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Composite Optics Inc (COI) has designed and constructed a Portable Far-Field Antenna Test Chamber to complement their Large Compact Range. The need for this chamber arose after COI won a contract to design, build, and test hundreds of small broadband antenna elements. Because of the portability requirement, COI chose to procure and modify an industrial container, suitable for transportation on a standard flatbed trailer. This paper discusses the design, fabrication, and installation of a chamber, suitable for pattern measurements of small (<2 feet) antennas in the 6-18 GHz frequency range.
For greatest efficiency and accuracy in measuring patterns of a circularly polarized antenna on a planar near field range (NFR), a recommended procedure is to use a fast switched, dual circularly polarized probe. With such equipment one obtains complete pattern and polarization data from a single scan of the antenna aperture. For our task of measuring high gain shaped beam apertures, measurement efficiency is further improved by using a moderately high gain (about 12 dBi) probe that has been accurately calibrated for patterns, polarization, and gain over the test frequency band. Such a probe allows scan data point spacing to be typically at least one wavelength, thus keeping scan time minimized with acceptably small aliasing (data spacing) error. The measured near field amplitude and phase data is transformed via computer to produce the angular spectrum that is further processed to remove the effect of the probe patterns, i.e. probe correction. The final output is a set of (principal and cross) circular polarized far field patterns. However on one occasion, due to fast breaking changes in requirements, we were unable to obtain a calibrated circular polarized probe in the available time. For this test we used an available calibrated 12 dBi fast-switched dual linear-polarized probe with software capable of processing principal and cross circular-polarized far field patterns. As anticipated, we found from preliminary tests that the predicted low cross-polarized shaped beam pattern was not achieved when using the calibrated fast Ku band probe switch. Further tests showed the problem to be due to small errors in calibration of the probe switch. This paper will discuss test and analysis details of this problem and methods of solution.
When mounted on spacecraft , pattern of some antennas are perturbed by the presence of satellite body. The prediction of antenna performances including satellite structure effect is generally done at early stage of antenna design but is limited in terms of model complexity. The test on full spacecraft & in far field condition is then necessary. This solution is very expensive as it means for test at satellite level to use Compact antenna Test Range in order to satisfy cleanliness aspects. For the Meteosat Second Generation (MSG) program test on the toroidal antennas need to be performed on different model including a flight model. A good compromise was to use the external omnidirectional antenna range and a part of satellite structure representing the major contributor for the antenna pattern as identified via numerical analysis. The external range offer possibilities that cannot be reached in Compact range, e.g. low cost, full sphere pattern, low frequency range.
Obtaining far-field radiation patterns of high frequency antennas (>80Ghz) from near-field measurements has been an important issue in the last twenty years. However with frequencies increasing into the millimetre and sub-millimetre bands, questions have been raised about possible limitations on the assessment of such antennas and in particular the measurement of phase. The PTP phase retrieval algorithm addresses the problem by extracting the phase from the knowledge of two amplitude data sets in the near-field. The accuracy of the algorithm is studied by simulation and measurement by means of a numerical/statistical approach. Pseudo-random phase apertures can be generated using Zernike polynomials, which in turn can be used as initial estimates for the algorithm. This paper shows some simulated and measured results for various separations. It can be seen that different pseudo-random phase functions can affect the accuracy of phase retrieved results in particular when the distance between planes is considerably small in relation to the AUT size.
In this paper, an iterative algorithm for the retrieval of the radial component of the electric field is described to be used in matrix source reconstruction methods that deal with spherical measurement. A source-field decoupled integral equations are presented, making it necessary the use of a radial field retrieval algorithm to calculate the equivalent magnetic currents (EMC) in the antenna plane from the angular components of the electric field. The technique is applied in near field to far field (NF-FF) transformations using spherical ranges. With the presented technique, some drawbacks, inherent to the intensive resolution of the integral equations that appears in the methods based on equivalent currents, are overcome. Verification with simulated results as well as measurement results are presented.
The complexity of modern antennas has resulted in the need to increase the productivity of ranges by orders of magnitude. This has been achieved by a combination of improved measurement techniques, faster instrumentation and by increased automation of the measurement process. This paper concentrates on automated measurement systems, and describes the requirements necessary to make such systems effective in production testing, and in research and development settings. The paper also describes one such implementation - the MI Technologies Model MI-3000 Acquisition and Analysis Workstation - that was designed specifically to cmnply with these requirements The paper discusses several important factors that must be considered in the design of automated measurement systems, including: (1) Enhancing range productivity; (2) Interfacing with instrumentation from a large number of suppliers; (3) Providing a uniform front-end for the measurement setup and operation that must be largely independent of the choice of the hardware configu rations or the type of range (near-field or far-field); (4) Making the test results available in a format that simplifies transition to external commercial and user program med applications; (5) Providing powerful scripting capability to facilitate end-user program ming and customization; (6) Using a development paradigm that allows incremental binary upgrades of new features and instruments. The paper also discusses computational hardware issues and software paradigms that help achieve the requirements.
A software's user-interface design determines how productive someone will be in a accomplishing a given task. This is particularly true in the area of antenna measurement and analysis. The MiDAS software package is used as an example of how software can be specifically designed to focus on enhancing efficiency by implementing an advanced human-machine interlace. Simple yet critical aspects such as minimized menu access, integrated, user friendly error checking and help, and clear, consistent, and integrated features help to improve productivity, reduce errors and save time. In addition, design principles such as having only one interface for all antenna measurement disciplines (e.g., near-field and far-field), reduces the time needed for training which, in turn, lowers costs. This paper explores how the implementation of such a user interface can be used as a paradigm for increasing efficiency in the field of antenna measurement and analysis.
TRW, working with several subcontractors, is building a Compact Antenna Test Range (CATR) in one of its existing buildings. This range will replace the function of a two mile long far-field range. Lehman Chambers Corp. provided the CATR Anechoic Chamber with Cuming Corp. Microwave Absorber. Mission Research Corp. provided the CATR Rolled Edge Reflector and feeds. M.I. Technologies is configuring TRW supplied positioners with new translators for AUT positioning. The system will operate with both the M.I. Technologies 3000 System software and TRW software. We will be using an existing S/A 1795 receiver for the RF portion of the system with HP sources. Completion of the range is scheduled by the beginning of the 4th quarter 2000. This paper will provide an overview of the system design and constraints. Individual portions of the CATR will be described in detail including decisions made to reduce the overall cost of the system and fit into an existing budget.
A reconstruction method that calculates bi-dimensional equivalent magnetic currents from the tangential electric field components over a hemispherical region is presented. The method is applied for diagnosis as well as for near field to far Field (NF-FF) transformation. The method is well suited for antenna radiation pattern measurement using a near-field spherical acquisition system in anechoic chamber.
This paper is focused on a recent installation of a probe array for direct far-field. measurement. Such an array has been installed in a well-established compact antenna test range at CNES called BCMA in Toulouse, France. It describes the interests of using such multi-sensor approach for characterizing directive antennas within far-field conditions without any mechanical movements. The paper shows how this facility has been dimensioned for operating over frequencies ranging from 7 GHz up to 15 GHz. Performances and general descriptions of both the probe array and its associated instrumentation will be given. A specific calibration procedure that has been studied and implemented is discussed and finally preliminary results are shown.
This paper is focused on a recent installation of a probe array for direct far-field. measurement. Such an array has been installed in a well-established compact antenna test range at CNES called BCMA in Toulouse, France. It describes the interests of using such multi-sensor approach for characterizing directive antennas within far-field conditions without any mechanical movements. The paper shows how this facility has been dimensioned for operating over frequencies ranging from 7 GHz up to 15 GHz. Performances and general descriptions of both the probe array and its associated instrumentation will be given. A specific calibration procedure that has been studied and implemented is discussed and finally preliminary results are shown.
The purpose for this advanced development program was to advance the flatness level on an RF/IR Beam combiner. The developed beam combiner minimized transmission losses for RF signals between 1 GHz and 40 GHz and maximized total transmission for RF signals between 8 GHz and 18 GHz. The combiner maximized IR reflectance for IR radiation (2µm to 13 tm). Two 12 inch units were delivered to NAWC-WPNS for evaluation. The combiners produced an average transmission losses in the range of 0.4 dB between 1 and 33 GHz and 0.8 dB between 33 GHz and 40 GHz. Reflectivity in the Infrared was measured at 87% with the use of a 3.39 µm laser source. The combiners were manufactured on PolyOxyMethyle (POM); they are highly crystalline structures, very flat (mold driven), with unique acetal resins structures. POMs are a variant of thermo plastics, are made by free radical polymerization initiated by a peroxide or azo catalyst, or by redox polymerization. Four basic polymerization processes may be used to produce good RF transmission acrylic resins. Using POM as the host material, a Frequency Selective Surface (FSS) using a low pass configuration, was Gold sputtered on the host material surface. The results produced a mirror like surface, highly visible and IR reflective, and very transmissive in the RF domain. These combiners are to be used for the anechoic chamber testing of dual mode missile seeker systems. The missile systems required in an anechoic chamber measurements, far field illumination from both IR signals and RF signals. The dual mode beam combiner allows spatially coherent signals to illuminate the missile seeker under test. Results of these development, seems to indicate that larger combiners can be fabricated on optically flat materials (e.g. fused silica) with flatness of 12 µm. This will allow the next generation seeker heads, operating with large focal plane arrays, to be stimulated in an anechoic chamber environment.
Phase retrieval is an important issue related to the reconstruction of SAR/ISAR images, when phase information is lost or unavailable. In this paper, an iterative algorithm is formulated which demonstrates the ability to perform phase retrieval with minimal set of constrains on the imaged object. This iterative algorithm requires only rough knowledge of the size of the imaged body and the amplitude of the received, far-field, radiation in the various frequencies and/or aspect angels (for I D or 2D image). By applying iterations between the two planes of the imaged body and the plane of the RADAR reflections (as a function of aspect angles and frequencies), a good reconstruction of the phase and the amplitude of the imaged body as well as the phase of the received radiation, are obtained. The algorithm can be used in the problem of imaging body in motion where motion compensation is difficult or in applications involving mm wave images, where phase information is lost in the turbulent atmosphere.
Time domain (TD) antenna measurements have been successfully implemented in far field ranges [1,2]. The short acquisition times and the wide-band nature of the measurements make this regime a potential alternative to classical frequency domain measurements. Due to the measurement versatility offered by compact ranges, the implementation of TD measurements becomes especially attractive. This paper presents the modelling of the compact range performance in TD. In addition, a statistical evaluation criterion to assess the quiet zone quality is formulated. The results obtained show that this type of measurements can be successfully implemented in compact ranges.
The growing need of ultra-wide band measurements has promoted the research on real time domain (TD) antenna measurements. Theory has been already established, but practices still under development until the measurement regime becomes fully operational. In the Delft University Chamber for Antenna Measurements (DUCAT) there have been already provided outstanding results in a TD far-field configuration. A TD far field model of the facility has been developed in order to provide a key to improve the range performance and accuracy. This paper presents the model and considerations for establishing TD error correction techniques.
The growing need of ultra-wide band measurements has promoted the research on real time domain (TD) antenna measurements. Theory has been already established, but practices still under development until the measurement regime becomes fully operational. In the Delft University Chamber for Antenna Measurements (DUCAT) there have been already provided outstanding results in a TD far-field configuration. A TD far field model of the facility has been developed in order to provide a key to improve the range performance and accuracy. This paper presents the model and considerations for establishing TD error correction techniques.
Modelling of the field in the quiet zone (QZ) of a compact range is a difficult task since the edges of the range reflectors are designed not to radiate into the quiet zone. As a consequence the edges of the range reflectors are complicated to model electromagnetically. In the present paper we compare modelling by physical optics (PO) with modelling by the uniform geometrical theory of diffraction (GTD). The investigation is carried out on a double reflector range with rectangular serrated reflectors. It is found that the range far field determined by PO is best explained by a ray model for reflectors having a double straight edge, which suggests to apply a GTD model on reflectors with straight edges but with attenuated diffraction contribution. Both PO and GTD results are shown and compared to measurements.
Compact Antenna Test Ranges are eminently suitable for obtaining the far-field patterns of various types of antennas provided that the frequency is not too low. Typically, a low frequency limit of 1 or 2 GHz is realizable. There are, however a number of important applications between 500 and 1000 MHz for antenna diameters between 1 and 3 meters. The far field distance R = 2D2/l is just too large for an indoor far field range. It is generally accepted at present that a good solution for an indoor range for these kind of measurements is very difficult to realize. In this paper the low frequency performance of single and dual-reflector Compact Antenna Test Ranges will be investigated. It will be shown that with carefully designed serrations and feeds, excellent antenna measurements can be carried out at frequencies below 1.0 GHz for a large number of applications. For purposes of comparison, low frequency performance of a compact range with so called blended rolled edges will be presented as well.
Compact Antenna Test Ranges are eminently suitable for obtaining the far-field patterns of various types of antennas provided that the frequency is not too low. Typically, a low frequency limit of 1 or 2 GHz is realizable. There are, however a number of important applications between 500 and 1000 MHz for antenna diameters between 1 and 3 meters. The far field distance R = 2D2/l is just too large for an indoor far field range. It is generally accepted at present that a good solution for an indoor range for these kind of measurements is very difficult to realize. In this paper the low frequency performance of single and dual-reflector Compact Antenna Test Ranges will be investigated. It will be shown that with carefully designed serrations and feeds, excellent antenna measurements can be carried out at frequencies below 1.0 GHz for a large number of applications. For purposes of comparison, low frequency performance of a compact range with so called blended rolled edges will be presented as well.
The objective of this study is to develop a new techniq ue to compensate the instrumentation errors of an antenna near-field test range. The methodology presented demonstrates that it is feasible to calculate the far-field radiation from near-field measurement with one deconvolution that will include all the errors introduced by the instrmentation. Measrements were performed on a standard gain horn as a reference and the analysis includes a theoretical comparison with a computer model of the standard gain horn, simulated using WIPL. Furthermore, four scenarios of error in the system flatness were analyzed, to verify that the technique is capable of correcting planarity errors.