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Abstract— Indoor antenna ranges must have the walls, floor and ceiling treated with RF absorber. The normal incidence performance of the absorber is usually provided by the manufacturers of the materials; however, the bi-static or off angle performance must also be known. In reference [1], a polynomial approximation was introduced that gave a prediction of the reflected energy from pyramidal absorber. In this paper, the approximations are used to predict the quiet zone (QZ) performance of several anechoic chambers. These predictions are compared with full wave analysis performed in CST Suite®. A 12 m wide by 22 m long with a height of 12 m chamber was analyzed at 700 MHz. The QZ performance was compared to the polynomial predictions showing a difference of less than 2.2 dB. In addition, comparisons are made with measurements of the QZ performance of anechoic chambers. Measurements performed per the free space VSWR method of three different chambers are compared with the prediction that uses the polynomials presented in [1]. The chambers are: a 18 m long by 11.5 m wide and 11.5 m in height operating from 100M MHz to 12 GHz; a 13.41 m by6.1 m by 6.1 m operating from 800 MHz to 6 GHz; and a 14 m long by 4.12 m by 4.27 m operating in the X band. The results show that the polynomial approximations can be used to give a reasonably accurate and safe prediction of the QZ performance of anechoic chambers. [1] V. Rodriguez and E. Barry, “A polynomial approximation for the Prediciotn of Reflected Energy from Pyramidal RF Absorbers,” Proceedeings of the 38th annual Symposium of the Antenna Measurement Techniques Association (AMTA 2016), pp. 155–160, October 2016.
Abstract— Tilting the receive end wall of a compact range anechoic chamber to improve Radar Cross-Section (RCS) measurements has been a tool of the trade used since the earliest days of anechoic chambers. A preliminary analysis using geometrical optics (GO) validates this technique. The GO approach however ignores the backscattering modes from the reflected waves from a field of absorber. In this paper, a series of numerical experiments are performed comparing a straight wall and a tilted wall to show the effects on both the quiet zone and the energy reflected back towards the source antenna. Two Absorber covered walls are simulated. Both walls are illuminated with a standard gain horn (SGH). The effects of a wall tilted back 20° are computed. The simulations are done for 72-inch long absorber for the frequency range covering from 500 MHz to 1 GHz. The ripple on a 10 ft (3.05 m) quiet zone (QZ) is measured for the vertical wall and the tilted wall. In addition to the QZ analysis a time-domain analysis is performed. The reflected pulse at the excitation antenna is compared for the two back wall configurations Results show that tilting the wall improves measurements at some frequencies but causes a higher return at other frequencies; indicating this method does not provide a broadband advantage. Keywords: Anechoic Chamber Design, Radar Cross Section Measurements, Geometrical Optics
In June of this year, DSC completed the installation of a turnkey RCS measurement system that is used for in-process verification (IPV) and final component validation using standard near field QC techniques in an echoic chamber. The delivered system included a radar, antennas, shroud, ogive pylon, foam column, elevators for each – column and pylon, automated pit covers, test bodies, target transport carts, and calibration targets. The system automatically loads test objects on the correct target support system, requiring no action by the operator to connect a target onto the azimuth over elevation “tophat” positioner – it is all automatic. The user interface is designed to be operated by production line workers, greatly reducing the need for experienced RCS test engineers. Simple pass/fail indicators are shown to the test technicians, while a full detailed data set is stored for engineering review and analysis. A wall display guides users through a test sequence for target handling and starting the radar. Radar data collection of all azimuth and elevation angles and target motion are initiated from a single button push. This is followed by all data processing necessary to conduct the ATP on the parts providing a pass/fail report on dozens of parameters. The application of production line quality automation to RCS measurements improves the repeatability of the measurements, greatly reduces both measurement time as well as overhead time, and allows systems operators to become more interchangeable. This highly successful project, which was completed on-time and on-budget, will be discussed. This discussion will include radar performance, antenna and shroud design, target handling, data processing and analysis software, and the control system that automates all the functions that are required for RCS measurements.
This paper presents the results of a new measurement technique to determine antenna system noise temperature using data acquired from a planar near-field measurement. The ratio of antenna gain to system noise temperature (G/T) is usually determined in a single measurement when the antenna is alternately pointed towards the “cold sky” and a hot radio source such as the sun or a star with a known flux density. The antenna gain is routinely determined from near-field measurements and with the development of this new technique, the system noise temperature can also be determined. The ratio of G/T can therefore be determined from planar near-field data without moving the antenna to an outdoor range. The noise temperature is obtained by using the plane-wave spectrum of the planar near-field data and focusing on the portion of the spectrum in the evanescent or “imaginary space” portion of the spectrum. Near-field data is obtained using a data point spacing of l/4 or smaller and the plane-wave spectrum is calculated without applying any probe correction or Cos(q) factor. The spectrum is calculated over real space corresponding to propagating modes of the far-field pattern and also the evanescent or imaginary space region where . Actual evanescent modes are highly attenuated in the latter region and therefore the spectrum in this region must be produced by “errors” in the measured data. Some error sources such as multiple reflections will produce distinct localized lobes in the evanescent region and these are recognized and correctly identified by using a data point spacing of less than l/2 to avoid aliasing errors in the far-field pattern. It has been observed that the plane wave spectrum beyond these localized lobes becomes random with a uniform average power. This region of the spectrum must be produced by random noise in the near-field data that is produced by all sources of thermal noise in the electronics and radiated noise sources received by the antenna. By analysing and calibrating this portion of the spectrum in the evanescent region the near-field noise power can be deduced and the corresponding noise temperature determined. Simulated and measured data will be presented to illustrate and validate the measurement and analysis techniques. Keywords — Planar Near-Field, G/T, Figure-of-Merit Measurements, Simulation, Plane Wave Spectrum.
For high speed and high data-rate communications, operating frequency bands of wireless communication systems have been moving to submillimeter frequency range and their bandwidths have been broadening. IEEE 802.15 THz Interest Group (IEEE 802.15 IGthz) has been performing a channel characteristics study for future indoor millimeter and submillimeter wireless communications in the frequency range of 75 - 110 GHz and 270 - 320 GHz. Specular reflectance data of indoor interior materials is a prerequisite to analysis of the channel characteristics of new indoor millimeter and submillimeter wireless communications. Specular reflectiondescribed by the law of reflection states that the direction of the incident wave and the direction of the reflected wave make the same angle with respect to the surface normal, thus theangle of incidence is equal to that of reflection. This paper describes a specular reflectance measurement system and shows measurement result of dielectric plates in the frequency range from 110 GHz to 325 GHz. Specular reflectance measurement system consists of an S-parameters measurement system and a specular reflectance measurement apparatus. The S-parameters measurement system consists of a 67 GHz vector network analyzer used as the main frame and three frequency extenders which are operating at three frequency bands (D-band (110 -170 GHz), G-band (140-220 GHz) and J-band (220-325 GHz)), respectively. The specular reflectance measurement apparatus consists of a transmitting part, a receiving part, and a MUT holder which is positioned in the middle of the transmitting and receiving parts. During the specular reflectance measurement, the transmitting part is fixed while the MUT holder and receiving part are coaxial-rotating with 1:2 speed ratio. The transmitting and receiving frequency extenders are installed on the transmitting and receiving parts, respectively. For the specular reflectance measurement, one measures the transmission coefficient (S21_MUT) corresponding to the specular reflectance of an MUT mounted on the MUT holder. After replacing the MUT with a metal plate, one measures the transmission coefficient (S21_metal) corresponding to the specular reflectance of the metal plate, assumed to be -1. Specular reflectance of the MUT is obtained by taking the ratio (S21_MUT/S21_metal) of the respective transmission coefficients corresponding to the specular reflectance of the MUT and the metal plate. Multiple reflection effects between the transmitting and receiving antennas can be averaged out and minimized by averaging the transmission coefficients measured with changing the separation distances between the two antennas by ?/8 interval (i.e. initial distance + n·?/8, n=0,1,2,3). Specular reflectances of dielectric plates are measured in the 30° to 70° incident angle range with the developed measurement system in the frequency range from 110 GHz to 325 GHz. Description of the detailed measurement system and measurement result will be presented at the symposium.
Temperature change cause thermal expansion of the antenna materials and will have an important impact on antenna performances. In some applications it is sufficient to calculate the antenna deformation due to temperature by mechanical analysis and determine the RF impact by EM analysis tools. However, if the environmental conditions of the final antenna are stringent and considered critical as in some military and civil applications in the space and aeronautics domain, the thermal performance of the antenna must be determined by experiment. Typical temperature testing ranges for civil applications are often between -50°C and +80°C but can be much more extensive for special applications. This paper present a simple and easy method for thermal testing of antennas in a fast spherical near field measurement facilities such as multi-probe system. During the thermal testing, the antenna is maintained inside a RF transparent thermally insulated container including the local heating and cooling equipment. The fast testing provided by the multi-probe system allow to measure the temperature dependence of the antenna at several different temperatures within the investigation range. The method will be illustrated for the cold measurement case but the extension to the full cold-hot temperature range is trivial.
The expanding market for millimeter wave antennas is drivinga need for high performance near-field antenna measurement systems at these frequencies. Traditionally at millimeter waves, acquisition of two orthogonal polarizations have been achieved through mechanical rotation of a single polarized probe and an associated frequency conversion module. This generally results in the collection of two complete spherical data sets, one for each polarization,with both acquisitions significantly separated in time. To enable improvements in both measurement speed and accuracy, MVG have developed a new high performance dual polarized feed in V-band (50GHz-75GHz). This probe has been integrated in a millimeter wave Spherical Near-Field (SNF) system via two parallel receiver channels that are simultaneously sampled. This architecture more than doubles the acquisition speed and additionally ensures that the two polarization components are sampled at precisely the same point in space and time. This is particularly important when performing accurate polarization analysis (e.g. conversion of dual linear polarization to spherical/elliptical polarizations). The two measurement channels are calibrated via radiated boresight measurements over a range of polarization angles, generating a four term “ortho-mode” correction matrix vs. frequency. The SNF probe is based on an axially corrugated aperture providing a medium gain pattern (14dBi). The probe provides symmetric cuts and low cross-polarization levels in the diagonal planes. The directivity/beam-width of the aperture has been tailored to the measurement system, ensuring proper AUT illumination and sufficient gain to compensate for free space path loss. Dual polarization capability is achieved with an integrated turnstile OMT feeding directly into the probe circular waveguide and a conical matching stub at the bottom. Thanks to the balanced feed used for each polarization, the port-to-port coupling is sufficiently low to allow for simultaneous acquisition of the two linear field components. Input ports are based on standard WR-15 waveguide to simplify the integration with the front-end (dual channel receiver). The paper will present the detailed description and measured performances of the new dual polarized SNF probe. Additionally, measurement time and achieved accuracy will be compared between the single polarization probe architecture and the dual polarized probe installed in the same spherical near-field antenna measurement system.
CubeSats represent a major paradigm shift for the satellite community and access to space in general. Traditionally, the design trend for satellites focused on durability, long lifetimes, and high performance, which translates to a high cost and lengthy time to deployment. CubeSats, on the other hand, compromise performance and lifetime with the goal to dramatically reduce costs and development time. Their small size allows launching as a secondary payload which is a key factor in cost reduction. The chassis dimensions (typically 3U to 6U) makes it difficult to integrate high performance wireless systems into the CubeSat chassis. A major limitation is the volume required for a high-gain antenna. Deployable, high-gain antennas are attractive for CubeSats, especially ones that can be stowed in a compact footprint. Deployment strategy is a major consideration for designers, and current attention has focused on developing large apertures that deploy outside the CubeSat chassis (e.g. umbrella or truss-net reflectors). However, little work has been done to develop ultra-compact, deployable antennas with moderate aperture sizes that seamlessly integrate with the chassis. We propose a novel CubeSat antenna concept that utilizes a near-field Gregorian reflectarray. The feed is a planar array conformal to the CubeSat surface that radiates an effective plane wave in its near-field zone. A parabolic subreflector focuses the plane wave towards the focus of the main reflectarray aperture, which has been designed to emulate an offset parabolic main reflector. This reflectarray is also conformal to the CubeSat chassis. The novelty of this design lies in the deployment strategy, where only the small subreflector is reoriented for deployment. This overall design avoids cable movement and maintains a compact volume when stowed, while achieving desirable efficiencies. We will present our compact antenna arrangement for Ka-band operation with an aperture of 209mm which integrates with a 6U CubeSat chassis. The challenges in the design are threefold: developing a compact, efficient planar array for plane wave generation; developing an offset, efficient reflectarray; and developing tools for diffraction analysis of the full system. We also present measured performance for various segments of this system using UCLA bipolar planar near-field system to avoid gravitational loading and issues with linear probe motion.
GTRI has been developing a method for insertion phase calibration, as discussed in the paper “Insertion Phase Calibration of Space-Fed Arrays,” which was presented at AMTA in 2015 [1]. This method has been implemented to characterize the phase response of phase shifters in a system currently under fabrication at GTRI. One of the primary requirements for the phased-array antenna of this system is a maximum RMS phase error. The RMS phase error for this array is influenced by a variety of error sources, including phase shifter quantization, beam steering computer (BSC) algorithmic error, phase shifter unpredictability error, test fixture induced error, phase shifter thermal drift, and phase shifter frequency dependency. Each of these error sources has been categorized as either a non-deterministic error, whose behavior can be statistically characterized but not calibrated out, or as a deterministic error, whose behavior can be characterized and potentially calibrated out. The non-deterministic errors include element unpredictability, which is induced by the inability of an individual phase shifter to precisely repeat a given phase command, and errors induced by the calibration test fixture itself. The deterministic errors include phase shifter quantization error, which is a function of the phase state bit precision, BSC algorithmic error, which is driven by the numerical preciseness of calculation of the commanded phase states for each element, thermal driven phase drift, and phase shifter frequency dependency across the band of operation. To calibrate the insertion phase and phase-state response curves for all phase shifters used in the system, a custom-built calibration fixture was constructed into a septum wall that separates two semi-anechoic chambers. The realized phase-error budget of the system under fabrication was affected directly by the accuracy of both the calibration method and this fixture. We will present our analysis of all phase-error sources as they contribute to the overall phase-error design goal of the system. We have shown how the design and implementation of both the calibration fixture and methodology meet that goal.
The uncertainty of the far field, obtained from antenna planar near field measurements, against the dynamic range is investigated by means of statistical analysis. The dynamic range is usually limited by the noise floor for low level signals and by the receiver saturation for high level signals. The noise level could be important for high measurement rate, which requires the usage of a high signal level to ensure a sufficient signal to noise ratio. As a result the nonlinearities are increasing, thus a compromise must be accomplished. To evaluate the effects of the limited near field dynamic range on the far field, numerical simulations are performed for dipoles array. Initially, the synthetic near field data corresponding to a given antenna under test were generated and directly processed to yield the corresponding far field patterns. Many far field parameters such as gain, beam width, maximum sidelobe level, etc. are determined and recorded as the error-free values of these parameters. Afterwards, the synthetic near field data are deliberately corrupted by noise and receiver nonlinearities while varying the amplitude through small, medium and large values. The error-corrupted near field data are processed to yield the far field patterns, and the error-corrupted values of the far field parameters are calculated. Finally, a statistical analysis was conducted by means of comparison between the error-corrupted parameters and the error-free parameters to provide a quantitative evaluation of the effects of near field errors on the different far field parameters.
Wave scattering from a perfectly conducting sphere provides an important example for theoretical studies as well as RCS calibrations [1, 2]. At the Boeing 9-77 Range and the Millimeter Wave Range in Seattle, we measured spheres of large and small diameters, supported by strings or a foam tower, and through a wide range of frequencies. In addition to co-polarized calibration, the emphasis was also on uncertainty analysis in order to verify that the experiments carried out under different conditions were mutually consistent [3]. Aside from the well-defined conditions for an indoor range, metal spheres may be dropped from the air free fall while being measured [4]. A news article on January 5, 2016, reported that three metal spheres were picked up in three provinces in northern Vietnam [5]. Though details of the experiments were obscure, from the pictures they happened to correspond to spheres of sizes from large to small. Based on our experiences, some speculation will be discussed. References [1]. E. F. Knott, "Radar Cross Section Measurements," (Van Nostrand Reinhold, New York, 1993), pp. 176-180, (on spheres and the Mie series). [2]. E. F. Knott, E. F. Shaeffer, and M. T. Tuley, "Radar Cross Section," (Artech House, 2nd ed, 1993), pp. 86 & 234-235, (on creeping waves). [3]. P. S. P. Wei, A. W. Reed, C. N. Ericksen, and J. P. Rupp, “Uncertainty Analysis and Inter-Range Comparison on RCS Measurements from Spheres,” Proc. 26th AMTA, pp. 294-299 (2004). [4]. “Mysterious silver balls fall down on town; can the black helicopters be far behind?” By Steve Vogel, The Seattle Times, August 7, 2000, (from the Washington Post). [5]. “3 mysterious spheres fall onto 3 Vietnam provinces,” Tuoi Tre, Tue, 05 Jan 2016. http://www.sott.net/article/309800-3-mysterious-spheres-fall-onto-3-Vietnam-provinces
The Meteosat Third Generation series will comprise four imaging and two sounding satellites. The MTG-I imaging satellites will carry the Flexible Combined Imager (FCI) and the Lightning Imager. The MTG-S sounding satellites – a first for Meteosat – will carry an Infrared Sounder (IRS) and an Ultraviolet Visible Near-Infrared spectrometer, which will be provided by ESA as the GMES Sentinel-4 mission. On the MTG-I satellites, FCI will scan the full Earth disc every 10 minutes using 16 spectral channels at very high spatial resolutions, from 2 km to 0.5 km. In fast imagery mode it will be capable of a repeat cycle of 2.5 minutes over a quarter of the disc. The MTG-I satellites include a Data Collection System (DCS) & Geostationary Search and Rescue (GEOSAR) payload. The DCS supports meteorology and weather prediction. The GEOSAR transponder will be operated within the COSPAS-SARSAT system. Distress alert signals are received by MTG-I in UHF band and transmitted to ground in L-band for distribution to rescue mission control centers. Developed by Thales Alenia Space Italy, the DCS and GEOSAR UHF and L-band patch array antennas have been designed to operate aboard MTG-I satellites. The Engineering Model of the MTG antenna assembly with mockup has been tested inside ESA’s Hybrid European RF and Antenna Test Zone (HERTZ) chamber. The spherical near field tests performed on the antenna stand-alone and on the antenna mounted on the mockup were aimed at identifying impact of the large satellite structure on radiation pattern of the two medium gain antennas at UHF- and L-band. Taking into account the frequency of operation and the type of antenna under test, the major contributors to the measurement error are the room scattering and the probe-AUT mutual coupling. For this reason, dedicated measurements and analysis have been performed, in order to estimate the uncertainty in the most realistic way. The other parameters have been estimated based on past experience and knowledge on the measurement system. Several additional measurements were performed in order to produce dedicated uncertainty budgets for the stand-alone and with mockup tests and for the two frequency bands UHF and L-Band.
BIANCHA (BIstatic ANechoic CHAmber) is a singular facility located at the premises of the National Institute for Aerospace Technology (INTA), Spain, and was devised to perform a wide variety of electromagnetic tests and to research into innovative measurement techniques that may need high positioning accuracy. With this facility, both monostatic and bistatic tests can be performed, providing capability for a variety of electromagnetic measurements, such as the electromagnetic characterization of a material, the extraction of the bistatic radar cross section (RCS) of a target, near-field antenna measurements or material absorption measurements by replicating the NRL arch system. BIANCHA consists of two elevated scanning arms holding two antenna probes. While one scanning arm sweeps from one horizon to the other, the second scanning arm is mounted on the azimuth turntable. As a result, BIANCHA provides capability to perform measurements at any combination of angles, establishing a bistatic, spherical field scanner. In this regard, it is worth noting that in the last years, a renewed interest has arisen in bistatic radar. Some of the main reasons behind this renaissance are the recent advances in passive radar systems added to the advantages that bistatic radar can offer to detect stealth platforms. On the other hand, with the aim of developing new aeronautic materials with desired specifications, research on the electromagnetic properties of materials have also attracted much attention, demanding engineers and scientists to assess how these materials may affect the radar response of a target. Consequently, this paper introduces BIANCHA and demonstrates its applicability for these purposes by presenting results of different tests for different applications: a bistatic scattering analysis of scaled aircraft targets and the extraction of the electromagnetic properties of composite materials utilized in an actual aeronautical platform.
An innovative method for the diagnosis of large reflector antennas from far field data in radio astronomical application is presented, which is based on the optimization of the number and the location of the far field sampling points required to retrieve the antenna status in terms of feed misalignments. In these applications a continuous monitoring of the Antenna Under Test (AUT), and its subsequent reassessment, is necessary to guarantee the optimal performances of the radiotelescope. The goal of the method is to reduce the measurement time length to minimize the effects of the time variations of both the measurement setup and of the environmental conditions, as well as the issues raised by the complex tracking of the source determined by a prolonged acquisition process. Furthermore, a short measurement process helps to shorten the idle time forced by the maintenance activity. The field radiated by the AUT is described by the aperture field method. The effects of the feed misalignments are modeled in terms of an aberration function, and the relationship between this function and the Far Field Pattern is recast in the linear map by expanding on a proper set of basis functions the perturbation function of the Aperture Field. These basis functions are determined using the Principal Component Analysis. Accordingly, from the Far Field Pattern, assumed measured in amplitude and phase, the unknown parameters defining the antenna status can be retrieved. The number and the position of the samples is then found by a Singular Values Optimization (SVO).
The possibility to use Near Field (NF) representation of antenna measurements in terms of equivalent currents, implemented in the commercial tool INSIGHT, is recently available in most CEM solvers. This method allows to use measured data to enhance numerical simulations in complex and/or large scenarios where antennas are installed. In the past this approach has been investigated and validated by determining the antenna radiation pattern in different antenna placement conditions. The aim of this paper is to present how this method can be extended for simulation of antenna coupling. Indeed using this innovative approach, after antennas are measured, their measured models can be imported in CEM tools and coupling with other radiators in arbitrary configurations can be simulated. No information about mechanical and/or electrical design of the measured antenna model are needed by the CEM tool, since the measured NF model in terms of equivalent currents already fully represents the antenna. Investigations have been performed on a H/V polarized array of three identical elements. Only the radiation pattern of the central element of the array has been measured, then starting from the measured data, the coupling between the other elements has been simulated by numerical tools. Accuracy of the procedure has been checked comparing the simulated results with the measured data of the entire array antenna. The testing procedure combining measurements and simulations consists of the following stages: · Measurement of the single element of the array and creation of the measured NF source representation. · Importing NF source in the CEM tool and placement in the array configuration. · Numerical simulation of the antenna coupling between the measured model and the other two elements of the array. Each element has two feeding ports implementing the dual H/V polarization. Preliminary analysis of the coupling is simulated and comparison with the measured data of the entire array agreement is acceptable. This study is currently under development for improving the accuracy of the results and including new test cases of different complexity.
Compact Antenna Test Range (CATR) provide convenient testing, directly in far-field conditions of antenna systems placed in the Quiet Zone (QZ). Polarization performance is often the reason that a more expensive, complex, compensated dual reflector CATR is chosen rather than a single reflector CATR. For this reason, minimizing the QZ cross-polarization of a single reflector CATR has been a challenge for the industry for many years. A new, dual polarised feed, based on conjugate matching of the undesired cross polar field in the QZ on a full wave-guide band, has recently been developed, manufactured and tested. The CXR feed (cross polar reduction feed) has shown to significantly improve the QZ cross-polar discrimination of standard single reflector CATR systems. In previous papers, the CXR feed concept has been discussed and proved using a limited scope demonstrator and numerical analysis. In this paper, for the first time, the exhaustive testing of the dual polarised feed operating in the extended WR-75 waveguide band (10-16 GHz) is presented. Accuracy improvements, achieved in antenna cross-polar testing, using this feed is also illustrated by measured examples.
In order to achieve high accuracy in measuring sidelobes and/or nulls in antenna patterns, it is necessary to use a test system with very high dynamic range. This is particularly important when the antenna has extremely high gain such as those used for certain satellite communications or radio astronomy applications or when transmit power is limited relative to range loss as is often the case in millimeter wave applications. For several years, commercially available antenna measurement receivers have offered a dynamic range as high as 135dB for such applications. This dynamic range has been made possible, in part, by a simple correlator in the receiver’s DSP chain. In this paper, we model the various sources of error in a test signal due to imperfections and uncertainties of the test equipment and the physical environment and analyze these models as they propagate through the receive chain. The results of that analysis demonstrate the correlator’s ability to reduce carrier frequency offset (CFO) and local oscillator (LO) phase noise to offer the fidelity of test signal necessary to achieve extremely high dynamic ranges of up to 135dB.
“RTCA DO-213 Minimal Operation Performance Standards For Nose-Mounted Radomes” is a document frequently referenced in nose-radome testing requirements for commercial aircraft. This document was produced and is maintained by the Radio Technical Commission for Aeronautics (RTCA). The specifications of weather-radar systems have recently changed within RTCA’s DO-220A, and as a result DO-213 was updated to DO-213A in March, 2016, to ensure that radome requirements are consistent with those of the weather radar. In addition to the new requirements for radome evaluation, several existing requirements were clarified. These clarifications addressed such things as suitability of near-field measurements, proper procedures and processing, and appropriate measurement geometries. RTCA coordinated the document revision, with the bulk of the technical inputs coming from a broad-based working group. This working group had representatives from radar, aircraft, and radome manufacturers, government agencies, and providers and users of radome-testing systems. When requirements were added or when common practice conflicted with existing requirements, there was considerable effort and analysis employed to ensure that each change or clarification was truly required. Nevertheless, DO-213A has some significant impacts to many existing radome-testing facilities. This paper discusses the significant changes in DO-213A and their implications for radome test facilities, concentrating on after-repair radome electrical testing.
The Compensated Compact Range (CCR) 75/60 of Airbus DS GmbH is the state-of-the art indoor test facility for real-time RF measurements of satellite antennas within a frequency range from 1 to 200 GHz. The CCR is composed of a two reflector system, a main reflector and a sub-reflector, to create a cross-polar-compensated plane wave in the test zone. However, even such a sophisticated design has residual cross-polar components due to the contribution of the range feed, edge diffraction from the reflector system, as well as from the serrations and imperfect absorbers. To improve and optimize the RF performance of the CCR, detailed EM simulation models are developed in order to solve the related forward scattering problem [1, 2, 3]. In spite of this it is also of great importance to analyze the CCR in a different perspective to gain insight into the CCR. To this aim, an approach based on plane wave spectrum analysis combined with inverse scattering and imaging techniques is proposed. The proposed approach firstly computes the plane wave spectrum of the measured or simulated data taken in the quite zone by using 2D Fast Fourier Transform (FFT). Then, the measured or simulated field is back-propagated by using an inverse scattering approach. By considering the geometrical shape information of the main reflector, the current distribution on the reflector is imaged. The reconstructed images help to clearly identify the effects of. Appropriate windowing is applied to the computed plane wave (angular) spectrum in order to locate and image the echoes. Based on the investigation carried out with the proposed approach, it turns out that the area of the main reflector should be increased to reduce the disturbing impact of the serrations. This investigation also shows that increasing the size of the sub-reflector does not help to improve the plane wave uniformity of the fields in the test zone. In order to test the proposed method against the experimental data, which is not in a suitable format for FFT, the measured data is interpolated to equally spaced data in a Cartesian coordinate system. The experimental results, which are obtained by processing both co and cross polar measurements, show very good agreement with the results obtained by using synthetic data. References [1] A. Geise, J. Migl, J. Hartmann, H-J. Steiner, “Full Wave Simulation of Compensated Compact Ranges at Lower Frequencies”, AMTA 33th Annual Symposium, 16 – 21 October 2011 in Englewood Colorado, USA. [2] C. H. Schmidt, A. Geise, J. Migl, H-J. Steiner, H.-H. Viskum, “A Detailed PO/ PTD GRASP Simulation Model for Compensated Compact Range Analysis with Arbitrarily Shaped Serrations”, AMTA 35th Annual Symphosium, 6 – 11 October 2013 in Colombus Ohio, USA. [3] O. Borries, P. Meincke, E. Jorgensen, C. H. Schmidt, “Design and Validation of Compact Antenna Test Ranges using Computational EM”, AMTA 37th Annual Symphosium , 11 – 16 October 2015 in Long Beach, CA, USA.
Antennas utilized as probes, sources, and for gain comparison are typically specified to have excellent cross polarization levels, often on the order of 50 dB below the primary polarization component. In many cases, these antennas are fed with a waveguide-to-coaxial adapter, which can be sourced from a multitude of vendors. Depending on the design and construction of the adapter, and the distance from the excitation probe to antenna aperture, the adapter itself can contribute significantly to the degradation of the polarization purity of the antenna. These adapters typically use one of several methods to achieve a good impedance match across their bandwidths, including tuning screws, posts and stubs. These tuning elements may be arranged asymmetrically and can cause the waveguide to be overmoded locally. Additionally, there is wide variance in the separation of the adapter excitation probe and waveguide electrical flanges, which may not be long enough to suppress the higher order modal content. In this paper, we study the effects of adapter to antenna aperture coupling, including the coupling of fields local to the current probe as well as those that are induced by design asymmetries. The results of the analysis lead to a number of rules of thumb which can be used to ensure that the antenna polarization purity is optimized.