AMTA Paper Archive
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Wideband Double-Ridged TEM Horn for Nondestructive Evaluation and Imaging Applications
Antenna performance plays a significant role in synthetic aperture radar (SAR) image quality, particularly for nondestructive evaluation (NDE) applications. To obtain high image quality and target detectability, SAR imaging systems should possess good resolution (cross- and along-range), and a relatively large penetration depth. Consequently, the antenna used must be wideband with a relatively wide beamwidth for high resolution and operate at low starting frequency for sufficient penetration depth. Meanwhile, antenna aperture size should be small rendering it sufficiently portable for scanning purposes or when employed within imaging arrays. However, increasing frequency bandwidth, reducing minimum frequency of operation while maintaining small aperture size (resulting in wide beamwidth), all at the same time is difficult. To this end, double-ridged horn (DRH) antenna, with flared aperture for improved radiation efficiency and performance is found to provide a good compromise among these parameters. Therefore, an improved modified design of DRH is proposed. The dimensions of its geometry are optimized to provide low unwanted reflections. Curved surfaces are attached at the end of the two ridged walls for better aperture matching. The final aperture size of the antenna is 230 ? 140 mm2, operating in the 0.5-4.0 GHz frequency range, and with a relatively wide beamwidth in its near-field region where most NDE imaging measurements are conducted. Measured reflection coefficient by using the fabricated antenna is used to verify the simulation results. Comparisons are also made with similar designs of DRH found in the literature showing that the proposed antenna has smaller electrical length with respect to the lowest operating frequency for designs without using absorbing material. Moreover, to conduct wideband SAR imaging, a new phase calibration method, using a small electric field monopole probe, to measure the phase change between the antenna aperture center and the input feed port for each frequency component is developed. Imaging results over a large concrete slab with delamination and voids simulated by foam and plastic sheets show that the proposed calibration approach works well, and the proposed antenna can effectively detect all of these defects with different scattering properties.
Balun Design for CISPR 16-1-5 Calibration and Reference Test Site Verification
The CISPR 16-1-5 standard requires site attenuation (SA) measurements for the validation of Calibration Test Sites (CALTS) and Reference Test Sites (REFTS). CALTS validation requires horizontally-polarized SA measurements, while REFTS validation requires both horizontally- and vertically-polarized measurements. These measurements are made with tuned linear dipole antennas driven from coaxial transmission lines via balancing networks (baluns). According to the CISPR standard, the effects of the baluns are removed with a substitution measurement. Specifically, the baluns are connected back-to-back (balanced to balanced) with the elements removed and the port-to-port insertion loss then measured. This insertion loss is then subtracted from the port-to-port insertion loss with the antennas assembled and in place on the OATS. Thus, the measurement is a true RF substitution measurement. The baluns must be perfectly symmetric for this measurement to be sound. It is then accurate only if the baluns are very well matched simultaneously to both to the coaxial transmission lines and the dipole antennas. Essentially, the dipole-to-dipole transmission, the 2-port network which is substituted, would have to behave as a matched attenuator. In the CISPR standard SA measurements are made a a minimum of 24 specific frequencies between 30 and 1000 MHz. The height of the transmitting antenna above the ground plane in all cases is 2 m, but the height of the receive antenna varies in order to avoid a transmission null. For each one of these measurements it is possible to obtain a perfect match for each dipole antenna. However, the matching network would be different for each frequency and also for the different heights involved. Thus, there is impetus to use broadband baluns and resistive matching pads. If this approach is selected, neither dipole can be perfectly matched. Moreover, if the balun is required to operate over a broad bandwidth, it is difficult for itsperformance to be made so good that it could be considered ideal. By employing a full 4-port model for antenna-to-antenna transmission on an OATS between linear dipoles with imperfect baluns and thus unbalanced antennas, we assess measurement error for topologies of balun/attenuator combinations for the CISPR 16-1-5 SA measurements.
The Cost of Accuracy - Mechanical Systems
Accuracy in a measurement campaign is dependent on many factors. Some of these factors are in the physical components used, the requirements of the electromagnetics involved and the procedural requirements of the campaign. This paper will focus on how the mechanical accuracy of the equipment can impact total cost. The current stage in the life cycle of the AUT (design, production, repair) also impacts total cost. The affordability of the accuracy in terms of more costly equipment, calibration processes and operator and test range time may be the determining factor. Throughput needs may limit the accuracy that can be obtained. The accuracies required for each metric must then be evaluated against the accuracy of an available test range(s) or the renovation of an existing range or construction of a new range to meet the accuracy requirements. Two case studies included in this paper are: 1) the improvement of the positioning accuracy of a rotator via custom hardware and calibration for a severe global positioning accuracy specification and 2) the improvement of the planarity of an X-Y scanner system for use at increasing frequencies.
Nearfield Measurements on Integrated Antennas with a Frequency Convertor and Embedded Local Oscillator
Near-field measurements on antennas require magnitude and phase information dependent on the antenna position to support the near-field to far-field transformations. Modern active antennas are often integrated into frequency converters with embedded local oscillators (LO). For example, devices ranging from small 5G transceivers to large satellite payloads often need to be tested with the antenna integrated into the overall solution. There is no access to the embedded LO signal in these systems. The unknown phase of the embedded LO masks or corrupts the near-field phase measurement of the integrated antenna under test. A novel solution to this challenge is presented based on a new Vector Network Analyzer (VNA) platform. The system utilizes two stimulus signals (a measurement signal and a pilot signal) to characterize the antenna under test which is integrated into the frequency convertor. The pilot signal captures the phase information of the embedded LO, allowing the measurement signal to capture the antenna's magnitude and phase pattern as the antenna under test is moved within the near-field region.
Aerosol Jet printed antenna for vehicular communications
3D-printing methods presents unique opportunities for new antenna applications. One of these applications of particular interest is integrating antennas onto automotive vehicle bodies. Currently the automotive industry is experiencing a growth in number of on vehicle antennas to support connectivity and internet of things. This combined with the physical nature of automotive designs (large areas of non-conductive materials) results in an ideal implementation of 3D-printed technology. Key technologies of implementation include both cellular and vehicle to everything communications (V2X) as these play a critical role to the implementation of the connected vehicle. For the cellular operations connectivity can require up to 4 MIMO antennas operating from 600 MHz to 5 GHz. In addition, V2X operates in the 5.9 GHz frequency band, requiring up to 2 antennas. The result is a large number of varied types of antennas. Therefore, additive manufacturing techniques is an ideal technology to simplify and progress automotive antenna design and production. Moreover, Aerosol Jet Printing (AJP), as a contactless technique, can be exploited to fabricate conformal antennas. AJP allows the development of electronic components on any curved or flat body and gives the opportunity to mix different materials to print on the unique surfaces found in the automotive industry. The presented antenna is designed and simulated using Ansys HFSS and fabricated using Optomec Aerosol Jet Printer. The antenna is initially printed using the Clariant Prelect TPS 50 G2 silver ink on the Rogers Ultralam 3850 (LCP) substrate and then techniques are developed to print the antenna on the ABS substrate that is taken from a plastic trunk lid of a commercial vehicle. The antenna is dual-band, operating at the cellular and C-V2X bands and has an omnidirectional pattern at the cellular frequencies where its average realized gain on H-plane, as simulated in the ANSYS EM software, is 0.2 dBi at 836 MHz and -4dBi at 5.9 GHz. The antenna fabricated on LCP using Additive Manufacturing and is measured in a Satimo spherical nearfield chamber with a resulting average realized gain on H-plane is -1.8 dBi at 800 MHz and -3dBi at 5.9 GHz.
Robot-Based Antenna and Radar Measurement System at the RWTH Aachen University
High precision antenna measurements can be carried out in different ways, for example directly in the far-field, in a compact antenna test range (CATR) or in a near-field range. Far-field measurements have the disadvantage that they require a lot of space and are sensitive to environmental influences. Although these effects can be avoided with a CATR, these systems are demanding and expensive. For this reason, simplifying near-field measurement setups are often preferred, whereby three main methods have become established: planar near-field (PNF), cylindrical near-field (CNF) and especially spherical near-field (SNF) measurements. Current measurement setups are usually optimized for one of these techniques and are therefore only of limited use for the other methods. Recent developments have focused on robotic measurement systems, which are able to overcome the boundaries between the different measurement techniques. Due to the high number of degrees of freedom and an almost unlimited positioning and orientation possibility in space, these systems offer numerous advantages due to their flexibility. This allows the same measurement system to be used seamlessly to perform PNF, CNF and SNF measurements. Even for more demanding measurement procedures, for example based on compressed sensing, robotic systems create the possibility to efficiently approach the required sampling points. At the Institute of High Frequency Technology at RWTH Aachen University, such a robot-based measurement setup is currently being established. In addition to the six-axis robot arm, the system has two additional axes, specifically a linear axis on whose slide a rotary axis is mounted. In the currently used configuration, the antenna under test is mounted on the axis of rotation, while the probe antenna is installed at the robotic arm. This results in a total of eight degrees of freedom combined in a novel test range design, which distinguishes the measurement setup from existing ones. Further details on the measurement setup, the implementation of antenna and radar measurements and the operation of the entire system will be explained.
SOLR Calibration Using Planar Offset Short in Free-space Material Measurement
Electrical material parameters such as permittivity and permeability are a prerequisite to analysis and to design of EM devices and systems.For the measurements of the EM material parameters, coaxial/waveguide methods and cavity method are used in low frequency range whereas free-space method is suitable in high frequency range. In free-space method, one of the non-destructive methods without prior machining of a MUT (Material Under Test), TRL (Thru-Reflect-Line) calibration method is used when the free-space measurement system has a linear slide to precisely adjust the separation distance between transmit (Tx) and receive (Rx) antennas, and GRL (Gated-Reflect-Line) calibration method in the case that the separation distance between the two antennas is fixed. As one of the well-known calibration methods, SOLR (Short-Open-Load-Reciprocal) calibration method assumes seven unknowns in the free-space material measurement configuration, i.e., the port-#1-side directivity, match, and tracking (E_DF, E_SF, E_RF) between the VNA test port #1 and the MUT, the port-#2-side directivity, match, and tracking (E_DR, E_SR, E_RR) between the VNA test port #2 and the MUT, and the quotient ?/…. This calibration, first performs two one-port calibrations at the port-#1-side and port-#2-side to determine (E_DF, E_SF, E_RF) and (E_DR, E_SR, E_RR) using three reflection standards, and then performs one transmission measurement using a reciprocal two-port standard (in this case, thru) for determining ?/…. Calibration of a free-space material measurement system by using SOLR method requires three free-space reflection standards. Recently, a planar offset short is proposed as a free-space reflection standard because its reflection property has the magnitude of unity and the phase proportional to the offset of the offset short. This paper proposes the SOLR method using three planar offset shorts with the respective offset of (0, ?/6, 2?/6) for calibrating a free-space measurement system. Effects due to the thickness of the MUT are compensated by a de-embedding process. The thinner the thickness is, the better results this method can get. The proposed method does not require a linear slide to precisely adjust the separation distance between Tx and Rx antennas of the measurement system. Theoretical details and measurement results will be presented at the symposium.
Mitigation Techniques for the Concealment of a New Fire Suppression Network and HVAC System Within a Pre-Existing Large Anechoic Chamber
Anechoic chamber performance is largely dependent on the chamber layout and effectiveness of the RF absorbing material. Over time, absorbers begin to degrade and need to be replaced. Also, new health and safety standards, combined with more modern building fire code regulations, can necessitate updates to a chamber's absorber layout. These factors led to the complete restoration of the Canadian Space Agency's largest anechoic chamber, which is located at the David Florida Laboratory in Ottawa, Canada. Ideally, the internal walls and ceiling of an anechoic chamber should be free of intrusions to facilitate the installation of RF absorbers. Unfortunately, because of the chamber's coupled structure to the building, this was not possible and an extensive sprinkler system and large air circulation vents were installed within the chamber. In this paper, their respective impacts on reflectivity performance is studied and novel mitigation techniques are introduced. Based on practical considerations, these techniques were used to conceal the infrastructure of the fire suppression system and HVAC ductwork inside the anechoic chamber; initial measurements appear to indicate their validity. The techniques and lessons learned from this exercise may be applied by others considering a similar endeavor.
Additive Manufactured 3:1 Bandwidth Dual-Polarized Range Antenna
A set of new 3:1 Dual-Polarized Antennas has been developed for use in near-field ranges as the probe or range antenna and for use as a Compact Antenna Test Range (CATR) feed . Key development parameters of the antenna are: a wideband impedance match to the coaxial feed line, E and H-plane 1 dB beam widths in excess of 30 degrees, -30 dB on axis cross-polarization, minimum polarization tilt and a phase center that varies over a small region near the aperture. To accomplish these design parameters, a family of range antennas has been developed and previously introduced . Two versions of the antenna have been manufactured and tested for performance. A 2-6 GHz version has been developed using traditional machining techniques and a 6-18 GHz version has been produced using additive manufacturing (3D printing) techniques. In this paper, we focus on the performance of the 6-18 GHz antenna produced using additive manufacturing. The measured performance of the antenna will be presented and compared to previous simulation. The advantages of additive manufacturing for this type antenna will be discussed. Finally, the applicability of the antenna as a CATR feed and its use in near-field scanning will be discussed.
Antenna measurement system using optical fiber link and vertical articulated robot.
5th generation mobile network will use 28 GHz band and 38 GHz band in Japan. We developed compact type antenna measurement system using optical fiber link and vertical articulated robot for 5G antenna measurement. Our developed optical fiber system consists of 850 nm multi-mode VCSEL (Vertical cavity surface emitting laser diode) and PD-TIA (Photo diode with transimpedance amplifier). Our optical fiber link can use for microwave measurement from 10 MHZ to 30 GHz with 90 dB dynamic range and up to 40 GHz with 70 dB dynamic range. Our using vertical articulated robot has 6-axis 1 m length arm that can hold WR-28 open ended waveguide probe (OEWG).
Measurement Traceability in the CISPR 16-1-6 pattern measurements for CISPR 16-1-4 Site Validations
The publication of CISPR 16-1-6  in 2107 marked a significant change in the CISPR documents, for the first time the consideration of how to perform antenna pattern measurements in and determine the associated estimate of the uncertainty of those measurement. This is a look at that technique and presentation of how that helps and relates to measurement traceability.
Influence of the Phase Uncertainty in Spherical Wave Expansion in the Millimeter-Wave Range
Phase uncertainty in antenna measurements introduces significant errors to the amplitude of the transformed pattern in Spherical Wave Expansion (SWE). To get a better understanding of the impact of phase errors, the measured phase error of a Low Noise Amplifier (LNA) is synthesized as a random phase error and subsequently added to the measured antenna patterns of three different antennas during the SWE. The resulting erroneous patterns are compared with the measured reference patterns and the error magnitude and probability distribution are studied. It is proven that the introduced errors to the transformed far-field patterns can be substantial. Furthermore, the relation between the antenna type and the error level and distribution is elaborated. The error level is different for the three antennas and the error level distribution is dependent on the mode spectra of the antennas.
Measurements of Non-Metallic Targets for the Austin RCS Benchmark Suite
A simulation-supported measurement campaign was conducted to collect monostatic radar cross section (RCS) data as part of a larger effort to establish the Austin RCS Benchmark Suite, a publicly available benchmark suite for quantifying the performance of RCS simulations. In order to demonstrate the impact of materials on RCS simulation and measurement, various mixed-material targets were built and measured. The results are reported for three targets: (i) Solid Resin Almond: an almond-shaped low-loss homogeneous target with the characteristic length of ~10-in. (ii) Open Tail-Coated Almond: the surface of the solid resin almond's tail portion was coated with a highly conductive silver, effectively forming a resin-filled open cavity with metallic walls. (iii) Closed Tail-Coated Almond: the resin almond was manufactured in two pieces, the tail piece was coated completely with silver coating (creating a closed metallic surface), and the two pieces were joined. The measured material properties of the resin are reported; the RCS measurement setup, data collection, and post processing are detailed; and the uncertainty in measured data is quantified with the help of simulations.
GSS (Gated-Short-Short) Calibration for Free-space Material Measurements in millimeter-Wave Frequency Band
Electrical properties of materials are requisite to design electromagnetic (EM) devices and systems. Free-space material measurement method, where the measurands are the free-space scattering parameters of MUT (Material Under Test) located at the middle of transmit (Tx)/receive (Rx) antennas, is suitable for non-destructively testing MUT without prior machining and physical contact in high frequencies. In this paper, GSS (Gated-Short-Short) calibration method using a planar offset short is proposed for calibrating a free-space material measurement system and the measurement result is shown in W-band (75-110 GHz).
Personal Near-field System
In 1987 the author built the world's first Personal Near-field antenna measurement System (PNS). This led to the formation of Nearfield Systems Inc. (NSI) a company that became a major manufacturer of commercial near-field antenna measurement systems. After leaving NSI in 2015 several new personal antenna measurement tools were built including a modern updated PNS. The new PNS consists of a portable XY scanner, a hand held microwave analyzer and a laptop computer running custom software. The PNS was then further generalized into a modular electromagnetic field imaging tool called "Radio Camera". The Radio Camera measures electromagnetic fields as a n-dimensional function of swept independent parameters. The multidimensional data sets are processed with geometric and spectral transformations and then visualized. This paper provides an overview of the new PNS and Radio Camera, discusses operational considerations, and compares it with the technology of the original 1987 PNS. Today it is practical for companies, schools and individuals to build low-cost personal antenna measurement systems that are fully capable of meeting modern industry measurement standards. These systems can be further enhanced to explore and visualize electromagnetic fields in new and interesting ways.
Reduced Aperture Flanged Rectangular Waveguide Probe for Measurement of Conductor Backed Uniaxial Materials
An algorithm is developed for the non-destructive extraction of constitutive parameters from uniaxial anisotropic materials backed by a conductive layer. A method of moments-based approach is used in conjunction with a previously-determined Green function. A dominant-mode analysis is done for rapid comparison of the derived forward model with that of commercially-available software. Finally, laboratory measurements are taken to compare this approach to that of a destructive, high-precision method.
A Review of the Changes and Additions to the Antenna Measurement Standard IEEE Std 149
The IEEE Standard 149, Standard Test Procedures for Antennas, has not been revised since 1979. Over the years the Standard was reaffirmed, that is, its validity was re-established by the IEEE APS Standards Committee, without any changes. Recently however, the IEEE Standards Association stopped the practice of reaffirming standards. This change in policy by the IEEE has been the "medicine" that this Standard needed. A working group was organized and a project authorization request (PAR) was approved by IEEE for the document to be updated. In this paper, the expected changes to the document are described and commented. The main change is to convert the Standard to a recommended practice document. Additionally, some new techniques to measure antennas, such as the use of reverberation chambers for efficiency measurements and more information on compact ranges, is discussed. Other topics inserted are more guidance on indoor ranges and an updated section on instrumentation. Most importantly, a discussion on uncertainty is included. The result will be a very useful document for those designing and evaluating antenna test facilities, and those performing the antenna measurements.
Proposed Changes and Updates on IEEE Std 1128 - Recommended Practice on Absorber Evaluation
The last published version of the IEEE Std 1128 is the 1998 edition. It is titled "Recommended Practice for RF Absorber Evaluation in the Range of 30 MHz to 5 GHz". Over the years, the document has been used widely for absorber evaluations in electromagnetic compatibility (EMC) applications as well as in antenna and microwave measurement applications. Besides the obvious frequency range which needs to be expanded to satisfy today's applications, several areas are in need of an update. The proposed document will change the upper frequency limit to 40 GHz (with provisions in the document to potentially extend above 40 GHz based on test methods). Measurement uncertainties were not discussed in the IEEE Std. 1128-1998. In the new edition, measurement instrumentation and test methods are expected to be updated with guidance on estimating measurement uncertainties. In the proposed document, a section on absorber evaluations for high power applications is planned, and fire properties and test methods will be included.
Robotically Controlled Pattern Measurements of 60 GHz Phased Array Antenna
The characterization of antenna radiation patterns in the millimeter wave band are particularly challenging. This is due to the fact that a misalignment of just a few millimeters between the probe and the antenna can generate substantial measurement errors. This paper describes a strategy to reduce measurement errors by introducing a highly precise measurement system using a 6-axis small robotic arm to characterize the performance of a phased array antenna operating at 60 GHz. The position accuracy of the robotic arm itself is approximately 20 m and a maximum far field distance of approximately 380 mm can be achieved. The robot is programmed to perform a spherical trajectory around the array with stops every 0.5⁰ along the path to gather the measured gain. It operates continuously by communicating with a computer, which triggers the network analyzer at preprogrammed locations. The system is tested initially using two horn antennas as the antenna under test (AUT), and the results are presented.
On the Minimum Range Length for Performing Accurate Direct Far-Field Over-the-Air Measurements
Over-the-air (OTA) performance evaluation requires large investments in anechoic environments. The question of minimizing the test distance is hence critical, and even more in this time where millimeter-wave technologies are about to be largely deployed in 5G devices. A recent publication has identified that direct far-field measurements can be accurately carried out at a much shorter range length than the well-known Fraunhofer distance. This paper introduces a further validation of this reduced distance, by employing an innovative method to simulate spherical measurements with arbitrary DUT, test probes and range lengths. The studies carried out confirm the relevance of this shorter distance, not only for the evaluation of the peak equivalent istropic radiated power (EIRP) or sensitivity (EIS), but also for the total radiated power (TRP) or sensitivity (TIS). In addition, it is demonstrated that the usual assumption that the TRP or TIS measurement is almost independent from the range length is flawed. Two main reasons relating to the test antenna are established which create this dependence: (i) OTA test probes have a finite resolution, and (ii) the probe and instrumentation typically captures the magnitude of two components of the E-field, which are not straightforwardly related to the power density in the near-field.
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