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A computer simulation for prediction of equivalent system temperature is presented. The figure-of-merit for a receiving system is given by the ratio of the receiving system gain by the equivalent system temperature (G/Ts). While the gain, G, can be well characterized by laboratory measurements, measurements of system temperature, Ts, taken in the laboratory do not correspond well to measurements in outdoors, due to a myriad of environmental factors. A computer methodology to statistically characterize the noise performance of a satellite earth station receiver in the operational environment was developed for the Department of Commerce National Institute for Standards and Technology, as of a Small Business Innovation Research contract. The result of Phase 2 of the SBIR is an implementation of this computer methodology called the Receiving System Analysis Tool. This paper describes the methodology, the RSAT simulation, and its application to SATCOM terminal analysis.
Properly designed elevated antenna ranges, that are to be used on aircraft sized structures, at VHF and UHF frequencies, are prohibitively large. Conventional ground reflection ranges can measure only one frequency at a time because the source antenna height must be set for each frequency. This paper describes a broadband antenna ground reflection range that has been designed for the purpose of making antenna pattern measurements at arbitrary frequencies between 30 MHz and 400 MHz on aircraft sized vehicles. This design uses multiple transmit antenna elements with the complex weighted excitation determined by the use of genetic algorithms.
This paper is concerned with the measurement and analysis of a circularly polarized, flat plate patch array receiving antenna at 12.5 GHz. Input impedance and far field pattern measurements of the antenna over the frequency band from 10 to 15 GHz were performed. The small Compact Range (CR) facility of the Ohio State University Electro Science Laboratory OSU/ESL was used to measure the gain pattern. Gain pattern measurement of the antenna was done by using the gain comparison method. A broadband (2-18 GHz), constant phase pyramidal horn antenna was used as a reference. The data were analyzed to determine the radiation efficiency of the antenna.
Compact range reflector edge diffraction can be reduced by placing a well-designed R-card fence in front of the reflector edges. The impact of this fence can be expressed mainly in terms of its ability to attenuate transmitted energy through the R-card. Thus, the resistance of the R-card is synthesized to satisfy a chosen GO aperture taper. A Kaiser-Bessel taper produces an ideal taper transition and hence a large target zone at the lowest operating frequency. Since a proper design requires that the R-card be located near the curved reflector edge, multi flat R-card segments are designed and assembled around the periphery of the reflector. The R-cards then attenuate the transmitted edge diffracted field and direct the reflected signal away from the test zone onto the anechoic chamber walls, which results in a significant improvement in the uniformity of the test zone fields.
It is known that electromagnetic signalls can penetrate through non-metallic barriers such as building walls. A hand-held Sythetic Aperture Radar (SAR) unit capable of transmitting and receiving such signals is desirable in various military and civilian applications. Theoretical and experimental issues associated with through-wall Ultra Wide Band (UWB) SAR imaging of buildings are studied here. It may be inconvenient and impractical for a hand-held unit to collect data at uniformly spaced positions. A backprojection algorithm is developed for the case where spatial sampling is not uniform. In addition, a spherical wavefront (as opposed to a uniformly planar wave front) is assumed in the algorithm to account for the proximity of a radar unit relative to a target scene. Images of simulations using point targets and measurements of canonical targets such as a corner reflector and a cylinder are generated. Images of a standing human in free-field and through-wall are compared.
Ths paper demonstrates the plane wave, pattern subtraction method for performing range compensation of full-sphere antenna patterns measured on a fixed line-of-sight far-field range. The range field is measured on the surface of a sphere and a plane wave model of the range field illuminating the antenna under test (AUT) is determined. The range compensation algorithm uses information contained in both the plane wave model and the AUT pattern measurement to estimate the error pattern that is added to the measured AUT pattern by an extraneous source. This estimated error pattern is subtracted from the antenna pattern measurement to obtain a compensated pattern. The compensated pattern and estimated error pattern are improved iteratively. This paper demonstrates the technique using measured data. The AUT is measured in a far-field anechoic chamber that contains a secondary horn antenna located 20 degrees off-axis from the range antenna, which is used as an extraneous source. The AUT is a 474 element planar array operating at a frequency of 9.33 GHz.
For improvement of the measurement accuracy of compact range test facilities under the constraint of maintaining the realtime measurement capability, a versatile hardgating system has been developed at the Fachhochschule Munchen. With this measurement and diagnostic tool a flexible, computer controlled variation of the pulse widths down to some ns can be performed to obtain a high spatial resolution. Besides selective measurements of the quiet zone field with suppressed interferers it is also possible to select particular inte fering field contributions in order to determine their amplitude and direction of incidence. The paper describes the hardgating system and the measurement results obtained with low and high gain antennas in the compensated compact range test facility at the Fachhochschule Munchen.
In 1997 ORBIT/FR and Dornier Satellitensysteme (DSS), a corporate unit of Daimler-Benz Aerospace, agreed on strategic cooperation in the area of Compact Range products. This includes a licence agreement which allows ORBIT/FR to use the DSS developed reflector manufacturing technology utilizing steel castings to produce the highest precision reflectors machined for quiet zone sizes up to 8 x 12 ft. The standard product line includes both single reflector ORBIT/FR designs and the cross-polar compensated double reflector DSS design. Chelton (Electrostatics) Ltd. In Marlow, UK, is the first ORBIT/FR customer to receive a compact range using DSS technology. This radome measurement system uses a single reflector compact range with quiet zone of 4 x 6 ft. Other components include antenna, radome, and feed positioners, an HP 8530 based RF system, FR959 software and absorbers. Special software was developed to fully automate the entire radome acceptance test (up to 30 hours of acquisition and data evaluation) with a single command.
In a networked antenna measurement laboratory implementing Intranet technologies provides significant benefits. Some of the benefits include efficient data transfer, remote test setup, remote monitoring and control and ease of data analysis. This paper first summarizes some of the options available and considerations in incorporating an Intranet architecture in an antenna measurement laboratory. Relative merits and pitfalls of some of the solutions are discussed. Performance issues and tradeoffs are outlined. The David Florida Laboratory (DFL) RF Facility experience in implementing an Intranet based operation is presented.
Whether for speed or accuracy, it is often necessary to rapidly switch antenna beams during testing. Most current systems require a control line for each RF switch position or phase shifter bit [1,2]. Due to the need for slip rings, the number of bits that can be controlled by this method is limited. In addition, the voltage drop and interference over long lines limit the practical range lengths that can use these "wire-per-bit" techniques. A serial bit stream followed by a serial to parallel conversion is the usual approach to controlling a large number of switches with only a few lines. However, the serial bit stream approach is quite slow. This paper will present a high speed switch box that can control an arbitrary number of RF switches and phase shifters using only two control lines that can go very long distances. The electronic circuits and software interface of this box will be covered.
The objective of this research effort was to design, fabricate and test an RF and Infrared (IR) beam combiner for use at multiple missile simulation laboratories. The ideal combiner, in the transmission mode, should provide minimum attenuation to RF signals between 1 and 100 GHz (very broad band spectral coverage); in the reflective mode, the combiner will provide maximum reflection of infrared signals between 3 and 12 µm. These combiners will be used for the testing of multi-spectral missile systems at NAWC/ WD located at China Lake, CA. The innovative approach taken by MRC, for the development of the Dichroic Beam combiner, used practical implementations of Frequency Selective Surface (FSS) theory. The advantage of this technique over dielectric coatings or metallic coatings is that it optimizes RF throughput (attenuation is no longer a function of the thickness of the metal) while increasing reflectivity in the infrared. The approach taken resulted in the development of dichroic elements which are efficient at transmitting RF and reflecting IR; the delivered hardware was also manufactured having large physical sizes and odd dimensions.
During the design of spacecraft antennas a well defined geometrical configuration of antenna components is supposed. Also the requirements for the accuracy of the antenna integration normally will be given. The antenna alignment processes have to ensure, that the designed configuration with the required accuracy can be met. Additionally the antenna pointing has to be determined with respect to the RF measurement facility. In this paper the concepts are treated, how to determine the actual and the designed orientation and location of the components of the space antennas during subsystem and system level integration and tests. This includes also the definition of needed references for the antenna components, the creation and application of coordinates or orientation matrices at manufacturing or integration level, the used coordinate systems and the attainable accuracy for different methods. For the evaluation of the RF pattern performance, the correlation between the spacecraft coordinate system and the facility coordinate system has to be known. Basic principles of this pointing alignment and an error analysis of the measurement accuracy will be explained. The presented concepts are based on the experience at DSS' test facilities with various antenna types and agreed with different antenna manufacturers and customers.
Offset parabolic reflector Compact Ranges are limited for cross polarization measurements in comparison to compensated dual reflector systems. This means that, in some cases, the crosspolar measurements at low levels show a significant content of the compact range reflector cross polar. An investigation has been carried out at INTA to reduce the crosspolarization measurement errors levels to those of a compensated dual reflector system by the application of vector deconvolution techniques. Results are shown of the validation of the algorithm in a far-field range where a crosspolar field is introduced by depointing the transmitter antenna.
Large Compact Ranges for test zone sizes of 6 meters or can be used for both payload or advanced antenna and RCS testing. In order to determine the range accuracy, test zone field evaluation is required. For physically large test zone dimensions, scanning of the test-zone fields is difficult and impractical in most situations. Furthermore, the accuracy of planar or plane-polar scanners is usually not sufficient for applications above 10 GHz. An alternative approach is the RCS reference target method where the test zone field is derived from the RCS measurement of a flat plate. Such a target can be manufactured as a single sheet aluminium honeycomb structure with rectangular or circular cross section. Reference targets with large dimensions and high surface accuracy are available. Consequently, test-zone fields can be accurately determined for test zone diameters up to about 10 meters and frequencies up to 100 GHz. In this paper the application of this method will be demonstrated at the Compact Payload Test Range (CPTR) at ESA/ESTEC. Large rectangular plate has been used for field determination within a test-zone of 5.5 meters. A 2 meter diameter circular flat plate has been used to map the residual cross-polarization level within the test zone. It will be shown that valuable information about range performance (amplitude, phase and cross-polarization) can be accurately retrieved from the RCS measurements
ORBIT/FR designed and manufactured a plane wave scanner of unprecedented accuracy. It was delivered to Intespace in Toulouse, France, to verify the compact range quiet zone performance of the compact range system installed by Dornier Satellitensysteme GmbH. The design is of the plane polar type. The linear axis has an accurate travel range of 5.5 meters with additional acceleration and deceleration ranges. The polar axis has a travel range of over 180 degrees, so that a full circular plan of 5.5 meters in diameter can be evaluated. The mechanical overall planarity is better than ± 80 micrometers peak to peak. This is equivalent to ± 3.8° phase at 40 GHz. Special attention was given to the design of the RF cable track. A maximum phase variation equal to the mechanical accuracy was specified. However, no phase variation was noticed due to cable movements, even at 40 GHz. A new application for this scanner was to verify the actual boresight of the plane wave in both normal and so-called scanned boresight applications (compact range feed moved out of the focal point). For this purpose, the scanner was equipped with an optical mirror cube. Overall system alignment accuracies of 0.01° were typically achieved.
Diagnostic tools for the determination of the excitation coefficients of a multifeed antenna based on pattern measurements are extremely useful during a spacecraft antenna design. Due to the complexity of state of the art multifeed antennas, it is not straight forward to trace back to the location of possible error sources, if deficiencies or non-compliance's are detected during an antenna measurement campaign. Therefore a method was developed and tested at DSS which directly determines all effective excitation coefficients from pattern measurements. The method approximates the measured composite array pattern a set of computed element beam pattern, weighted by a set of unknown excitation coefficients. The resulting equation system is solved using the Method of Moments (MoM). The tool was extensively tested at DSS. The accuracy obtained for the calculations of the coefficients was in the 2% range beeing compareable to the accuracy of Beam Forming Network (BFN} measurements using a network analyser. In this paper the theoretical background of the method as well as some application cases will be described.
The effect of the platform in the radiation pattern of antennae on board satellites, aircraft or ships has to be taken into account in order to know the actual performance of antenna systems. To have an evaluation of this effect, software prediction codes are developed, providing a fast, cost efficient and comfortable solution compared to the usual measurement campaigns. Nevertheless, these codes have to be validated. Specific tests have been done in order to validate the prediction code FASANT, developed by the Universidad de Cantabria from Spain and based on the Uniform Theory of Diffraction (UTD). A description of the code is first done to follow with the measurement project that has been performed at the INTA facilities in Madrid. A mountable mock-up of the Hispasat satellite has been used to obtain different configurations. Special geometrical shapes have been added to the satellite platform to check for different scattering effects.
Most often when performing antenna and RCS measurements, integrating the results is performed with some type of computer generated simulation or model of the application scenario. In the case of Missile Engagements for Fuze Radars, there is an opportunity to engage full size targets in a near real engagement. The missile fuze antenna can be mounted on the test cart which is able to position the fuze antenna in azimuth, pitch and roll. For instrumentation the MESA Facility has available a PN coded BiPhase multi-range gate radar system. Various Full size targets are available for use in the arena. The target are positioned for a multitude of trajectories utilizing an overhead target positioning system. The Overhead Target Positioning System suspends and moves the targets using a multipoint string system that controls, Pitch, Roll, height, and azimuth positioning. The Overhead Target Positioning System (OTS) is also controlled in lateral movement. (across the range) This paper will show the verification of antenna patterns and RCS returns of full size targets using the MESA Radar system, and verification of these measurements using a hardware in loop fuze radar system simultaneously.
The Georgia Tech Research Institute (GTRI), under contract to the U.S. Air Force 46 Test Group, Radar Target Scattering Division (RATSCAT), at Holloman AFB, NM, has designed and developed a fully polarimetric, bistatic coherent radar measurement system (BICOMS). It will be used to measure both the monostatic and bistatic radar cross section (RCS) of targets, as well as create two-dimensional, extremely high-resolution images of monostatic and bistatic signature data. BICOMS consists of a fixed radar unit (FRU) and a mobile radar unit (MRU), each of which is capable of independent monostatic operation as well as simultaneous coherent monostatic and bistatic operation. The two radar systems are coherently locked via a microwave fiber optic link (FOL). This paper discusses the key system features of the BICOMS.
Responses in turntable imagery are properly focused if they behave as fixed point scatterers in the focal plane chosen for polar formatting. Other responses, be they generated by more complicated back- scattering or by fixed point scatterers outside the focal plane, have a curved phase. This curved phase can be used to recognize responses due to reflection between separated scatterers, and to determine the locations of the contributing scatterers, whether the scatterers are located on the target, its mount, or the turntable. For nonzero depression angles, the phase curvature can also be used to measure the height of a point reflector.