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This paper describes an automated ellipticity measurement system for ultra-wideband (UWB) circular-polarization antennas. The system comprises a double-ridged horn (DRH) antenna, a high-precision polarization rotator, an antenna-under-test (AUT) positioner, a vector network analyzer (VNA), and a controlling computer. The liner-polarized DRH antenna typically rotates 360° in 5°-intervals controlled by the rotator. At each angle, the VNA sweeps an ultra-wide bandwidth to measure the path gain. The least squares method was employed to find the axial ratio (r >= 1) and inclination angle at each frequency by fitting the plots to an anticipated peanut shell curve. Since the conventional cross polarization discrimination (XPD) has been defined for narrowband antennas, we proposed the wideband XPD as a frequency integration of the square of the circular polarization ratio (x), where x = (r + 1) / (r - 1), embracing a certain bandwidth. The wideband XPD represents the total power ratio between co- and cross-polarizations in the bandwidth. We measured the ellipticity and the wideband XPD of an axial-mode helical antenna using this system.
ABSTRACT This paper describes a broadband radome measurement method that provides insertion loss performance referenced to circularly polarized radiation. The measurements are performed using linearly polarized sources and post processing is employed to convert to circular polarization. The method reduces measurement errors encountered using circularly polarized sources that traditionally have poor cross polarization isolation.
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.
This paper is designed to illustrate the technical advances in Network Analyzers and how they can be effectively utilized in an RCS test range. The Hewlett-Packard 8530A [1 - 4] has been utilized in antenna test ranges since the 1980’s and will be used as a reference comparison. Advances in network analyzer hardware and software provide increased functionality, speed and accuracy for RCS measurements. A typical RCS full polarization matrix imaging measurement will be used to illustrate these advances in technology. Range gating, digital and down-range resolution and alias-free range topics will be discussed illustrating the technical advances that can be utilized in an RCS test range. Flexibility of network analyzer hardware will also illustrate the effectiveness of reducing measurement hardware complexity resulting in an increase in measurement speed and accuracy.
Co-polarized and cross-polarized radar cross sections (RCS) are required to completely characterize a complex target. However, it is common for a RCS range to measure only the co-polarized RCS. This practice is primarily due to the inability to produce accurate cross-polarization analysis data for the calibration targets. The most commonly used calibration targets, spheres and cylinders, cannot be used to calibrate cross-polarized RCS due to lack of cross-polarized returns. In this paper, we consider objects that can potentially be used as calibration targets for cross-polarization measurements. Specifically, we numerically study the cross-polarized responses of the Tungsten rod, the grooved cylinder, and triangular dihedrals. Co-polarized measurement data are also included in this initial assessment. From this initial study, we find the counter-balanced dihedral to be a suitable calibration target for cross-polarized measurements.
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.
This paper presents background information and experiment procedures for an antenna measurement laboratory course to be held in a new anechoic chamber at California Polytechnic State University. The lab consists of five experiments and one design project intended to give students practical experience with antenna measurement techniques and to creatively apply analytical skills to design, construct, and test antennas that meet given specifications. The experiments reinforce antenna principles including E-field polarization, antenna gain, radiation patterns, image theory, and frequency response. In addition to the experiment procedures, this paper presents the design and characterization of Helical Beam (RHCP and LHCP) and Discone antennas, a Dipole Antenna near Planar and Corner Reflectors, and Dipoles with and without a balun. These antennas demonstrate polarization, antenna gain, broadband matching characteristics, image theory, and feedline radiation due to unbalanced currents. Measured radiation patterns, gain, and axial ratio (helical only) show excellent correlation to theoretical predictions.
Exploitation of MIMO (Multiple-Input Multiple-Output) system in laptop type device, which size is adequate to integrate several antennas on it, would be the solution to increase attainable capacity e.g. in wireless local area networks (WLAN). Thus, a microstrip prototype antenna with two polarizations is developed for MIMO and also for diversity system purposes. Firstly, two antennas of this type were placed against to each other, which guarantees a good coverage over a whole propagation area. Secondly, two antennas of this type were placed next to each other. The simulated radiation patterns of the prototype antenna are used in the capacity studies of MIMO system using real indoor propagation data. The effect of shadowing by human body as well as different tilting angles of “laptop cover/screen” are considered. Further, different locations of the “device” in azimuth plane were considered identifying the fluctuation of the results due to the environmental and antenna properties. The developed antenna systems perform well as compared to the ideal dipole system.
This paper presents the complete Antennas radiated performance measurement process within the frame of the AMC12 satellite program for SES-AMERICOM customer, from antenna sub-system level to spacecraft system level. Three long focal offset antennas are implemented on AMC12 spacecraft (see Figure 1-1). Each antenna was measured at both sub-system and system levels, within two different test ranges: • a Near-Field Antenna Test Range (NFATR), • a Compact Antenna Test Range (CATR), at sub-system and system levels respectively. Comparisons for co-polarization gain, XPD and co-polarization isolation between predictions and sub-system measurements on one part, between sub-system and system measurements on the second part will be presented. An effective correlation will be shown at each level. Two antennas are located on the West panel of the spacecraft. This configuration required to measure one antenna in presence of the adjacent reflector with the aim to validate the minimal coupling effect according to the conclusion of the antenna design. With this measurement method, all the physical effects are taken into account and the RF performances are directly representative of in- orbit spacecraft deployed configuration. Comparisons between sub-system level measurements and predictions will be presented.
A general approach is introduced for estimating uncertainties in far-field parameters obtained from spherical near-field measurements. Although the analysis is incomplete at present, we expect that as the measurement radius increases, our results will transform smoothly into the far-field case, where uncertainties depend on the on-axis gain and polarization of the probe and on the measurements in the far-field direction of interest.
A prototype design of the dielectric rod antenna is discussed. This novel design is suitable for nearfield probing application in that it provides broad bandwidth, dual-polarization and low RCS. The design details are provided in this document along with measurement data associated with important antenna characteristics such as VSWR and far-field radiation pattern
For a planar near-field range, it is sometimes convenient to use a linearly polarized probe to measure a circularly polarized antenna. The quality of the circular polarization of the test-antenna is determined by the measured axial ratio. This requires the amplitude and phase from two near-field scans, one scan with the probe polarization oriented horizontally and another vertically. A lateral probe position error between the horizontal and vertical orientations can occur if the probe is not aligned properly with the probe polarization rotator. This particular probe position error affects the accuracy of the axial ratio in the main beam if the beam of the test antenna is not perpendicular to the scan plane. This paper presents analysis and measurement examples that demonstrate the relationship between the errors in the axial ratio and the lateral probe position. It is shown that the axial ratio, within the main beam, is not sensitive to the lateral probe position error when the beam is normal to the scan plane. However, the error in the axial ratio in the main beam can be quite significant with a small lateral probe position error if the antenna beam is tilted at an angle with respect to the scan plane. A simple phase correction algorithm is presented that is useful for measured data from an electrically large aperture.
Probe calibration is a prerequisite for performing high accuracy near-field antenna measurements. One convenient technique that has been used with confidence for years consists of using two auxiliary antennas in conjunction with the probe-to-be-calibrated. Inherent to this technique is a calibration of all three antennas. So far the technique has mostly been applied to measure polarization and gain characteristics. It is demonstrated how the technique can be extended to also measure an antenna’s phase-versus-frequency characteristic.
At a Department of Defense antenna measurement laboratory, an important measurement is the accurate measurement of gain for circularly polarized antennas. An additional requirement is that a wide population of engineers and technicians that do not spend a significant amount of time using the facility make the measurements as they test the antennas for their projects. The objective was to create a highly automated, accurate test structure that was easily used by visiting engineers to make high quality measurements. Consistency of results across the user population was a paramount requirement. This paper describes the instrumentation and software used to meet this objective. The paper describes basic measurement techniques, the exploitation of instrumentation capabilities to make the measurements, the software processing of the data and the graphical user interface that was developed to make the test process essentially a “one button” operation. Significant components in the test scenario were the ability to accurately collect data on a linearly polarized Standard Gain Horn in orthogonal polarizations without inducing errors caused by various axes of motion and to provide channel imbalance correction for the orthogonal channels of the instrumentation and range.
MTI Technology and Engineering Ltd. in Israel has installed an antenna test facility for the development and production testing of communication link antennas. Link antennas are typically high gain, medium size (< 2 ft) and medium to high frequency (10 to 50 GHz), with strict requirements on sidelobes, back-radiation and cross-polarization. Production testing is typically done on the main cuts. The facility is also used for PTMP and WLL antennas down to 2 GHz. This is an ideal requirement for a small size compact range. The ORBIT/FR single reflector compact range with a cylindrical quiet zone of a size 4 x 4 ft (diameter x length) was selected. The performance is compliant to international regulations (e.g. FCC, ETSI, DTI-MPT), and has a cross polarization as low as –40 dB for 0.4-m antennas. The total chamber size is 31 x 18 x 15 ft (L x W x H). The positioner system is roll over model tower over azimuth over lower slide. The instrumentation is Agilent 8530 based. The system was installed and qualified in late 2002. Qualification was performed from 2 to 50 GHz for quiet zone field probing and antenna sidelobe level accuracy testing. A system description, as well as an excerpt of the qualification data are presented in the paper.
New taper chamber feed section was created for numerical analysis. To launch the undisturbed electromagnetic wave into the test zone, newly designed dual polarized aperture-matched blade mode bowtie (ABB) antenna was designed and implemented at the vertex of the feed section of the tapered chamber. For the accurate calculation, wall type absorber samples are obtained and measured. These values are included for realistic configurations. From the simulated time domain result, field distributions at the aperture of the feed sections are investigated. Determination of the usable spaces for different frequencies is discussed. Also, cross-talk levels are presented since the feed antenna designed for dual polarization.
Sub-millimeter wave holograms can be used as collimating elements in compact antenna test ranges. The fabrication of very large holograms can be facilitated using a modified hologram illumination with amplitude taper. The modified illumination also removes the current polarization limitation to a vertical polarization in the hologram operation. Shaped beam illuminating the hologram is achieved with a dual reflector feed system with two shaped hyperbolic reflectors. In this paper, the design of the quasi-optical reflector feed system with developed ray-tracing based reflector synthesis procedure is described. Simulation and measurement results of the dual reflector feed beam at 310 GHz are presented. The measured quietzone of a demonstration hologram fed with the dual reflector feed system is also shown.
The Intelsat-IX spacecraft carries a C- and Ku-Band payload. It provides coverages from five different orbital locations over Atlantic (AOR) and Indian (IOR) ocean regions. The feed arrays for the C-band multifeed offset parabolic reflector antennas were designed, manufactured and tested by EADS Astrium GmbH in Munich, Germany. Design drivers for the antenna subsystem were the high power requirement for the transmit antenna and stringent isolation specification for both transmit and receive antennas. The final designs feature as many as 145 feed horns and up to ten switches. Due to the complexity of the beam forming network and the large number of SCRIMP (Short Circular Ring loaded Horn with Minimized Cross-Polarization) horns at every feed array a special test philosophy was introduced in order to detect any malfunction of the array at an early stage of the antenna assembly and integration. This paper will present details of the applied test sequence starting at the initial beam forming network measurements and the intermediate near-field feed testing under extreme environmental conditions up to the final antenna testing in a compact range at unit and at spacecraft level. The used inhouse data evaluation software platform allows the evaluation of any measurement at any stage of the testing sequence independent of the actual applied losses and /or design error allocations.
The National RCS Test Facility (NRTF) has designed, fabricated, and implemented an efficient and robust calibration procedure and test body applicable to pylon based monostatic RCS measurements. Our unique calibration test body provides physical separation between the calibration device and pylon allowing the pylon to be outside the range gate of the calibration device. This separation reduces the calibration device uncertainty due to target support contamination and interaction. Spectral analysis and feature extraction of rotational dihedral/dipole data allows further rejection of background noise and clutter that possess different angular dependencies from those of the dihedral/dipole. Due to the significant reduction in the achievable crosspolarization isolation that occurs with a small degree of positioning error in dihedral/dipole roll angle, a data driven search algorithm has been developed to select the two dihedral/dipole angles used by the polarimetric distortion compensation algorithm.
This paper presents results from a tracking and classification radar that is contained in a coffee-can sized cylinder that sits directly on the ground. The 50 mW radar operates in the 3.1 to 3.6 GHz band using horizontal polarization. The results from earlier radar propagation channel studies will be discussed, including propagation characteristics as a function of polarization and frequency band. The design for this radar that exploits the channel propagation characteristics will be described. Data from tracking of vehicles and humans will be presented. Examples of the range profiles of groups of humans and of moving vehicles will be shown. We will also show a test of the capability of such a system to track humans through building walls.