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The paper presents an example of the design process undertaken to determine the RCS response of LO features mounted on a test body. Although not unique, the example considers the various aspects which determine the accuracy of the final data in the design of the experiment and signal processing. The high quality of experimental results illustrate the potential of using an integrated approach in which the designs of the test body, the measurement process, the signal processing techniques, and validation of results are optimally applied to meet the objective not achievable by conventional means.
Antennas characteristics can be measured in two ways. lfrequency Domain Method (FDM) is more widely known. The main measuring instruments: Microwave Generator and Receiver. In Time Domain Method (TDM) measurements are fulfilled by using superwide band pulses. The main measuring instruments: Pulse Generator and Sampling Oscilloscope. TDM shows a number of advantages but for narrow-band antennas TDM is difficult to apply and FDM is required. At the testing polygons aimed to measure various antennas we set equipment allowing to use both measurement methods. For TDM we used a two channel sampling converter SD200 of Geozondas production with bandwidth 0-18 GHz. To unify measurements we developed a 3-channel sampling converter SD303 allowing besides pulse to measure sine wave amplitude and phase difference in dynamic range 100 dB. The third channel is used for synchronization. Thus the same instrument assures antenna measurements both in TDM and FDM. At 100 m distance the following characteristics are obtained in Time and Frequency Domains Measurements: Bandwidth 1- 18 GHz. Antenna pattern dynamic range 60 dB Gain measurement accuracy 0.5 dB Phase difference between 2 antennas error 0.5 - 3° (depends on frequency). Hardware, software and digital signal processing algorithms are considered.
Characterization of radiated EMI by means of near zone measurements is examined by computer simulations. Electric field radiated by a test structure is expanded in spherical wave modes. The influence of the number of spherical wave modes on the accuracy to predict the maximum far-field magnitude and the total radiated power is examined. The examinations of this paper support the electric field measurements of small equipment at small measurement distances in the standard radiated EMI frequency range 30 - 1000 MHz. Results are presented as a function kr0, where k is the wave number and r 0 is the radius of the minimum sphere which fully encloses the EUT. Results of this paper give valuable guidelines for choosing an appropriate number of measurement locations for predicting the far field by means of a near-zone measurement.
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.
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.
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.
The Seeker Test and Evaluation Facility (STEF) located on Range C-52A at Eglin AFB FL. is used to perform high-resolution multispectral (EO-IR-RF-MMW) signature measurements of US and foreign ground vehicles primarily to support the Research, Development, Test and Evaluation (RDT&E) of smart weapons (seekers, sensors and Countermeasure techniques). In order to support two major DOD signature measurement programs in 1997 this facility required significant range upgrades and enhancements to realize reduced background levels, increase measurement accuracy and improve radar system reliability. These modifications include the addition of a 350'X 120' asphalt ground plane, a new secure target support facility, a redesigned low RCS shroud for the target turntable and a new core radar system (Lintek elan) and data acquisition/analysis capability for the existing radars Millimeter-Wave Instrumentation, High Resolution, Imaging Radar System - MIHRIRS). This paper describes the performance increase gained as a result of this effort and provides information on site characterization and radar instrumentation improvements as well as examples of measured RCS of typical ground vehicle signatures and ISAR imagery
Full polarimetric scattering measurements are increasingly being required for radar cross-section (RCS) tests. Conventional co-and cross-polarization calibrations fail to take into account the small amount of antenna cross-polarization that will be present for any practical antenna. In contrast, full polarimetric calibrations take into account and compensate for the cross-polarization the calibration process. We present a full polarimetric calibration procedure and a simulation-based performance study quantifying how well the procedure improves measurement accuracy over conventional independent channel calibration.
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.
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.
This paper describes a new multi-purpose planar & cylindrical near-field antenna test facility installed at the Royal Netherlands Navy (RNN). In this paper an overview is given of the initial list of requirements that was generated and the process of selecting the best type of measurement facility to address these. A description of the facility is given and an outline of the accuracy of the planar/cylindrical near-field scanner is presented. The paper contains details of the extensive validation program and measured data demonstrating the performance of the system.
Recently, RCS measurements were made of several common calibration objects of various sizes in the Boeing 9-77 Range. A study was conducted to examine the accuracy and errors induced by using each as a calibration target with a string support system. This paper presents the results of the study. Two of the objects, i.e., the 14"-ultrasphere and the 4.5"-dia. cylinder, are found to perform the best in that they exhibit the least departures (error) from theory. The measured departures of 0.2 to 0.3 dB are consistent with the temporal drift of the radar in several hours.
This paper presents a new method of separating and evaluating the effects of each residual reflection caused by antenna measurement environment by distance changing technique. The effects represent radiation patterns caused by residual reflections (hereafter, error patterns). The key processes of this new method are to suppress sidelobes of a Fourier spectrum applying a window as a function of the distance with the purpose of obtaining an accurate spectrum of reflections and to separate error patterns each other using a gating technique at each angle. Using this method applying the above two processes, we can evaluate the error pattern for each reflection source with accuracy. The validity of this method is confirmed by a computer simulation. This method is especially useful to detect the position of each reflection source in a case of evaluation for antenna test range.
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.
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.
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.
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.