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Comparison activities in which a number of measurement facilities compare their measurements of the same antenna in a standard configuration have become important for documentation and validation of laboratory expertise and competence. It is also mandatory to have regular participation in such activities to obtain and maintain accreditations like ISO 17025. The main goal of the facility comparison activities is to provide a formal opportunity for the participants to validate and document their achieved measurement accuracy and procedures by comparison with other facilities. Since 2004, comparison campaigns with different scopes have been conducted on antenna measurements within various European activities: EurAAP (European Association on Antennas and Propagation) supported by the European Cooperation in Science and Technology (COST) in the programs ASSIST IC0603 and VISTA IC1102 and the 6th EU framework network “Antenna Centre of Excellence” (ACE). Results of these activities have led to improvement in antenna measurement procedures and protocols in facilities and contributions to standards. Due to the direct benefits to the participants, the activities have been very successful and partial results have been published in IEEE referenced papers during the years. The large amount of measured data available have fostered fruitful discussion and research on the improvement of standard procedures, protocols and tools for performance verification like the facility comparison campaigns. As a further benefit, the campaigns have initiated a dialogue among different laboratories throughout Europe and USA and is spreading into Asia. In this paper we report on a recent EurAAP facility comparison campaign involving a medium gain ridge horn, MVI-SH800. The campaign covers measurement in the L and C band frequencies in different facilities in Europe and USA. The horn is equipped with an absorber plate to enhance the correlation in different facilities by reducing the sensibility to the measurement set-up. The results of 8 facilities will be shown in terms of gain and directivity patterns, equivalent noise level and the declared uncertainty will be checked against the whole set of measurements.
In this paper, a novel compact 2-channel MIMO antenna design for all cellular and Wi-Fi communication needs from vehicular is discussed. The entire antenna system fits within the 13cm (diameter) by 9cm (height) volume. It consists of 2 vertical multi-band cellular antenna elements and two vertical multi-band Wi-Fi antenna elements. All four antennas share a 13cm diameter circular ground plane. Each antenna element design is a PCB based slot-loaded multi-band monopole. This particular element design as well as their mounting positions were chosen to minimize mutual coupling and blockage in order to maximize MIMO performance, i.e. diversity gain. In addition, the center region of the antenna volume also accommodates a raised L1-band GPS antenna. A prototype antenna was subsequently fabricated. The measured antenna performance compared well with simulated results before and after being mounted on a 4 feet diameter ground plane. The effect of the radome was also assessed and was found to be insignificant. The cellular antenna produced realized gain of over 2 dBi in lower cellular band (0.7 GHz to 1 GHz), and over 5dBi in the higher cellular band (1.7-2.1GHz and 2.3GHz-2.5GHz). The Wi-Fi antenna produced realized gain of over 5dBi in both 2.4 GHz and 5.8 GHz bands. The far-field pattern correlation coefficient was also calculated to evaluate the diversity gain performance of antenna system. For the cellular band, the correlation number is lower than 0.55 for 0.7 to 1 GHz, and lower than 0.35 for all the other band. For the entire Wi-Fi band, the correlation number is lower than 0.4.
Dual polarized probes with wide bandwidth operational capabilities are convenient for accurate and time efficient Planar Near Field (PNF) antenna testing. Nevertheless, traditional probe designs are often limited in terms of bandwidth and their electrically large size leads to high scattering in PNF measurements with short probe-AUT distances. An innovative octave band probe design is presented in this paper with minimum scattering characteristics. The scattering minimization is mainly obtained by an electrically small and axially symmetric aperture of 0.4? diameter at the lowest frequency. The aperture provide a near constant directivity in the full bandwidth and very low cross polar. The probe is fed by a balanced ortho-mode junction (OMJ) with external feeding circuitry to obtain high polarization purity. This paper discuss the design considerations, technical and implementation trade-offs and show experimental results on the manufactured hardware.
When antenna near-field (NF) measurement within small electrical distance is needed, such as miniaturization of the measurement device or measurement of a low-frequency DUT, the coaxial cables connected to the probes will significantly but inevitably disturb the fields. The measurement accuracy is therefore compromised. In this paper, a novel probe design is proposed by replacing coaxial cable with optical fiber to minimize the disturbance. In this design, the RF-over-Fiber (RoF) technology is applied in signal transmission with Vertical-Cavity Surface-Emitting Laser (VCSEL) and photodiode (PD) as the transmitter and receiver respectively. The VCSEL is powered via optical fiber with Power-over-Fiber (PoF) technology. A power laser emits optical power which is guided by optical fiber to illuminate a miniaturized photovoltaic (PV) element. The PV element serves as a voltage source for the VCSEL. A spherical, multi-probe, NF measurement design with 60cm-diameter is built for portable DUT operated between 0.6 to 2.6GHz. There are 64 probes installed along the two arches for both theta and phi polarizations, so mechanical rotation is needed only on phi axis. Thanks to the high RF transparency of the probes, there is no need to wrap absorbers around the probes to shield the cables. Another spherical NF measurement prototype is also under development. It is half-spherical (10m-diameter) for large DUT, such as vehicles, with low frequency antenna, namely, 70MHz to 600MHz. At this frequency range, to the best of our knowledge, there is no effective and accurate way to measure the radiation performance because the disturbance on the EM fields by the coaxial cables is obviously not negligible.
Temperature change cause thermal expansion of the antenna materials and will have an important impact on antenna performances. In some applications it is sufficient to calculate the antenna deformation due to temperature by mechanical analysis and determine the RF impact by EM analysis tools. However, if the environmental conditions of the final antenna are stringent and considered critical as in some military and civil applications in the space and aeronautics domain, the thermal performance of the antenna must be determined by experiment. Typical temperature testing ranges for civil applications are often between -50°C and +80°C but can be much more extensive for special applications. This paper present a simple and easy method for thermal testing of antennas in a fast spherical near field measurement facilities such as multi-probe system. During the thermal testing, the antenna is maintained inside a RF transparent thermally insulated container including the local heating and cooling equipment. The fast testing provided by the multi-probe system allow to measure the temperature dependence of the antenna at several different temperatures within the investigation range. The method will be illustrated for the cold measurement case but the extension to the full cold-hot temperature range is trivial.
Low-profile vertically polarized end-fire radiating antennas with wide bandwidth have been used in the wireless systems of a variety of vehicles and aircraft. Many antennas conforming to these specifications have been designed in recent years for operation in microwave frequencies; however, there is interest in the ability to scale these designs to support millimeter wave applications. This work will utilize modeling and simulation, fabrication, and measurements to characterize, scale, and optimize a coupled microstrip resonator antenna. All modeling and simulation will be performed using CST Microwave Studio. The antenna will consist of a trapezoidal launcher along with several rows of coupled microstrip resonators that will be milled from Rogers RT/Duroid 5880 printed circuit board. The coaxial fed trapezoidal launcher will be utilized as a reflector and will allow realization of quasi-plane waves at the interface between the launcher and the microstrip resonators. The rows of coupled microstrip resonators decrease in the length along the endfire direction to provide increased endfire directivity. The resonant frequencies of the antenna will be determined mainly by the dimensions of the trapezoidal launcher, microstrip resonators, and the gaps between them. The design for this antenna is based off the antenna documented in Compact Wideband and Low-Profile Antenna Mountable on Large Metallic Surfaces (Zhang, Pedersen,IEEE TAP, VOL. 65, NO. 1, JANUARY 2017). Initial modeling and simulation of the documented antenna have shown good agreement with the authors findings. Simulating a reduction to the antenna dimensions has shown promising performance into millimeter wave frequencies including a 73.7% fractional bandwidth (36-78GHz) for VSWR < 2. Since these reduced dimensions can’t be easily fabricated a slightly modified version of the antenna will be modeled and simulated as described above. The antenna will then be fabricated and measured to validate the accuracy of the model. Once validated, the antenna model will be scaled up to millimeter wave frequencies and simulated to predict performance.
Gain is a principal property of antennas; it is essential in establishing the link budget for communication and sensing systems through its presence in Friis’ transmission formula and the radar range equation. The experimental determination of antenna gain is most often based on a gain-transfer technique involving a reference antenna for which the gain has been calibrated to high accuracy; this is typically a pyramidal horn antenna [1]. The required accuracy of antenna gain obviously depend on the application; in some cases it can very high, ±0.1 dB or less, and this implies an even higher accuracy, of the order of ±0.01dB, for the gain reference antenna. This work investigates the accuracy to which a gain reference antenna can be calibrated; the investigation is based on experimental spherical near-field antenna measurements [2] and computational integral equation / method of moments simulations [3]. While calibration of gain reference antennas has been studied in many previous works, even works from early 1950s [4]-[6], this work is novel in systematically supporting measurements with full-wave simulations. Such simulations facilitate the study of e.g. the effect of multiple reflections between antennas at short distances. We study two absolute calibration techniques for the gain of pyramidal horn antennas. The first technique determines gain as the product of directivity and radiation efficiency; this technique has been referred to as the pattern integration technique [7] (which is not an entirely adequate designation since gain cannot be determined from the radiation pattern). The second technique determines the gain from Friis’ transmission formula [8] for two identical antennas; this technique is generally referred to as the two-antenna technique [1]. These two calibration techniques involve very different steps and contain very different sources of error; for both techniques our investigation involves measurements as well as simulations. For the pattern integration technique we compare experimental and computational results for the directivity and demonstrate agreement within one-hundredth of a dB. The radiation efficiency is calculated by different techniques based on the surface impedance boundary condition for the metallic walls of the pyramidal horn. This technique is not influenced by proximity effects or by impedance mismatch between the measurement system and the gain reference antenna. For the two-antenna techniques we compare experimental and computational results for the gain and we compare the calculated distance-dependence with that of the extrapolation technique [9]. It is demonstrated how the use of the phase center distance in Friis’ transmission formula notably decreases the necessary separation between the antennas for a required accuracy, but that multiple reflections may then become a limiting factor. This technique is highly influenced by the impedance mismatch that must be accurately accounted for. We compare the gain values resulting from the pattern integration technique and the two-antenna technique, including their very different uncertainty estimates, for a C-band standard gain horn. The work is related to an on-going ESA project at the DTU-ESA Spherical Near-Field Antenna Test Facility for the on-ground calibration of the scatterometer antennas of the EUMETSAT MetOp Second Generation B-series satellites. IEEE Standard – Test Procedures for Antennas, Std 149-1979, IEEE & John Wiley & Sons, 1979. J.E. Hansen, “Spherical Near-Field Antenna Measurements”, Peter Perigrinus Ltd., London 1987. www.wipl-d.com W.C. Jakes, “Gain of Electromagnetic Horns”, Proceedings of the IRE, pp. 160-162, February 1951. E.H. Braun, “Gain of Electromagnetic Horns”, Proceedings of the IRE, pp. 109-115, January 1953. W.T. Slayton, “Design and Calibration of Microwave Antenna Gain Standards”, Naval Research Laboratory, Washington D.C., November 1954. A. Ludwig, J. Hardy, and R. Norman, “Gain Calibration of a Horn Antenna Using Pattern Integration”, Technical Report 32-1572, Jet Propulsion Laboratory, California Institute of Technology, October 1972. H.T. Friis, “A Note on a Simple Transmission Formula”, Proceedings of the I.R.E. and Waves and Electrons, pp. 254-256, May 1946. A.C. Newell, R.C. Baird, P.F. Wacker, “Accurate Measurement of Antenna Gain and Polarization at Reduced Distances by an Extrapolation Technique”, IEEE Transactions on Antenna and Propagation, vol. 21, no. 4, pp. 418-431, July 1973.
In high-gain array applications such as satellite communications and radars, low sidelobe level is a key performance requirement. Applying a magnitude tapering profile across the aperture is a common way to suppress the sidelobes. Other realizes sidelobe level control method via phase variation across the aperture. Common ways for implementing aperture magnitude taper include applying lumped resistors or introducing proper series feeding, etc. This paper discusses about 33-35 GHz fixed-beam, low-sidelobe array antenna design. In order to minimize the number of the feed network, the 11x32 Ka-band array is composed of 32 sequentially-fed 11-element subarrays. Also, to maximize the antenna efficiency, the Chebyshev tapering selected for achieving -35 dB sidelobe levels was accomplished using a combination of un-even power divider, mismatched feed lines, and different feedline lengths. This approach allows it to achieve magnitude taper control from -0.5 dB to -26 dB from 33 to 35 GHz without using resistors. The unequal power divider arrangement reduces mismatch loss my 1.3dB compared to conventional 2-way even dividers in the corporate feeding network. The paper also studies the impact of the amplitude and phase uncertainty among array elements on the degradation of the sidelobe performance. An 11x32 planar patch array prototype is designed, fabricated and measured. The array obtains a realized gain of 19 dBi with Azimuth 3dB beamwidth of 1.0 degree and -23 dB sidelobe.
The evaluation of RF Sensors often requires a test capability where various RF targets are presented to the Unit Under Test (UUT). These targets may need to be dynamic in time, represent multiple targets and/or decoys, emulate dynamic motion, and simulate real world RF environmental conditions. An RF Target Simulator can be employed to perform these functions and is the focus of this paper. The total test system is usually called Hardware in the Loop (HITL) involving the sensor mounted on a Flight Motion Simulator (FMS), the RF Target Simulator presenting the RF Scene, and a Simulation Computer that dynamically controls everything in real time. The realization of a highly effective target simulator, one that truly meets the user’s needs at an affordable cost, is the result of understanding the complex interrelationship of requirements, architecture and constraints. In this presentation, those relationships are examined in seven areas of discussion, employing examples of realized systems; Determining the necessary test zone volume Determining the necessary quality of RF target signal Sizing the field of view, range and facilities Creating each target’s RF signal Creating RF target motion Integration and real-time operation within the range Locating and minimizing the effects of error sources
In the last years different advances in Near-Field (NF) measurements have been proposed. Among the others, the ones of interest here are: the determination of the number and spatial distribution of sampling points, the introduction of scanning strategies aimed to reduce the measurement time, the adoption of a proper representation, for the unknowns of interest, able to improve the reliability of the characterization [1]. In particular, the use of Prolate Spheroidal Wave Functions (PSWFs) for the expansion of the aperture field has proven effective to take into account for the quasi-band-limitedness of both the aperture field and the Plane Wave Spectrum. Furthermore, using a proper expansion is an important step of the Singular Value Optimization (SVO) approach, wherein the number of the spatial distribution of the NF samples are determined as the ones reducing the ill-conditioning of the problem [1]. Up to now, rectangular PSWFs has been successfully exploited to perform optimized NF characterizations of rectangular aperture antennas. Recently, we tackled the extension to the case of circular apertures. The difficulties related to the stability and accuracy of the numerical evaluation of the Circular PSWFs have been assessed in [2], showing the benefits due to the use of a proper expansion, with respect to standard backpropagation. Furthermore, the circular PSWFs expansion correctly takes into account for the spectral radiating support, with respect suboptimal representation of the rectangular case. The aim of the paper is to show how the circular PSWFs expansion can be fruitfully exploited in the NF characterization of circular aperture antennas. Experimental results will be presented to support the performance of the method. [1] A. Capozzoli, C. Curcio, G. D’Elia, A. Liseno, “Singular value optimization in plane-polar near-field antenna characterization”, IEEE Antennas Prop. Mag., vol. 52, n. 2, 103-112, Apr. 2010. [2] A. Capozzoli, C. Curcio, G. D’Elia, A. Liseno, “Prolate Function Expansion of Circularly Supported Aperture Fields in Near-Field Antenna Characterization”, European Conference on Antennas and Propagation 2017, Paris 19-24 March 2017.
The expanding market for millimeter wave antennas is drivinga need for high performance near-field antenna measurement systems at these frequencies. Traditionally at millimeter waves, acquisition of two orthogonal polarizations have been achieved through mechanical rotation of a single polarized probe and an associated frequency conversion module. This generally results in the collection of two complete spherical data sets, one for each polarization,with both acquisitions significantly separated in time. To enable improvements in both measurement speed and accuracy, MVG have developed a new high performance dual polarized feed in V-band (50GHz-75GHz). This probe has been integrated in a millimeter wave Spherical Near-Field (SNF) system via two parallel receiver channels that are simultaneously sampled. This architecture more than doubles the acquisition speed and additionally ensures that the two polarization components are sampled at precisely the same point in space and time. This is particularly important when performing accurate polarization analysis (e.g. conversion of dual linear polarization to spherical/elliptical polarizations). The two measurement channels are calibrated via radiated boresight measurements over a range of polarization angles, generating a four term “ortho-mode” correction matrix vs. frequency. The SNF probe is based on an axially corrugated aperture providing a medium gain pattern (14dBi). The probe provides symmetric cuts and low cross-polarization levels in the diagonal planes. The directivity/beam-width of the aperture has been tailored to the measurement system, ensuring proper AUT illumination and sufficient gain to compensate for free space path loss. Dual polarization capability is achieved with an integrated turnstile OMT feeding directly into the probe circular waveguide and a conical matching stub at the bottom. Thanks to the balanced feed used for each polarization, the port-to-port coupling is sufficiently low to allow for simultaneous acquisition of the two linear field components. Input ports are based on standard WR-15 waveguide to simplify the integration with the front-end (dual channel receiver). The paper will present the detailed description and measured performances of the new dual polarized SNF probe. Additionally, measurement time and achieved accuracy will be compared between the single polarization probe architecture and the dual polarized probe installed in the same spherical near-field antenna measurement system.
CubeSats represent a major paradigm shift for the satellite community and access to space in general. Traditionally, the design trend for satellites focused on durability, long lifetimes, and high performance, which translates to a high cost and lengthy time to deployment. CubeSats, on the other hand, compromise performance and lifetime with the goal to dramatically reduce costs and development time. Their small size allows launching as a secondary payload which is a key factor in cost reduction. The chassis dimensions (typically 3U to 6U) makes it difficult to integrate high performance wireless systems into the CubeSat chassis. A major limitation is the volume required for a high-gain antenna. Deployable, high-gain antennas are attractive for CubeSats, especially ones that can be stowed in a compact footprint. Deployment strategy is a major consideration for designers, and current attention has focused on developing large apertures that deploy outside the CubeSat chassis (e.g. umbrella or truss-net reflectors). However, little work has been done to develop ultra-compact, deployable antennas with moderate aperture sizes that seamlessly integrate with the chassis. We propose a novel CubeSat antenna concept that utilizes a near-field Gregorian reflectarray. The feed is a planar array conformal to the CubeSat surface that radiates an effective plane wave in its near-field zone. A parabolic subreflector focuses the plane wave towards the focus of the main reflectarray aperture, which has been designed to emulate an offset parabolic main reflector. This reflectarray is also conformal to the CubeSat chassis. The novelty of this design lies in the deployment strategy, where only the small subreflector is reoriented for deployment. This overall design avoids cable movement and maintains a compact volume when stowed, while achieving desirable efficiencies. We will present our compact antenna arrangement for Ka-band operation with an aperture of 209mm which integrates with a 6U CubeSat chassis. The challenges in the design are threefold: developing a compact, efficient planar array for plane wave generation; developing an offset, efficient reflectarray; and developing tools for diffraction analysis of the full system. We also present measured performance for various segments of this system using UCLA bipolar planar near-field system to avoid gravitational loading and issues with linear probe motion.
NIST has been using coordinated robotics in the Configurable Robotic Milli-Meter wave Antenna (CROMMA) system to assess antenna performance and radiative emissions since 2010. The focus to date has been using coordinated motion to arbitrarily position and correct antenna alignment for high frequency (>60 GHz) applications. Coordinated robotic motion was originally chosen to overcome the systematic alignment and range configurability limitations inherent in legacy stacked-stage ranges. A limitation with CROMMA is the relatively small spatial reach of the robotic arm (2.5 m), which limits antenna size and the number of wavelengths in separation achievable for lower frequencies. To overcome these limitations and address other dynamic testing requirements, NIST proposed the Large Antenna Positioning System (LAPS). The LAPS consists of two kinematically linked robotic systems, one of which is integrated with an 8 m linear rail system. The stationary robot is a 6 axes, 2.5m horizontal/4.4m vertical reach robotic arm, while the robot integrated with the linear rail system is a 6 axes, 3m horizontal/5.5m vertical reach robot arm. This configuration allows antennas to be positioned within a 5m x 6m x 10m volume. The motion system can operate in either a coordinated or independent motion control state, allowing independent or dynamic dual-robot motion. The coordinated capabilities of the system are designed to support not only traditional antenna measurement geometries (i.e. spherical, cylindrical, planar, gain-extrapolation), but also intended to be used to dynamically interact with changing RF conditions. The robots can independently scan or interrogate multiple bearings of a device under test, or trace out complex 6D paths during system testing. Initial data on performance of the system, including comparison of robot kinematics, RF acquired data, and physical locations verified by a laser tracker, will be presented.
Cellular Base Stations require efficient performance validation methods. One performance criterion is the Station radiation pattern. In directive pattern measurements, it is well documented that the Compact Antenna Test Range (CATR) and the Spherical Near Field (SNF) methods produce equivalent patterns. However, Base Station radiation patterns are not necessarily directive to the extent necessary for equivalent patterns among CATR and SNF methods. In deploying a number of Spherical Near Field and point source Compact Antenna Test Range (CATR) test facilities, we have observed the radiation pattern of base station antennas are more sensitive to the mount in a CATR than in a Spherical Near Field Antenna Test Range. This fact conflicts with intuition and theory. A barbeque spit positioner has been deployed in both spherical near field and point source compact ranges. Recently the point source compact range has been observed to yield patterns noticeable different depending on the antenna mount to the spit. On the other hand, the Spherical Near field implementation, in at least two deployments to Germany, has NOT manifested such a dependence on the mount, or, perhaps, such a dependency exists and yet has not been recognized. Measured Data will be presented showing radiation dependencies upon the mount in a CATR and SNF implementation. Explanations as to the Root Cause will be stated.
As part of the Lockheed Martin (LM) Additive Manufacturing (AM) Initiative, the Rotary Mission System antenna group has been developing a new and improved Additive Spiral Antenna (ASA) for both transmit and receive applications. This is a collaboration effort between LM engineering and LM manufacturing for a low cost and high performance antenna for manyultra-wide band(UWB) applications in both military and commercial market sectors. Unlike other conventional spiral designs, thisrecently emerging Additive Manufacturing capabilities allow extra spiral antenna miniaturizations without additional gain bandwidth performance penalties. This is achieved by leveraging unique low cost AM abilities to form complex and thus much more efficient 3D shapes to increase spiral antenna radiation efficiency, approaching the Chu’s gain bandwidth limitation. An initial prototype ASA was designed and tested in 2016 and showed very encouraging results. The measured ASA performance indicated nearly the same antenna performance as our current conventional production spiral antenna having multi-decade frequency band performance. More importantly, the ASA aperture size was significantly reduced by more than 50% with excellent transmit and receive gain efficiency and power handling capabilities. This paper will describe this ASA prototype design approaches and antenna near field and far field compact range measurement results along with material characterizations to demonstrate Additive Manufacturing technology can enhance antenna performance that otherwise not realizable with conventional fabrications. In addition, an integrated optimum balun length electromagnetic band gap (EBG) cavity design further reduces the antenna depth by over 70% will be presented. This is realized by use of high power and high temperature honeycomb absorbers in conjunction to electromagnetic band gap (EBG) cavity design for achieving high efficiency and low cavity profile, with total antenna volume reduction by nearly 3x. Some discussions will be provided for solving high thermal issues associated with ASA’s transmit capabilities.
To meet the ever increasing need for wireless communication bandwidth, the proposed 5G new radio access technology will utilize techniques such as beamforming and massive MIMO which have not seen widespread adoption in any previous wireless technology. It will also attempt to use millimeter wave frequencies for mobile communication at a scale never seen in previous defense and satellite applications. These decisions will have a drastic impact on the test methods used to validate the operation and performance of new radio designs, requiring radiated test techniques to replace tests that are traditionally performed conducted. This paper will touch on various issues the industry must address, and the current work in 3GPP to develop the basis for these test techniques before the radio design has even been completed.
Positioning in near-field antenna measurements is crucial and often an absolute position accuracy of ?\50 is required. This can be difficult to achieve in practice, e.g. for robotic arm measurement systems and/or high frequencies. Therefore, optical measurement devices are used to precisely measure the position and orientation. The information can be used to correct the position and orientation during the measurement or in the near-field to far-field transformation. The latter has the benefit that the measurement acquisition is typically faster because no additional correction movements are needed. Different methods for correction of non-ideal measurement positions in r, ? and f have been presented in the past. However, often not only the relative position but also the orientation between the antenna under test (AUT) and the probe coordinate system is not perfect. So far, correction and investigation of the related non-ideal probe orientations has been neglected due to the assumption that the probe receiving pattern is broad. In this paper, non-ideal probe orientations will be investigated and a spherical wave expansion procedure which corrects non-ideal probe orientations and positions will be presented. This is achieved by including an arbitrary probe pointing in the probe response calculation by additional Euler rotations of the probe receiving coefficients. The introduced pointwise higher-order probe correction scheme allows an exact spherical wave expansion of the radiated AUT field. The transformation is based on solving a system of linear equations and, thus, has a higher complexity compared to Fourier-based methods. However, it will be shown that most of the calculations can be precomputed during the acquisition and that solving the linear equation system can be accelerated by using iterative techniques such as the conjugate gradient method. The applicability of the proposed method is demonstrated by measurements where an intentional misalignment is introduced. Furthermore, the method can be used to include full probe correction in the translated spherical wave expansion algorithm. In conclusion, the proposed procedure is a beneficial extension of spherical wave expansion methods and can be applied in different measurement scenarios.
New requirements in the field of autonomous driving and large bandwidth telecommunication are currently driving the research in millimeter-wave technologies, which resulted in many novel applications such as automotive radar sensing, vital signs monitoring and security scanners. Experimental data on scattering phenomena is however only scarcely available in this frequency domain. In this work, a new mono- and bistatic radar cross section (RCS) measurement facility is detailed, addressing in particular angular dependent reflection and transmission characterization of special RF material, e.g. radome or absorbing material and complex functional material (frequency selective surfaces, metamaterials), RCS measurements for the system design of novel radar devices and functions or for the benchmark of novel computational electromagnetics methods. This versatile measurement system is fully polarimetric and operates at W-band frequencies (75 to 110 GHz) in an anechoic chamber. Moreover, the mechanical assembly is capable of 360° target rotation and a large variation of the bistatic angle (25° to 335°). The system uses two identical horn lens antennas with an opening angle of 3° placed at a distance of 1 m from the target. The static transceiver is fed through an orthomode transducer (OMT) combining horizontal and vertical polarized waves from standard VNA frequency extenders. A compact and lightweight receiving unit rotating around the target was built from an equal OMT and a pair of frequency down-converters connected to low noise amplifiers increasing the dynamic range. The cross-polarization isolation of the OMTs is better than 23 dB and the signal to noise ratio in the anechoic chamber is 60 dB. In this paper, the facility including the mm-wave system is deeply studied along with exemplary measurements such as the permittivity determination of a thin polyester film through Brewster angle determination. A polarimetric calibration is adapted, relying on canonical targets complemented by a novel highly cross-polarizing wire mesh fabricated in screen printing with highly conductive inks. Using a double slit experiment, the accuracy of the mechanical positioning system was determined to be better than 0.1°. The presented RCS measurements are in good agreement with analytical and numerical simulation.
Time and Direction of Arrival (TADOA) analysis of field probe data has been an accepted method for characterizing stray signals in an antenna measurement range for many years ([1], [2]). Recent uncertainty investigations at the OneRY range have shown a need for increased resolution to isolate and characterize energy in TADOA images so that resources can be carefully applied to reduce the uncertainty from these stray signals. This is accomplished by modeling the TADAO image as the solution to a Basis Pursuit (BP) l1 minimization problem. This paper outlines the model development and shows concrete examples from OneRY field probe data where BP allows for the identification of stray energy which was previously difficult to find. We also show how the BP optimization context can be using to remove contamination from the data through the inclusion of additional basis functions ([3]). I.J. Gupta, E.K. Walton, W.D. Burnside, “Time and Direction of Arrival Estimation of Stray Signals in a RCS/Antenna Range,” Proc. of 18th Annual Meeting of the Antenna Measurement Techniques Association (AMTA '96), Seattle WA, September 30-October 3, 1996, pp. 411-416. I.J. Gupta, T.D. Moore, “Time Domain Processing of Range Probe Data for Stray Signal Analysis,” Proc. of 21st Annual Meeting of the Antenna Measurement Techniques Association (AMTA '99), Monterey Bay CA, October 4-8, 1999, pp. 213-218. B.E. Fischer, I.J. LaHaie, M.H. Hawks, T. Conn, “On the use of Basis Pursuit and a Forward Operator Dictionary to Separate Specific Background Types from Target RCS Data,” Proc. of 36th Annual Meeting of the Antenna Measurement Techniques Association (AMTA '14), Tucson AZ, October 12-17, 2014, pp. 85-90.
The paper summarizes the performance of a new near-field to far-field (NF/FF) transform approach for a VHF vehicle mounted AUT test case, and compares the approach with the spherical measurement approach. The NF/FF transformation is based on the solution of an inverse problem in which the measured NF and predicted FF values are attributed to a set of equivalent electric and magnetic surface currents which lie on a convex arbitrary surface that is conformal to the antenna under test (AUT). The NF points are conformal to the AUT, reducing the number of samples and relaxing positioning requirements used in conventional spherical, NF/FF geometries. A pseudo inversion of the matrix representing the mapping of the equivalent sources into the near-field samples is obtained by using the singular value decomposition (SVD), which is used to form an approximation of the inverse of the matrix. This inverse, when multiplied by the NF measurement vector, solves for the efficiently radiating components of the current, which are used to compute the FF in a straightforward manner. Keywords—Antenna Near-Field to Far-Field Transformation, Electromagnetic Inverse Problems.