurements from outside of the radome, the arm is stored below ground level and is covered.
Antenna measurement techniques historically have been dominated by an assumption that an antenna is a discrete component of the overall electronic system into which it is built. Under this assumption, the measurement technique is to remove the antenna from its host electronic system and place it in a generic test system to measure the gain, pattern, etc. Although this technique still applies to many antenna measurements, it does not work well in cellular/PCS handset measurement applications because cellular/PCS handsets exhibit significant electromagnetic coupling to the human holding the phone. Therefore, the antenna should be measured in situ with a person holding the phone or, for practical reasons, with a mannequin arranged such that it can hold the phone. The mannequin is placed on an azimuth positioner and a near-field probe is moved on a very accurate circular arch from zenith to a significant angle below the mobile phone horizon plane. A description of the chamber and system, and measured results are provided.
In this paper, a near-field time domain scattering measurement technique is described. Near-field measurements are typically performed for radiation applications but not scattering applications. This time domain measurement approach borrows from many of the principles developed in the frequency domain and is ideally suited for broadband scattering characterization. The goal of determining the scattered far-fields of a structure is accomplished by the transformation of near-field data collected over a planar sampling surface. The scattered near-fields were generated with a probe excited by a fast rise time step. In particular, the near-fields were sampled with a second probe and digitized using a digital sampling oscilloscope. The bandwidth of the excitation pulse was approximately 15 GHz. The overall accuracy of this approach is examined through a comparison of the transformed far-field pattern to a numerical calculation.
Over the past six years the Navy has developed a portable measurement capability. As part of the validation of this tool a comparison test was developed to understand the issues involving testing complex targets in a near-field cluttered environment. The test was designed to evaluate not only the effects of near field curvature, but how clutter from ceiling and walls have an effect on the accuracy of the measurement. The test measured all test objects in the far-field as a baseline, then repeated the same measurements at five different near-field configurations. The results of the test will be shown on a simple 15 ft. pole target, along with the metrics for evaluation of the results.
Three common methods of measuring circularly antennas on a far-zone range are: using a spinning linear source antenna (SPIN-LIN), measuring the magnitude and with a linearly polarized source antenna in two orthogonal positions (MAG-PHS), and using a circularly polarized source antenna (CIRC-SRC). The MAG-PHS and CIRC-SRC methods are also used in a near-field or com pact range. The SPIN-LIN method is useful because an accur te measurement of the axial ratio and gain can be made without the need to measure phase. The MAG-PHS method is the most general method and can also completely characterize the polarization of the test antenna. The CIRC-SRC method is the simplest and least time-consuming measurement if the antenna response to only one polarization is needed. The choice of measurement method is dictated by schedule, accuracy requirements, and budget. An analysis is presented that provides errors in the measured gain, relative gain pattern, and phase of the test antenna depending on the polarization characteristics of the source and test antennas. These results are useful for deciding which measurement method is the most appropriate to use for a particular job. These results are also useful when constructing more complete error budgets.
Concise mathematical relations have been derived for Planar Near-Field measurements that quantify the effects of x, y and z-position errors on antenna parameters such as gain, sidelobe level, pointing, and cross polarization. Because of the complexity of the theory, similar relations for spherical near-field measurements have not been developed. The requirements for the spherical coordinate system are generally defined in terms of the alignment parameters such as orthogonality and intersection of axes, q-zero, x zero and y-zero rather than individual errors in q , f and r. Mechanical, optical and electrical techniques have been developed to achieve these alignments. This paper will report on the development of methods to estimate the antenna parameter errors that will result from spherical alignment errors for typical antennas.
DATE is a portable, rapid assembled, planar near field measurement system for ERIEYE Airborne Early Warning System. DATE shall be used both as a production range at Ericsson Microwave Systems (EMW) and as a maintenance equipment delivered with the ERIEYE AEW System. Up to now ERIEYE has been measured and phase aligned at EMW's large nearfield range. The active antenna is interfaced through a Beam Steering Computer (BSC) and hardware interface. The disadvantages with this approach is a slow communication speed and reduced Built In Test. Since the large nearfield range is designed to meet the requirements from many different antenna types the transport, mounting, alignment and range error analysis are very time and personnel consuming. The DATE-scope is to provide a portable planar near field test system that's custom-made for ERIEYE. The time from stored system to completed measurement shall be very short and performed by a "non antenna test engineer". This is done by: • Incorporate the BSC as a radar-mode. • Use the radar receiver and transmitter for RF measurement. • Reduce alignment time and complexity by a common alignment system for antenna and scanner. Scanner alignment for very high position accuracy. • Automatic Advanced Data Processing: Transformation from near field to far field to excitation to new T/R-module setting-up-table in one step.
The Marine Corps desired a portable test system for the AN/TPS-59 radar antenna (a large, 15.2 feet by 29.1 feet, L-band phased array antenna) to verify on site performance. The test system was also required to be capable of antenna acceptance testing at the overhaul depot. An innovative mechanical design using commercial off-themshelf (COTS) products paved the way for the development of this low-cost system. The low-frequency, moderate-sidelobe antenna characteristics allowed for flexibility in mechanical scanner design. The near-field scanner attaches directly to the antenna and is aligned in place. The Hewlett-Packard 8530 Antenna Measurement System is employed for data collection. An interface from the computer to the antenna was designed for beam steering control (BSC). LabVIEW software controls the HP8530, the near-field scanner, BSC, and other miscellaneous RF hardware. Digital Visual Fortran 5.0 and Matlab are used to run the National Institute of Standards and Technology (NIST) near field programs.
Probe correction is required to accurately determine the far-field pattern of an antenna from near-field measurements. At Raytheon Primary Standards Laboratory (PSL) in El Segundo, CA, data acquisition hardware, instrument control software, and a mechanical positioning system have been developed and used with an HP Network Analyzer/Receiver system to perform these measurements. Using a three antenna technique, the on-axis and polarization parameters of a linearly (or circularly) polarized probe are calibrated. The relative far-field pattern of the probe is then measured utilizing the two nominal, orthogonal polarizations of the source antenna. All measurements are stepped in frequency and use a time domain gating technique. The probe and the source antenna are optically aligned to the interface and unique, kinematic designed interface flanges allow repeatable mounting of the antennas to the test station.
Phase-space expansion of spatial near-field data is an expansion into functions that are spatially and spectrally localized. We have previously shown that such a phase-space representation (PSR) can be useful for both antenna radiation phenomenology and evaluating the quality of planar near-field measurements. In this paper, we use the coefficient of a phase-space expansion for filtering. It will be shown that the contribution of some error components is stronger in a particular region of the phase-space. One can take advantage of this fact for phase-space filtering. Two sources of error, namely staggered data grid, and.AUT-room interaction; are considered in this paper. For imperfect probe spacing, we shall show that this technique is particularly attractive when the true probe location is unavailable. In the second example, we shall show that the PSR filtering can reduce the side lobe contamination due to AUT/room interactions.
Practical antenna applications require accurate characterization of the antenna, including both the amplitude and phase performance. Recent advances in antenna measurement technologies allow the antenna to be measured in various indoor facilities with a well controlled environment. However, measurements that take a long time to complete can still suffer phase drift and variation due to the movement of RF cable as well as changes in the chamber environment. Without proper phase correction, the measured antenna pattern performance may not satisfy the desired requirement. Consequently, it is very important to have appropriate methods for phase correction in order to obtain more accurate results. In this paper, a simple procedure for phase correction of volumetric spherical near field antenna measurement is presented. In this method, only a few additional measurements are needed for correcting the phase variation observed in the original volumetric pattern. Application of the phase corrected pattern has been found to satisfy the desired antenna performance.
The technique is based on a non-redundant and non-uniform representation of the near-field on the measurement plane and performs an estimation of the fields samples outside the measurement region. Thanks to the non-uniformity distribution of the samples, also the estimation of a limited number of them allows a significant improvement in the far field reconstruction. The numerical and experimental investigation presented in this paper confirms the effectiveness and flexibility of the technique, which requires a low computational effort.