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.)
A portable handheld antenna array system (SARBAR) capable of generating high-resolution two dimensional spotlight radar images is designed and built. The design goals were to build a portable device with maximum sensitivity, that can generate zonal images of a target at close range, and produce live updates of the scene (goal of 10 image per second). To achieve the design goals, an array antenna setting with separate transmit and receive elements have been used. The radar system is based on conventional FM-CW homodyne radar. The novelty of the design, however, is that for each FM CW waveform, the signal is successively routed through all the transmit elements and received from the designated receive elements. The transmit/ receive switching is such that a complete scan over the entire frequency and aspect interval is obtained in less than 80 msec. This allows image update rates that make the SARBAR resemble a video camcorder.
Contoured multi-beams achieved by multi-feed reflector antennas, realized in modern communication satellites, like Intelsat VIII and IX generations satellite, require an economic measurement of their antenna characteristic. Further, highly accurate, but also fast and therefore real-time measurements are assumed to be applied for the testing of the antenna performance. For that aim, the Compensated Compact Range CCR 75/60, applied at e.g. Space Systems Loral (SSL) in Palo Alto (USA), at ALCATEL in Cannes (France), at the MISTRAL facility in Toulouse (France) and at Astrium GmbH (Germany) was developed and installed by Astrium GmbH. In order to optimize the measurement accuracy of the CCR, detailed error analyses and investigations for improvement measures were performed. Within this paper, the accuracy analyses and improvement steps will be presented in order to establish accuracy values, which can be realized in state-of-the-art compact range test facilities.
This paper will draw the attention to a revolutionary new, extremely mobile and flexible approach on a nearfield test facility concept for outdoor measurements. After addressing the current measurement dilemma, the potential measurement objects are indicated, covering application areas in telecommunication, defense, air traffic management, research and verification of outdoor antenna & RCS test facilities. Further an outlook will be given on the future and urgent necessity on measurements of the radiated performances of outdoor antenna installations. The presented antenna test facility is based on a remotecontrolled and floating platform, enabling probing of electromagnetic fields within relatively large air volumes of up to 100 x 100 x 100 meters. In combination with precise position techniques, accurate measurements of up to 20 GHz are considered to be achievable. The design philosophy and system concept will be explained. The paper concludes with a prediction on the system performance and with a brief realization schedule. The proposed ANTF concept will allow detailed radiation analyses in unprecedented depth and quality, representing a real breakthrough in characterizing electromagnetic fields in open air test sites (OATS).
Choosing the proper antenna range configuration is important in making accurate measurements and verifying antenna performance. This paper will describe the steps involved so the antenna engineer can select and specify the best antenna range configuration for a given antenna. It will describe the factors involved in choosing between near-field systems versus far-field systems, and the different scan types involved. It will explain the advantages of each type of antenna range and how the choices are affected by such factors as aperture size, frequency range, gain, beamwidth, polarization, field of view, sidelobe levels, and backlobe characterization desires. This paper will help the antenna engineer identify, understand, and evaluate the applicable characteristics and will help him in specifying the proper antenna range for testing the antenna.
The radiation properties of an antenna are defined in the far field, since this is the environment that they will operate. Creating far field conditions when testing a large aperture antenna is quite challenging. This is particularly true if testing occurs within the confines of an anechoic chamber, or if other complicating field characteristics (like angle-of-arrival simulation) are desired. Rather than attempt to generate a true planewave in the usual manner, we propose an instrument that creates a field distribution in the near field of a transmit array that is planewave-like in nature only over specified regions of interest (a region occupied by an antenna under test, for example); we do not require that the incident field be a true planewave at other locations. In these other locations the field is free to assume any value demanded by the governing equations of electromagnetics. By relaxing the requirement on the electromagnetic field in the test volume, we considerably reduce the complexity of the problem and define a tractable problem with a potential engineering solution.
The NUWC/NPT Overwater Arch Antenna Range consists of a 70 ft radius measurement arch located over an elevated 90 ft x 65 ft salt water pool. This facility, located outdoors, presents mechanical and electrical challenges. Measurement accuracy and precision are a function of environmental parameters (including unwanted signals), physical plant and instrumentation characteristics. Measured data variation will be presented along with techniques which could be employed to improve range performance.
A calibration uncertainty analysis was conducted for the Air Force Research Laboratory’s (AFRL) Advanced Compact Range (ACR) in 2000 [1]. This analysis was a key component of the Radar Cross Section (RCS) ISO-25 (ANSI-Z- 540) Range Certification Demonstration Project. The scope of the RCS uncertainty analysis for the demonstration project was limited to calibration targets. Since that time we have initiated a detailed RCS uncertainty analysis for a more typical target measured in the ACR. A “more typical” target is one that is much larger with respect to wavelength than the calibration targets and characterized by a wide dynamic range of RCS scattering levels. We choose a 10’ ogive as the target due to the fact it is a large target, exhibits a wide dynamic range of scattering, and the scattering levels can be predicted using readily available CEM codes. We will present the methodology for the uncertainty analysis and detailed analyses of selected component uncertainties. The aspects of the uncertainty analysis that are unique to the “typical target” (i.e., a non calibration target) will be emphasized.
The on-orbit performance of communication satellites is measured for two reasons. First, the satellite’s compliance with specified performance must be evaluated by measurements conducted shortly after the satellite’s launch. Second, satellite performance over its lifetime must be monitored and diagnostic capabilities augmenting telemetry data must be provided if performance anomalies develop during the satellite’s lifetime. Necessarily, these measurements quantify the system level performance of the satellite with specially developed and calibrated test terminals.
The Antenna Branch of NAVSEA Crane was tasked to design and formulate a plan to pattern test a CWI Illuminator antenna in line of sight with a SATCOM antenna. The Navy has problems finding new places aboard ship to mount antennas without having interaction between them. The separation would be about 19 feet, within the near field zone of the Illuminator. The testing was performed on a 2000 foot outdoor range. A special test fixture was designed by Crane Engineering to mount both the Illuminator and the SATCOM to their proposed mounting locations. The unique characteristic of this measurement approach is the mounting of both the FCS antenna and the SATCOM antenna and radome on a test fixture, which allows complete pattern measurements with different antenna orientations relative to each other. A limited raster scan was used for collecting the data in a 3-D result. Baseline data files were collected without the SATCOM present for comparisons. A Matlab program written to evaluate the results. The proposed mounting location produced unacceptable results in the radiating pattern of the Illuminator antenna. Crane Engineering calculated a new mounting location from the results of the data taken in the Raster scan. Subsequent testing was done and proved to be a valid location for the Illuminators test requirements.
This paper describes a novel system that overcomes the inaccuracies in antenna radiation pattern measurements caused by multipath propagation. The system operates by specifically compensating for the effects of unwanted signals rather than by attempting to remove, or minimize, their effects through the use of screens or baffles or an anechoic chamber. Compensation is achieved through the use of an equalization technique, the parameters of the equalizer(s) being determined from a special measurement of the antenna range under consideration. The method is generally applicable; it may be implemented ab initio in new indoor or outdoor ranges, or retrofitted to existing ranges to improve accuracy. Most importantly, however, the basic idea leads to the design of a completely new type of real-time 3-D range in which sensors are placed on the surface of an imaginary sphere surrounding the antenna under test (AUT), and an anechoic chamber is not required.
When using an array antenna for measurements, small phase imbalances between the sum and difference channels may occur due to a variety of factors. This imbalance may arise due to unequal line lengths, twists or bends in the cabling, leakage, improper connections, or a variety of other factors. In the ideal phase array antenna one lobe of the difference pattern should be inphase with the sum pattern, and the other lobe should be 180° out-of-phase. When a phase imbalance occurs between the sum and difference channels, errors occur in determining the antenna beam deflection due to the presence of a radome. By taking the ratio of the difference to sum channel data a phase correction factor may be determined. Application of this phase factor to the difference channel data will phase align the sum and difference channels so the correct deflection may be determined. This correction factor will be frequency dependent.
With the continued growth of mobile communications and the emergence of wireless LAN and personal area networks (PAN), there is an increased need to accurately measure the antenna properties for omnidirectional antennas and antenna systems. Furthermore, it is very desirable that antenna measurement systems be flexible to support a variety of antenna configurations and form factors. In this paper, we assess the performance of two measurement configurations utilizing dielectric positioners. These configurations comprise a traditional roll-over-azimuth antenna positioner and an arm-overturntable system such as that used in ORBIT/FR’s Advanced Spherical Cellular Near-Field (ASCENT) product. The results show that both configurations offer demonstrable improvements over conventional metallic positioners, and the arm-based system provides the highest accuracy for omnidirectional antennas.
This paper presents a 'mid-range' calibration technique, now being developed for a 60 ft. diameter reflector site. With this technique, near-field amplitude and phase is collected at a calibration tower as the reflector scans across it. The mid-range '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 standard measurement techniques. A particular advantage is that the system, once set-up, can be used on a regular basis without impacting site operations.
When making large scale RCS measurements at outdoor ground bounce ranges, vector background subtraction is often not performed. To get a clean measurement, range engineers must control the backscatter from the target supports that mainly dictate the background level. Presently, nearly all ranges use single high gain antennas to concentrate incident field energy onto the target, but single antennas have physical limitations for controlling the incident field energy in the target support region. To improve the incident field distribution, an array of transmitting elements can be used instead of a single radiator. With an array, engineers can control the illumination in both vertical and cross range dimensions, making it possible to concentrate the incident field energy on the target while reducing the field level over the target supports. This paper describes ground bounce range and incident field modeling, shows beamforming applied to foam column scattering, and demonstrates that a 2-dimensional array can improve the cross range phase taper. It also discusses design sensitivity issues.
As part of an ESA/ESOC development project [1] a set of three planar Ka band Frequency Selective Surface (FSS) mirrors were designed. For design verification purposes a set of FSS samples of sufficient size (about 220mm by 250mm) to demonstrate their design was manufactured. The RF performance of these samples was measured on a planar near field scanner at ERA Technology and on a compact antenna test range (CATR) at ESA/ESTEC for test comparison purposes. The FSS were designed to operate over a narrow range of RF incidence angles (30º + 1º). Hence, it was important for test purposes that the FSS samples be illuminated by a near plane wave. This was achieved with a 220mm offset reflector. As the FSS samples were relatively small it was also desirable that any edge effects should not significantly influence the measurement. Hence, the test reflector antenna was designed to operate with a tapered RF distribution of –20 dB at its edges. A precision framework was constructed to hold the FSS samples at the required incidence angle. The two methods of measurement show remarkable agreement and indicate that the differential pass-band phase and amplitude performance of the FSS samples can be measured to within approximately 1 degree of phase and about 0.03 dB of amplitude
The fundamental concepts of operation of a Planewave Generator1 (PWG) were described in an earlier paper. In the present paper the measured performance of a proof of performance experiment are reported. First, we will briefly describe the concepts and architecture of the experimental configuration. Next, measurements of the electromagnetic field created by the PWG prototype in a specified test zone will be presented. A planewave figure of merit (FOM) has been defined earlier, and the measured FOM of the PWG will be compared with the FOMs of the field of a single antenna, and of a uniformly illuminated transmit array. We first discuss the experimental strategy, and our use of superposition to minimize the hardware required for the demonstration. We then present measured data that shows that a minimally configured PWG can produce field distributions that are planewave-like over a limited spatial extent, and that its field demonstrates planewave qualities that significantly exceed those achievable by a typical transmit antenna, or uniformly-illuminated array. We also present data that relates the size and quality of the planewave-like field in a test zone in terms of the number of elements in the PWG transmitting array. Finally, we present a scaling relation for the PWG, and show that the radiated field produced by the experimental hardware agrees well with the field predicted by simulation.
In real life, most radar targets are located outdoors. Here we present results from outdoor broadband RCS measurements at the X-, Ka- and W-band of “Holger”, a metallized model-scale aircraft with cavities. RCS vs. angle data in the wing plane (0° elevation) were recorded at discrete frequencies (9, 35 and 94 GHz) in both horizontal (HH) and vertical (VV) polarizations. ISAR data at 7-13, 32-38 and 92-97 GHz were acquired. Results from a 104.1 m ground range and a 162.7 m free space range will be compared.
This paper presents a pragmatic approach in the determination and measurement of RF Power on RF systems in the presence of Voltage Standing Waves Ratio (VSWR). Information is provided to determine the RF Power measurement ambiguities produced by the VSWR of cables, pads and loads which ultimately affect and perturb the readings associated with both CW and Peak Power meters. A comparison of presently available commercial RF Power Meters is also provided which include their maximum metering ambiguities, their performance under dynamic range and their absolute metering accuracies. The paper also provides a simple equation for determining your system ambiguities (in dBs) based on the aggregate of the individual components within the RF path and their individual VSWR effects. Experimental data and calculated data are also presented with excellent correlation. Recommendations are also provided in the process of enhancing RF power measuring procedures.
The S parameter measurement of large sheet materials has been limited to microwave frequencies due to a lack of test apparatus that could properly illuminate the materials with a uniform electromagnetic wave in a confined space at lower frequencies. Boeing Mesa has developed a unique test system that overcomes this limitation. The current design will perform S11 and S12 measurements from 0.125 to 40 GHz in five bands. Sample sizes up to 4 ft. wide, 8+ ft. long, and 12 inches thick, can be tested in sections by sliding the sample into the test fixture. Apertures up to 46 inches square can be provided in the aperture plate. The angle of incidence can be adjusted from 0 degrees to 45 degrees.
Measurement of material properties, at radio frequencies (RF) including microwave and millimeter-wave frequencies, is a critical issue for RF polymer research and development. RF polymers are polymer composites specifically designed for specified electrical and magnetic properties within a required frequency band of operation. In this paper, we investigate the methods required to determine the RF permittivity and permeability in the RF band for RF polymers.