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In this paper, a method is presented that allows for the experimental verification of far-field conditions in a direct far-field measurement setup. The method is based on a relativedistance sweep (i.e., increasing the distance by linearly translating one antenna) and on the Friis equation. The presented method is only valid for one specified direction and is therefore well suited to assess whether or not far-field conditions are achieved when performing an absolute measurement, such as a maximum gain or effective-isotropic-radiated-power (EIRP) measurement. It is shown that antenna measurement uncertainties due to the finite antenna separation, scattering, positional inaccuracies, drift and noise on the order of hundredths of dBs around 30 GHz for a separation on the order of 1 m can be obtained. Using this method, it is also experimentally shown that whether or not farfield conditions are met depends not on one but on both antennas in a two-antenna measurement setup. This implies that, strictly speaking, the far-field distance cannot be determined by solely considering the largest antenna in a two-antenna measurement setup.
An origami-based Tightly Coupled Dipole Array (TCDA) is proposed for small satellite applications. The array is formed by a two-layered structure using rigid and flexible substrates to enable accordion-like folding. The proposed TCDA operates across 0.4-2.4 GHz with VSWR < 3 at broadside and across 0.6-2.4 GHz with VSWR < 3 when scanning down to 45 in the E-, D-, and H-plane. An 8 prototype was fabricated using Kapton Polyimide and FR4 and tested to verify the bandwidth and gain of the origami array. The fabricated prototype was demonstrated to be packable, low-profile, and lightweight (only 1.1kg). Notably, when packed, the array has a one-dimensional size reduction of 75%. As will be discussed, the packing compression is made possible by eliminating vertical PCB boards and incorporating the balun feeds within the dipole layer. To our knowledge, this is one of the first foldable, low profile, and low-scanning ultra-wideband arrays in the literature.
An active S-band dual-polarized multifunction phased array radar (MPAR), the Advanced Technology Demonstrator (ATD), has recently been developed for weather sensing and aircraft surveillance. The ATD is an active electronically scanned array (AESA) with 4864 transmit/receive (T/R) modules and was installed in a spherical radome. Simulations and a novel phased array measurement technique have been explored to assess the impact of high reflectivity from a wet radome during rain that can potentially induce voltages exceeding the transmit amplifier breakdown voltage. The measurement technique uses array elements radiating one at a time to illuminate the radome, and uses superposition to quantify the received signal power in a reference antenna on the face of the array. It is shown that when the radome surface is wet and highly reflective, certain electronic steering angles sum to a large reflected signal focused on the array face. This measurement technique can be used prior to high-power phased array radar operation to monitor the magnitude of reflections and help avoid element transmit amplifier failures.
This paper presents comparison of planar near field (PNF), cylindrical near field (CNF) and compact antenna test range (CATR) measurements for Standard Gain Horn (SGH) at K (18-25 GHz) and Ku-band (10-15 GHz) and metamaterial based high gain flat panel antenna at Ku-band. The effect of azimuth step size, number of cylindrical modes and radial distance error on CNF measurement accuracy are presented. The advantage of CNF for wide/large scan angles is discussed and measured results for metamaterial antenna at high scan angles are compared with those of CATR. Measurement time comparison between PNF and CNF is presented. One of the limitations of CNF compared to PNF is angular coverage in the elevation plane and this aspect is tried to be addressed supported by measured results.
The equivalence principle allows for the replacement of a radiating structure with a Huygens’s box resulting from a near-field scan obtained from either simulations or measurements. The near-field on the surface enclosing the structure is replaced by a set of equivalent electric and magnetic dipoles that can be used as sources for numerical simulations. In this manner, problems of high complexity can be handled, using less unknowns, by separately addressing the radiating structure and the surrounding diffracting objects. Furthermore, sometimes the antenna model is not available, and it must be considered as a black box. However, important challenges arise when the Huygens’s box approaches a surrounding structure. Indeed, the near-field resulting from discretized equivalent dipoles presents a singularity at each dipole’s position. Therefore, the obtained fields with the equivalent dipoles are not valid in the close vicinity of the Huygens’s box. A novel method is proposed to handle the aforementioned singularity. It is based on the interpolation of the electromagnetic field between the non-singular region and the surface of the box. The field on the non-singular region is obtained using equivalence principle whereas the near field scan data is used to retrieve the field on the box surface.
This contribution presents a way to manufacture antennae, which allows to both effectively simplify the production and reduce associated costs as well as the weight. Amongst other examples for aperture antennae this is shown for a configuration given by the slotted waveguide antenna toolkit presented in [1]. In simplified terms the procedure consists of shaping the HF-transparent rigid foam to the size of the antenna’s cavity, attaching the connector(s) and electroplating it with copper. The manufacturing steps are shown in detail, which is followed by a characterization including the weight as well as the antenna performance such as S11 and the antenna pattern for horizontal polarization. These results validate the applicability of the presented method and open windows of opportunities especially in contexts in which intricate cavities and weight pose critical issues.
With the event of integrated and multi-standard wireless links, phaseless antenna measurements are attracting more and more interest in research. Especially in the context of connected and automated driving, antennas, frontends, and digital signal processing units merge into telematic units and require new methods for performance evaluation in the installed state. The measurement of the phase diagram and the exact absolute positioning of electrically large antennas, i.e., antennas interacting with the car body, present challenges for safety-relevant applications and reliable test methods. This paper describes a way to determine the position of automotive antennas in the installed state with sub-wavelength precision from phaseless measurements. Realistic LTE uplink signals were used as test signals as they would be transmitted by an active device in a real-world scenario. The localization algorithm is based on orthogonal power measurements of the transmitted signal on a cylinder surface and a non-linear optimization. By comparison with a conventional localization based on spherical far-field data, an accuracy of the approach of less than 1 cm was achieved, which is less than λ/16 at the considered frequency of 1870 MHz.
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].
An antenna measurement system at the Institute of High Frequency Technology at RWTH Aachen University is being established containing a six-axis robot arm allowing the realization of numerous measurement geometries. Room scattering is one of the most crucial uncertainty terms in every antenna measurement which becomes even more interesting in a dynamic scattering situation. To determine the scatteringinduced interference caused by the robot, a motion-capable model is developed and firstly simulated using the multi-level fast multipole method between 8GHz and 12GHz to qualitatively assess the surface currents. Secondly, asymptotic simulations are carried out using physical optics for the most important robot positions at 60GHz which is in the frequency range where the system is operated. For example, differences in the same simulation points of up to 20dB are shown for different robot positions. Based on the simulation results, the measurement sequences can be optimized by selecting a trajectory which reduces the scattering effects. In addition, the strongest scattering sources of the robot are identified in order to cover these parts by absorbers. Therefore, the knowledge gained from the simulations can be applied to the measurement system to improve the performance of antenna measurements.
The validity and viability of using frequency domain mode filtering to qualify an EMC chamber above 1 GHz has been demonstrated in a previous study [1]. The novel approach overcomes the difficulties with under sampling encountered in the traditional spatial sampling method adopted by CISPR 16-1-4, and it also has the distinct advantage over the time domain method adopted by ANSI C63.25.1 in that broadband and low ring-down antennas are not required. In this study, we further examine one of the assumptions made in the previous study to translate the quasi-far-field pattern to the rotation center. The approximate method is compared to a more rigorous method by using a quasi-far-field to far-field transformation first before applying the phase translation and subsequent mode filtering. In this paper, we further validate the method by conducting an intercomparison study based on measurements conducted in a 3 m anechoic chamber to show the correlations of the mode filtering method to the CISPR and the time domain (TD) site VSWR methods. We demonstrate how the proposed method improves the test repeatability, lowers measurement uncertainties, and increases measurement efficiencies.
Instrumentation radar metrology waveform techniques that simultaneously transmit two orthogonal sequences of orthogonal electromagnetic polarizations are explored for applicability toward both static and dynamic RCS signature and ultra-wideband imaging measurements using simultaneous H-pol and V-pol (SHV) waveforms. Static, pulsed measurements with independent transmit polarizations are modulated and radiated; reflections from a depolarizing target are measured where the return signals are coherently combined. Each transmit polarization is independently modulated using a diverse phase sequence, which leaves a unique “fingerprint” by which the orthogonal polarization separation is achieved. Using only the coherent combination and associated transmit and receive RF channel characterizations, the original measurements are reconstructed. Simulations serve as a baseline for measured results, from generating pure SHV waveforms and then providing simultaneous full scattering matrix (FSM) measurements, in order to achieve greater purity of FSM signatures, while reducing measurement times by a factor of two.
This work presents the concept and design of an antenna element, aimed at 5G time division duplex (TDD)-based digital massive MIMO applications, operating in millimeter waves (mm-waves). The proposed radiating structure is based on printed slot antennas, fed by a substrate integrated coaxial line (SICL) for significantly reducing mutual coupling among the array elements. Furthermore, the slot has its own cavity for creating a broadsidedirection beam, without increasing mutual coupling. Numerical results demonstrate 1.31 GHz bandwidth at 26 GHz, 6.4 dBi gain and beamwidth of 70° and 80° in the main orthogonal planes. A two-element array is reported as a proof-of-concept and the mutual coupling between its elements has been kept lower than 32 dB from 25 to 27 GHz, illustrating its potential for scalability to high-order massive antenna TDD arrays.
A compact ultra-wideband (UWB) antenna operating from 300 MHz to 6 GHz was developed for operating with a Lunar Heat Flow Radiometer (LHR) system is presented. The antenna was required to fit within 36 cm x 36 cm x 10 cm volume with an emphasis of small antenna height so that it can be mounted under rovers. This paper presents an innovated design which combine a dielectric-loaded TEM horn mode from 2 GHz to 6 GHz and bowtie dipole mode 300 MHz to 2 GHz. The simulation results show a minimum realized gain of 2.2 dBi at 300 MHz and the gain monotonically increases to approximately 15 dBi at 6 GHz and maintains approximately constant gain and patterns from 2 to 6 GHz
A Spherical Passive/Active Radar Calibration System (SPARCS) has been designed as an advanced, airborne, radar calibration device (CD). SPARCS is currently under development as an autonomous, battery-powered, high-endurance, flying platform. This self-contained, multi-function radar calibration and diagnostic system functions as 1) a Passive Spherical Reflector, 2) an Active RF Repeater, 3) a Synthetic Target Generator, and 4) an UWB RF Sensor and Data Recorder of the radar under test or the localized RF environment. This innovative CD exploits major advances in commercial technology during the past decade associated with autonomous airborne drones and miniaturized digital RF systems on chips (RFSoCs), and other miniature electronics. Emphasis has been placed on a recoverable, reusable CD that enables precision calibrations over extensive open-air test volumes used for dynamic aircraft RCS measurement, test and verification, or time space position information (TSPI) test range tracking radars. This paper highlights early efforts to parameterize and develop SPARCS, including advances in autonomous navigation and flight time, electric ducted fan performance, radar screens for thruster inlet and outlet ports, active calibration functionality, and improving calibration uncertainty. SPARCS will provide an unprecedented capability for radar instrumentation calibration, target emulation, environmental assessment and in situ, real-time calibration.
In Multi-Probe (MP) based measurement systems, the standard procedure is to calibrate the probe array with a well-known reference antenna [1]. This procedure equalizes amplitude, phase, and polarization characteristics of each probe array element. In Planar Near Field (PNF) systems, the probe pattern impact is usually more pronounced than in other near field scan geometries, such as spherical. Thus, the probe pattern must be compensated during post-processing for more accurate measurements at wider angles. While the probe array calibration ensures the on-axis equalization, the probe array elements still have individual pattern difference due to finite manufacturing accuracy and absorber interaction. Probe compensation using an equivalent probe pattern of the array has been shown to be very effective and accurate for MP PNF systems [2]. In this paper we compare two methods to determine the equivalent probe pattern for a given MP PNF system. We also discuss the acceptable limits of pattern variation within the array versus measurement accuracy as a design parameter for MP PNF systems.
Radar sensors are an essential component in the automotive sector and take over safety-relevant functions in the field of autonomous driving. Therefore, the need for validation of automotive radar systems is increasing. Within this paper, a measurement setup for automated static and dynamic tests of integrated radar sensors is set up in the robot-based measurement chamber available at the Institute of High Frequency Technology, RWTH Aachen University. The system parameters two-way pattern, range and speed resolution as well as angular resolution and separation capability are measured and analyzed for an integrated automotive radar sensor. The measured results show the expected performance of the radar system and point out the high variability of the built setup.
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>
Accurate characterization of locomotive antennas is key to safe and robust railway signaling and control communication. With the introduction of new technologies and the foreseeable migration from the GSM-R standard towards FRMCS, new wireless applications and specifications arise, and suitable antenna solutions need to be developed and tested. Moreover, the rooftops of modern locomotives present a dense and harsh environment; therefore, potential antenna mounting spaces should be carefully evaluated to avoid undesirable degradations of the antenna radiation patterns. Due to the electrically large and complex structure of locomotives, full-scale testing is challenging to perform, especially under laboratory conditions. Antenna measurements with geometrically scaled models present a powerful alternative to address this issue. In this paper, we present and discuss antenna measurement results of a scaled locomotive mockup. The mockup incorporates two different cabin geometries, one with a step-like rooftop contour, and one with a smooth slightly tilted geometry. First, the optimum scaling factor was identified and validated through numerical simulations. Afterwards, antenna measurements with a scaled locomotive mockup were carried out in our automotive antenna measurement facility VISTA. The measured results were compared with the numerical simulations, where a good correlation above 80% was found. Secondly, the impact of the rooftop geometries, and superstructures on the roof has been investigated for a range of operational frequencies between 700 and 2600 MHz. The results reveal that the parasitic impact of the antenna environment becomes more pronounced at higher frequencies.
In this paper, a design of a linear-to-circular polarization converter based on a 3D printed anisotropic metamaterial substrate (AMS) is presented. The AMS is a stack of thin sheets of acrylonitrile butadiene styrene (ABS) material, with air gaps in between, placed over a ground plane. This produces a metamaterial structure composed of periodic anisotropic unit cells, enabling the conversion of a linearly polarised (LP) incident wave to a circular polarised (CP) reflected wave. Results demonstrate that the proposed 3D printed AMS provides good angular stability. Using the AMS as a substrate, a CP antenna application is proposed operating within the L1 GPS reducing the complexity of designing/feeding and fabricating of the primary antenna.
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.