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CEA-Cesta has developed a new phased array antenna for RCS dual polarization wide bandwidth measurement in V/UHF bands. This array enables us to enhance signal to noise ratio especially at low frequencies. It is composed of 3 sub arrays dedicated each to one frequency band. The innovative design allows installing it in one of CEA/CESTA RCS facilities called “CAMELIA”. In order to validate this array in the highest sub-band [700 to 2000MHz], we measured in both HH and VV polarizations the near field RCS of a 2.5m long NASA almond target. This canonical object has been made of polystyrene coated with conducting nickel varnish. It has been hung on an eight wires rotating positionner. The results are compared with the data acquired in a classical RCS compact range and with the output of the 3D finite element code called ODYSSEE developed at CEA.
Typically radome tests are performed on outdoor far field ranges or compact ranges. ORBIT/FR has designed, build and qualified a unique spherical near-field radome test facility for the nose-mounted radomes of commercial traffic aircraft for the so-called “after repair” tests according to the international standard RTCA/DO-213, as well as the aircraft manufacturers Component Maintenance Manuals. The facility is extremely compact (chamber size 5.7 m x 5.2 m x 3.2 + 0.7 m, L x W x H), can handle radomes as small as used on the Canadair and as large as used on the Airbus-380 and can be installed directly in the repair workshop for such radomes. The tests performed are transmission efficiency and side lobe level increase. The system is completely automated, so that a workshop technician can operate the facility. Utmost attention has been paid to operational aspects and both operator and equipment safety. After the measurements are done, a test report is fully automatically generated according to RTCA requirements and classifications. The facility is equipped to test all standard Airbus, Boeing, Canadair and Dash nose radomes.
A large rolled edge compact range system featuring a 12’H x 16’W quiet zone has been designed, fabricated, installed, and tested in a large aerospace test facility. During the program, a high precision alignment methodology was utilized in conjunction with electromagnetic prediction capability to verify both mechanical and electrical performance while still under trial assembly conditions at the factory. A coherent laser radar (CLR) was utilized to measure the reflector surface on a very fine grid, and the electromagnetic (EM) quiet zone performance was calculated from the raw CLR data using a Physical Optics (PO) model. Despite extremely high surface accuracy of the panels, this evaluation methodology highlighted systematic alignment errors in the reflector system, and guided the process of correcting these errors to achieve a final factory verification assembly for the entire 20’H x 24’W reflector system of better than 0.001” over the quiet zone section of the reflector, and 0.004” rms over the entire reflector. This procedure was also utilized for the on-site installation to achieve alignment of the reflector to an AUT positioning system using the CLR, as the positioning system and chamber were already existing and operational. Thus, it was required to align the reflector to the positioning system, and not the positioning system to the reflector as is usually the case. A unique vertical carousel feed system was also aligned using this procedure. Predicted EM results were again used to finalize alignment on site prior to quiet zone field probe evaluation. This paper summarizes the overall alignment and EM evaluation process, and presents results for the installed compact range reflector system.
Satellite TV reflectors for home use, provided to the public by service companies such as DIRECTV, have many features which must be adequately characterized prior to design release, including: • Multiple Beam Frequency Re-use • FCC Sidelobe Envelope Verification • Circular Polarization Isolation These features must be adequately tested at frequencies up to Ku band and beyond. The use of a far-field range is impractical, as some of the reflectors measure several feet in diameter, and thus requires a range length of several hundred feet at Ku band. Near-field testing requires a full scan to determine a single cut for evaluation of FCC compliant sidelobe performance. Thus, a compact range is a logical alternative for measurement of this class of antennas. The compact range can provide a quick assessment of multiple beam coverage performance and pass/fail analysis against FCC sidelobe curve specifications. In addition, the feeds for these antennas often use Low Noise Block (LNB) Downconverters that are built in as part of the feed assembly. Measuring the output of an LNB does not yield the phase information required to determine all polarization parameters. A spinning linear measurement with some unique processing was implemented on this range to determine the full polarization characterization, using some elementary assumptions about polarization sense. This paper describes the implementation of a compact range based measurement facility for satellite antenna testing, with emphasis on the circular polarization measurement of the LNB assembly, capability for comparison against FCC sidelobe levels, and measurement of offset beams featuring frequency re-use capability.
A transmission line system has been developed for an electromagnetically transparent antenna array. The goal was to provide equal signal distribution to the array elements while maintaining the transmissivity of the antenna. The transmission lines consist of microstrip directional power couplers which are fed in series. This reduces the transmission line length needed. The transmission line was built, tested, and integrated with an array of circular polarized array elements mounted over a frequency selective surface (FSS) ground plane. Preliminary bench tests performed on the integrated array with a small test dipole indicated that the transmission lines provided uniform signal distribution. Outdoor far field measurements of the integrated antenna indicated that the antenna performance was satisfactory. The integrated antenna array was tested in the compact range located at the ElectroScience Laboratory at The Ohio State University. These tests were used to accurately characterize the antenna performance at S band and the transmissivity properties of the integrated array at L band. The measured antenna pattern and beamwidth were consistent with predictions. Transmissivity of the antenna as viewed by a second antenna was also consistent with predictions.
A large compact range facility required a foam column for RCS testing where the center of the quiet zone was six meters above the floor level. The RCS measurement after vector background subtraction, had to be accurate down to a –50 dBsm level from 1.5 GHz to 40 GHz. A foam column was constructed from a single billet of material. The foam column was evaluated as to its RCS level in both whole body and ISAR imaging modes. This paper describes the specification, construction and RCS evaluation of this column in the compact range facility. The column was evaluated at single frequencies and with RCS images from 2 GHz to 36 GHz using a gated CW radar. Data is presented that shows the effects of the column on the response of a calibration sphere and the response of the column itself. A study of the foam column imaging response used as the background for vector background subtraction is also described. Targets in the –60 dBsm range were successfully imaged with vector background subtraction of the foam column.
The performance of modern Satellites Antennas and Payloads is characterized by physical parameters like e.g. Antenna Pattern and Gain; EIRP, Flux Density, G/T and the overall PIM-performance. The available time frame for measurement of these parameters is getting constantly shorter. The EADS Astrium GmbH Compensated Compact Range (CCR) allows a time efficient measurement of all payload parameters with high accuracy under controlled environmental conditions. In addition to an efficient measurement facility high-performance measurement equipment is required. The economical budgets of most space programs demand the application of well-known measurement techniques in a cost efficient way. EADS Astrium GmbH supported by Agilent Technologies GmbH has developed an easy to handle and therefore cost optimized measurement platform for Satellite Payload Measurements. This platform consists mainly of a generic Agilent switch matrix operating up to 40GHz which can be connected to a wide range of measurement equipment. The matrix allows a highly flexible routing of the RF uplink and downlink signals including reference paths. Integrated and/or external RF components, like amplifiers, attenuators, and hybrids can be added to the paths, depending on the required test configuration. Starting from a minimum configuration the system can be modularly upgraded to satisfy any further test requirements. The software interface utilizes standard protocols and can be therefore easily addressed by any user specific measurement software. The EADS Astrium GmbH Advanced Antenna Measurement System (AAMS) includes an optional payload toolbox which provides a modular concept expandable for additional test functions.
The measurement uncertainties for base station antenna gain measurement are in general very high, ± 1dB could normally be expected and there are examples of much higher uncertainties. Applying the uncertainties above to the cell planning tools gives at the end a very large uncertainty on the number of cells needed to cover an area. The extra cost for this uncertainty could be an extra 15-20% of the site costs or 10-20% less coverage than expected. This paper identifies the different uncertainty sources and suggests how to optimize the measurement set-up to reduce uncertainties as much as possible during the measurement and compensate for the remaining uncertainties after the measurement.
The electromagnetic field as projected by a 12 ft. prime focus offset fed compact range reflector with r-card edge terminations located in an existing chamber 20 ft. high, 30 ft. wide and 66 ft. long was probed using a broadband antenna to sample the field at 12 inch increments from the center line to the anechoic chamber wall. The purpose of the test was to evaluate the field roll off in dB to see if a narrower room would significantly impact the performance of the existing reflector system. The new chamber is 20 ft. high, 20 ft. wide and 40 ft. long. The probe data at six frequencies from 2.1 to 17.8 GHz indicated that 10 ft. off the center line the measured field level was -20 dB or greater below the level of the test region, which was our maximum acceptable field level goal. It is expected that the sidewall absorber will provide over 20 dB of bistatic attenuation for a total reflected field level of -40 dB, and is sufficient for conducting antenna pattern measurements in an anechoic chamber. Key Words: Compact Range, R-Card Terminations, Absorber Performance
This paper describes the first experience gained with a new carbon composite compact range reflector (C3R2). The reflector’s backup structure is made entirely of carbon fiber reinforced composite material. An outstanding advantage of this design is its superior mechanical and thermal-environmental stability. This yields improvement in the overall performance. We have revised the process by which compact range reflectors are designed and modeled, making use of professionally authored software. We describe the results of electromagnetic field probe measurements made at the factory. Special attention is given to new results at W-band – in the 75 to 100 GHz regime.
A generally practiced way to improve the sidelobe accuracy in antenna measurements is by repeating and averaging the measurements in different positions in the quiet zone (also referred to as APC or AAPC, depending on the application). An alternative new way for improving the accuracy of compact range measurements is by moving the compact range feed in different locations. This can easily be achieved for both horizontal and vertical directions. Although feed scanning causes a boresight shift, this can be easily compensated if the feed positions are selected intelligently. A significant measurement speed improvement can be realized by using multiple feeds in the relevant locations, instead of moving a single feed sequentially into these locations. Feed scanning APC has been successfully tested in the Ericsson Microwave Systems Compact Range, where it is now practiced in high accuracy radar antenna measurements.
A new antenna and RCS measurements facility consisting of four anechoic chambers has recently been constructed at MIT Lincoln Laboratory. The facility was designed with a rapid prototyping focus. The four chambers include a tapered chamber covering the 225 MHz to 18 GHz band, a millimeter wave rectangular chamber covering 4 to 100 GHz, a large rectangular anechoic chamber covering 150 MHz to 20 GHz, and a large compact range covering 400 MHz to 100 GHz. The compact range will be highlighted.
Compact range reflectors, in general, are designed so that the parabolic section of the reflector is equal or larger in size than the desired quiet zone size. Next, proper edge treatment (serrated edge or blended rolled edge) is applied to the parabolic section to reduce the diffraction from the rim of the parabolic section in the quiet zone. With proper edge treatment, the reflector size can be bigger than the available space. Thus, there is a need to reduce the overall size of the reflector. In the case of blended rolled edge compact range reflectors, the total surface is a reflecting surface. Also, near the junction between the parabolic section and the edge rolled section, the surface is very close to the parabolic section. Thus, the fields reflected from this part of the reflector are nearly planar and can be used to increase the size of the quiet zone. This, in turn reduces the total size of the reflector. This concept has been applied to design a blended rolled edge reflector for MIT Lincoln Laboratory's new compact range. In this paper, the design approach will be presented and analytical performance of the reflector will be discussed. It will be shown that the over all performance of the reflector is better than the performance of the same size reflectors designed using the conventional approach.
Antennas that are used aboard next generation airborne, maritime and ground vehicles are increasingly required to satisfy both conventional radiation pattern and gain requirements as well as new radar cross section (RCS) requirements. In response to these requirements, Nurad and ORBIT/FR recently completed design, installation, and verification of a high performance, multi-purpose antenna and RCS measurement facility at the Nurad site in Baltimore, Maryland. This compact range facility features a 60x36x26 foot shielded anechoic chamber and a precision machined, serrated edge, offset-fed reflector system that produces a 5.3’H x 8’W x 8’L quiet zone over the 2-50 GHz frequency range. The facility includes a unique feed room structure that positions the primary radar components close to the feed mount for RCS measurements, and allows for easy change of compact range feed antennas. A removable pylon assembly is used for test body support during RCS testing, and a unique add on section to the pylon rotator allows for inclusion of a roll axis that enables measurement of small and medium size antenna assemblies without removing the pylon. Measurements performed on low RCS standard targets and antennas made in the chamber demonstrate that the chamber provides a high performance measurement environment while providing ease of use and rapid configuration and target changeover.
The incident .eld in the quiet zone on a compact range has been probed in a two dimensional grid. From the probe data, error sources have been identi.ed and a model have been created for the quiet zone. The model can be used for antenna measurement simulations. This could be used to calculate the expected interference levels in a real measurement. The measurement range analyzed here has a single, diagonally fed, serrated re.ector. The room measures 11×11×21 m3 and the quiet zone is a cylinder with 3 m diameter and length. The analysis have been done with two dimensional FFT and MUSIC for identi.cation of the directions to the error sources. Then the complex amplitudes for the major directions have been solved. The identi.ed error sources models the quiet zone ripple, in addition to that, the model includes a taper which models the feed.
The Geometrical Optics characteristics of single parabolic reflector compact range systems are presented in rules of thumb for amplitude taper, phase taper and cross polarization. This is illustrated on four different range configurations (two different focal lengths and two different offset angles). Also the influence of the feed system in regard to far field diagram and alignment is discussed for typical low and medium gain corrugated feeds. No diffraction effects are discussed in this paper. With the use of the rules of thumb, a fast and yet precise qualitative and quantitative analysis, optimization and trade off can be made for a compact range optimized for the available space as well as the application.
Computer generated holograms can be used as collimating elements in compact antenna test ranges (CATRs). Recently, a 1.5 m parabolic antenna, the ADMIRALS representative test object (RTO), was tested at 322 GHz using a hologram based CATR that was built specifically for these tests. In this paper, the construction of the compact range is discussed. A 3meter hologram was used to realize a 1.8 meter diameter quiet-zone. The measured quiet-zone field amplitude and phase and the measured H-plane radiation pattern cut of the RTO are presented. The measured -3 dB beam width of the antenna was 0.050º in the H-plane.
This paper presents a Radar Crossed Section (RCS) time-domain near-field measurement and its Inverse Synthetic Aperture Radar (ISAR) imaging. The target includes a pyramidal horn and a metallic aircraft scale model. A pulse generator excites the transmit antenna and a digital sampling unit collects the data at the receiving side. A time gating window is subsequently applied to reject the multiple reflections. An efficient 3-D algorithm for ISAR based on time-domain near-field data is presented. The test results for six cases demonstrate excellent ISAR images. In particular the geometry of 3-D reconstructed target can be displayed in perspective manner. The advantage of using time-domain near-field measurements is three-fold. First, it reduces measurement time in the order of one-tenth compared to frequency-domain measurements. Second, it mitigates the multiple reflection effects via time gating. Third, near-field measurements require relatively little real estate which reduces the cost tremendously since a compact range is not needed.
There is a trend within the RCS community to use squatty cylinders in place of spheres for calibration. A higher degree of accuracy can be achieved; however, cylinder calibrations require much more precision in the alignment procedures. This effort is doubled when the dual calibration target is also a cylinder. The dual calibration test article could be a sphere thus reducing calibration efforts as long as good correlation exists between theory and measurement sphere data. A series of measurements were collected at the NASA Langley Research Center Compact Range Pilot Facility to study measurement errors of spheres atop foam columns to determine their feasibility for dual calibration use.
Millimeter wave antennas are typically small in physical cross-section, and thus require only a small quiet or test zone illumination area when undergoing standard antenna tests. Lockheed Martin Missiles and Fire Control had a requirement for a test zone diameter of less than 1 foot in order to test millimeter wave antennas required as part of research and development programs. ORBIT/FR developed a unique portable test facility that is inclusive of a “minicompact range” reflector system featuring a rolled edge design with a nominal 12 inch diameter quiet zone. The compact range is integrally mounted into a portable anechoic chamber assembly that measures 60”H x 52”W x 84”L. The chamber features a “hatch” type opening that allows easy access inside the chamber interior, and the entire assembly is easily relocated using a built-in set of casters. An AL-060-1P miniature positioner allows for feed polarization adjustment, and an AL-160-1 provides azimuth rotation for the antenna under test. Corrugated feeds allow precise control of the reflector illumination within the small chamber assembly, allowing excellent quiet zone performance to be realized. Although the primary frequency band of operation is Ka band, the reflector exhibits excellent performance at Ku band, and is capable of operating down to X band as well. The integrated facility is utilized with the Agilent Performance Network Analyzer (PNA) and the 959Spectrum Antenna Measurement Workstation to provide a complete small antenna, high frequency measurement solution. A detailed description of the system, as well as performance results, are presented in this paper.