AMTA Paper Archive


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A Three-axis Shielded Loop Probe for the Experimental Characterization of Vehicular Wireless Power Transfer Systems
James McLean, James Wooten, Robert Sutton, October 2024

The experimental characterization of vehicular wireless power transfer (WPT) systems, requires the measurement of all three components of the near magnetic field. The in-situ characterization of dynamic WPT systems requires the near-simultaneous measurement of these quantities. A WPT system can produce an intense near electric field and hence substantial electric field rejection is required of the magnetic field probes. A conventional shielded loop can provide this rejection, but co-locating three such loops with orthogonal axes presents several challenges. Here such a three-axis shielded loop is presented along with a detailed analysis of the isolation between the component loops and the electric field rejection. Discussion of the use of the probe in dynamic WPT characterization is provided.

Over-the-Air Performance Evaluation of NB-IoT over Non-Terrestrial Networks
Jun Luo, Edwin Mendivil, Michael Christopher, Laura Burris, Dayan Gao, October 2024

In this paper, the Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS) of Narrowband Internet of Things (NB-IoT) over Non-Terrestrial Networks (NTN) in the Anechoic Chamber (AC) are investigated. The following contributions are presented. Firstly, for the first time based on authors' best knowledge, this paper presents the Over-the-Air (OTA) TRP/TIS performance of NB-IoT NTN in the AC. Secondly, detailed analysis including test repeatability, measurement uncertainty, and test time etc. are given as well. The early exit algorithm for NB-IoT TIS based on Chi-Square distribution is investigated, and significant improvements have been found from the test results. Thirdly, various key NB-IoT NTN specific parameters, such as Round-Trip Time (RTT), Doppler shift, signal fading, and others have been discussed too. For TIS, we use 2 different RTT configurations (0 ms and 255 ms) to perform the tests, and give the corresponding analysis. Finally, some suggestions are being proposed for the future test methodology developing.

Compact Homodyne Extrapolation System (CHEXS)
Joshua Gordon, Ben Moser, October 2024

We present on a novel gain extrapolation antenna range, the Compact Homodyne Extrapolation System (CHEXS), that can achieve absolute antenna gain measurements with uncertainties of +/-0.1 dB or better with as few at 10 data points and is significantly more compact, up to six times shorter than conventional gain extrapolation ranges. This compact gain extrapolation range achieves these beneficial attributes by measuring the homodyne signal that occurs naturally between two directional antennas that often exhibit strong third order mutual coupling at close proximity. The design and operation of the CHEXS is presented along with gain measurements of NIST reference standard gain antennas which are shown to be equivalent to those obtained using a conventional gain extrapolation range.

Low Cost, Wide Range Smart Cloth Tracking and Localization System
Jake Connolly, Angel Abreu, Matt Koeing, Nathan Stephenson, Mahrukh Khan, October 2024

This paper presents a tracking and localization system for passive RFID tags. The localization and tracking system comprise a rotatable RFID reader and sixteen fixed passive tags spread around the room. By strategically positioning passive tags, we demonstrate the possibility of tracking and localizing any passive RFID tag that enters the system. The localization algorithm represents each tag as an x and y coordinate, with the reader representing the origin. The algorithm runs every 0.5 seconds to update all tag locations. The algorithm uses the distance that the passive tag is from the reader and the angle from the positive x-axis the tag lies on to locate the passive RFID tag. The algorithm finds distance using the RSSI (Received Signal Strength Indicator) value and the tag's angle by taking the active tags' average position in that region. This system is helpful for localization and tracking applications. In environments like warehouses or large outdoor areas, where it's crucial to track items or individuals across a vast space.

Sub-6 5G Dual-Port 16 Element Patch Antenna Array Designed and Built with The Brick-Based Antenna Design Methodology
UmutBulus, October 2021

The brick-based antenna design is a new concept to the literature. Metals and dielectrics are in brick-form to let the antenna designers connect and disconnect the cells easily. Designing and prototyping an antenna takes only a few minutes with this concept. Antenna engineers directly build their design in front of a network analyzer and iterate to reach their requirements. This hardware-based antenna design solution also creates a design cycle of measure-iterate instead of simulate­iterate. This study starts with introducing this new method and continues with a dual-port 3.5 GHz patch antenna design and measurement. After the single antenna reaches the target frequencies, the 16 element 4x4 planar patch antenna array is built and measured.

Standard Definitions of Terms for Antennas and Radio Wave Propagation
Vikass Monebhurrun, October 2019

The standard definitions of terms for antennas and radio wave propagation are provided in IEEE Std. 145-2013 and IEEE Std. 211-2018, respectively. These documents define the accepted and harmonized terminology used in the fields of antennas and propagation. Arbitrary use and misuse of fundamental terms are still observed in technical papers and presentations at conferences.

Measurement of RF Absorber at Large Angles of Incidence using Spectral Domain Transformations
Vince Rodriguez, Brett Walkenhorst, Jorgen Bruun, October 2019

Pyramidal RF absorber, widely used in indoor antenna ranges, is designed to minimize reflectivity by creating an impedance transform from free space to the impedance of the absorber material. The pyramidal shape provides this transition quite well at normal incidence. It has been shown in [1] that pyramidal RF absorber performs very well up to angles of incidence of about 45 degrees off-normal, but at wider angles of incidence, the performance degrades significantly. Unfortunately, it is very difficult to perform RF absorber measurements at large oblique incidence angles. In such measurements, the reflected path and the direct path between the antennas are very close in length, making it difficult to use time-domain gating techniques to eliminate the direct coupling. In this paper, a novel approach for performing oblique RF absorber measurements is introduced based on spectral domain transformations. Preliminary measurements using this technique have been compared to RF simulations. Results appear to indicate that this approach is a valid way to perform RF absorber reflectivity measurements at highly oblique incidence angles.

GSS (Gated-Short-Short) Calibration for Free-space Material Measurements in millimeter-Wave Frequency Band
Jin-Seob Kang, Jeong-Hwan Kim, October 2019

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).

Topology for Maintaining Symmetry in Hybrid LPDA-Broadband-Dipole Antennas
James Mclean, October 2019

Topologies for hybrid LPDA-broadband-dipole antennas (hybrid antennas) are systematically presented and evaluated regarding their ability to provide symmetric response as defined and required in recent standards. The symmetry property of the hybrid antenna is fundamentally related to the intrinsic infinite balun, the choke structure, and the matching transformer for the broadband dipole, if one is employed. In general, hybrid antennas incorporating matching transformers are more symmetric if the transformer is effectively center-tapped. More specifically, in a hybrid antenna employing an impedance matching transformer derived from an equal-delay hybrid, the sum port can be advantageously connected via a low-impedance load to the center of a symmetric choke arrangement. A specific topology for a hybrid LPDA-broadband-dipole antenna is given here which employs a 1:4 impedance transforming balun between the LPDA and broadband dipole but at the same time provides symmetry such that the antenna satisfies the requirements given in recent standards. Thus, the advantages of the impedance transforming balun are realized, but the symmetry of the antenna is maintained. Finally, it is shown that a hybrid antenna satisfies the symmetry requirements if a 180 • rotation about the bore sight axis is equivalent to a 180 • electrical phase shift in the source and that this behavior is obtained with a combination of 2-fold rotational symmetry in the radiating structure and electrical symmetry in the intrinsic balun structure.

A Review of the CW-Ambient Technique for Measuring G/T in a Planar Near-Field Antenna Range
Ryan T Cutshall, Brett T Walkenhorst, Justin Dobbins, Jacob Freking, Bruce Williams, October 2019

Techniques for measuring G/T have been previously presented at AMTA; however, there are very few papers that discuss how to measure G/T in a near-field antenna range. One recent paper discussed such a method and gave a brief description within the larger context of satellite payload testing [1]. The paper's treatment of G/T was necessarily brief and gives rise to several questions in relation to the proposed method. Other papers that treated this topic required the antenna aperture to be separable from the back-end electronics, which may not be possible in all cases [2-3]. In this paper, we discuss in great detail a slightly modified version of the G/T measurement method presented in [1]. A signal and noise power diagram is presented that can be useful for understanding how system signal-to-noise ratio (SNR) relates to G/T, and a few common misconceptions concerning the topic of G/T are addressed. The CW-Ambient technique for computing G/T of a Unit Under Test (UUT) from measurements in a planar near-field system is described in detail, and a list of assumptions inherent to the CW-Ambient technique is presented. Finally, the validity of the CW-Ambient technique is assessed by analyzing measured data collected from a separable UUT.

Experimental Verification of 3D Metal Printed Dual Circular-Polarized Horn Antenna at V-Band
Ningning Luo, Ghanshyam Mishra, Satish K Sharma, Xinhua Yu, October 2019

In this paper, a 3D metal printed dual circular-polarized horn antenna operating in the V-band is proposed, built and tested. This antenna consists of a horn and a circular waveguide, a single groove polarizer and is side-fed by orthogonally placed rectangular waveguide ports. The groove is placed at 45° with respect to the input ports and provides a phase delay of 90° to generate right-or left-hand circular polarization (RHCP or LHCP). The proposed antenna provides symmetric patterns for all planes and exhibits polarization isolation of more than 30 dB at broadside. This antenna is analyzed to realize wide impedance matching bandwidth and wide 3dB axial ratio (AR) bandwidth. A prototype of the horn antenna has been fabricated using 3D metal printing technology. Metal material with finite surface roughness is considered when modeling this antenna.

Feasibility of Coaxial Resonators for Permittivity Measurements of Pressurized Gases
Jose Oliverio Alvarez, October 2019

This paper investigates numerically the feasibility of using quarter wavelength coaxial resonators for permittivity measurements of pressurized gases, as found in the subsurface. The non-short-circuited end of the resonator is facing the inside of a pressure cell and is filled with pressure resistant, low-loss dielectric material. Results show that as pressure increases, the corresponding increase in dielectric constant can be detected through a shift in the resonant frequency of |S11| and confirmed by a change in the phase of S11.

Extraction of Magneto-Dielectric Properties from Metal-Backed Free-Space Reflectivity
R D Geryak, J W Schultz, October 2019

Intrinsic magnetic and dielectric properties of magneto-dielectric composites are typically determined at microwave frequencies with both transmission and reflection data. An iterative method, such as root-finding, is often used to extract the properties in a frequency-by-frequency basis. In some situations, materials may be manufactured on a metal substrate that prevents transmission data from being obtained. This happens when the materials are too fragile or too strongly bonded to the substrate for removal and must be characterized with the metal substrate in place. This paper compares two different free-space extraction algorithms, developed for the simultaneous extraction of complex permittivity and permeability from metal-backed reflection. One of the algorithms relies on reflection measurements of the same material with two known thicknesses. The second method takes advantage of wide bandwidth measurements to fit the reflection to analytical models (e.g. Debye). The accuracy of these methods are evaluated and the stability criteria for the techniques will be discussed, as well as the tolerance of the techniques to various measurement errors.

Top-loaded 60:1 Wideband Direction-Finding Sensor
Amy Robinson, Gregor Lasser, October 2019

A wideband, four element array is designed to create suitable radiation patterns for angle of arrival estimation over a field of view of 0 • to 80 • in elevation and 360 • in azimuth, using the Cramer-Rao Lower Bound (CRLB) as the figure of merit. The antenna elements are truncated monocones over a circular ground plane and operate over 100 MHz to 6 GHz. A study of the antenna geometry was performed to meet size constraints while minimizing the reflection losses at the input for frequencies up to 1 GHz. A method is presented to find the ideal loading impedance required for each frequency using multiport S-parameters derived from field simulations. The loading improves the maximum return loss from 0.4 dB to 6 dB. The study reveals a trade-off between minimal reflection losses and direction finding (DF) performance evaluated using the CRLB over the operating frequency. For the best investigated geometry using top loading the maximum root mean square error of the azimuth DF estimate remains below 13 • .

Waveguide-integrated Rydberg Atom-based RF Field Detector for Near-field Antenna Measurements
Matthew T Simons, Abdulaziz H Haddab, Joshua A Gordon, Christopher L Holloway, October 2019

We demonstrate simultaneous amplitude and phase measurements of a radio-frequency (RF) field through the use of a Rydberg atom-based sensor embedded inside a waveguiding structure. This measurement uses the Rydberg atom-based sensor in a mixer configuration, which requires the presence of a local oscillator (LO) RF field. The waveguiding structure supplies the LO field. The combined waveguide and Rydberg atom system is used to measure phase and amplitude in the near-field of a horn antenna to extract the far-field pattern.

A Review of the Changes and Additions to the Antenna Measurement Standard IEEE Std 149
Vince Rodriguez, Jeff Fordham, Lars Foged, October 2019

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
Zhong Chen, Vince Rodriguez, October 2019

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.

Small Antenna Testing in a Compact Antenna Test Range
S F Gregson, C G Parini, S Pivnenko, October 2019

The Compact Antenna Test Range (CATR) was initially conceived as an efficient way of testing electrically large antennas at very much reduced, fixed, range lengths than would otherwise be the case. However, when testing lower gain, physically smaller antennas, the measurements can become susceptible to inhomogeneities within the CATR QZ including phenomena associated with edge diffraction effects, feed spill-over, chamber multipath etc. Whilst it has been demonstrated experimentally that many of these measurement artefacts may be effectively mitigated using standard and modern more sophisticated post-processing techniques. This paper supports those findings through simulation of the direct and indirect far field ranges and by careful examination of the data processing chain. Results are presented, the relative success of the various techniques examined and the utility of this is set, and expounded, in the context of modern, i.e. 5G, communications systems.

Validation of Electromagnetic Compatibility Chambers with a Spherical Wave Expansion Approach
Cosme Culotta-López, Zhong Chen, Thomas M Gemmer, Dirk Heberling, October 2019

Electromagnetic Compatibility (EMC) radiated emissions measurements above 1 GHz are performed in a nominal free space environment as required by international standards, typically in an anechoic chamber. In an EMC chamber, the test zone consists of a circular region defined by a turn table, where an equipment under test is rotated and measured. The test zone is commonly referred to as quiet zone (QZ). Due to the non-ideal nature of absorbers, multiple reflections in the chamber affect the quality of the QZ. The constructive and destructive interferences from the reflections form standing waves in the QZ. The maximum value of the standing wave is used as the figure of merit for validation of testing facilities. Site Voltage Standing Wave Ratio (sVSWR) as specified in CISPR 16-1-4 is broadly used for the validation of test sites above 1 GHz. This method requires the measurement of six positions along a linear 40 cm transmission path at various locations in the QZ, with a frequency step of no greater than 50 MHz using an omnidirectional-like antenna (e.g. a dipole). Concerns have been raised that this method delivers an overly optimistic result due to both spatial and frequency domain undersampling. In this work, an alternative method to sVSWR for the validation of EMC chambers based on Spherical Mode Coefficients (SMC) is proposed. Two 90 •-rotated measurement cuts of an omnidirectional-like antenna are acquired around the periphery of the circular QZ. The measured situation and cut is replicated by applying translation and rotation of spherical waves to the known SMCs of the used omnidirectional-like antenna and transforming using the spherical wave expansion. The generated and measured cut are compared and the characteristics of the chamber are extracted. The major advantage of this method is the relatively high measurement speed and reliability.

Non-contact Characterization of Antenna Impedance, Gain and Pattern through Open-Fixture Network Calibration
Seckin Sahin, Niru K Nahar, Kubilay Sertel, October 2019

We present a novel, non-contact characterization technique for simultaneous characterization of conventional antenna parameters, including the antenna port input impedance, antenna gain and its radiation pattern, without requiring a network analyzer connection to the antenna port. The test antenna and the network analyzer are considered as a 2-port open-air fixture whose network representation corresponds to the desired antenna parameters. The unknown network parameters of the 2-port open-air fixture are determined via a novel calibration process using 4 offset-short termination standards. The error parameters determined by the calibration are then related to the test antenna port impedance and its gain as a function of frequency. Furthermore, the radiation pattern of the test antenna can also be characterized using measured reflection coefficient at the network analyzer port for two offset-short terminations of the test antenna port, while rotating the test antenna over the desired angular range. This novel technique is particularly attractive for installed-antenna applications where an active connection to the test antenna port is either difficult or undesirable, such as on-chip antennas and implanted antennas, to name a few. To demonstrate the efficacy our new method, we present the measured impedance, gain and radiation pattern of a diagonal-horn antenna operating over 360-450 GHz, and a lens-integrated planar butterfly antenna for the 220-325GHz band.







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