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Digital Beam-Forming Antenna Range
Toshiba Corporation, working with Nearfield Systems Inc., has a fully digital antenna measurement system for digital beam-forming (DBF) antennas. The DBF test facility is integrated with the large 35m x 16m vertical near-field range installed at Toshiba in 1997 , and includes the NSI Panther 6500 DBF Receiver as the primary measurement receiver. The DBF system was installed in March 1999 and has been used extensively to test and characterize a number of complex, high performance DBF antennas. A DBF antenna typically incorporates an analog-to digital (AID) converter at the IF stage of the transmit/receive (T/R) module. The digital IF signals are transferred to a digital beam-forming computer, which digitally constructs, or forms, the actual antenna pattern, or beams. Since the interfaces to the DBF antenna are all digital, the usual microwave mixers and down-converters are incompatible. The NSI Panther 6500 is designed to interface directly with DBF antennas and allows up to 8 channels of I and Q digital input (16 bits each) with 90 dB dynamic range per channel. The NSI DBF receiver solves the DBF interface problem while providing enhanced performance over conventional microwave instrumentation. .
New Compact Antenna Test Range at Allgon Systems AB
Allgon Systems AB has put a new compact antenna test range into operation in July 2000. The investment was triggered by Allgon's planned move to a new building. An indoor facility was preferred for fast and efficient operation. The present primary application is the measurements of base station antennas. The compact range is constructed using a single reflector with serrated edges. A sophisticated feed carrousel enables automatic changing of 3 feed systems. The size of the quiet zone is 3 meters. The initial frequency range is from 800 to 6000 MHz. However, the reflector accuracy allows future extensions to 40 GHz and higher. The cha mber size is 21 x 12 x 10.5 m (L x W x H). Absorber layout comprises 24, 36 and 48 inch absorbers. An overhead crane spans the entire facility. The positioner system is configured as roll over azimuth with a lower elevation over azimuth for pick-u p and small elevation angle measurements. Different sizes of masts and roll positioners are available, depending on the AUT. Instrumentation is based on a HP 8753. Software is based on the FR-959 Plus. Antenna measurement results show the performance of the facility.
Millimeter Testing at Large Facilities -- Quiet Zone Exceeding 3 Meters
This paper describes the results of a research program performed to support a Ball product development. Of particular interest to the customer was demonstrating the ability to make inexpensive measurements of millimeter antennas by retrofitting harmonic frequency converters into existing range instrumentation and evaluating whether the range had sufficient quiet zone quality to evaluate extremely beam efficient radiometers.
A Fully Automated Antenna Measurement Channel Power and Air Sensitivity Test Integrated System
A versatile instrumentation system for automatically measuring both antennas and performing the Air sensitivity & Channel Power test. The system is capable of being easily reconfigured to perform standard FF antenna measurements using a model tower configuration which includes a dielectric mast with a rotary “head” mounted on an azimuth turntable or automated air sensitivity and channel power measurements for both GSM and CDMA mobile cellular devices. The air sensitivity test module iterates until the desired user defined frame error rate is reached at the preset scan positions and than records the data. The system also contains analysis capabilities for all modes of measurement. The paper will summarize the system configuration and the features of this integrated test system.
Phase-Dependent RCS Measurements
Free space, coherent radar cross section measurements on a moving target trace a circle centered on the origin of the complex (I,Q) plane. Noise introduces only small random variations in the radius of the circle. In real measurement configurations, additional signals are present due to background, clutter, targetmount interaction, instrumentation and the average of the time-dependent system drift. Such signals are important contributors to the uncertainty in radar cross section measurements. These time-independent complex signals will translate the origin of the circle to a complex point (I0,Q0). Such data are then defined by the three parameters (I0,Q0), the center of the circle, and st, the radar cross section of the target. Data obtained when a target is moved relative to its support pylon can be separated into phasedependent and phase-independent components using the techniques of (1) three-parameter numerical optimization, (2) least-median-squares fit, (3) adaptive forward-backward finite-impulse response procedure, and (4) orthogonal distance regression applied to a circle fit. We determine three parameters with known and acceptable uncertainties. However, the contribution of systematic errors due to unwanted in-phase electric signals must still be carefully evaluated.
An Evaluation of Errors Encountered Using the NUWC/NPT Overwater Arch Antenna Measurement Range
The NUWC/NPT Overwater Arch Antenna Range consists of a 70 ft radius measurement arch located over an elevated 90 ft x 65 ft salt water pool. This facility, located outdoors, presents mechanical and electrical challenges. Measurement accuracy and precision are a function of environmental parameters (including unwanted signals), physical plant and instrumentation characteristics. Measured data variation will be presented along with techniques which could be employed to improve range performance.
Active Stability Control of Pulsed IF Radars
This paper presents the design and performance characteristics of a novel active stability control capability that Aeroflex Incorporated has developed and implemented in the élan-2000 pulsed-IF instrumentation radar. The real-time technique incorporates an internal power reference loop that continuously monitors and compensates for phase and amplitude drifts within the radar RF analog circuitry through high-speed processing of the streaming data collections. Vector corrections are applied to each recorded data point, using internal loop samples of the transmit pulse from a common RF channel and digitizer, without degrading other overall system performance capabilities. Demonstrated stability levels exceed –50 dB over the full operational RF bandwidth, for periods of several hours, with environmental temperature variations of several degrees. This measurement mode provides ~30 dB of improvement over conventional instrumentation radar systems under similar test conditions, which consequently enables significant improvements in measurement applications incorporating background subtraction or where extremely stable system parameters are required.
Portable Dechirp-On-Receive Radar
Sensor Concepts Inc. has prototyped a fast, lightweight, dechirp-on-receive radar called the SCI-Lr to provide the capability of a range instrumentation radar in a highly portable package. The small weight, size and power requirements of the SCI-Lr allow a variety of new deployment options for the user including in a small general aviation aircraft or on a mountaintop that is accessible only by four wheel drive. Pulse rates up to 20 KHz enables investigation of high Doppler bandwidth phenomenon such as ground vehicle microdoppler features. The dual integration from dechirp-on-receive matched filtering in fast time and Doppler processing in slow time provides high sensitivity with low output power. Planned enhancements of waveform bandwidth up to 2 GHz , frequency operation between .2 and 18 GHz and pulseto- pulse polarization switching will provide high information content for target discrimination. The flexibility provided by the hardware is augmented by software tools to examine data in near real time to monitor data quality and sufficiency. A variety of applications are being investigated including RCS measurement, SAR and ISAR imaging, Ground Moving Target Indication, and signature collection for ATC.
Applications for Coordinated Motion in Radome Testing
Traditional data collection strategy for antenna measurement is to perform a step and scan operation. This method moves a particular axis while holding all other source and AUT axes in a fixed location. Modern radome measurements require the coordinated motion of two or more axes due to the desired measurements, the radome testing geometries or a combination of both. An example would be transmission efficiency testing of a radome associated with a tracking antenna. In this measurement scenario, the antenna azimuth and elevation axes must maintain an orientation along the range axis while the radome is moved in front of the antenna. The axis coordination could be linear or non-linear in nature. This paper describes the concept of coordinated motion and the needs for coordinated motion in radome measurements that have been identified. Additional potential applications for coordinated motion in radome measurements are described. Two methods of coordinated motion that have been implemented in instrumentation are described. They are geared motion, which is a linear master/slave relationship between two axes and generalized coordinated motion where the relationship of axes motion is described via linear or non-linear equations.
SOLANGE, An Enhanced RCS Measurement Facility of Full Size Aircraft
This paper describes the RCS measurement test facilities, CHEOPS, STRADI and SOLANGE which are operated in the Technical Center for Information Warfare (CELAR) in France, with a particular focus on SOLANGE. CHEOPS is an anechoïc chamber convenient for the measurement of small missiles as well as antennas measurement. STRADI is an outdoor facility, which is convenient for measurement of land vehicles, helicopters and large antennas. SOLANGE is an indoor RCS measurement facility used to measure long missiles and aircraft. Originally built in 1985, SOLANGE has been continuously upgraded to fulfill all customers requirements in the field of RCS measurement. Thanks to the in house radar instrumentation and data processing software, SOLANGE can reach a very good performance on small or big RCS targets from 200 MHz to 18 GHz. The UHF/VHF capacity has been recently enhanced thanks to the upgrade of the positioning system and the cooperation between CELAR and CEA.
Far-Field Range Design by Using Finite-Difference Time-Domain Method
An indoor far-field range consists of the appropriate instrumentation and an anechoic chamber. In most of cases, the construction of the anechoic chamber is a laboring task and costs at a great expense. To save the money and labor, efforts for the range design are needed before the chamber been constructed. In this paper, the finite-difference time-domain (FDTD) method is employed to establish the design criteria for the far-field ranges. The commercial package named “FIDELITYTM”, based on FDTD algorithm released by Zeland Software, Inc., is used for the numerical calculations. To emulate the test procedure of the free-space VSWR technique, the electric fields of the points on the scanning axis are recorded during the simulation. And then, by plotting the amplitude ripples calculated from the recorded data, the range performance can be evaluated. The criteria of chamber layout, absorber arrangement, and source antenna selection and placement will be presented and discussed.
Pulsed Antenna Measurements With the Agilent PNA Microwave Network Analyzer
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.
A Highly Automated Approach to Obtaining Accurate Circularly Polarized Antenna Gain
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.
Compact Antenna Test Facility for Link Antennas
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.
Cheetah PNA RCS and Antenna Measurement System
System Planning Corporation (SPC) is pleased to announce our new instrumentation radar measurement system denoted the Cheetah radar line. This radar system is based around the new Agilent PNA series of network analyzers. The PNA operates from 0.1 to 67 GHz and is utilized for making gated CW or CW RCS and Antenna measurements. The PNA has a built in synthesizer that allows the unit to be used without costly external synthesizers and external mixers. The PNA also has four identical receiving channels, two signal and two reference, that permit simultaneous co and cross pol measurements to be made. PNA IF bandwidth is selectable from 1 Hz to 40 kHz to optimize measurement sensitivity, dynamic range and speed. Using the segmented sweep feature of the PNA a single frequency sweep can be broken into segments, to further optimize the sensitivity, dynamic range, and speed. Each segment can have its own start and stop frequency, frequency step size, IF BW and power level. SPC has developed the high speed RF gating, low noise RF preamplifiers and high speed digital timing system, which allow maximum sensitivity, full up gated CW or CW radar measurements using the PNA. SPC has coupled the system to the CompuQuest 1541 RCS and Antenna Data Acquisition and Data Analysis Processing Software. This exciting new product line offers reduced cost and improved performance over current network analyzer based systems using the HP 8530, 8510, etc. Performance improvements are in the reduced noise figure, sensitivity, dynamic range and measurement speed. Measurement speeds are increased by at least a magnitude of order over the older systems and in some cases a couple of orders of magnitude.
HP8530 Compatible mm-Wave Front-End Instrumentation for Octave Band Coherent Antenna Measurements
Upcoming space exploration missions will have microwave instruments operating well beyond 100 GHz. Test techniques and instrumentation have to keep up with these developments. Although most of these instruments operate in a few narrow bands, a test engineer, faced with the combined requirements of a range of instruments will prefer full octave band coverage. As a goal, he would like to have the same functionality as at lower frequencies, i.e. sweep or step frequency capability, high dynamic range in the order of 80 dB, coherent, computer controllable and compatible with existing receiver equipment (HP8530). A concept based on a Backward Wave Oscillator, locked by PLL to a synthesizer was chosen. On the receiver side, sub-harmonic mixing was applied. The 110-170 GHz band was chosen as a first step to test the concept. The realized equipment has unsurpassed performance in terms of band coverage and dynamic range. In fact, all the requirements were achieved.
Thermal Sensitivity of a Compact Range
The ability to perform radar cross section (RCS) measurements, where background subtraction is applied, requires a measurement system that is very stable throughout the measurement time span. Background subtraction allows the measurement of low RCS components mounted in high RCS test bodies by permitting the scattering from the test body to be removed by coherently subtracting the test body (background) RCS from the target RCS measurement. Amplitude and phase variation of the illumination signal between the time that the target and background measurements are performed will limit the quality of subtraction achievable. Modern instrumentation radars can maintain extraordinary stability when exposed to controlled temperature environments, but controlling the temperature of a large compact range can be difficult. Other components of the measurement system, such as the reflector, can also be influenced by temperature fluctuations. Methods of controlling the thermal environment can have significant consequences. Lessons learned in the Advanced Compact Range at the Air Force Research Laboratory will be described.
Time-Frequency Analysis of Time Varying Spectra with Application to Rotocraft Testing
The time-dependent spectrum of rotating structures presents many significant challenges to radar cross section (RCS) test design, instrumentation parameter selection, signal processing methodology, data analysis, and data interpretation. This paper presents a multi-dimensional signal processing tool and a suite of associated data products, based on an efficiently scripted test design and execution strategy, that are responsive to the high throughput, high data volume requirements and real time data analysis demands associated with rotorcraft testing. We specifically address the NRTF’s realization of a suite of spectral, cepstral and statistical signal processing tools supported by animation that facilitate near-real time parametric data analysis and interpretation.
Comparison of Instrumentation for (Sub) mm-Wave Frequencies
Upcoming space exploration missions will have microwave instruments operating well beyond 100 GHz. Test techniques and instrumentation have to keep up with these developments. Although most of these instruments operate in a few narrow bands, a test engineer, faced with the combined requirements of a range of instruments will prefer full octave band coverage. As a goal, he would like to have the same functionality as at lower frequencies, i.e. sweep or step frequency capability, high dynamic range, coherent, computer controllable and compatible with existing receiver equipment (HP8530). A concept based on a Backward Wave Oscillator, locked by PLL to a synthesizer was chosen for the 110-170 GHz band. For the next leap, the 170-260 GHz band, a solid- state concept based on multipliers has been chosen. The experience with both systems and the pro’s and cons will be clarified
Measurements of the CloudSat Collimating Antenna Assembly Experiences at 94 GHz on Two Antenna Ranges
This paper presents measurements of the CloudSat Collimating Antenna (CA) as fabricated for the 94.05 GHz CloudSat radar, which is to be used to measure moisture profiles in the atmosphere. The CloudSat CA is a 3 reflector system consisting of the 3 "final" (relative to the transmitted energy) reflecting surfaces of the CloudSat instrument. This assembly was fed by a horn designed to approximate the illumination from a Quasi-Optical Transmission Line (QOTL). This same horn was employed as a "standard" for measurement of the CA gain via substitution, and its patterns were also measured (this substitution represents a departure from the standard insertion loss technique in the near field range). The CloudSat CA presented a substantial measurement challenge because of the frequency and the electrical size of the aperture is approximately 600 wavelengths in diameter, with a nominal beamwidth of 0.11 degrees. In addition, very high accuracy was needed to characterize the lower sidelobe levels of this antenna. The CA measurements were performed on a 3122-ft outdoor range (this distance was 41% of the far field requirement), which were immediately followed by measurements in an indoor cylindrical Near Field (NF) range. The instrumentation challenges, electrical, mechanical, and environmental are described. Comparison of the outdoor vs. indoor pattern data is presented, as well as the effect of the application of tie-scans to the near field data.
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