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FROM ON-WAFER TEST TO OREAST-CANCER DETECTION: VNAs find use cases extending from IoT to medical and materials-science applications.

Vector network analyzers are versatile instruments offering top operating frequencies extending from megahertz and lower ranges up to hundreds of gigahertz. They handle test-and-measurement chores ranging from power-supply design and debug to characterization of mmWave devices used in 5G systems and beyond. In addition to serving in the electronics lab, the availability of low-cost, compact, USB-connected VNAs in the gigahertz ranges is opening up the use of the instruments in materials-science, medical, and other applications areas. While IoT and 5G are key applications focuses, the applicability of the instruments extends from power-distribution-network (PDN) impedance measurements to breast-cancer detection.

A look at recently introduced VNAs and options highlights the ranges of specifications, capabilities, formfactors, features, and applications.

According to Rich Pieciak, product manager for vector network analyzers at Rohde & Schwarz, "The most recently introduced vector network analyzer platforms from Rohde & Schwarz are the R&S ZNA family, in the high-performance segment, and the R&S ZNBT40 platform, which expands our multiport solutions to 40 GHz."

"The new VectorStar ME7838G system is the latest version of the broadband line of VectorStar VNAs," said Steve Reyes, VNA product manager at Anritsu Co. "The single-sweep range is from 70 kHz to 220 GHz through a 0.6-mm DC connector. The VNA is geared toward on-wafer applications, including device characterization." He continued, "On-wafer measurements are taking on a more significant role in new transceiver designs for emerging microwave communication applications."

"Recently Keysight introduced network analyzes in three formfactors--USB, modular PXI, and benchtop," said Matt Campbell, product marketing engineer, Keysight Technologies Inc. "We have existing models in all three form factors already, but the wide application coverage makes the new models special. Now you can fully characterize devices, no matter which formfactor you're using while using the same GUI and remote API."

Subbaiah Pemmaiah, application engineer, Copper Mountain Technologies, said the SC5065 2-port 6.5-GHz and SC5090 2-port 9-GHz VNAs are the newest additions to the company's product line. "These VNAs are compact in size and yet capable of providing excellent 140-dB dynamic range at 10-Hz IF, 16-ms/point measurement speed, and a higher output power up to +15 dBm," he said.

Roger Denker, general manager, MegiQ, said recent products include the USBdriven VNA-0460 6-GHz, 2-port VNA with PC software and the MegiQ VNA0460e 6-GHz, 3-port VNA with built-in bias-T and bias voltage/current generator. "We are developing a new generation VNA with a wider frequency range and more baseband processing applications," he said. As for application areas, "We see a growing business in RF tools for IoT development," he said. "We also see innovative applications in detection using VNAs to map reflection patterns." Denker said MegiQ offers calibration kits for UFL connector-based measurements and balanced measurements, affordable 6-GHz SMA calibration kits, and an application programing interface for production testing and other automated tasks.

Jason Chonko, applications marketing manager at SIGLENT Technologies North America, said SIGLENT's newest VNA, the SVA1032X analyzer, "... extends our vector measurements from 100 kHz up to 3.2 GHz. The SVA Series features an easy-to-use interface and solid performance in a lightweight benchtop design."

Picotest sells the OMICRON Lab Bode 100, the Keysight E5061B, and the R&S ZNL, according to Steve Sandler, CEO of Picotest. "The Bode 100 is our low-cost, low-frequency VNA and the most popular," he said. "It is a true VNA (not just a frequency response analyzer) that goes to 50 MHz and supports S-parameter measurement (sn ands2j) and touchstone output." He said Picotest supports a range of applications with a selection of signal-injector accessories and probes that can be used to measure components as well as circuits.

"It should be noted that Picotest makes accessories for all VNAs," Sandler continued. "We are the largest developer of support hardware. Many of our products are essential; you can't make the measurement with the VNA without an accessory we make. We have the largest offering of signal injectors, probes, and PDN cables." He added that the company also offers training, specialized demo boards, and tutorials.

VNA differentiators

When asked what is unique about his company's vector network analyzers, Reyes said, "The Anritsu Non-Linear Transmission Line (NLTL) harmonic sampler provides optimum performance of high-frequency measurements with excellent noise-floor performance and dynamic range. The compact Anritsu NLTL modules offer industry-best calibration and measurement stability at millimeter-wave (mmWave) frequencies."

"With exceptional measurement performance becoming standard, it's hard to buy a bad network analyzer these days," said Campbell. "Looking beyond measurement performance, Keysight considers the many methods required to characterize modern RF devices--spectrum analysis, fixtured measurements, noise-figure/parameters, as well as new methods to accurately characterize your device using active-parameters and EVM/ACPR. On our network analyzers, we simplify RF characterization by offering the broadest software and measurement application portfolio in the industry."

"The R&S ZNA family has exceptional RF characteristics, highlighted by sensitivity, power sweep range, and linearity," said Pieciak. "It also has a modern user interface and a unique hardware architecture with four internal phase-coherent sources that provide new measurement versatility for testing mixers or other frequency-translating devices such as satellite up/downconverters or TR modules.

A second internal local oscillator source speeds up mixer measurements or can be used as an additional source--for example, as the LO (up to 26.5 GHz) for the mixer under test. High power accuracy with extremely short control times is achieved with the R&S ZNA digital automatic level control (ALC), even in combination with external test setups."

He continued, "The R&S ZNBT40 is a turn-key solution for measurements up to 40 GHz that provides unparalleled measurement accuracy up to 24 ports and under high power requirements."

"All our VNAs are USB-based," commented Pemmaiah at Copper Mountain Technologies. "This form factor separates the measurement module (which is the VNA) from the processing module (a PC), thereby providing advantages such as compact size, flexibility, and security as well as automation support and speed. The compact size of the analyzers makes for a much smaller and lighter instrument, which increases options for testing."

The company supports both Windows and Linux. "The VNA application can be run from larger desktop computers to smaller board computers," Pemmaiah said. "The ability from the USB formfactor to use newer computers offers engineers larger storage space and eliminates the need for data purging or hard-drive removal in secure environments." A test-automation program and the VNA application can run on the same computer, which can improve the overall measurement speed, he said, adding, "Our engineering team is available to support users with automation scripts at all times. In addition, the superior internal wideband coupler design and the advanced DSP+FPGA processors have helped achieve wide dynamic range and fast measurement speed."

Denker said MegiQ offers small formfactor, low-priced lab-grade VNAs with color-guided calibration on the front panel, a built-in matching-circuit calculator and simulator, and built-in bias-T and bias voltage/current generator (to allow for parametric measurements). He added that the VNAs are optimized for IoT development workflow and provide for easy to store/recall full measurements and setup as well as readable (noncryptic) graphic reports.

Mark Ashcroft, RF business development manager, Pico Technology, said that despite several recent new entrants in the USB-controlled VNA space, "The PicoVNAs continue to hold the leading low price, high-performance position. The PicoVNAs are full-function professional metrology instruments that will typically match or exceed the measurement accuracy of all other 6-GHz VNAs on the market. It is not lost upon educationalists and lab or test managers that this powerful combination of low cost and high capability presents the opportunity for every student or engineer to now have a VNA each. How long have we all waited for that? In industry, let alone education!"

According to Chonko at SIGLENT, "The SVA Series incorporates a novel design that enables a number of operation modes that can be used to troubleshoot a number of common RF/broadcast issues." The instrument includes a spectrum-analyzer mode for monitoring transmitters and interference investigations, a VNA mode for RF device and cable characterization, an optional distance-to-fault mode for cable-integrity tests, and optional digital demodulation with I/Q demod. "The instrument also features a 10-in. touchscreen with up to four-trace overlay, USB mouse/ keyboard support, and onboard web control for remote operations and monitoring without programming," he said.

"The Bode 100 is unique in its combination of capability, ease of use, and price point," said Sandler at Picotest. "Priced at $5,400, it is almost one-third the cost of its nearest major competitor with significantly more features. It is the only VNA that natively includes our unique NISM noninvasive stability software."

VNA trends

"Continuation into the mmWave frequencies for fundamental communication bands is a major trend, as is the continued requirement for device characterization beyond 110 GHz for accurate device modeling and simulation," said Reyes at Anritsu. "Another trend is the integration of subsystems into wafers with advancements in wafer composition, thus requiring in situ on-wafer calibration and measurement."

"As devices for RF applications become more highly integrated, complete characterization requires more than passive S-parameters," said Campbell at Keysight. Customers may have to perform active parameter measurements to accurately characterize gain vs. traditional S-parameters, as well as spectrum analysis, pulsed measurements, and noise-figure measurements, he said, adding, "We expect to see more customers streamlining their workflows by performing multiple types of measurements with their network analyzers."

"As devices get more compact and complex, the higher number of ports and operating frequencies are driving more test-time reductions," commented Pieciak at Rohde & Schwarz. "Having the ability to perform a suite of tests that fully characterizes a device with minimal setup increases test yields and drives down recurring test costs."

Copper Mountain Technologies has seen an increase in demand for portable handheld VNAs that support material measurement applications, said Pemmaiah. "5G has pivoted the need for analyzers capable of characterizing components in the mmWave frequencies," he said. "This has also increased the necessity of characterizing the material dielectric properties. The compactness and the portability of some of Copper Mountain Technologies' VNAs have paved way to use the analyzers on a robotic arm, to mount it on a drone for remote measurements, and even send it in space."

"The IoT market is booming," said Denker at MegiQ. Consequently, many engineers are faced with implementing RF circuits and antennas--tasks they are not necessarily trained to do. "Engineers need no-nonsense, easy-to-use VNAs to start developing wireless applications," Denker emphasized.

Chonko also cited the IoT and a trend on the low end of the spectrum toward increasing capabilities at lower price points. "Ten years ago, there were almost no options for low-cost VNAs," he said. "You had to settle for a used unit or pay $20k or more for a basic instrument. That has changed dramatically in the past few years, due to the increased demand for RF testing in IoT research and development."

Chonko added, "On the high end, 5G is driving technology advancement and capabilities to higher frequencies than ever before, with systems over 100 GHz commonly available."

Sandler at Picotest said more manufacturers are addressing power-integrity applications, with most manufacturers now supporting the 2-port shunt-through impedance measurement and offering Picotest's NISM noninvasive stability software.

Challenges from IoT to 5G

VNA users face new challenges as they confront 5G and the IoT. "5G and IoT bring new frequencies to customers who haven't worked in the millimeter-wave frequency range before," said Campbell at Keysight. "At higher frequencies you have smaller margins for error, and you need to pay careful attention to your hardware setup--a small cable shift after calibration can cause large phase errors, for example." He said that in addition to providing test equipment for 5G and IoT, "We help our customers enhance their expertise in new test challenges by sharing our experience through webinars, papers, and presentations. Using new measurement methods along with VNA correction techniques applied to EVM measurements offers more repeatably and accurate measurements."

"Technology advancements in areas such as beamforming, utilized by 5G architecture, are necessitating system and component performance validation at many operational states, each of which require accurate characterization," said Pieciak at Rohde & Schwarz. "This higher port count, with associated calibration, raises the likelihood of measurement errors, so all advances focused on providing a single-point connection to a device under test, preceded by guided calibration steps, would greatly increase measurement accuracy and heighten overall test confidence."

When asked what challenges his customers are facing, Reyes at Anritsu said they want to conduct accurate, cost-efficient on-wafer measurements via multiple measurement capability per probe-station setup. "The key for improved probe-station efficiency and productivity to achieve this goal is to have broad frequency coverage using small compact modules," he said. "The VectorStar ME7838G system provides the widest broadband frequency coverage with the smallest, lightest mmWave modules, for excellent measurement capabilities and easy installation on smaller probe stations."

"With new technologies, frequencies of operation climb to the mmWave regions to accommodate wider data bandwidths," said Pemmaiah at Copper Mountain Technologies. "At these higher frequencies, cost of owning test equipment such as a VNA becomes generally very expensive because of the wideband architecture. To overcome this challenge, Copper Mountain Technologies offers an economical approach to use a low-frequency (9-GHz) base VNA with frequency-extender modules like the FET1854 (18 to 54 GHz), FEV-15 (50 to 75 GHz), FEV-12 (60 to 90 GHz), and FEV-10 (75 to 110 GHz), which operate only in the mmWave band region." This approach offers two advantages. "First, the cost will be a fraction of the cost of a wide-band VNA which might cover the entire range," he said. "Second, the frequency extender 'head' can be placed physically close to the DUT. This minimizes signal loss and improves the dynamic range of the measurement."

When asked about trends, Ashcroft at Pico Technology said, "I want to focus here upon IoT and materials-measurement proliferation, because both of these introduce microwave design and the need to use a VNA to, for instance, digital engineers, small companies, and scientists that have never used these technologies before. It is these demands that have driven Pico's simplified GUI design, with which, we are proud to say, first-time users are typically able to perform a calibration, check their calibration against the optional PicoVNA verification standard, and perform accurate measurements right from opening the box."

He also cited a partnership between Pico and the computer-aided-design company NI/AWR. "The PicoVNA now has an AWR Connected' wizard that can control and import measurement data from the VNA right into the AWR Design Environment," he said, adding that AWR's Microwave Office or VSS (Visual System Simulator) can either use the measurements within a simulation or for direct comparison of simulation with the real-world. "Students and newbie microwave engineers alike can enter and quickly transition between all of the 'Design-Simulate-Implement-Validate-Iterate' phases of the development cycle," he added.

"The biggest challenges are the lack of experience and knowledge," said Chonko at SIGLENT. As with most engineering disciplines, RF design has its own language and common rules that differ from analog and digital design, presenting challenges to traditional analog and digital companies that now want to integrate RF so that they can capture pieces of the IoT market. "But it isn't nearly as simple as 'adding a radio' to the block diagram," Chonko said. "Along with this are the proper test techniques and processes to ensure success and the additional knowledge and testing required when adding an intentional radiator for FCC/compliance testing--when to use a certain test for a certain problem, etc. SIGLENT is constantly building up our applications library to assist customers in getting started. We consider ourselves partners to our customers. If they are successful, we will be too."

IoT, 5G, and beyond

A variety of applications areas are emerging, including IoT and 5G but extending to materials science and medicine. Chonko at SIGLENT commented that while IoT and broadcast testing have the largest growth possibilities from his perspective, "Basic science and material characterization are an important part of the VNA market and represent a stable and consistent customer group."

Campbell at Keysight drilled down on 5G. "Multiport phased-array antennas address 5G's need for faster wireless data transmission, but they come with unique test challenges," he said. "Modern transmitters and receivers operate at low power levels over wide bandwidths and require extreme measurement precision to characterize. Low-power measurements have little room for error, but switch-based multiport measurement setups degrade the network analyzer's accuracy. Keysight's response to the growing need for multiport test is modular multiport network analyzers like the M980xA Series, which reduce uncertainty with exceptional performance--no matter how many ports you use."

"Continued advances in high-speed digital design are clearly taking on more importance with regard to signal integrity," said Pieciak at Rohde & Schwarz. "The proliferation of differing standards and corresponding board layouts are necessitating new ways of probing and analyzing signals in both frequency and time domains. The need for high-performing multiport testing arises from steered antenna arrays for radar systems or 5G antenna arrays."

Pemmaiah at Copper Mountain Technologies cited materials measurements. "Recently, VNAs seem to be getting more popular in medical and agricultural research," he said. "Among the most recent breakthroughs, the CMT C1209 2-port 9-GHz VNA was used to detect cancer cells to provide a safe and cost-effective solution for breast-cancer screening. MammoWave from Umbria Bioengineering Technologies (UBT) utilizes two antennas, and each is connected to a port of the VNA. (1) Screening is performed with the patient laying in a face-down position. The antennas rotate around the cup, without any compression, performing measurements approximately every four degrees. The measurements from the VNA are then processed through UBT's software to detect the presence of suspected tumors in the breast tissue."

Ashcroft at Pico Technology cited antenna matching, gigabit data-cable test, material dielectric properties, and penetrative imaging as applications that have grown strongly in recent years and continue to do so. "All of these proliferate to industries that typically haven't previously owned a VNA, heard of S-parameters, or made these measurements before," he said. "Uncluttered ease of use and fast, high-quality measurements are everything here. Imaging in particular is demanding of speed," such as PicoVNAs' to 5,500 full and corrected 2-port measurements per second (10,000 per second if measuring only [s.sub.11] or [s.sub.21]).

Sandler at Picotest said that power integrity has emerged as an important application today for VNAs. "PDN impedance is a vital design parameter that must both be simulated and tested in order for most high-speed digital and other low-voltage applications to be designed, debugged, and validated," he said. "No longer can the power supply be designed apart from the PCB, decoupling, and load circuitry. They must be designed together, and the main way in which performance is measured is via the VNA impedance measurement."

VNA options

Vendors offer a variety of options for their VNA products. For example, "Anritsu offers the ability to upgrade lower frequency 2-port VectorStar VNAs to higher frequencies, up to 220 GHz, as well as up to 4-port configurations without extensive modification to the existing 2-port systems," said Reyes. "That is one customer benefit of the modular approach Anritsu has taken with its mmWave and 4-port systems."

"One problem customers run into when testing high-performance 5G components is that the residual error vector magnitude (EVM) of their test setup is close to the EVM of the component under test," said Campbell at Keysight. "Therefore, it is hard to differentiate the component's EVM from the test setup's EVM. Our new modulation distortion application for the PNA-X provides space to clearly see the device's performance with the lowest residual EVM in the industry. The PNA-X's exceptional error correction helps remove noise and uncertainty from EVM, adjacent channel power (ACP), noise power ratio (NPR), and band power measurements."

According to Pieciak at Rohde & Schwarz, the R&S ZNA offers a multichannel architecture of eight coherent receivers in the 4-port model, all accessible from the front panel of the instrument, and two internal LOs. "With the vector-corrected mixer option and coherent sources, phase measurements on frequency-converting devices can be performed with ease, without the need for reconverting or reference mixers," he said. "Corresponding group-delay measurements can also be made with ease, utilizing a 2-tone measurement technique that can be used on frequency-translation devices with or without the embedded LO access."

Copper Mountain Technologies VNAs come with time-domain analysis and gating as standard features in the software, according to Pemmaiah. The software can be used in demo mode and downloaded for free from the website. "Having time-domain and gating included has led to additional measurement capabilities using just a VNA," he said. "Frequency offset and vector-mixer-measurement capabilities are another standard feature in the VNA software and is an important feature for 5G development."

Pemmaiah added, "The new Epsilometer solution offers dielectric material measurements for specimens with thickness 0.3 to 3 mm. This solution utilizes an advanced computational electromagnetic modeling to compute the dielectric permittivity with ourR60 1-port VNA. This makes the overall solution very cost effective compared to the existing solution available in the market. The 4-port VNAs also come with balanced measurement capability, which is very useful for signal-integrity measurements."

"Pico has been busy supplementing the PicoVNA product line with a low-cost network metrology training kit aimed at trainers, universities, and training centers," said Ashcroft. "Paired with only a VNA, the PCB-based kit facilitates calibration and measurement of both passive and active devices, lines, and lumped-element networks." Training supports the use of, display of, and embedding and de-embedding of S-parameters; reference plane shift; time-domain reflectometry; and nonlinear effects such as PldB and PM due to AM compressions. "Additionally, the Network Metrology Training Kits are supplied with their full AWR Microwave Office design project file," he said. "This allows students and trainers to leverage the AWR Connected' partnership discussed above. They are able to open the design project, simulate and perhaps modify each element, and then compare with real-world measurements that they can make with the kit. Full engagement with an entire microwave design cycle right there in the classroom!"

According to Chonko, the SIGLENT SVA1X Series offers several options that can quickly provide clear answers to tricky troubleshooting issues. "For broadcast and interference monitoring, the Advanced Measurement toolkit includes an onscreen waterfall plot as well as ACP, OBW, and a number of other common measurement types," he said. "Engineers working on wireless data transfer may be interested in viewing transmission performance. Here, demodulation analysis is available for common analog and digital modulation schemes including I/Q demodulation up to 256 QAM."

In addition, Chonko said, "For technicians performing antenna tower work finding breaks and impedance differences throughout cable runs and adapter troubleshooting, the distance-to-fault (DTF) option is available. There is also an EMI option that provides instrument settings specifically designed to help shed light on electromagnetic compatibility and interference issues."

Sandler cited Picotest's NISM. "This is a critically important technology for today's power-supply designers," he said. "There are many situations where a Bode plot cannot be made or is not accurate. For many switchers, POLs, linear regulators, references, and op-amps, output impedance is the way to accurately test stability. This software accessory converts output impedance to stability/phase margin. It is available for or included with several VNAs including Keysight's E5061B/ E5071C, Rohde & Schwarz's ZNL/ZNLE, and OMICRON Lab Bode 100. Several other analyzers from Anritsu and Copper Mountain are in the process of incorporating it with the free Picotest NISM API toolkit. Picotest also offers many accessories for power-integrity measurements and even specialized coaxial cables, specifically designed for the 2-port shunt through impedance measurement."

Ease of use

Vector network analyzers are typically considered difficult to use by novices, yet experts might be reluctant to see any changes in operation. Vendors offer several strategies to cope.

"Anritsu offers a choice of menu-guided setup or advanced controls," said Reyes. "For example, our Mixer Setup menu helps users configure the system for mixer measurements. If more advanced control is needed, the VectorStar Multiple Source Control provides extensive access into the configuration of the sources and receivers.

"The vast application coverage of network analyzers can intimidate new users, but we organize our user interface to give experts the functionality they expect while keeping the fundamentals accessible to beginners," said Campbell at Keysight. "For basic measurements, users can press the 'New Trace' button and easily adjust all of the relevant parameters in one pop-up. For advanced measurements on the PNA family, beginners can follow the Device Measurement eXpert (DMX) assistant tool to configure and optimize complex measurements. These enhancements for beginners do not interrupt traditional workflows that experts may prefer."

"Ease of use was of key importance in the design of the R&S ZNA platform," said Pieciak. "A DUT-centric test approach was incorporated to allow for straightforward parameter entry depending on the measurement task at hand, with two independent touchscreens providing convenient access to the pertinent setup and measurements menus."

Pemmaiah at Copper Mountain Technologies described VNAs as complex instruments due to the versatility they provide. "With the addition of new features and methods, the complexity only increases," he said. "In addition to providing webinars and tutorials, Copper Mountain Technologies also offers plugins to help users with a quick and easy way to perform specific types of measurements."

According to Denker, "MegiQ products focus on the measurements and the results, not merely on the equipment. Our goal is to provide an out-of-the-box measuring solution for wireless developers. Our VNA-Sandbox with tutorial makes it easy to get started with VNA measurements, and it provides a starting point for wireless product development. MegiQ offers a UFL and balanced toolkit for small applications."

"There is a balance when it comes to creating a user interface (UI) that pleases both new and experienced users," said Chonko. "SIGLENTs approach has been to put standard measurement functions where they traditionally have been but to add shortcut buttons or menu items that make it easier to perform tasks that are often repeated. Touchscreen, mouse/ keyboard support, and a web control interface that exactly copies the front panel UI also aid in minimizing the learning curve." He added, "We are also constantly building videos and other content to help guide customers in proper instrumentation usage."

Sandler at Picotest takes exception to the claim that VNAs are difficult to use. "This sentiment is at least 10 years behind the times," he said. "Take a look at the latest Bode 100 VNA software. It is incredibly easy to use. Fully wizard-driven, it eases the test setup and the data analysis by both describing the test setup and walking the user through the measurement setup. Everything is software-driven on one screen. This is not the HP3577. Gone are the days when Bode, Nyquist, Nichols, or impedance plots were challenging to obtain, interpret, and publish. Now look at today's oscilloscopes. They are far more complicated."

Sandler continued, "Having said that, I think much of the hard-to-use issue was wrapped up in the 'hard to interpret' box. Engineers are still not taught S-parameter theory or network-analyzer usage in schools. Introductions to the VNA at the college level is sorely lacking. It is not clear why, given there are many low-cost solutions, and the importance of impedance measurement is critical to designing all types of circuits."

REFERENCE

(1.) "9 GHz VNA Used in MammoWave Breast Cancer Detection System," Case Study, Copper Mountain Technologies.

By Rick Nelson, Interim Chief Editor

Caption: Rohde & Schwarz R&S ZNA vector network analyzer.

Caption: MegiQ USB-driven VNA-0460 6-GHz, 2-port VNA and VNA-0460e 6-GHz 3-port VNA.

Caption: Anritsu VectorStar ME7838G broadband VNA

Caption: Copper Mountain Technologies low-frequency base VNA with frequency-extender modules.

Caption: Pico Technology PicoVNA 106 6-GHz vector network analyzer
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Title Annotation:SPECIAL REPORT
Author:Nelson, Rick
Publication:EE-Evaluation Engineering
Date:Jan 1, 2020
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