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Instrumentation

Advances in Instrumentation and Positioners for Millimeter-Wave Antenna Measurements
Bert Schluper,Patrick Pelland, November 2014

Applications using millimeter-wave antennas have taken off in recent years. Examples include wireless HDTV, automotive radar, imaging and space communications. NSI has delivered dozens of antenna measurement systems operating at mm-wave frequencies. These systems are capable of measuring a wide variety of antenna types, including antennas with waveguide inputs, coaxial inputs and wafer antennas that require a probing station. The NSI systems are all based on standard mm-wave modules from vendors such as OML, Rohde & Schwarz and Virginia Diodes. This paper will present considerations for implementation of these systems, including providing the correct RF and LO power levels, the impact of harmonics, and interoperability with coaxial solutions. It will also investigate mechanical aspects such as application of waveguide rotary joints, size and weight reduction, and scanner geometries for spherical near-field and far-field measurements. The paper will also compare the performance of the various mm-wave solutions. Radiation patterns acquired using some of these near-field test systems will be shared, along with some of the challenges encountered when performing mm-wave measurements in the near-field.

Effects of a Non-Ideal Plane Wave on Compact Range Measurements
David Wayne,Jeffrey Fordham, John McKenna, November 2014

Performance requirements for compact ranges are typically specified as metrics describing the quiet zone's electromagnetic-field quality. The typical metrics are amplitude taper and ripple, phase variation, and cross polarization. Acceptance testing of compact ranges involves phase probing of the quiet zone to confirm that these metrics are within their specified limits. It is expected that if the metrics are met, then measurements of an antenna placed within that quiet zone will have acceptably low uncertainty. However, a literature search on the relationship of these parameters to resultant errors in antenna measurement yields limited published documentation on the subject. Various methods for determining the uncertainty in antenna measurements have been previously developed and presented for far-field and near-field antenna measurements. An uncertainty analysis for a compact range would include, as one of its terms, the quality of the field illuminating on the antenna of interest. In a compact range, the illumination is non-ideal in amplitude, phase and polarization. Error sources such as reflector surface inaccuracies, chamber-induced stray signals, reflector and edge treatment geometry, and instrumentation RF leakage, perturb the illumination from ideal.

Measurement of Operational Orientations Using Coordinate Transforms and Polarization Rotations
Douglas Morgan, November 2014

Antenna and Radar Cross Section (RCS) measurements are often required for orientation sets (cuts) that are difficult or impossible to produce with the positioning instrumentation available in a given lab.  This paper describes a general coordinate transform, combined with a general polarization rotation to correct for these orientation differences.  The technique is general, and three specific examples from actual test programs are provided.  The first is for an RCS measurement of a component mounted in a flat-top test fixture.  The component is designed to be mounted in a platform at an orientation not feasible for the flat-top fixture, and the test matrix calls for conic angle cuts of the platform.  The transforms result in a coordinated, simultaneous two-axis motion profile and corresponding polarization rotations yielding the same information as if the component had been mounted in the actual platform.  The second example is for a pattern measurement of an antenna suite mounted on a cylindrical platform (such as a projectile).  In this case, the test matrix calls for a roll-cut, but the range positioning system does not include a roll positioner.  The transforms again result in a coordinated, simultaneous two-axis motion profile and corresponding polarization rotations to provide the same information as the required roll-cut but without the use of a roll positioner.  Finally, the third example is for an antenna pattern measurement consisting of an extremely large number of cuts consisting of conic yaw cuts, roll cuts and pitch cuts.  The chosen method involves the use of the Boeing string suspension system to produce great-circle cuts at various pitch angles combined with the use of the coordinate and polarization transforms to emulate, off-line, any arbitrary cut over any axis or even multiple axes. Keywords:  Algorithm, Positioning, Polarization, Coordinates, RCS

Implementation of a Burst-Mode Technique and Variable Coherent Integration to Minimize Radar Data Collection Time
Christopher Fry,Charles Walters, John Raber, November 2013

Abstract— Compact ranges are ideal settings for collecting low-RCS measurement data at high pulse rates. However, until recently, two operating constraints have limited the efficiency of instrumentation radar systems in this setting: (1) system delays limiting Pulse Repetition Frequency (PRF) and (2) fixed integration across frequency resulting in more time spent on certain frequencies than required. In this paper, we demonstrate the capability to significantly increase data throughput by using a Burst-Mode to increase the usable PRF and a frequency table editing mode to vary integration levels across the frequency bandwidth. A major factor in the choice of PRF for a specific application is system hardware delays. We describe the use of a Burst-Mode of operation in the MkVe Radar to reduce delays caused by physical layout of the instrumentation hardware. Burst-Mode essentially removes setup time in the system, reducing the time between pulses to the roundtrip time of flight from the antenna to the target. Most pulsed-IF instrumentation radar users fix the coherent integration level for the entire measurement waveform, even though the set level of integration may not be required at all frequencies to achieve the desired sensitivity. We describe the use of a frequency table Parameter Editor Mode in the MkVe that allows the integration level to vary for each step in the waveform. We demonstrate the use of both methods to reduce data collection time by a factor of seven using a MkVe Radar installed in a compact range.

Reconfigurable Beamwidth Antenna Array using Phase Adjustment of Array Elements
Ali Moghaddar, R Jerry Jost, Robert Reynolds, October 2013

Reconfigurable radar antennas with rapid, real-time control of the radiation pattern beamwidth provide expanded performance for many instrumentation radar applications, including RCS signature measurement and dynamic Time Space Position Information (TSPI) radar tracking applications. Adaptive adjustment of antenna radiation patterns was traditionally accomplished by electro-mechanically selecting predefined aperture dimensions that corresponded to desired beamwidths (e.g., ? ?/D). For an array antenna consisting of as few as 200 elements, beam shaping can be accomplished by adjusting the relative phase of individual array elements, a technique defined as beam spoiling or decollimation. This paper analyzes an operational radar antenna array incorporating reconfigurable beamwidth and beam shape through independent phase control of each subaperture. By adjusting the relative phase of radiating elements, the system can illuminate a programmable field of regard with full transmit power. For this array, the phase distributions across the elements map to a smaller "virtual aperture" displaced behind the physical array. Theoretical and measured results are presented to validate the reconfigurable array pattern control technique.

Common Radar Cross Section & Antenna Gain Measurement Calibration
Douglas Morgan,Boeing Test & Evaluation, November 2012

Radar Cross Section (RCS) and Antenna measurement ranges share many common features and are often used for both purposes. Calibration of these dual-purpose ranges is typically done using the substitution method for both RCS and antenna testing, but with separate RCS and antenna standards. RCS standards are typically based on a geometric shape having a well known theoretical value – and corresponding small uncertainty. By contrast, antenna standards typically must be “calibrated” in a separate antenna calibration system to be used as a gain standard, often yielding higher uncertainties. This paper presents an efficient method for transferring an RCS measurement calibration to an antenna measurement range configuration, allowing a range to be used for both purposes with a single calibration. Insight into the best ways to re-configure the instrumentation between RCS and antenna testing is included. Validation measurements from a compact range are included along with an uncertainty analysis of the method.

Making Transient Antenna Measurements
Roger Dygert, Steven R. Nichols, November 2012

In addition to steady state performance, antennas also have transient responses that need to be characterized. As antennas become more complex, such as active phased arrays, the transient responses of the antennas also become more complex. Transient responses are a function of internal antenna interactions such as coupling and VSWR, active circuitry, and components such as phase shifters and attenuators. This paper will show techniques for measuring antenna transient responses. The first measurements utilize standard instrumentation capable of sampling at up to 4 MHz, giving 250 nS time resolution of the transient effect. Recognizing that some transient measurements require finer time resolution, a higher sampling rate prototype receiver was developed with 1 nS time resolution. After verification of its performance, the prototype receiver was used to measure the transient effects of a 50 nS pulse through a broadband antenna. The spectrum of the pulse yields information on the time and frequency domain responses of the antenna. Phased arrays may exhibit transient signals when switching between beam directions as well as switching between frequencies. The methods presented in this paper are applicable to both.

Near-field Antenna Measurement of an Active Phased Array Antenna for a New-Generation Weather Radar
Y. Masuda,T. Kumamoto, F. Mizutani, H. Handa, M. Tanabe, November 2011

We are developing a new-generation weather radar to observe and predict short-term weather phenomena like severe storms, gust and so on. Therefore, an active phased array antenna (APAA) with digital beam-forming (DBF) receivers could be used for the new-generation weather radar to reduce the observation time. In Toshiba Corporation, 33m x 16m vertical near-field antenna range including the digital instrumentation receivers have been working for multi-beam DBF antenna measurements. This near-field antenna range is used to evaluate the performance of an APAA. In this paper, we describe the characteristics of this new-generation weather radar and the APAA. And we demonstrate the antenna measurement set-up using the near-field antenna range and the measurement results of this antenna.

Advanced Antenna Measurement System Architectures
S. Nichols, November 2011

Since the early days of antenna pattern recorders, advances in instrumentation and computers have enabled measurement systems to become highly automated and much more capable. Automated systems have provided higher productivity, more efficient use of test facilities, and the ability to acquire more data in less time. In recent years, measurement speeds of microwave receivers and vector network analyzers have advanced considerably. However, to take full advantage of these speed improvements, the measurement system architecture must be carefully considered. Small differences in instrument timing that are repeated many times can make large differences in system measurement time. This paper describes a general method of calculating system measurement time based on the primary factors that affect system timing, including position trigger detection, frequency switching time, multiplexer switching time, receiver measurement time, and timing overhead associated with triggers, sweeps, and measurements. It also shows how key features of instruments available today can be used along with improved antenna measurement system architectures to optimize system throughput.

A HIGH PERFORMANCE STATE OF THE ART PLANAR HYBRID SCANNER
Uri Shemer,Arnaud Gandois, November 2010

An Indian Defense Research and Development Organization (DRDO) laboratory has commissioned a state-of-the-art indoor far-field antenna test facility in 2009. This facility supports highly accurate measurement of a wide range of antenna types over 1.12–40 GHz. Owing to the heavy usage of this range, it was decided to enhance the existing facility to include a Hybrid Planar Near-Field facility for high speed accurate antenna measurements with minimal changes to the existing chamber configuration. The scanner is implemented as a highly innovative Hybrid T-type scanner, with a Y-axis that consists of a Linear Multi-Probe array and a traditional single probe configuration. The linear Multi-Probe array consists of two sets of dual polarized probes each one covering a sub set of the full frequency range. In particular one set covers the 1.0-6.0GHz band (operational from 400MHz) and the other set covers the 6.0 to 18.0GHz band. The traditional Single Probe configuration includes a set of Open Ended Waveguide Probes to facilitate an operational frequency range of 1.12 – 40.0GHz, as in the existing Far Field system. The Hybrid scanner is placed along the sidewall opposite the door, on the DUT positioner side. The major benefit of this layout is that there is no need to change the basic design of the chamber and it is built according to the original plans. When the chamber is used in the far-field mode, the tower is moved to the end of the horizontal axis in the direction of the corner of the chamber. The tower sides that face away from the chamber corner are covered with absorbing material to reduce reflections from the tower. Assuming that the chamber is intended to measure directional antennas, the existence of the tower behind and to the side of the AUT is expected to introduce minimal interference. The high speed linear Multi-Probe array has typical measurement speeds ranging between 5 and 15 minutes at 5 frequencies and 2 polarizations. Instrumentation is based on an Agilent PNA E8362B. Software is based on the MiDAS 6.0 package for both Single Probe & Multi Probe modes. A Real-Time Controller (RTC), accompanied by a 4-port RF switch, facilitates multi-port antenna measurements, with the possibility of interfacing to an active antenna.

Radiation Pattern Measurement of Reconfigurable Slotted Ultra Wideband Antenna
Yusnita Rahayu,Razali Ngah, Tharek Abdul Rahman, November 2010

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 NOVEL SPHERICAL SCANNER SYSTEM FOR WIRELESS TELEMATICS MEASUREMENTS
Carl Sirles,Beau Hart, James Huff, John Mantovani, November 2009

Modern vehicle telematics subsystems often employ wireless interfaces. The design and evaluation of these subsystems involves measurement of antenna characteristics or Over-The-Air (OTA) performance of the subsystem as installed in a vehicle. Several subsystems servicing multiple user applications may be installed in a single vehicle, with antenna structures located anywhere on or within the vehicle. In general, the radiation characteristics of each subsystem must be measured over a partial spherical surface surrounding the vehicle and of sufficient radius to be outside the reactive near-field of the Device Under Test (DUT). This paper describes a distributed axis spherical scanning system designed for vehicle applications. The elevation axis which supports the probe antenna has a measurement radius of 25 ft (7.62m). The elevation positioner is supported on a hydraulic vertical lift axis to permit the adjustment of the measurement coordinate origin to be in the same horizontal plane as the DUT phase center. The measurement instrumentation system supports VNA based antenna pattern measurements or active OTA testing of telematics subsystems. The system is suitable for outdoor or indoor measurement facilities. An outdoor installation is described.

Generation of a pseudo time domain holography from frequency swept measurements
Javier Marti-Canales (European Space Agency),L.P. Ligthart (Technical University of Delft), November 2008

This paper presents the methodology to generate a pseudo time domain holography from frequency swept measurements. This is an approximation to the time domain holography (TDH) invented by the authors [1,2], which opens a new possibility for antenna diagnostics using conventional instrumentation and in the absence of time domain measurements. Practical examples using two spaceborne antennas are provided and discussed.

Cost Effective Extension of Antenna Measurement and Calibration Capabilities up to 80 GHz using a 40 GHz Vector Network Analyzer
Thomas Kleine-Ostmann (Physikalisch-Technische Bundesanstalt),Thorsten Schrader (Physikalisch-Technische Bundesanstalt), Vince Rodriguez (ETS-Lindgren), Zhong Chen (ETS-Lindgren), November 2008

The extension of the frequency range for commercial applications of mm-waves to 80 GHz and beyond often requires extended antenna characterization capabilities both at manufacturer and end-user facilities. Presently, most measurements are based on direct measurements using vector network analyzers (VNAs). VNAs that cover a continuous frequency range up to 67 GHz are commercially available. Above 50 GHz, extensions based on external mixers in waveguide technology are typically utilized. They require a tunable local oscillator (LO) that is usually provided by the two additional ports of a 4-port VNA. However, these extensions not only are restricted in bandwidth but also require a significant financial investment especially considering the fact that the expensive 4-port instrumentation is needed. As most laboratories already have conventional 2-port VNAs usable up to 10 GHz or higher and most antenna characterizations are based on transmission measurements, we present a simple extension scheme based on external mixers and a fixed frequency LO that allows for transmission factor measurements. We demonstrate the feasibility of such an extension scheme for transmissions between a pair of horn antennas ranging up to 60 GHz. The measurements include variation of antenna spacing and steering angle and are verified with a computational analysis based on the finite differences time-domain (FDTD) method.

RF Material Design, Measurement and Instrumentation: Optimization of an X-band Composite Reflector through Material Characterization and Testing
Todd McNeill (Eclipse Composites Engineering ),Dan McCarthy (Air Force Research Laboratory), Dave Widauf (Eclipse Composites Engineering ), David Legare (Air Force Research Laboratory ), George Hansen (Metal Matrix Composites), November 2008

A recent project to develop and optimize the RF reflectivity of a Composite/nano-material, X-band reflector was pursued by a team lead at AFRL – RF Technology Branch. This was accomplished by iterative testing and signal pattern measurements performed at the AFRL-Rome Laboratory that provided critical feedback affecting the laminate design and configuration of the composite reflector. Testing of multiple configurations of composite reflectors provided data that was key to successful progression throughout the product engineering cycle, and accomplished the following milestones: . Initial performance verification . Characterization of influential material constituents . Optimization of design Eclipse Composites Engineering, along with metallic nano-material supplier Metal Matrix Composites worked to develop a composite dish with reflective properties identical to the baseline metallic reflector model. Through various methods of testing, the reflective influence of each material constituent was characterized and the relative effect within the overall composite laminate was modeled. Based on initial measurements, prototype articles were fabricated for testing and comparative evaluation. This project demonstrates the critical feedback loop between measurement/testing and design/development leading to the successful production of a segmented composite reflector that is lighter weight, more durable, with increased performance in the field to support today’s military and commercial operations.

Performance Considerations for Pulsed Antenna Measurements
Dave Fooshe (Nearfield Systems Inc.), November 2008

Previous AMTA papers have discussed pulsed antenna measurements and the importance of parameters such as pulse width, pulse repetition frequency (PRF) and receiver dynamic range in determining the appropriate technique for performing pulsed measurements. Typically, the pulse width and PRF determine the IF bandwidth required of the instrumentation receiver to achieve a specific level of receiver performance. Less emphasis has been given to the receiver timing and synchronization required to achieve optimum performance for a full pulsed antenna measurement scenario. This paper will discuss receiver timing considerations and show examples of scan time performance during high-speed pulsed measurements. Inter-pulse and intra-pulse measurements will be compared with respect to their impact on measurement time. Pulse profile measurements will be examined to show the importance of a fast synchronous receiver for sub-microsecond pulse characterization. Pulsed antenna pattern results will also be presented and compared with CW measurements.

CONSIDERATIONS FOR VHF GAIN MEASUREMENTS OVER SEAWATER
John P. Casey (Naval Undersea Warfare Center),Stephen M. Davis (Naval Undersea Warfare Center), Bruce Greenhalgh (Naval Undersea Warfare Center), Rodney P. Gudz (Naval Undersea Warfare Center), Paul M. Mileski (Naval Undersea Warfare Center), Paul Medeiros (Naval Undersea Warfare Center), David A. Tonn (Naval Undersea Warfare Center), Hailu M. Waka (Naval Undersea Warfare Center), Isaac M. Wheeler (Naval Undersea Warfare Center), November 2008

Methods for measuring the gain of an antenna at low frequencies (i.e. below 30 MHz) operating at or near the surface of the ocean on an open-air antenna range have been considered and reported previously. These methods employ a groundwave correction approach and a virtual reference antenna consisting of an idealized quarter wave monopole. However, this approach is not appropriate for application at the shorter wavelengths that occur in the VHF band owing to a variety of factors. In this paper, we shall discuss some of the issues associated with the use of the more conventional substitution method for measuring the gain of an unknown antenna that is operating near the air-sea interface. Issues and challenges related to instrumentation, antenna siting, range assessment, multipath effects, and reference measurements shall be considered.

Assessment of a Planar Near-Field Range for Quiet-Zone Measurements at 650 GHz
Matti Vaaja,Antti Räisänen, Janne Häkli, Juha Mallat, November 2007

Planar near-field probing is used in the optimisation of the quiet-zone of a hologram-based compact antenna test range (CATR). In this paper, the measurement instrumentation for 650 GHz operation is introduced and the potential measurement errors in the quiet-zone measurements are identified. Applicable error correction and compensation methods are discussed and the total measurement accuracy is calculated.

Quasi-optical instrumentation for the Planck FM telescope RF alignment verification measurements at 320 GHz
Maurice Paquay,Dennis Dubruel, Gilbert FORMA, Javier Marti-Canales, Richard Wylde, November 2007

In the Flight Model (FM) of the PLANCK telescope, the feed horns are connected to either HEMTs or bolometers operating at cryogenic temperatures to detect the Cosmic Microwave Background radiometric signal. For the purpose of an overall alignment verification at ambient temperature, reflectivity measurements will be performed using an auxiliary feed horn that is terminated with a switching diode. This verification test will be conducted at 320 GHz, to benefit from the narrow beam and a high sensitivity to misalignment. To perform the reflectivity measurements, an additional “circulator” with low loss and high isolation between transmit and return channels had to be developed. Besides that, the circulator co-locates the phase centres of both Tx and Rx range antennas on the focal point of the CATR, which allows monostatic reflectivity measurements. Quasi-optical techniques have been used to design a circulator that meets these requirements. The assembly has been developed, tested and used for reflectivity measurements.

Next Generation Phase Coherent Microwave Instrumentation Receiver
Dave Fooshe,Dan Slater, November 2007

The next generation of antennas will benefit from advanced instrumentation receivers capable of providing simultaneous analog and digital IF inputs, better TR pulse synchronization and high resolution pulse profiling. One such receiver uses a synergistic combination of a tightly coupled FPGA based beam controller, high performance analog digitizers, multiple FPGA based digital signal processors and a new mathematical programming environment. The FPGA signal processor provides direct digital downconversion, high resolution pulse processing and dynamically reconfigurable time and frequency gated matched filter signal integration. The signal processing functions are fully scriptable, providing spectral analysis, various other types of transform analysis, instantaneous demodulation, pulse characterization, noise estimation and more. Advanced mathematical tools combined with novel user interface technologies provide multiple intuitive views into the test setup, error analysis and measurement environment.







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