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The evolution of cellular communication technologies has been replicated by the automotive industry with modern vehicles being almost universally fitted, as a bare minimum, with a radio system, a cellular communication system and Bluetooth capability. Higher end vehicles have additional capabilities such as WiFi, GNSS, TPMS, smart keyless entry and smart start/stop feature. All these systems are highly integrated as part of the vehicle's infotainment unit and they must operate satisfactorily in a co-existing manner. Automotive wireless testing is currently facing several challenging aspects with one such aspect being MIMO OTA (Multiple-Input-Multiple-Output Over-The-Air) testing of the terrestrial cellular communication system of the vehicle. In this paper, we will examine the current approach for MIMO OTA testing in the 4G and 5G cellular environments and discuss various scenarios on how existing techniques can be adapted to support MIMO OTA testing in the automotive industry. MIMO OTA testing is typically carried out either using conducted testing techniques or using a Multi Probe Anechoic Chamber (MPAC); both these methods have their advantages and limitations and, to a certain extent, a degree of applicability to a very large article under test. This paper covers these two established MIMO OTA testing techniques and considers their applicability to the automotive MIMO OTA testing scene. Following on from this analysis and the challenges exposed herein, additional MIMO OTA test methods are put forward along with an assessment of how well they perform in an automotive test environment.
Internet of things (IoT) has impacted global supply chains in terms of improving performance and increasing productivity. Modern IoT devices such as Radio Frequency Identification (RFID) tags play a pivotal role in packaging surveillance and monitoring of products as it moves along the supply chain. Additionally, recently these tags are equipped with sensing elements that convert the traceability-centric supply chain to value-centric by enhancing visibility of the nature of product as it moves along the supply chain. To utilize the full potential of such IoT technologies, an intelligent network planning is a pre-requisite that ensures good and reliable communication between the RFID tags, the reader, and the cloud. Traditionally, optimal positioning of these RFID devices to obtain a complete coverage is a difficult task that requires careful planning and physical experimentation which involves investing significant time and financial resources. To avoid such limitations, computer aided simulation of positioning the devices allows engineers to explore different scenarios to ensure complete coverage within a given area within a short time frame. The design and coverage planning of various entities of the RFID infrastructure is pivotal in realizing value-centric approach towards supply chain management. In this paper, two different case studies are presented that utilizes a grid-based optimization approach for coverage planning of passive and active RFID tags. For this purpose, first, a high-frequency solver FEKO is used for designing the RFID reader and tag antenna. Second, for the coverage analysis, a wave propagation tool WinProp is used for optimizing the position of the RFID readers and tags. The antennas are designed to operate at a UHF RFID frequency (915 MHz) and a semi-industrial warehouse setting is used for network planning. The details of the design and simulation of the individual entities of the RFID infrastructure along with two different scenarios for coverage analysis of active (battery-powered) RFID tags and passive (battery-less) RFID tags are presented in the paper. These simulations are the first step towards realizing the value-centric supply chain management approach.
Anechoic chambers used for Electromagnetic Compatibility (EMC) measurements above 1 GHz are qualified based on the Site Voltage Standing Wave Ratio (SVSWR) method as per the international standard CISPR 16-1-4. The SVSWR measurements consist of a series of scalar measurements using a dipole-like antenna placed along several linear transmission paths that are located at the edge of the quiet zone (QZ). The measurement process is conceptually similar to measuring VSWR using a slotted line and a moving probe. A full set of tests is time consuming because of the number of positions, antenna heights, polarizations and frequencies that are generally required. To reduce the test burden, the SVSWR method intentionally under-samples the measurement by requiring only 6 measurement points along each 40 cm long linear path to characterize the standing wave. As a result, the test results are generally overly optimistic. At microwave frequencies (note the upper frequency limit is 18 GHz), this under-sampling becomes far more pronounced. In this paper, we explore the effectiveness of using Cylindrical Mode Coefficients (CMC) based frequency domain mode filtering techniques to obtain the VSWR. Here, we place the test antenna on the outer edge of the turntable to obtain a full rotational pattern cut of amplitude and phase data. The antenna is then mathematically translated to the rotation center, whereupon a band-pass filter that tightly encloses the test antenna mode spectrum is applied. The difference between the mode filtered antenna pattern and the original perturbed pattern is attributed to chamber reflections. The measurement is comparatively easy to implement with no special positioning equipment needed. In this paper we present measured results taken from two horizontal polarization measurements (where the antennas were oriented 90 degrees from each other), and one vertical polarization measurement. For an EMC chamber test at a fixed height, an entire measurement campaign reduces to taking three vector pattern cuts. In contrast to the conventional technique, the proposed novel method does not suffer from positional under-sampling, so it is well-placed to be applied at microwave frequencies and above.
In numerical simulation of antenna problems, accuracy of antenna representations is essential to ensure the reliability of results. Integration of measured Near Field (NF) representation of antenna in Computational Electromagnetic (CEM) solvers opens new perspectives to solve this problem. Moreover, it is possible to replace the simulated model of the antenna by a measured model, which represents the real antenna. No additional information about mechanical and/or electrical design of the antenna is required by the numerical solvers. Indeed, the measured NF model in terms of equivalent currents already provides a complete and detailed representation of the antenna itself. The applicability of this approach has been already studied for complex and/or large scenarios, antenna placement, scattering problems and EMC applications. Another interesting use of the combination between measurement and simulation is to enhance the evaluation of the antenna coupling. Previous investigations have been carried out on an H/V polarized array of three identical cavity-backed cross-dipole antennas. In this study only the radiation pattern of the central element of the array was measured (in a stand-alone configuration). Its representation in terms of equivalent currents was integrated in the simulation, for the calculation of the coupling with other elements. For each element two feeding ports, H/V polarization, have been investigated. In particular, measured patterns at five frequency points were used to determine the antenna coupling over the whole frequency band by simulation. A good agreement was found between the measured mutual S parameters on the real array and results obtained by the combination between measurement and simulations. This investigation demonstrated the validity of this approach. In this paper a continuation of the previous study will be performed, exploring the following topics: Enhancement of the representation of the NF source by inclusion of placement boundary condition. Use of measured NF source models to represent another element of the array, not only the central one. The calculation of the antenna coupling will be determined for these new configurations.
Building on the theory of spiral near-field acquisitions, the authors present a novel spiral acquisition implemented in a spherical near-field (SNF) chamber for a large automotive application. This new spiral permits the relaxation of certain restrictions associated with the standard spiral. Specifically, it allows us to eliminate extra or redundant rings beyond the poles, allows for greater control of the angular velocity ratio (i.e. gear ratio) between the theta and phi physical positioning axes, and does not require that the theta axis retrace between acquisitions. In this paper, we describe the new spiral?s motivations, implementation, advantages, and measurement results. We first discuss the new spiral sampling, its mathematical definition, and its comparison to a standard spiral. Next, we describe the practical considerations and implementation of the coordinated motion between theta and phi for spiral sampling over a spherical surface. Next, we present the results showing good pattern agreement between conventional SNF and the new spiral method. We also discuss the reductions in near-field acquisition time and total test time that were achieved using the new spiral.
The Benefield Anechoic Facility (BAF) at Edwards Air Force Base is the world's largest known anechoic chamber. Due to its unmatched size and complement of test equipment, the BAF hosts far-field pattern measurements at all azimuth angles and multiple simultaneous elevations of installed antennas on large aircraft across a frequency range of 0.1 - 18 GHz. Antenna tests at the BAF rapidly produce large quantities of data, which often require immediate analysis to allow system owners to make relevant improvements. Historically, the BAF had accomplished quality assurance manually. Analysis was accomplished post-test by customers and the BAF team. Today, the BAF team has developed scripts that use kernel density estimation and basic machine learning to automatically check incoming data for errors and highlight unusual results for review. During a 2019 test of over sixty installed antennas on a B-1B bomber, the BAF team used these scripts to produce calibrated, quality-assured antenna patterns in near real-time. Rapid processing brings deficiencies to the customer's attention fast enough to allow corrections to be applied and re-tested during the same test event ? highly significant and valuable as aircraft and BAF schedule times are limited and may be a one-time opportunity to gather required data. This paper will explore the algorithm used to evaluate antenna patterns, as well as the expected characteristics of patterns that enable the selection of relevant data. Development and application of this algorithm found that using kernel density estimation to calculate the number of maxima in a pattern's distribution of gain values, then performing this recursively over only the main lobe, can identify problems such as incorrect switching, mismatched transmission lines, and multipath. Algorithm optimization was achieved using generated data, then verified by applying the algorithm to previous test data. For the B-1B, the script searched for data that deviated from an expected pattern with clean main and side lobes, minimal frequency dependency, and a low-power noise distribution at all azimuth angles outside the lobes. Finally, this paper will discuss the results of using this algorithm during a live test, and future improvements and applications for this data processing technique.
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.
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.
Recently, lack of configurable radio environments which requires new signals to be created for data transmission results in increased power consumption has been identified as one of the major challenges in wireless communications. This challenge is argued to be preventing wireless network operators from realizing intelligent, sensing and computing platforms. On the other hand, programmable, frequency-selective surfaces, smart reflectarrays or mirrors, embedding arrays of low-cost antennas or coating surfaces with reconfigurable meta-surfaces are considered to be potential solutions. Highly reconfigurable reflectarrays provide electronic beam steering, as the patch elements can be tuned and modified for real time beam steering. Using tunable materials and lumped components are the most widely used techniques for emerging reconfigurable reflectarrays. Devices using tunable materials such as liquid crystals, ferroelectrics, and graphene have been proposed. The major hurdles in developing highly reconfigurable reflectarrays include keeping reflection losses as low as possible, reflection phase range as wide as possible, and being able to achieve wide beam widths such that all the patch elements can receive the incident signals from distant feeds. We propose an ultra-reconfigurable device based on the insulator-to-metal transition property of VO2. A VO2 layer is placed on a high-density micro-heater matrix consisting of pixels that can be switched on via electronic control. Controlling the pixels in this manner, heat can be transferred to the selected areas of the VO2 layer and convert to highly conductive metallic phase. This technique allows dynamically changing the shape of the reflection antenna surface with high speed. We numerically investigated the heat activated switching and RF reflection characteristics of a reflectarray designed for potential 5G applications operating in 32-86 GHz. It consists of heating pixels with the size of 615 x 615 um which can generate metallic VO2 patches or arbitrary shapes with the same spatial resolution. Our analyses resulted in large phase range of ~360 deg and low loss between -0.13 dB to -0.48 dB. The proposed device can serve as a novel platform for ultra-reconfigurable reflectarrays and metasurfaces for various of RF applications in wide a spectral range.
With growing communications, nowadays there are increasingly sophisticated antenna systems with associated electronics aboard aircrafts. Placement of antennas for various systems is a challenge due to the coupling between the antennas and the resulting co-site interference. Advances in electromagnetic (EM) simulations have significantly improved the design process to assess coupling between various antennas resulting in reduced testing time and costs. While it is ideal to use the actual simulation models of antennas during the design process, system designers normally do not have access to the simulation models (or CAD models) of the antennas for various reasons, such as antenna vendor confidentiality etc. It then becomes essential that actual antenna simulation models to be replaced with accurate representation using equivalent sources, such as near fields, far fields etc. In this paper, antenna coupling, and co-site interference calculations are demonstrated using equivalent antenna with near field sources representation installed on electrically large platform such as a commercial airplane. Advanced hybrid EM solutions using both full wave solvers, such as Method of Moments (MoM) and asymptotic solvers such as Large Element Physical Optics (LE-PO) are used for computationally efficient simulations. In this paper, we present a series of case studies using different configurations of equivalent antenna representations mounted on electrically large platform (aircraft). To illustrate the process, near field patterns are computed for a monocone antenna at 1 GHz. The real antennas are replaced by the equivalent near field sources and the antenna coupling is computed when installed on an electrically large platform. LE-PO method is used for electrically large platform to simulate this model for all the configurations. Equivalent antenna representation coupling results are in good agreement with the S-Parameter values obtained using real antenna mounted on the electrically large platform. A detailed analysis on Out of Band coupling are also performed for all these configurations and will be presented.
Over the years many methods have been developed and used for measuring permittivity and permeability of materials. The most widely used methods are: 1) free-space techniques; 2) cavity perturbation techniques; and 3) transmission line of waveguide methods. Each technique has its own advantages and limitations. The free-space methods are employed when the material is available in a big sheet form. These measurements are less accurate because of unwanted reflections from surrounding objects, difficulty in launching a plane wave in a limited space, and unwanted diffraction from the edges of the sample. The resonant cavity measurement or cavity perturbation techniques are more accurate. Recently "epsilon-near-zero (ENZ) metamaterials have received much attention for several interesting phenomena like super-coupling, transparency and cloaking devices and pattern reshaping at microwave and optical frequencies. The rapid growth and excitement of ENZ materials was due to their ability to achieve very long wavelength in zero permittivity material, allowing propagation in a static-like manner. This paper presents the evaluation of complex dielectric permittivity and magnetic permeability of materials using planar ENZ tunnel structure with substrate integrated waveguide technology. The changes in resonance frequency and quality factor are related to the dielectric permittivity and magnetic permeability properties of the sample through Cavity Perturbation Technique. ENZ tunnel structure has very high sensitivity, which yields more accurate results when compared to other techniques, such as perturbation of conventional cavities. Design, optimization, and simulation of the ENZ tunnel structure at microwave frequencies is presented. Simulations are performed on various dielectric and magnetic samples using the cavity perturbation technique of the ENZ tunnel structure and validated with measured data.
To build a reliable wireless communication for biomedical implant devices, many researches on the implantable antenna design have been performed to satisfy various requirements and constraints such as antenna shape, biocompatibility, miniaturization, and broad operation frequency. In addition to the wireless communication, it is also important to stably transfer wireless power required for the implanted devices to work continuously in a human body because normal battery cannot be a permanent power source inside a human body. For a wireless power transfer system applicable to implantable medical devices, two techniques based on a different theoretical background has been considered: Inductive coupling in near-field region and antenna coupling in far-field region. The inductive coupling is more advantage in terms of low specific absorption rate, but it requires high Q which limits the operation bandwidth. However, the antenna coupling is a critical limitation in transmitting power due to SAR (Specific Absorption Rate) although the antenna is well designed to achieve high power coupling. In this work, inductive coupling based WPT system is designed inside the implanted antenna not to require additional space and thickness. The implanted antenna is designed with a rectangular shaped PIFA (Planar Inverted F Antenna) using the medical implant communication service (MICS) band (402-405MHz) recommended by the Federal Communications Commission (FCC). Also, the WPT system is designed to operate at the industrial scientific medical (ISM) band, 13.56MHz, to easily implement a resonant coil with high ??-factor. Furthermore, the mutual effects between the WPT coil and the antenna are studied in terms of impedance, efficiencies, and SAR. Finally, the fact that how much maximum power can be delivered from the outside to the designed WPT system indicates that magnetic coupling is more promising than the antenna coupling for implantable medical devices.
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.
The 18-term NIST error model is a common tool for analyzing potential sources of error in antenna measurements. One of the error terms to be considered describes the phase errors occurring in a measurement system. However, this quantity plays a rather negligible role for conventional ranges, such as roll-over-azimuth positioning systems. In particular, the contribution caused by flexing cables is normally insignificant. This results from the fixed installation of the cables or the decoupling of the movement at important points using rotary joints. Current developments in the field of antenna measurement technology focus, among other things, on performing measurements using industrial robot arms. These are characterized by their high flexibility regarding the various measurement sequences, such as planar, cylindrical or spherical measurements. However, it is to be expected that the high freedom of positioning possibilities will introduce additional phase uncertainties, since the RF cables in the cable carrier chain of the robot arm itself are often not decoupled. Instead, a single cable is used for each signal path, which follows the movements of the robot. The robot-based measurement system at the Institute of High Frequency Technology at RWTH Aachen University has been designed for frequencies above 60 GHz, where phase stability is a challenging task. Depending on the setup, it may even be required to pass Intermediate Frequency (IF) signals on the same cable as the Local Oscillator (LO) signals. This results in different test cases for the phase deviations depending on the frequency range of the IF (279 MHz) and LO (typically 10 GHz to 18 GHz) signals. Additional factors such as the measurement path of the robot or the position of the linear axis must also be taken into account. Therefore, a thorough analysis of the phase uncertainties caused due to flexing cables is of outstanding importance for robot-based measurement systems.
There have been a number of numerical analyses of RF absorber presented in the literature. These analyses, however, tend to focus on the reflectivity of the material and not on the radar cross section (RCS) that it presents. Brumley studied the RCS of RF absorbers for the purpose of estimating the background RCS of anechoic ranges [1]. The study was done empirically; obtaining measurements of the RF absorber and looking at the RCS of different pyramids and wedges, with and without paint. Brumley presents some potential methods to improving the RCS signature of the range, thus reducing the background RCS of the site. In this paper, the suggestions presented by Brumley are revisited. Specifically, his recommendation for the twisted pyramid configuration which he was unable to measure due to the lack of absorber samples available for use in the test. In addition to the twisted pyramid, Brumley's approach of inserting smaller pyramids in the valleys of a larger pyramidal arrangement to reduce the edges parallel to the incoming wave are also presented. Different carbon loadings are modeled for the inserted pyramids. One is the standard loading of the inserted pyramid, and the other is the same loading as the main larger pyramidal arrangement such that all the absorber on the wall has the same material properties. Numerical studies are performed using time domain techniques as well as frequency domain techniques. The model is validated by comparing the RCS of a flat square plate with the theoretical solution. The results validate the data and the suggestions presented in [1] and present ways of improving some of the solutions by adjusting the material properties of the absorber.
Financial impacts often drive decisions to repurpose existing ranges instead of procuring new measurement facilities. These existing ranges have fixed geometries (height, width and length) that were set when the range was originally constructed and often are designed for a different purpose. The inability to set the geometry precludes the range designer from using the range geometry to improve measurement performance. Thus, the performance of the range is mostly dependent on the RF absorber and the range antenna directivity. In rectangular-shaped ranges for example, the lateral surfaces, side walls, ceiling and floor, are the critical surfaces to address in RF absorber arrangement. In this paper, numerical analyses of Chebyshev arrangements as well as dragon tail or tilted absorber are studied. This paper also analyzes the performance of Chebyshev absorber for normal incidence and for oblique incidence along with the proper arrangement of the Chebyshev period. While certainly these have been discussed previously in the literature, this paper consolidates the previous information and illustrates it with numerical examples to help the reader understand the best approach to use when repurposing a range.
One of the main disadvantages of Spherical Near-Field (SNF) measurements is their acquisition time. This is due to the need of sampling a whole sphere around the Antenna Under Test (AUT) to perform the Near-Field-to-Far-Field Transformation (NFFFT). A step of the NFFFT is to decompose the measured signal in each one of the spherical waves it consists of, thus retrieving the Spherical Mode Coefficients (SMCs) associated to the AUT. Under typical measurement conditions, the SMCs of most physical AUTs prove sparse, i.e., most of their terms are zero or neglectable. Using this assumption, the system of linear equations with the SMCs as variables can be solved with fewer equations, that is, fewer measurement samples. This is done by applying an l1-minimization solver, following classical methodology from the field of compressed sensing. However, the location of the measurement points that generate non-redundant equations is not trivial. In typical compressed-sensing applications, a random sampling matrix is taken. Since a random matrix is inefficient for the acquisition with mechanical roll-over-azimuth positioner systems, a recent approach is to take an equidistant distribution of points on elevation and to calculate their corresponding pair on azimuth that delivers the minimum coherence of the sampling matrix. However, the number of sampling points M required for a successful reconstruction depends on the sparsity level of the SMCs of the unknown AUT, making its choice critical and based on a pessimistic approach. A method for the adaptive choice of M is suggested. After the acquisition of a starting set of M_0 measurement points, chosen using phase transition diagrams, the SMCs are estimated online with few iterations of an l1-minimization algorithm. Afterwards, further points are acquired, and the SMCs are estimated again using them. Following the evolution and the decrease of the variation between estimates, it is possible to truncate the measurement at a point where a successful reconstruction is guaranteed. The method for the construction of a minimum-coherent sampling matrix for adaptive acquisition and the truncation criteria for a specific accuracy are discussed with a focus onimplementation, and supported with numerical experiments, performed with measurementdata.
The electrical alignment of the positioner of the Antenna Under Test (AUT) is an important issue to be accounted for before any antenna measurement can take place in a spherical near-field measurement facility. This is because the spherical transmission formula requires the AUT to be scanned on the surface of a sphere. Typically, the tower has been aligned by optical means but, usually, it is necessary to translate it along some axis to place the AUT in the center of the measurement sphere. Furthermore, mounting the AUT can alter the alignment due to its gravitational load. Therefore, alignment of the tower after mounting the AUT is a critical step, which is accomplished with the so-called flip tests [1]. These flip tests, which can detect only the axis intersection and zero-? errors of a roll over azimuth system, have been discussed in the past, for example [1-2], but not as extensively as their importance would require. Moreover, there were no analytical proofs provided for the error formulas given, which forces the interested researcher to derive them again in order to comprehend them and adapt them to his measurement facility. This paper starts with a concise and thorough presentation of how the flip-tests are performed in practice, as well as their theoretical justification. In the second part, the paper presents a novel idea regarding the interdependence of the alignment errors. It has been observed experimentally that two linear coupled equations can model their behavior. Consequently, they can be fully corrected simultaneously with only two flip-tests, without the need of correcting each one in small steps. Simulation tests were performed validating these results. Finally, the paper concludes with addressing a few miscellaneous issues that are inevitably risen by the nature of this procedure, such as the effect of the antenna gain, the positioning of the probe and the distance between the AUT and the probe.
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.
While the use of antennas in automobiles was earlier confined to AM and FM radio, most vehicles that we see today employ antennas additionally for satellite navigation, remote keyless entry etc. More number of antennas are likely to be needed in the future in vehicles for the purposes of internet and video browsing, collision avoidance radar systems, and for communication either between vehicles or between vehicles and infrastructure. Over the years, many planar monopole antennas that utilized patch slotting techniques have provided the desired multiband operation. But the choice of shape, size and position of slots in most of these works has been experimental and no generalized approach has been adopted. Fractal antennas, more particularly, those using the self-similar Sierpinski gasket geometries facilitate log periodic multiband behaviour. Although, the planar monopole configuration of this antenna geometry can be more useful candidate for most automotive applications, it has been found that the impedance mismatch at design frequency is a common problem in these antennas. We demonstrate a simple solution to this problem by considering an example of a third iterated gasket antenna of height 100 mm that has a geometric scale factor of 0.5. When the substrate of this antenna is loaded with a combination of SRR and strip wire on its rear side, a negative time delay gets added to the wave travelling inside the medium which results into the miniaturization of antenna. The CST MWS simulations clearly indicate this effect through the reduction of initial frequency resonances of 0.464 GHz, 1.568 GHz, 3.336 GHz and 6.2 GHz to 0.456 GHz, 1.312 GHz, 2.576 GHz and 5.032 GHz. The implementation of SRR-strip wire combination as a NFRP element in the antenna structure provided the impedance match at the reduced set of frequencies which is reflected in terms of improved return loss The loaded antenna structure provided gains of 2.44 dB, 4.74 dB, 5.7 dB and 6.2 dB respectively at the corresponding multiband frequencies. Based on such performance, the DNG-MTM loaded planar gasket monopole antennas of different heights can be expected to replace other planar monopole antennas for multiband automotive applications.