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Probe position errors, specifically the uncertainty in the theta and phi position of the probe on the measurement sphere, are one of the sources of error in the calculated far-field and hologram patterns derived from spherical near-field measurements. Until recently, we have relied on analytical results for planar position errors to provide a guideline for specifying the required accuracy of a spherical measurement system. This guideline is that the angular error should not result in translation along the arc of the minimum sphere of more than ?/100. As a result of recent simulation and analysis, expressions have been derived that relate more specifically to spherical near-field measurements. Using the dimensions of the Antenna Under Test (AUT), its directivity, the radius of the sphere (the minimum sphere) enclosing all radiating surfaces and the frequency we can estimate the errors that will result from a given position error. These results can be used to specify and design a measurement system for a desired level of accuracy and to estimate the measurement uncertainty in a measurement system.
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.
In this paper, we describe the process used to align a large spherical near-field test system. The probe positioner consists of a cantilevered arc design with a probe path radius of five meters and a scan angle of 180°. The AUT positioner consists of an MI Technologies Model 51230 azimuth positioner with a high-precision encoder. The system is aligned using an SMX Tracker 4000 tracking laser interferometer. Alignment into a spherical system is achieved by initially defining two cylindrical systems; a primary probe positioner based system and a secondary, AUT positioner based system. Sources of mechanical error in each of these systems are identified and techniques used to control these error sources are described.
Spectrum is presently one of the most valuable goods worldwide as the demand is permanently increasing and it can be traded only locally. The United States FCC has opened the spectrum from 3.1 GHz to 10.6 GHz, i.e. a bandwidth of 7.5 GHz, for unlicensed use with up to -41.25 dBm/MHz EIRP. Numerous applications in communications and sensor areas are showing up now. Like all wireless devices these devices have an antenna as integral part of the air interface. The antennas are modeled as linear time invariant (LTI) systems with a transfer function. The measurement of the antenna’s frequency dependent directional transfer function is described. Furthermore the measured transfer function is transformed into time domain, where it is used to characterize pulseshaping properties of the antennas. Additionally, measurements in time domain, which were performed with a pico-second pulse generator and a 50 GHz sampling oscilloscope, are presented and compared to the transformed frequency domain measurements. These measurements enable the realistic characterization of ultra wideband antennas for UWB link level simulations.
The use of multimode antennas to aid problems of direction finding (DF) has been examined and shown to provide benefit over standard interferometric techniques [8, 9]. In this work, we consider the issue of performing the DF in an adaptive processing environment. This work examines the use of the ADaptive Estimation / detection for sPecific Tasks (ADEPT) algorithm [3, 4]. The ADEPT algorithm performs weight optimization by maximizing the Fisher Information Matrix (FIM) as a Figure of Merit. Previous work by the authors has sought to characterize and optimize spiral antenna configurations based on the FIM [1, 2]. Measured spiral antenna data is utilized to examine the relative capability of the algorithm with a 4-arm spiral multimode antenna.
In measurements performed on remote, outdoor antenna ranges operating in the HF (2-30 MHz) band, it is desirable to have a method by which the effective heights of the reference loop antennas used on the range can be easily double checked on-site. A technique is presented that is based on one used in the VLF/LF (10-300 kHz) band. In this method, the effective height of an unknown loop antenna may be simply and accurately measured without the need for specialized or cumbersome test equipment. Results and limitations of the technique are presented along with its application at the NUWC Fishers Island Antenna Range.
This paper presents advances in the instrumentation techniques that can be used for the measurement and characterization of antennas that are to be tested in a pulsed mode of operation. A digital filtering process is described which allows accurate measurements under a wide range of pulse conditions using a single receiver. A novel approach to achieving point-on-pulse measurements using receiver time-gating at the IF frequency is described. Measurements made using an Agilent E8360 PNA series Microwave Network Analyzer are presented as a demonstration of a practical implementation of these techniques.
The direction of arrival of multiple coherent electromagnetic signals can be determined by measuring the pattern of an antenna probe when it is rotated off its phase center and then exciting a synthetic array with the same geometry as the probe measurement points using the signals received in the measurement. The offset and angle of sweep, which defines the aperture size required for separating the waves, depends upon the resolution required. The sampling resolution must also fall within the Nyquist sampling criteria.
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.
A continuous discussion exists in comparing the theoretical and measured performance differences of serrated versus rolled edge treatment for compact ranges. Since rolled edge reflectors are significantly more expensive, the price / performance trade off needs to be well justified. Such an evaluation is very application dependent. A large amount of measurement data has been published for serrated edges, and comparisons between serrated edge theoretical data and measurement data shows good agreement. However, only a very small amount of measuerement data has been published for rolled edge compact ranges. For evaluation purposes, ORBIT/FR built a rolled edge and a serrated edge compact range. Both were designed for 2 ft quiet zones and have equal focal length and offset angle. Measurement data was acquired for both configurations, and is presented here.
Instead of moving the antenna under test (AUT), it is possible to change the direction of arrival of the plane wave. This is done moving the feed horn in the reflector focal area. Scanning the feed antenna allows measurement of the AUT without moving it. This is useful in cases, when moving the AUT is difficult or even impossible. In the Compact Payload Test Range (CPTR) at ESA-ESTEC, the linearity of the scanning has been measured before [1] and scanning has been proven to be nearly linear (1%). What was not known, is that how do the quiet zone properties (amplitude and phase ripple) change during the scanning. It will be shown the basic properties of the quiet zone remained almost the same, but some other properties of the range were found.
Highly accurate antenna and payload measurements in antenna test facilities require highly accurate alignment and boresight determination. The Angle of Arrival (AoA) of the plane wave field in the quiet zone of the CCR Compensated Compact Range CCR 75/60 of EADS Astrium GmbH, installed at Alcatel Space in Cannes . France, has been measured using three different methods (optical geometrical determination using theodolites, Radar Cross Section (RCS) maximization, planar scanner phase plane alignment). The proposed paper describes the three methods and the performed measurement campaign and provides the correlation between the resulting angles via a comparison of the results. The achieved absolute worst case values of lower than 0.005° demonstrates the high level of accuracy reached during the campaigns.
A compact radar cross section (RCS) test range for scale model measurements is being developed. The test range is based on a phase hologram that converts the feed horn radiation to a plane wave needed for RCS determination. The measurements are performed at 310 GHz using continuous wave operation. A monostatic configuration is realized using a dielectric slab as a directional coupler. The main advantage of a scale model RCS range is that the dimensions of radar targets are scaled down in proportion to the wavelength. Therefore, RCS data of originally large objects can be measured indoors in a controlled environment. So far simple test objects such as metal spheres have been measured. The feasibility of the phase hologram RCS range has been verified. The basic operation and first measurement results of the monostatic measurement range are reported here.
This paper describes and discusses relevant performance issues concerning the quiet zone illumination of a baseline interferometer antenna using a compact range system. Typical baseline interferometer antennas are utilized for precision direction finding applications, and are designed on the principle of detecting the incoming phase wave front as a means to determine the direction of arrival of the detected signal. Quiet zone illumination of the antenna using a compact range deviates from the ideal illumination by introducing some levels of amplitude and phase taper and ripple. Unwanted relative differences in the illumination of the individual elements of the interferometer antenna will introduce errors in the subsequent analysis of the direction finding accuracy and precision of the array. Sources of these errors are examined in this paper, and relevant compact range performance trade-offs are discussed to optimize the range. Considerations are given to both utility of the range, as many interferometer antennas are broadband EW type arrays, and thus require single feed, single test broadband measurements, as well as to the accuracy in characterizing the performance of the interferometer over its full operating bandwidth. In addition, this paper discusses the analysis of high precision compact range field probe data, and the subsequent application of relevant statistical parameters to characterize the data. The analysis techniques utilized highlight the important performance features required of the compact range to effectively test baseline interferometers. The implementation of an automated utility is described that applies the relevant corrections, and applies the statistical algorithms, to the data to effectively reduce the data and summarize it in a fashion that provides immediate utility to the field probe test operator.
Shielded anechoic chambers have been extensively used to measure antennas for various applications. Recent proliferation of mobile telecommunications presented high demands for measurements of antennas that are used in mobile wireless handsets. Since antennas in mobile handsets are low-directive for better mobile links to base stations, they are capable of transmitting or receiving nearly all unwanted reflected signals from imperfections through various reflection and scattering paths in the anechoic chamber in addition to desired signal from the direct path during the measurements. The Quiet Zone (QZ) characterization method has to be re-examined. This paper presents measurements and analyses comparing the difference in chamber designs and verifications of anechoic chamber QZ’s. Through this development, design guidelines are provided to improve the anechoic chamber QZ signal-to-noise ratio for measuring low-directive antennas. Techniques derived from this requirement can also benefit for measurements of high sensitivity Radar-Cross-Section.
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.
This paper describes a family of new measurement systems, termed “test cells”, designed to satisfy the certification requirements of the Cellular Telephone & Internet Association’s (CTIA) “Method of Measurement for Radiated RF Power and Receiver Performance” test plan for wireless subscriber stations. These test cells employ simultaneous dual-axis mechanical scanning and operate in both far-field and near-field modes over the 750MHz to 6 GHz frequency range. Operation can be extended to higher frequencies through the use of suitable sampling antennas. Test cell facility configuration is detailed. Scanner layout and RF sampling antenna designs are discussed. Anechoic chamber characterization data is presented along with typical measured pattern and efficiency data for both broadbeam and directive AUT’s. Measurement test times for various test scenarios are discussed.