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Diagnostic techniques are crucial in antenna development and testing to enhance the Device Under Test (DUT) performances and identify the cause of possible failures in the qualification process. Among different approaches [1]-[8], it has been demonstrated that the equivalent currents method (EQC) [8]-[9], implemented in [10], is one of the most efficient for investigations in various application areas [11]-[13]. Indeed, the generality of the 3D reconstruction surface enclosing the DUT is a key feature, it ensures that this technique is unique and highly suitable for diagnostics, respect to traditional methods based on plane wave expansion. To handle electrically large problems, the EQC method has been initially based on a Fast Multipole Method (FMM) [14]. The recent advent of 5G technologies has led to an increasing need in terms of antenna electrical dimensions. Therefore, a novel technique based on a Nested Skeletonization Scheme (NSS) has been implemented to guarantee a further reduction of memory requirements and computational time. The new capability has been demonstrated in the past for a patch array antenna [15]. In this paper, the diagnostic capabilities of the EQC approach are applied to an early prototype of an electrically large array antenna for 5G antenna measurements applications [16].
Robot-based measurement systems typically have a larger tolerance with respect to their positioning accuracy than conventional systems, e.g. roll-over-azimuth positioners. However, for spherical near-field measurements, the positioning accuracy of the probe is an important uncertainty in the required near-field-to-far-field transformation. One way to account for those non-idealities is to use the higher-order pointwise probe correction (PPC). It allows to consider the actual position and orientation of the probe by additional rotations and translations of the probe receive coefficients. To evaluate the PPC, the occurring position tolerances and the differences in the transformed farfield patterns of a standard gain horn are investigated at 60GHz. Using an onset measurement as reference, it is shown that the PPC provides improvements of 41dB and 65dB for the co- and cross-polarized measurements, respectively. In addition, an offset measurement is shown where the measurement sphere is shifted relatively to the AUT. The pointwise implementation of the correction method allows to reproduce the far-field pattern without additional measurement points, while the transformation without PPC fails. Thus, the implementation of the PPC not only enables the processing of irregular sampling grids, but also increases the measurement accuracy by including the actual position and orientation of the probp>
Antenna measurement Intercomparison Campaigns represent a successful activity within the working group on antenna measurement of the European Association on Antennas and Propagation [1] since the group foundation in 2005. These campaigns, constitute an important resource for participating facilities to demonstrate their measurement proficiency, useful internally but also towards obtaining or maintaining official accreditations. In this paper we present the completion of a campaign involving a high gain X/Ku/Ka-band reflector, MVG SR40 fed by an MVG SH4000 Dual Ridge Horn. Preliminary results were shown in [2]. Results from seven facilities are compared through plots of gain/directivity patterns. The data is used to generate reference patterns and establish accurate gain performance data based on the uncertainty estimates provided by each facility. Statistical analysis of the measured data such as Equivalent Noise Level and Birge ratio of each measurement with respect to the established reference will also be shown.
Near-field far-field transformations (NFFFTs) are usually performed for time-harmonic fields. In cases where insitu antenna measurements are required and the antenna under test (AUT) is not accessible for specifically tailored test signals, the need for handling time-modulated fields arises. The shorttime measurement (STM) approach offers a way to deal with continuously modulated fields while a time-harmonic NFFFT can be employed. We present results of numerical simulations to demonstrate and characterize the STM approach for the case of a cylindrical measurement geometry as found in UAV-based antenna measurements. We further derive guidelines from the simulation results that describe the applicability of the STM for different measurement situations.
Earlier works have shown the benefits of imaging stray signals in a range with planar-scanner data. This paper discusses some additional tools that can be employed for stray-signal identification. Related range diagnostics are presented that employ Fourier spectral and holographic processing of 1D linear scans through the quiet zone. For the special case of a compact range, the interpretation of arrival angles from the paraboloidal reflector surface is explored. Measured data from multiple facilities are presented that were used to locate, quantify, and remedy the unwanted signals.
Full Probe Compensation (PC) techniques for Spherical Near Field (SNF) antenna measurements have recently been proposed and validated with success [1]-[4]. Such techniques allow the use of antennas with more than a decade of bandwidth as near field probes in most systems. The clear advantage is that multi-service/frequency measurements campaigns can be performed dramatically reducing the number of probes hence decreasing the downtime between two measurements. This is a highly desirable feature for modern antenna measurement applications such as automotive. The use of a dual-polarized probes further improves the measurement efficiency as two orthogonal field components are measured at the same time. The possible differences between the pattern radiated by the two ports of the probe should sometimes be considered to keep the overall measurement accuracy. The full PC technique objective of this paper accounts for generic dual-polarized probes and is validated for the first time. For this purpose, measurements of three monocone antennas from 450 to 6000 MHz performed with only one wideband (15:1) dual-polarized probe will be considered.
This paper presents antenna design and packaging consideration for near field communication (NFC) system that is being used in automotive security systems, and, more specifically, to an NFC reader for obtaining access to, and controlling activation of, a transportation vehicle such as a motor vehicle. Various important studies for automotive applications were performed in this work such as a magnetic wall method. This magnetic wall method can prevent the reduction in NFC reading range caused by proximity to body sheet metal. It provides a unique and superior magnetic shielding effect as compared to ferrite sheets because it is not temperature dependent and can be implemented with minimal cost and complexity. The proposed design can be easily fabricated on the back face of the NFC reader antenna PCB using conventional PCB techniques.
Owing to the increasing interest in high frequencies, as the millimeter wave range, wherein accurate phase measurements are increasingly difficult and expensive, phaseless near-field techniques are prime candidates for antenna characterization. In this paper, an experimental validation of a phaseless near-fieldfar- field (NF-FF) transformation with plane-polar scanning for antenna characterization is presented. A proper representation of problem unknowns and data, using the available information on the antenna under test (AUT) and on the scanning geometry, is adopted in order to improve the reliability and the accuracy of the proposed characterization algorithm. By exploiting the nonredundant sampling representations of electromagnetic fields and by using an oblate spheroid to model the AUT, a remarkable reduction (about 90%) of the required NF samples is achieved. Experimental results on data acquired at the University of Salerno Antenna Characterization Lab are reported to validate experimentally the effectiveness of the proposed characterization technique.
Cellular LTE MIMO downlink performance, for 4x4, 4x2, and 2x2 LTE MIMO architectures, in terms of average data throughput and availability, were investigated in an urban canyon environment of Frankfurt, Germany at 2110 MHz on a Sport Utility Vehicle (SUV) with metal and glass roofs for a virtual route. This study utilized the following measured antenna radiation patterns for total polarization on the SUV at 2110 MHz for the mobile station: 1) roof-mounted antenna on metal roof; 2) roof-mounted antenna on glass roof; 3) interior-mounted planarinverted F antenna; and 4) interior-mounted planar-inverted F antenna rotated 90 degrees. This research was carried out using a three-dimensional simulation software suite that enabled users to simulate electromagnetic wave propagation and wireless network planning. The following observations were obtained from this research. First, the MIMO architectures for the SUV with metal roof exhibited approximately 5% higher average data throughput levels compared to the same MIMO architectures on the SUV with glass roof. Second, the throughput availability for the 4x4 and 4x2 MIMO systems were comparable. Lastly, the average throughput for the 4x4 MIMO system was higher than the 4x2 and 2x2 MIMO systems for the SUV regardless of roof material.
The conventional method for comparing the performance of antenna-receiver systems is the classical G/T metric. The G/T metric is the ratio of antenna-circuitgainrelative to the thermal noise temperature evaluated at the input of the low noise amplifier; the thermal noise at the input to the LNA consists of the received sky noise, the LNA's effective input noise temperature, and post LNA noise referenced to the LNA's input. While this has been a standard for many years, it will be shown that G/T does an incomplete job of describing the performance under all conditions. The noise figure metric was developed as a characteristic describing signal-to-noise degradation to be applied to circuit based input/output topologies, and cannot easily be applied to hybrid systems such as an antenna-receiver system in which the input power is described by spatial field density levels, and the output power is stated in terms of a circuit-based voltage-current environment. This paper presents a noise figure metric which has been expanded to include systems that are a hybrid of wave and circuit characteristics such as the marriage of an antenna and receiver. It will also be shown that whereas a system's noise figure is dependent upon a chosen noise reference temperature, the intrinsic Effective Input Noise Temperature of the system is an invariant that does not change when a different reference temperature is selected. It will also be shown that, in contrast to G/T, the effective input noise temperature of an antenna/receiver system will accurately predict the system's output SNR for all values of system input SNR. It will be shown in detail, how to measure the antenna/receiver system's Effective Input Noise Temperature (TE), resulting in the following equation: TE = (TD1 - Y£ TD2 )/(Y - 1) Where: TD1 , and TD2 are measured noise power densities at the face of the antenna, TE is the Effective Input Noise Temperature of the system, and "Y" is the classical "Y factor" metric.
Three-antenna methods [1] are fundamental to modernantenna metrology. They enable the simultaneous determination of the on-axis polarizations and gains of three unknown antennas. For example, on-axis characterization of a probe antenna is necessary for the accurate far-field measurement of test antenna transmitting and receiving functions. Recently after renovation of antenna ranges, NIST has beeninvolved in an internal program to re-certify its polarizationcharacterization services. While reviewing the theory [2], werealized that a small modification to the standard algorithmcould improve the accuracy of the polarization determinationin many cases. Three-antenna techniques measure the antennas in pairswith one antenna of each pair rotating about its axis (Figure1). The ideal form of the measured signal is very simple (6). Previous methods [3][8], take an economical approach in which a minimal number of measurements are used to extractthe polarization parameters from the model. Some allow forthe averaging of multiple determinations to improve results. We propose, on the other hand, to use the discrete Fourier transform (DFT) to isolate the exp (¤i?) behavior in the data[9], [10]. The pair-polarization ratios (8) are easily computedfrom this transform. References [9] and [10] only came tolight after our analysis was completed. Rather the drop theproject, we have decided to offer this note as a tutorial andto call attention to what appears to be an under-appreciatedapproach to polarization measurement. All of the above methods work well when the error signalis small. Otherwise, the global nature of Fourier interpolationis expected to yield advantages over any local analysis. This hypothesis is supported by the simulations discussed below. Data were simulated for a number of combinations of axialratio, tilt angle, and sense of polarization. Noise was added atvarious levels. NOTE: The abstract refers to a figure, equations, and references not included in the abstract for brevity but which are available upon request
Three-antenna methods [1] are fundamental to modernantenna metrology. They enable the simultaneous determination of the on-axis polarizations and gains of three unknown antennas. For example, on-axis characterization of a probe antenna is necessary for the accurate far-field measurement of test antenna transmitting and receiving functions. Recently after renovation of antenna ranges, NIST has beeninvolved in an internal program to re-certify its polarizationcharacterization services. While reviewing the theory [2], werealized that a small modification to the standard algorithmcould improve the accuracy of the polarization determinationin many cases. Three-antenna techniques measure the antennas in pairswith one antenna of each pair rotating about its axis (Figure1). The ideal form of the measured signal is very simple (6). Previous methods [3][8], take an economical approach in which a minimal number of measurements are used to extractthe polarization parameters from the model. Some allow forthe averaging of multiple determinations to improve results. We propose, on the other hand, to use the discrete Fourier transform (DFT) to isolate the exp (¤i?) behavior in the data[9], [10]. The pair-polarization ratios (8) are easily computedfrom this transform. References [9] and [10] only came tolight after our analysis was completed. Rather the drop theproject, we have decided to offer this note as a tutorial andto call attention to what appears to be an under-appreciatedapproach to polarization measurement. All of the above methods work well when the error signalis small. Otherwise, the global nature of Fourier interpolationis expected to yield advantages over any local analysis. This hypothesis is supported by the simulations discussed below. Data were simulated for a number of combinations of axialratio, tilt angle, and sense of polarization. Noise was added atvarious levels. NOTE: The abstract refers to a figure, equations, and references not included in the abstract for brevity but which are available upon request
To characterize the radiation characteristics of an antenna, determining the power pattern of the antenna is often sufficient. In some cases, however, both the amplitude and phase response are important. For instance, for accurate channel modeling, the antenna has to be de-embedded, requiring knowledge of the complex radiation pattern of the antenna. A vector network analyzer typically measures complex S-parameters, hence, determining the complex radiation pattern seems like a straightforward task. When measuring at higher frequencies, as the wavelength becomes shorter, antenna phase measurements are very sensitive to positioning and alignment errors. Using sophisticated measurement tools, the position and orientation of the antennas can be determined, and this information can be used to correct the measurement data. The stringent requirements on positioning and alignment at millimeter-wave frequencies, however, makes correcting the data based on physical insight, in some cases, a more practical solution. The results of a radiation pattern measurement of a WR-28 rectangular open-ended waveguide will be shown in the full paper. The magnitude of the radiation pattern is symmetric in its two principal planes, which is to be expected, but the phase of the radiation pattern is not symmetric. To explain this lack of symmetry, a two-parameter misalignment model will be presented. It will be shown that the measured phase is much more sensitive to the misalignment than the measured magnitude, explaining why the symmetry is only lacking in the measured phase. Based on the 1,708 available planar cuts, the two parameters in the misalignment model are determined with great confidence. Subsequently, the parameters are used to correct the phase of the measured radiation pattern, restoring the expected symmetry in the phase measurement.
This paper presents a novel method using multiple compact antenna test range (CATR) reflectors to simulate the Radio Resource Management (RRM) measurements required for 5G devices capable of beam-forming in the millimeter wave frequency range (i.e. FR2). Four CATR reflectors are arranged on a semi-circle with the device under test (DUT) on a dual axis positioner in the center of the intersection of four planar waves in order to generate five sets of two Angles of Arrival (AoA), thereby capable of simulating multiple basestations from different directions for the 5G device to monitor and perform handovers. The reflectors create far-field conditions at the device under test (DUT) such that quiet zones of up to 20-30cm in size can be achieved. Absorber baffles are strategically placed as to reduce scattering from adjacent reflectors. In addition to RRM measurements, one reflector can be used to also perform in-band RF beam characterization[JMFL2] while additional reflectors can measure out of band emissions at the same time, thereby decreasing total measurement times by a factor of 2-3 times.
A signal source can introduce phase-measurement errors when its output crosses through internal frequency-band breaks. The source phaselock circuits in this band-break region sometimes report approximate phaselock before complete phaselock occurs. The result of this approximate phaselock is a minor error in the output frequency, which can lead to phase-measurement errors at the system level. The magnitude of the phase errors depends on the amount of frequency offset and the difference in electrical lengths between the measurement system's signal and phase-reference paths. If this behavior were deterministic, then the resulting phase errors might be tolerable. Unfortunately, it was found that the final settling time (measured in many hundreds of milliseconds) was not consistent, depended in part on the two specific frequencies surrounding the band break, became more confused if a second sweep encountered the band break before the first break had settled, and of course changed behavior if the frequencies were sequenced in reverse order or measured one at a time. The design approach described herein reduced to negligible the phase-measurement errors due to frequency errors in two large multioctave test systems. The approach relies on managing range transmission line lengths so that propagation time is sufficiently equal among the various signal and reference paths. Measured data are presented that show the advantage of the optimized system design.
In conventional Spherical Near-Field (SNF) antenna measurements, both amplitude and phase are necessary to obtain the Far Field (FF) of the Antenna Under Test (AUT) from the Near-Field (NF) measurements. However, phase measurements imply the use of expensive equipment, e.g., network analyzer, and rely on the assumption of having access to the reference phase, which is, for example, not the case in Over The Air (OTA) measurement scenarios. For these reasons, phaseless approaches gain attention and different methods have been investigated such as two-sphere techniques, indirect holography, or the use of different probes. Recent research on two-sphere techniques introduces algorithms originally developed for solving the so-called phase retrieval problem like PhaseLift or Wirtinger-Flow. Applied to SNF, the phase retrieval problem corresponds to obtaining the phase of the Spherical Mode Coefficients (SMCs) from amplitude NF measurements only. It has been shown that Wirtinger-Flow benefits from taking measurements over different structures, decreasing the redundancy. First investigations examined the combination of two spheres resp. a sphere and a plane and showed better reconstruction of the FF with the second combination. Furthermore, it has been shown that increasing the distance between both structures improves the reconstruction of the FF. Note that so far investigations have been based on the plane wave expansion. We currently deepen the knowledge presented above in a framework solely based on the spherical wave expansion. From a mathematical point of view, planes can be seen as spheres of infinite radius, i.e., a plane combined with a sphere may be interpreted as a special case of combining two spheres. This interpretation goes hand in hand with the observation that an increased radius difference between both spheres leads to better reconstruction performance. Consequently, we analyze different polyhedral sampling structures composed of planes (such as tetrahedrons or cubes), mimicking several spheres of infinite radius in different spatial directions. For the mathematical analysis of non-spherical structures in the basis of spherical waves, pointwise probe correction is used. First experiments show a better reconstruction of the FF compared to the standard two-spheres/sphere-plane sampling.
Chipless RFID is a subset of the RFID field where the tags possess no power source and no electronics. Information is instead stored in the structure of the tag and extracted by examining how the tag responds to an illuminating electromagnetic wave. These responses are most commonly viewed in the frequency-domain as a radar cross-section (RCS) vs. frequency response or as a complex reflection coefficient (S11) response. Binary codes are then assigned to the responses through a variety of procedures depending on the application and user preference. By manipulating the structure of the tag or the environment the tag is in, the response and therefore the binary code consequently experience changes. This mechanism is used to perform identification and sensing. While in simulation it is straightforward to extract the tag response, measurement poses additional challenges. These challenges include limited read range, extreme sensitivity to slight rotation or tilts of tags relative to the reader antenna, and noise in the response, all of which make it difficult to extract the response of tags and to verify proper tag performance. One sensing application of interest, is embedded materials characterization where the tag's response changes as a function of the dielectric properties of the material the tag is in. This work examines how microwave imaging with synthetic aperture radar (SAR) processing can be used to extract tag responses, verify tag performance (e.g., determine if tag manufacturing inaccuracies are present), and better understand tag environments in sensing applications. Through gaining a deeper understanding of the environment a tag is in (e.g., voids or material differences around a tag in an embedded application) during use in sensing applications, better models can be created. These models can then be used to help validate chipless RFID sensing approaches. Multiple tag designs - those with separated resonators and those with interlaced resonators - are utilized for this work to also understand the role and impact image resolution plays in the proposed techniques. This investigation is performed through a collection of simulations and measurements with a focus on using embedded chipless RFID tags for materials characterization applications.
RFID technology can be classified as active, passive, or chipless based on tag design. While active and passive tags rely on electronics to modulate and return the irradiating signal, chipless tags rely on geometry to produce a distinct signal which is viewed in the time-, frequency-, or spatial-domain. Within the field of chipless RFID, frequency-domain tags are the most popular and different design approaches with different polarization schemes have emerged. Primarily, these tag design approaches can be categorized as linearly polarized (LP), orientation insensitive (OI), and cross-polarizing. This diversity in tag designs leads to a variety of requirements for reader antennas and also leads to current reader antennas being non-universal (i.e., reader antennas can only be used for specific types of tags rather than all tags). LP and cross-polarizing tags require that the reader antennas have their polarization be perfectly aligned with that of the tag, as a small tag rotation with respect to the reader can greatly affect the response. Cross-polarizing tags additionally require either a dual-polarized reader antenna or a bistatic measurement setup. While specialized chipless RFID reader antennas and bistatic reading schemes have been developed, there are still limitations with these approaches, such as requiring tag/reader polarization alignment, hardware complexity, mutual coupling, and other related issues in bistatic setups. Tag interrogation with circular polarization (CP), however, accommodates the polarization diversity of different tag designs, while also relaxing the tag/reader relative alignment requirements. This work proposes a novel chipless RFID tag reading methodology that utilizes a single existing dual CP X-band (8.2-12.4 GHz) septum polarizer antenna as a universal (i.e., all types of tags) frequency-domain reader antenna that can generate and receive both right-hand and left-hand CP, as well as LP (through mathematical manipulation). This antenna has been optimized for this application and its specifications are provided. Additionally, through post processing the rotation offset of LP tags can be determined, a capability which can then be used for rotation sensing. To demonstrate the tag reading methodology and the rotation determination capabilities of the method, simulation and measurement results are presented for LP and OI tags.
As vehicle autonomy and active safety features become more advanced and ubiquitous, it becomes clear that vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication, together under the umbrella of vehicle-to everything (V2X), can help to enable these autonomous and active safety features by providing useful sensing and localized network capabilities. One problem facing the development of such communication networks is the difficulty involved in accurately predicting the key performance indicators (KPIs) associated with it - e.g., packet error rate (PER) and received signal strength indicator (RSSI) - for an arbitrary setup of antennas and occluders. In this paper we will present a model for V2X communications using a commercial simulation software, Altair's FEKO and WinProp suites, for predicting electromagnetic field intensity at microwave frequencies under different scenarios of antenna placement and occluder setup. We will also validate this model against field data collected using Cellular V2X (C-V2X) radios. We considered three distinct non-line-of-sight (NLOS) scenarios involving a pair of vehicles operating a CV2X inter-vehicle communication channel: 1. A stationary vehicle located directly behind a shipping container and a moving vehicle performing loops around it. 2. So-called urban canyon with tall metal walls on either side of the moving vehicle for a portion of its loop around the stationary vehicle. 3. Fully-covered tunnel, where both vehicles are moving, one leading the other around a loop and through a tunnel. We will discuss the simulations of these three scenarios in light of real-world data taken from field tests of identical scenarios, for the dual purposes of validating the simulation model against real-word data, and developing a model to predict the PER and RSSI at any theoretical receiver location. Together, these will allow us to perform a simulation for any arbitrary potential (NLOS) scenario and get an estimate of the channel PER and RSSI between any two spatial points, thereby help in developing standards for V2X communications, optimizing antenna placement for vehicles and infrastructure, and better understanding of these V2X systems overall.
In modern systems where RF front ends are tightly integrated, the parameters of passive aperture gain and active electronics noise figure become difficult to obtain, and, in many cases, impossible to measure directly. Instead, the parameter referred to as Gain over Noise Temperature, or G/T, becomes the performance metric of interest. Recently, the antenna measurement community has seen an increased demand to use near-field measurement systems for determining G/T values. Papers presented at AMTA over the past few years have shown that it is possible to determine G/T values using measurements taken in planar near-field antenna ranges. The CW-Ambient technique was one of the techniques proposed for computing G/T values by utilizing planar near-field measurements [1,2]. In this paper, we show how the CW-Ambient technique can also be applied to calculate G/T values in spherical near-field antenna measurement systems. This paper provides a brief summary of the CW-Ambient technique, and then presents the procedure and equations required for computing G/T using a spherical near-field system. To validate the recommended procedure, we compare predicted and measured G/T values for a separable unit under test (UUT). Since the passive aperture for this UUT is separable from the back-end active electronics, we measure the aperture gain of the UUT and the noise figure of the back-end electronics individually, and then compute the composite G/T value for this assembly. We then compare these composite values against G/T measurements from a spherical near-field antenna measurement system. We summarize these comparisons and provide conclusions regarding the validity of using a spherical near-field system to measure G/T.