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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.
Antenna performance plays a significant role in synthetic aperture radar (SAR) image quality, particularly for nondestructive evaluation (NDE) applications. To obtain high image quality and target detectability, SAR imaging systems should possess good resolution (cross- and along-range), and a relatively large penetration depth. Consequently, the antenna used must be wideband with a relatively wide beamwidth for high resolution and operate at low starting frequency for sufficient penetration depth. Meanwhile, antenna aperture size should be small rendering it sufficiently portable for scanning purposes or when employed within imaging arrays. However, increasing frequency bandwidth, reducing minimum frequency of operation while maintaining small aperture size (resulting in wide beamwidth), all at the same time is difficult. To this end, double-ridged horn (DRH) antenna, with flared aperture for improved radiation efficiency and performance is found to provide a good compromise among these parameters. Therefore, an improved modified design of DRH is proposed. The dimensions of its geometry are optimized to provide low unwanted reflections. Curved surfaces are attached at the end of the two ridged walls for better aperture matching. The final aperture size of the antenna is 230 ? 140 mm2, operating in the 0.5-4.0 GHz frequency range, and with a relatively wide beamwidth in its near-field region where most NDE imaging measurements are conducted. Measured reflection coefficient by using the fabricated antenna is used to verify the simulation results. Comparisons are also made with similar designs of DRH found in the literature showing that the proposed antenna has smaller electrical length with respect to the lowest operating frequency for designs without using absorbing material. Moreover, to conduct wideband SAR imaging, a new phase calibration method, using a small electric field monopole probe, to measure the phase change between the antenna aperture center and the input feed port for each frequency component is developed. Imaging results over a large concrete slab with delamination and voids simulated by foam and plastic sheets show that the proposed calibration approach works well, and the proposed antenna can effectively detect all of these defects with different scattering properties.
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.
This paper investigates on the use of under-sampling over the azimuthal dimension to reduce measurement time on spherical near-field scanning. This means that the number of angular phi samples is reduced, which allows to reduce the number of positioner steps, obtaining measurement time savings virtually proportional to the number of samples reduction. Of course this under-sampling introduces an error, which can be interpreted as an aliasing term over the retrieved Spherical Wave Expansion of the Antenna Under Test (AUT). The axial symmetry of the vast majority of antennas allows the application of significant under-sampling ratios with little aliasing errors. However, this information is not a priori known due to the lack of a reference AUT radiation pattern, or in the case of malfunctioning antennas with degraded symmetry. Here we proposed a measurement procedure for the exploitation of the AUT axial symmetry. The procedure consists on an iterative AUT measurement with increasing number of azimuthal cuts. As the number of cuts increases, the aliasing error decreases, thus obtaining the final radiation pattern with a lower uncertainty. We will introduce an aliasing error estimator, which estimates the error caused by the under-sampling without any a priori knowledge of the AUT. This estimator can be used as a stopping criterion of the iterative measurement procedure when the desired accuracy is achieved. The proposed technique will be demonstrated using different antennas, showing considerable reductions in measurement time with low errors in the transformed far-field pattern, and with the guarantee that the error is below a given threshold thanks to the derived estimator.
The CISPR 16-1-5 standard requires site attenuation (SA) measurements for the validation of Calibration Test Sites (CALTS) and Reference Test Sites (REFTS). CALTS validation requires horizontally-polarized SA measurements, while REFTS validation requires both horizontally- and vertically-polarized measurements. These measurements are made with tuned linear dipole antennas driven from coaxial transmission lines via balancing networks (baluns). According to the CISPR standard, the effects of the baluns are removed with a substitution measurement. Specifically, the baluns are connected back-to-back (balanced to balanced) with the elements removed and the port-to-port insertion loss then measured. This insertion loss is then subtracted from the port-to-port insertion loss with the antennas assembled and in place on the OATS. Thus, the measurement is a true RF substitution measurement. The baluns must be perfectly symmetric for this measurement to be sound. It is then accurate only if the baluns are very well matched simultaneously to both to the coaxial transmission lines and the dipole antennas. Essentially, the dipole-to-dipole transmission, the 2-port network which is substituted, would have to behave as a matched attenuator. In the CISPR standard SA measurements are made a a minimum of 24 specific frequencies between 30 and 1000 MHz. The height of the transmitting antenna above the ground plane in all cases is 2 m, but the height of the receive antenna varies in order to avoid a transmission null. For each one of these measurements it is possible to obtain a perfect match for each dipole antenna. However, the matching network would be different for each frequency and also for the different heights involved. Thus, there is impetus to use broadband baluns and resistive matching pads. If this approach is selected, neither dipole can be perfectly matched. Moreover, if the balun is required to operate over a broad bandwidth, it is difficult for itsperformance to be made so good that it could be considered ideal. By employing a full 4-port model for antenna-to-antenna transmission on an OATS between linear dipoles with imperfect baluns and thus unbalanced antennas, we assess measurement error for topologies of balun/attenuator combinations for the CISPR 16-1-5 SA measurements.
Direct far-field (DFF) testing has become the standard test methodology for sub-6 GHz over the air (OTA) testing of the physical layer of radio access networks with the far-field multi-probe anechoic chamber (FF-MPAC) being widely utilized for the test and verification of massive multiple input multiple output (Massive MIMO) antennas when operating in the presence of several users. The utilization of mm-wave bands within the 5th generation new radio (5G NR) specification has necessitated that since the user equipment should, preferably, be placed in the far-field of the base transceiver station (BTS) antenna, excessively large FF-MPAC test ranges are required or, the user equipment is paced at range-lengths shorter than that suggested by the classical Rayleigh criteria or, a modified compact antenna test range geometry must be developed and utilized. This paper presents a novel design for a new compact antenna test range (CATR) design that uses a parabolic toroid as the main reflector. The folded optics utilized within this design possesses superior pseudo-plane wave scanning capabilities than those available from equivalent, classical, point source offset parabolic reflector CATR designs. This wide-angle scanning capability is a crucial feature for successful over-the-air testing and measurement of mm-wave 5G NR Massive Multiple Input Multiple Output (MIMO) antenna systems within multi-user applications providing 60 degrees of azimuth scan and 15 degrees of elevation scan to the incoming plane wave at the AUT. CATR quiet-zone results are presented, compared and contrasted with more classical designs before results of the effects of the CATR test channel on a number of commonly encountered communication system figures of merit in wide scanning cases are presented.
Spherical wavefunction expansions (SWEs) form the basis for spherical near field measurements and are also very useful for the analytical assessment of antenna performance, e.g. achievable quality factor and directivity/gain. On the other hand multipole source expansions also have great utility. The cartesian multipole expansion in particular provides much physical insight to the behavior of compact sources of electromagnetic radiation. The relationship between cartesian multipoles and spherical wave function expansions is not one-to-one and is quite complicated as is evidenced by the equivalent multipole source configurations for low-order (up to radial index of 3) spherical wavefunctions previously given by W. V. T. Rusch. Here we provide a formalized approach to the determination of the spherical wave function expansion for a particular cartesian multipole source and also the cartesian multipole which would excite a particular spherical wavefunction. The impetus here is the modeling of couplers for wireless power transfer. One example of this is the so-called DD coupler for automotive wireless charging described in the SAE J2954 standard which can be modeled as a TE-to-z cartesian multipole consisting of four displaced magnetic dipoles. In terms of Harrington's cartesian multipole nomenclature, this source has an order of n=2 and m=1 for the TE-to-z electric vector potential. It excites two TE-to-R spherical wavefunctions, one with radial index of 1 and azimuthal index of 1 and the other with radial index of 3 and azimuthal index of 1. More complex multipole sources are required to describe more elaborate WPT couplers such as some associated with the Qi wireless charging standard. WPT systems necessarily operate with switched-mode sources and hard-switched rectifiers and therefore produce spectral components of current over a broad frequency range. Thus the behavior of the extraneous electromagnetic field at frequencies well above the fundamental is of great interest. The cartesian multipole representation of the WPT couplers facilitates the understanding of this extraneous electromagnetic field. The knowledge provided by such a multipole model would be useful in determining that measurements over a full sphere or hemisphere are absolutely necessary; that is, that typical emissions measurements are inadequate.
An automotive radar is known as providing the vehicle drivers with useful information such as the positions of the surrounding vehicles and the obstacles on the front, side, and rear of the driver. This information can beapplied to control the vehicle in an autonomous mode and helpthe vehicle to drive safely at night or in bad weather conditions. For example, the adaptive cruise control (ACC) radar system in a medium range operates to transmit an electromagnetic wave signal and receive the wave signal reflected from neighboring vehicles or obstacles and estimates the distances between the radar and the neighboring vehicles and their relative speeds by using the time difference between the two signals and the Doppler frequency variation. However, there are so many traffic situations on a road, and it is almost impossible to experiment the ACC radar system in all the real traffic scenario. Therefore, it is required to implement a simulation setup to cover all development process from designing a radar antenna to collecting radarsignal to identify any traffic situations. In this work, automatic ACC radar antennas are designed and applied to simulate a real traffic scenario. The radar antennas are designed to satisfy the ACC radar specification and loaded on a vehicle to transmit and receive RF signals in simulation environment. The radar antennas are designed with Altair Feko and the relative distances and speeds of the vehicles surrounding the radar built-in vehicle in a virtual traffic situation are obtained with Altair WinProp. In addition, a trihedral corner reflector (TCR) is also included in this study to calibrate the radar antenna system by comparing the reflected characteristics from a TCR target with those from a vehicle. Finally, the ACC antenna specification (beam-width) is evaluated in terms of how useful arethe data collected by a radar vehicle which overtakes a front vehicle.These datashould also provide a good basis to validate the results of experimental data for automotive radar system implementation.
With trending topics such as car-to-car communication or automotive radar, the evaluation of antenna performance, including the impact of the larger structure in which it is integrated, is a topic of rapidly growing interest. Implementing large anechoic chambers, supporting e.g. full-vehicle testing, is definitely an approach, which can serve as a reference. Nevertheless, the cost and complexity associated to such antenna test ranges are quite prohibitive. Some measurements eventually get close to impossible, as they involve unreasonable testing times and efforts, due, for instance, to the size to wavelength ratio of the DUT. This paper introduces an economic alternative, based on the convergence of measurements and full-wave simulation. The described method relies on a three-step approach: (i) measure the phasor electric field radiated by a smaller-size antenna module over a surface enclosing the test sample; (ii) use an algorithm to calculate equivalent electric and magnetic currents over a surface closely surrounding the DUT; (iii) inject these currents, as a Huygens source, into a full-wave solver, where the entire supporting structure is then taken into account. The relevance of the technique is demonstrated with a complex example, where a multilayer 8x8 antenna array frontend module operating at Ka-band is both evaluated numerically and experimentally. Two sets of simulations are created, where either the detailed numerical antenna model or the equivalent current surface is integrated under a radome at the nose of an aircraft. Key radiation parameters (peak gain, side lobe levels, etc.) are compared, showing the relevance of the approach. Its limitations and uncertainties are also discussed.
The characterization of 3D radiation pattern of antennas using spherical measurements techniques is nowadays a common testing procedure. However, the well-established technique using Spherical Harmonics (SH) can be time consuming since the required number of field samples is proportional to the square of the electrical length of the antenna. The main solution is to reduce as much as possible the number of field samples to reconstruct the antenna pattern. This can be achieved by either exploiting prior knowledge about the antenna or leveraging general properties common to the fields radiated by antennas field. Our approach uses the sparsity of the spherical harmonic expansion of the field radiated by antennas and only requires the maximum electrical dimension of the antenna and its frequency to set the truncation order of the harmonic series. It nonetheless requires the proper tuning of specific parameters to ensure that the antenna radiation patterns, reconstructed from a small number of sampling points, is accurate enough. First, the minimum number of field samples to ensure a proper interpolation must be set, the reconstruction accuracy (for undersampled data) is linked to the number of significant modes involved in the expansion: roughly speaking, the sparser, the better. Second, the data fidelity term and more specifically the error tolerance, common to all regularization scheme such as the sparse one at hand, must be carefully chosen. Finally, an efficient post-processing procedure, based on the rotation of the antenna, is proposed for improving the sparsity of its SH spectrum, and thus enables extracting as much information as possible from a given fast measurement data set. All these points are validated numerically and experimentally on spherical near and far-field data.
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.