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The design of a specialized reflector antenna set that supports dual polarization, dual beam widths, and an integrated wideband monopulse tracking capability in the X-band range is described in this paper. The reflector antenna code available at The Ohio State University has been used as the design tool. The design of such an antenna has posed several challenges in the feed and reflector assemblies. The requirement for an integrated wideband monopulse has resulted in a feed array that contains 5 rectangular feed elements with a center-to-center spacing of 1" and a diamond configuration. The 5 feed design has been selected to enable a shared feed array and reflector surface for both transmit and receive beams that eliminates the need for a high-power wideband receiver protector in the radar system. The center feed element is used for transmit waveform and the 4 outer elements are used as receive elements only. Each feed element operates with horizontally and vertically polarized waveforms, requiring a total of 8 waveguide input ports. In this paper, the challenges of the dual beam widths, dual polarized, integrated RCS and tracking antenna are delineated and the tradeoffs among several design configurations are shown. The final design is selected based on the performance predictions using The Ohio State University Reflector Antenna Code. The performance of the antenna has been validated at the OSU compact range for pattern and gain. Both the design and measurement data are presented in this paper.
Millimeter-wave measurements on spherical near-field scanning systems present a number of technical challenges to be overcome to guarantee accurate measurements are achieved. This paper will focus on the affect of mechanical alignment errors of the spherical rotator system on the antenna’s measured performance. Methods of precision alignment will be reviewed. Sensitivity to induced mechanical alignment errors and their affect on various antenna parameters will be shown and discussed. Correction methods for residual alignment errors will also be described. The study includes 38 and 48 GHz data on the Alphasat EM model offset reflector antenna measured by TeS in Tito, Italy on a NSI-700S-60 Spherical Nearfield system, as well as a 40 GHz waveguide array antenna measured by NSI on a similar NSI-700S-60 Spherical Nearfield System at its factory in Torrance, CA, USA.
This paper presents the results of radiation pattern measurement of small reconfigurable slotted ultra wideband (UWB) antennas. The measurements were conducted by using RF measurement and instrumentation facilities, software tools available at WCC of Universiti Teknologi Malaysia. The proposed slotted UWB antennas are having band notched frequency at Fixed Wireless Access (FWA), HIPERLAN and WLAN bands. Band-notched operation is achieved by incorporating some small gaps instead of PIN diodes into the slot antenna. It is found that by adjusting the total length of slot antenna to be about a half-wavelength or less at desired notched frequency [1-3], a destructive interference can take a place, thus causing the antenna to be non-responsive at that frequency. It was also observed that the measured radiation patterns, H-planes, are omni-directional with slightly gain decreased at boresight direction for measured frequencies. There are also more ripples occurred in the measured pattern compared with the simulated one.
A bi-lateral comparison of power gain for a V-band (50 to 75 GHz) Cassegrain antenna and a standard gain horn antenna has been performed between KRISS and NIST. Measurement parameters for this comparison are the power gain and complex reflection coefficient of the traveling standards, and their measurement frequencies are 65 GHz for the high-gain antenna and 50, 65, and 75 GHz for the horn antenna. All participants used the planar near-field scanning method for characterizing the high-gain antenna and the three-antenna extrapolation technique for characterizing the horn antenna. This paper summarizes the comparison and its measurement results with uncertainties. Generally, the agreement between results in all measurements is within the uncertainty of each participant except for the gain result of the horn antenna at 65 GHz.
This paper analyzes the applicability of near field scanners into existing compact test ranges. The analysis is motivated by creating multi-purpose test chambers having the advantages of both, near field systems and compact test ranges. This contribution comprises the discussion of near field scanners at several positions inside a typical compact test range. A ray tracing analysis is presented taking these positions into account in the assessment of near field errors due to multi-path reflections. It is presented how reflections from the absorbers and reflectors are differently impacting near field measurements of low, medium and high gain antennas. The impact is quantified in terms of error levels used in common near field error budgets. It is shown that the combined approach is realizable for specific configurations only.
Instruments for Earth observation working from W-Band up to mm-wave frequencies mainly use quasi-optical feed feeds (QOF) to illuminate the corresponding reflector antennas. The final design of the QOF for the Cloud Profiling Radar System (CPR) for the EarthCARE satellite has been finalized. The QOF is designed to perform polarization and frequency tuning, as well as the separation of transmit and receive channels. The final design verification was performed theoretically by Astrium with QUAST, a new add-on to the GRASP software, especially developed by TICRA for a fast and accurate set-up and analysis of quasi-optical networks. Within the paper, at first a short description of the QOF working at 94.05 GHz will be given. Secondly, the modeling of the QOF will be explained. At last the RF test setup will be described and comparisons between resulting calculated and measured antenna pattern will be shown.
The Global Precipitation Measurement (GPM) mission is a satellite based Earth science mission that will study the global precipitation from rain, ice and snow. A critical part of this satellite is the multi-frequency radiometer system that covers frequencies up to 183 GHz. Beam pointing and beam efficiency must be measured very accurately to calibrate the radiometer response. This paper will focus on the measurements of the offset reflector antenna operating up to 183 GHz using a Nearfield Systems Inc. (NSI) planar near-field measurement system and the special challenges that this presents. Results will be presented and the uncertainty in beam pointing will be discussed.
Most conventional spherical near-field scanning systems require the antenna under test to rotate in one or two axes. This paper will describe a novel rolling arch near-field scanner that transports a microwave probe over a hyper-hemispherical surface in front of the antenna. This unique scanning system allows the antenna to remain stationary and is very useful for cases where motion of the antenna is undesirable, due to its sensitivity to gravitational forces, need for convenient access, or special control lines or cooling equipment. This allows testing of stationary antennas over wide angles with accuracies and speeds that historically were only available from planar near-field systems. The probe is precisely positioned in space by a high precision structure augmented by dynamic motion compensation. The scanner can complete a hyper-hemispherical multi-beam, multi-frequency antenna measurement set of up to eight feet in diameter in less than one hour. The design challenges and chosen techniques for addressing these challenges will be reviewed and summarized in the paper.
Over-the-air (OTA) performance testing of wireless devices has become a major component of product qualification for today's wireless networks. The methodologies used currently expand on traditional passive antenna pattern measurement techniques and operate under the fundamental assumption that the radiation pattern of the DUT does not change for the duration of the test. Emerging wireless technologies such as MIMO that use multiple antennas and adaptive algorithms for communication violate that assumption. In addition, the enhanced feature set and higher complexity of these newer technologies means that there are other performance criteria to be evaluated beyond just radiated power and sensitivity. A new OTA test system has been developed that can simulate complex multipath systems in a fully anechoic environment. This technology allows evaluating the performance of the DUT in a host of simulated real-world environments. Existing spatial channel models used for conducted testing of these radios can be easily adapted to OTA testing. This paper describes the details of such a system, including requirements for calibration and validation, as well as showing typical test results and available metrics.
A well designed absorber configuration is a key factor for precise antenna measurements. Unfortunately, even a scanner covered with pyramidal absorbers can cause reflections that could degrade the measurement accuracy. A novel scanner absorber configuration using bent absorbers is presented in this paper. Another problem is that in most cases it is necessary to remove the absorbing material at the scanner to change the antenna under test. The absorbers covering the scanner suffer abrasion caused by the frequent manual movement. For this reason it was also the intention to find a faster and easier solution which also preserves the absorbing material. The new and the old absorber layout were benchmarked using a number of spherical nearfield measurements as well as time domain reflection measurements with a broadband probe antenna. A comparison of the results is also shown in this paper.
ABSTRACT A modern method is presented to measure small antenna efficiencies by implementing a variant of the WheelerCap method. As antennas become smaller in size, antenna efficiency typically decreases either because of matching functions or reductions in the antenna radiation resistance. It is important to know while designing small antennas, how much efficiency reduction can be tolerated before a particular design needs changing. Measuring antenna efficiency by integrating radiation functions is not a trivial task and prone to measurement errors. The modern method presented uses a plastic sphere which is internally coated with a highly conductive metallic paint, having low resistivity values (less than 0.1ohms per square), and useful to implement the Wheeler Cap measurements. The measurements are conducted with the use of a modern Agilent Vector Network Analyzer (VNA) which is calibrated to the antenna port (which includes any antenna matching networks). The apparatus was used to measure small “planar” antennas thus producing extremely good results. The paper presents the methodology used for the development of the apparatus and the measurement results.
Anechoic chambers simulate open air test conditions and are advantageous for testing avionics systems in a secure, quiet electromagnetic environment. The 412th Electronic Warfare Group’s Benefield Anechoic Facility (BAF), located at Edwards AFB, California was designed for testing systems in the radio frequency (RF) range from 500 MHz to 18 GHz. For frequencies below 500 MHz, the installed radar absorbent material (RAM) does not effectively absorb incident RF energy, thereby allowing undesired RF scattering off the chamber’s floor, ceiling, and walls. This leads directly to measurement inaccuracies and uncertainty in test data, which must be quantified for error analysis purposes. In order to meet the desired measurement accuracy goals of antenna pattern and isolation measurement tests below 500 MHz, RF scattering must be mitigated. BAF personnel developed a test methodology based on hardware gating, range tuning and improved RAM setup, to improve chamber measurement performance down to 100 MHz. Characterizing the chamber using this methodology is essential to understanding test zone performance and thus increases confidence in the data. This paper describes the test methodology used and how the test zone was characterized with resulting data.
We introduce a new type of planar near-field measurement technique for testing small antennas which, heretofore, have been traditionally tested via spherical or cylindrical scanning methods. Field acquisition in both these procedures is compromised to a certain extent by the fact that probe movement induces change in relative geometry with respect to, and thus interaction with, the anechoic chamber enclosure. Moreover, obstructing equipment, such as antenna pedestals, may significantly impede, or even reduce the available angular scope of any given scan. Our proposed procedure, by contrast, minimizes both the residual interaction contaminant and the threat of obstruction. We have in mind here a variant, a hybrid version of planar scanning wherein, on the one hand, we limit severely the size of the acquisition rectangle (and thus minimize the contaminating influence of a variable probe/chamber interaction), while, on the other, we really do collect near-field data throughout a complete range of solid angle around any candidate AUT, front, back, above, below, and on both sides. Such completeness is achieved through the mere stratagem of undertaking six independent planar scans with the AUT suitably rotated so as to expose to measurement, one by one, each of the faces of an enclosing virtual box. In the meanwhile, the inevitable AUT pedestal per se remains immobile and removed from any occupancy conflict with the scanned probe. We have accordingly named our new planar near-field data acquisition scheme the “Boxed Near-Field Measurement Procedure.” With subsequent use of our Field Mapping Algorithm (FMA), elsewhere reported, we obtain the entire field exactly, everywhere, both interior and exterior to the surrounding (virtual) box. In particular, we achieve enhanced accuracy in the far-field patterns of primary interest by virtue of the completeness of data acquisition and its relative freedom from spurious contamination. The angular completeness of data acquisition conferred by our procedure extends in principle to antennas of arbitrary size, provided, of course, that due provision is made for the necessary scope of measurement rectangles. The benefits are seen to be especially valuable in the case of narrow-beam antennas, whose back lobe pattern details, usually deemed as inaccessible and hence automatically forfeited during conventional (i.e., utilizing a “onefaced box,” in our new way of thinking) planar near-field testing, are thrust now into full view. Our new, full-enclosure planar acquisition technique as now described has been verified by analytic examples, as well as by hardware measurements, with excellent results evident throughout, as we are about to demonstrate.
Outdoor far- field antenna test ranges have declined in popularity due to the advent of alternative test methods, e.g., Near-Field Antenna ranges and Compact Antenna Test Ranges. They are also costly to maintain. A natural consequence of that trend is that far-field ranges are either shut down or rendered dormant for long periods of time. The latter was the situation for the NGAS (Northrop Grumman Aerospace Systems) CTS 10K Far-Field range. The Far-Field was an outdoor range with a 10,000’ range length, open transmit site and radome enclosed receive site. It had been dormant for 7 years and was needed for a unique test before the test site was vacated completely. This paper provides a brief description of the range, the upgrades made to address equipment obsolescence and the checkout process to ensure that the range would meet performance requirements. The range needed to operate from 100 MHz to 18 GHz. Therefore, range diagnostics were performed at various frequency points and swept measurements also executed. A Range Readiness report was created and presented internally. Elements of that report are shared in this paper.
A novel approach using Artificial Neural network (ANN) is proposed to identify the faulty elements present in a nonuniform linear array. The input to the neural network is amplitude of radiation pattern and output of neural network is the location of faulty elements. In this work, ANN is implemented with three algorithms; feed forward back propagation neural network, Radial Basis Function neural network (RBF) and Probabilistic neural network and their performance is compared. The network is trained with some of the possible faulty radiation patterns and tested with various measurement errors. It is proved that the method gives a high success rate.
Accurate knowledge of an RFID IC’s input impedance enables the design of performance-optimized RFID tags with a given IC. For this purpose, the most valuable information is the IC’s input impedance at its wake-up power, but as the impedance itself is power-dependent, few simple methods exist to extract this information. This paper presents a method, based on the joint use of computational electromagnetics, wireless RFID tag measurements and Monte Carlo simulations, to determine the input impedance of an UHF RFID tag chip at the wake-up power of the IC and the measurement uncertainty related to the result.
ABSTRACT
Abstract— Spherical near-.eld scanning measurements are used to determine the incident electromagnetic .elds within a test volume. Resultsfrom twoindependent approaches are comparedandfound to agree within estimated uncertainties.
The 18 terms technique, for the evaluation of the measurement error, was used to justify the differences between the measurement data obtained from the three facilities. In Addition a general description of the test setup and the principle error sources found during the finalization of the test setup are given.