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A method to solve the far-field distance problem is the usage of reflectors in order to transform the spherical wave from the feed antenna into a plane wave which ultimately leads to the same far-field condition but in a more compact way. Therefore, these facilities are called compact antenna test ranges (CATRs). However, the finite size of the reflector(s), despite edge treatment, is the main cause of erroneous signals impinging into the test zone in which an antenna under test (AUT) is characterized. Especially at lower frequencies, every further structure inside the test chamber, although covered with absorbers, is an additional source of scattered signals. One method of correcting stray signals and to improve the AUT measurement accuracy is to compensate the non-ideal test-zone field (TZF) via spherical wave expansion (SWE). For this technique, a complete description of the TZF, i.e. measurements on a closed surface around the test zone, is required. The most convenient approach is to use a spherical scanning surface. In ranges with a roll-over-azimuth positioning system, the spherical scanning can be realized by an additional measurement arm. Using the chamber positioning system, thus, strongly reduces the required additional hardware and makes spherical scanning of the test zone a practical approach. With the knowledge of the incident unwanted field components, AUT measurements carried out in the corresponding test zone are correctable. Spherical near-field measurements of the test zone created by the CATR installed at the Institute of High Frequency Technology, RWTH Aachen University are performed at a frequency of 2.4 GHz using a simple scanning arm. Reliability of the results is ensured by comparing the measurements to full-wave simulations of the CATR. The radiation pattern of a base transceiver station antenna serves as a test case and is subsequently corrected for the erroneous signals using the SWE.
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.
Motivation and background: With the increasing abundance and functionality of wireless communication systems, the requirements for virtual electromagnetic environments like shielded anechoic chambers, and the complexity of the test procedures increase accordingly. The scattering behavior of microwave absorbers is an essential indicator of their quality and suitability for use in such anechoic chambers. Current research activities deal with the revision of the IEEE standard 1128 on recommended practice for absorber characterization and give room for improved test procedures. Objectives and methods: In this paper, the angle-dependent backscattering of microwave absorbers was studied experimentally with respect to their different geometric shapes and material parameters. The dielectric permittivity of pyramidal and flat absorbers was measured between 1 GHz and 10 GHz, followed by systematic monostatic reflectivity measurements. Signal post-processing, including phase-coherent background subtraction and time-domain gating, were applied to minimize unwanted reflections and extract the wanted scattered signals. The radar cross-section (RCS) method was applied to derive the reflectivity with respect to different illumination angles for parallel and perpendicular polarizations. The results were compared to supplier specifications, electromagnetic simulations of the reflectivity, and the scattering pattern of a metal plate. Results and conclusions: The measurement results agree well with the numerical simulations. The data reveal that the reflectivity patterns of microwave absorbers are governed by their geometric shape, while the material properties do not modify the angular dependences qualitatively but result in a quantitative offset. Our findings help to improve the accuracy of monostatic RCS and absorber reflectivity measurements even further and lead to a better understanding of the physical origin of the scattering phenomena of microwave absorbers in general. Future work will extend our studies towards bi-static angle-dependent reflectivity measurements, in order to establish a consistent and comprehensive method for characterizing different types of microwave absorbers with respect to type, frequency, angle of illumination, angle of observation, and polarization. This research has been funded by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) under the grants HE3642/14-1 and BO4990/1-1 (Electromagnetic modeling of microwave absorbers - EMMA).
With the development of the Internet of Things (IoT) technology, the antenna becomes increasingly integrated and miniaturized. Vector Network Analyzer (VNA) is a standard instrument for characterizing antennas. However, IoT devices are small and scattered installed, which makes it costly to carry out in-field characterizing on IoT devices. Integrating an antenna characterizing system into IoT devices can release the difficulty significantly, but characterizing antennas usually requires a high-performance Analog to Digital Conversion system, which is expensive and power-consuming. However, the antennas are not required to be tested frequently, which means this is not a real-time application. Therefore, this paper proposes a method that can realize time-domain reflectometry based VNA with just a comparator or differential receiver. In this system, impulses are sent into the antenna, and the frequency response is captured by analyzing the time-domain reflection. Analog to Probability Conversion (APC), Probability Density Modulation (PDM), and Equivalent time sampling (ETS) concepts are used to reduce the real-time performance requirements of the ADC system, so that the cost and power consumption can be tolerable on a tiny IoT device. With this technology, the antennas could be characterized in-field and remotely, making the maintenance easier. This technology is implemented with Xilinx ZYNQ Ultrascale+ series FPGA. Two antennas are tested, and the experimental results show that the system can successfully measure the radiofrequency. The sampling rate is set to 89.6Ghz, and a micro-volt level voltage resolution is achieved. Since the essence of technology is a trade-off between time and performance, the sampling rate and resolution can be further increased theoretically according to specific applications.
The interest for mm- and sub-mm-wave systems has grown in the last years, mostly driven by communications and radar industries. In particular, the new generations of communications systems, Beyond 5G, put the focus in the use of these higher frequency bands, exploiting the large bandwidth availability to enable the transmission of high data rates. In this context, not only new wideband high-gain antenna concepts are needed, but also advances in the applied antenna measurement procedures. In this work, a D-band lens antenna design with gain larger than 30 dB is presented, which can be applied in point-to-multipoint communication scenarios. The elliptical lens, fabricated in low-cost plastic material, is fed by an aluminium split-block, with an interface to a standard WR-6 waveguide. The antenna covers 42% bandwidth with an aperture efficiency higher than 80%, and radiation efficiency higher than 86%. Wide-band radiation patterns are achieved thanks to a leaky-wave air cavity placed between the waveguide feeder and the lens, which enhances the feeder directivity inside the lens, bringing high illumination efficiency. The lens radiation pattern can be steered by displacing the feeder along the focal plane. The lens radiation patterns and gain have been characterized by means of a 50 cm range length spherical distributed-axis scanner, built in a compact anechoic chamber (absorber tip-to-tip dimension: 0.64 m x 1.25 m x 0.93 m). The elevation arm of the scanner is equipped with a new active dual-polarized probe, with integrated down-converters and diplexers. The introduced technology allows measurements in the 110 to 170 GHz range with a dynamic range better than 65 dB (1 kHz RBW, 0 dBi DUT gain assumptions). The agreement with full-wave simulations is excellent over the whole frequency band for the broadside beam and for a beam steering at 9?. The antenna S-parameters have been as well measured, validating full-wave simulation results. Overall, the design and modelling, manufacturing and measurement accuracy meet the challenging requirements in these high frequency bands.
Advanced driver assistance systems (ADAS), such as blind spot warning and braking assistants, have been in use for years to improve road security. ADAS are currently further promoted through the autonomous driving trend. Due to their cost / performance trade-off, the automotive industry perceives 4-D high-resolution radar sensors, as one of the backbones of autonomous driving. With human safety being at stake, the topic of calibration of these sensors is obviously of the utmost importance. Performing an accurate calibration requires a test condition where the target is in the far-field of the radar under test (RUT). Due to the requirements for angular resolutions, 77 / 79 GHz radars with 15 cm radiation aperture or more are quite common. Applying Fraunhofer formula then results into a necessary measurement range length of 11.5m. Because of the high cost of ownership of an adequate anechoic range, radar manufacturers usually limit their measurements to the strict minimum and try to simplify the calibration process. A typical approach is to go for a diagonal calibration where the target is always at boresight for each beam-formed pattern of the RUT. This technique however delivers a sub-optimal compensation of the RUT biases. In particular, it creates high peak-to-side-lobe ratios (PSLR), where energetic echoes are observable in directions of side lobes of each beam. This paper introduces a new system for radar measurements, made of a short-size focal length offset-fed compact antenna test range (CATR), interfaced with an analog echo generator. With a chamber size of only 0.9 m x 2 m x 1.6 m, the setup has been designed to test apertures up to 30 cm size. The quality of the quiet zone achieved is discussed in the paper, as well as various uncertainty contributions relating to radar measurements. Tests are presented which involve a latest generation 4-D imaging radar on chip (RoC). Results obtained in the CATR are compared to a reference 7 m far-field range. Diagonal and full angular calibrations of the RoC are carried out and analyzed, demonstrating an improvement of 10 dB PSLR when the target is swept over the complete azimuth region.
A near-field scanner has been upgraded, maintaining mechanical hardware more than 65 years old and extending it with suitable computer control to enable an 8.9x1.6m^2 scanplane. Already in 1957 X-band phase accuracies within 3 degrees were reported (ref.1). The facility is computer controlled, with servo's to enable position and polarisation control and a Rohde and Schwartz network analyser in the loop. It is positioned in an area near the main workshop and runs proprietary software for control, acquisition and transformation. An old satellite antenna has been aligned as Antenna Under Test (AUT) and measured near 12 GHz. It was measured before as reported in (ref.2). The antenna is an engineering model of an antenna used on the OTS satellite in mid 80's. It has a few properties which are worthwhile to use for inspection, to enable to get insight into scanner properties and transformation results. Deviation between electrical and mechanical axis, low cross polarisation, orthogonal channels and specific input impedance can be mentioned as points to verify and to control with verification measurements exploiting symmetries and flip-tests, rather than ticking off in an 18-term error budget usually adopted. Direct gain measurements have been established. The probe can be selected, either an open-ended waveguide or a circular waveguide with annular corrugation as probe for instance. It involves related discussion of probe correction. The first results show acceptable information for the facility, with initial comparison to previous results for pattern and absolute gain. It has allowed to survey alignment, assess scanner control properties and assess microwave component properties - with interest into direct gain measurements. A short historical description for the facility (ref.1) and antenna precedes a main discussion of the followed procedures and obtained results for the AUT with related discussion.
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.