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This paper will describe the measurement series performed on Global Horn flight antennas to be used on the Intelsat IX satellite series. The work was performed by MEMCO under contract to Space Systems I Loral. The Global Horn antenna system provides highly isolated RHCP and LHCP beams that cover the earth disc, as viewed from synchronous orbit. The corrugated wall horn is designed to maximize the gain at the edge of earth coverage angle, which in this case is defined as plus or minus 9.8 degrees from the beam peak. The horn has near perfect E-and H-plane amplitude and phase equality to achieve low off-axis cross-polarization (-55dB) across the earth disc. A well-matched orthomode transducer (OMT) and low axial ratio polarizer complete the antenna assembly. The paper will describe the anechoic chamber measurement series and techniques used to measure the circularly polarized cross-polarization isolation values in the -50dB (A.R.=0.05 dB) to -60dB (A.R.=0.02dB) region. Bench measurements of the polarizer, which has a measured axial ratio less than 0.02dB, will also be presented. Directive gain measurements of the flight antennas will also be presented and discussed. The techniques presented in this paper are also used by MEMCO to design and measure circularly and linearly polarized probes and source antennas used in Nearfield Scanners and Compact Antenna ranges.
A networked antenna measurement system based on Intranet technologies allows users to undertake different aspects of the measurement process (data acquisition, instrument control and analysis) remotely. It also allows for the efficient transfer of data between different nodes on the network. At the David Florida Laboratory, a project is currently underway to upgrade the antenna measurement system to a graphical user interface (GUI), developed in the LabVIEW Version 5.0 environment. Integral to this upgrade is the development and implementation of data analysis applications and a network based on Intranet technologies. The antenna measurement software application functions over the Intranet as a clienUserver model, which is designed to support a number of clients functioning concurrently on different machines. The design of the network permits use of a single server providing the control and interface between a client operation i.e. the test conductor and the data acquisition system. This paper describes the steps taken thus far to upgrade the antenna analysis software and provide an overview of the client server architecture developed and implemented using LabVIEW.
A sophisticated, low-cost Configuration Management Database (CMD) has been developed for the Active Array Measurement Test Bed (AAMTB) at the Crane Division, Naval Surlace Warlare Center, Crane, IN (NAVSURFWARCENDIV). By choosing three flexible COTS programs that feature object oriented models, a common programming language, and ODBC compliance, the software development and project cost was minimized. This paper describes how the database provides recording and retrieval of comprehensive hardware and software configurations of measurement test scans. Details of the database structure, including its advantages and limitations, are also presented.
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.
Dual gridded, shaped reflector antennas have been designed, manufactured and measured respectivily by ALENIA, AEROSPATIALE Les Mureaux and ALCATEL for the EUTELSAT "W" satellites program. The tight requirements, for coverage gain and cross-polar discrimination together with in-coverage cross-polar level less than 44 dB below the peak, required sophisticated techniques for design and measurements. ALENIA used optimisation and prediction techniques, which took into account thermal deformation effects and the multi-layer structure of the assembled dual gridded antennas. The optimisation process led to high performance antennas associated with the complex surface shapes. Moreover, including the actual manufactured reflector surfaces in the analysis, an excellent correlation between measurements and predictions have been obtained. Measurements were performed in the Alcatel Space Industries Compact Antenna Test Range in Cannes. ALCATEL invested into high polarisation purity illuminators and special hexapod tools in order to efficiently optimise the assembled antenna performance. The measurement optimisation process led to antennas which all met their requirements.
ARCS acquisition software for antenna and RCS measurements has been modified such that it is now based on LabWindows/CVI of National Instruments. With open system architecture, industry-standard tools and platform flexibility, new ARCS software delivers all components which are required for an advanced antenna and RCS measurement system. This means tht the portability and modularity of the software is increased considerably. Such a concept has the major advantage of simple adaptation/modification by the user, for instance by adding new menu pages. The virtual instrument concept of CVI guarantees easy adaptation of the newest interface technology, such as USB and firewire. Furthermore, there is a large base of instrument drivers which can be readily used to extend the measurement capabilities of ARCS in a minimum of time Special care is taken in the design of the user interface. This is to avoid complex procedu res for entering measurement parameters. Even less experienced operators must be comfortable with the software and be able to perform complex calibration and data acquisition procedures. Finally, a large number of application programs is written for advanced antenna and RCS calibration, microwave holography, ISAR imaging and frequency extrapolation techniques.
Design optimization and measurement of the Luneburg lens antennas are the focus of this paper. One of the important design aspects of an optimal Luneburg lens antenna is to construct a high performance lens with as low number of spherical shells as possible. In a uniform Luneburg lens, the gain is decreased and unwanted grating lobes are generated by reducing the number of shells. This deficiency in the radiation performance of the uniform lens may be overcomed by designing a non uniform lens antenna. The optimized non-uniform spherical lens antenna is designed utilizing the dyadic Green's function of the multi-layered dielectric sphere integrated with a Genetic Algorithm (GA)/Adaptive Cost Function optimizer. Additionally, a novel 2-shell lens antenna is studied and its performance is compared to the Luneburg lens. Finally, measured results for far field patterns and holographic images are shown for the Luneburg lens antenna using the UCLA's bi-polar near field facility.
The antennas used in an anechoic chamber illuminate not only the target but also the walls, thus generating spurious signals. This problem is particularly significant at low frequencies. This study describes improvements to a standard, rectangular horn. Several solutions are tested, such as lenses, prolongation of the horn face, metal boxes with absorbers surrounding the horn, etc. The best solution appears to be the prolongation of the horn faces, with the fitting of a metal plate with absorbers at the rear. However, as the dimension of the horn increases with the ogival plates, the horn/target interaction also has to be taken into account.
For many years the Navy has been using Anechoic Chambers and RF absorbing material. Recent events have brought into question the safety of RF absorbing material and the chambers which are covered with this material. Little, if any, information has been presented in the past to provide a solid picture of the actual danger that exists in these environments. A series of tests and inspections were conducted by the Navy on RF anechoic chambers and the materials inside. The materials were tested for fire susceptibility and chemically analyzed for salt compounds. Salt compounds have been used to make materials fire-safe. Results will be presented which show the susceptibility of various materials to fire from flames, electrical current and heat. A series of recommendations will be presented for using these materials in chambers to maintain safe working conditions.
This paper will show a solution to the problem of isolating defogger power connections from an automotive antenna using a tri-filer wound transformer with a ferrite core where the power current flow is organized so that the magnetic field induced by the heater power wires is canceled. The transformer coupling remains effective at low frequencies. A capacitive coupling link is used to permit the system to work at FM frequencies.
Measurements of the ERP radiated by an antenna and the ERP received from a distant antenna are addressed. Alternative measurement techniques are described and correction for polarization mismatch loss, pointing error and propagation loss is discussed. The statistics of the measurement errors are presented for error budget projections of measurement accuracy.
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.
In this paper, we will demonstrate a 16 channel multi-antenna UHF/L-band noise radar system. We will show applications to building penetration and ground penetration. We will show noise radar responses for humans walking on the other side of building walls, and buried objects, including land mines. We will discuss classification techniques, and show some techniques that yield initial success.
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.
Advances in the electromagnetic simulation of inflatable reflector antennas are described. Examples of proposed missions using inflatable antenna technology (IAT) are given. Techniques are presented to compensate for structural distortions using array feeds and subreflector shaping. It is possible to noticeably reduce the deteriorating effect of distortions using these compensation techniques. Additionally, the application of a technique based on focal plane diagnostics is summarized.
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.
A new measurement technique for integrated antennas is presented, which allows measurement of the radiation characteristics using a wafer-prober structure. This technique provides a simple inexpensive method of assessing the radiation characteristics of an integrated antenna. Unique difficulties in measuring and modeling integrated antennas are discussed.
This contribution will show how active frequency selective surfaces (AFSS) loaded with PIN and varactor diodes can be used concurrently to dynamically control the reflectivity characteristics of a microwave absorbers. The PIN and varactor diodes are used respectively to effect abrupt and gradual changes in an absorber's reflectivity characteristic.