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Shipboard phased array radar antennas typically have high gain, low sidelobe specifications, and testing after initial production, overhaul or repair often reveals sidelobes that fail specifications, requiring rework. Further, some systems only allow phase adjustments as a means to fine tune the pattern. To correct sidelobe failures in these systems, the phase distribution of the array is first mapped using near-field scanning techniques, then specific element phases are adjusted, such as by using phase shifters. The standard method of determining phase changes has been based on trying to achieve a nominal phase profile; however, this method does not allow targeting specific problematic sidelobes. The authors have developed a novel method, dubbed "Whack-a-Lobe", which targets suppression of specific sidelobes while minimizing other impacts to the pattern. Recognizing that far-field sidelobes are a summation of complex vectors of the individual elements in the direction of the sidelobe, the authors have developed a cross product technique that identifies elemental vectors orthogonal to a far-field sidelobe vector such that only a minimal phase change to these elemental vectors is needed to reduce the sidelobe level. This technique is targeted, deterministic, and reduces tuning cycles, labor hours and antenna test chamber time.
Antenna gain is the product of directivity and antenna loss. Antenna gain is typically measured by comparing the antenna under test (AUT) to a standard gain horn (SGH) or direct gain measurement using a calibrated probe. This requires an accurate account of power into the AUT and SGH, the loss of all test cables and switches must be measured to obtain an accurate AUT gain. Additionally, SGH calibration uncertainty reduces the quality of the measurement. The gain measurement technique describe here exploits the near-field range capability of accurately producing the pattern of high gain antennas. The near-field range allows the full wave capture of antenna aperture fields and transformation to the far-field with high resolution. The new technique uses the directivity obtained by integrating the far-field pattern, accounts for the spill-over energy not measured by the near-field range, and uses measured network losses of the AUT. It does not require measured losses of test cables and switches. Since AUT losses are typically measured as part of antenna integration the technique reduces overall measurement burden. Accurate calculation of spill-over energy is the key to success. The technique has been shown to yield better accuracy than the typical gain calibration method for multi-beam high gain antennas.
The US National Highway Traffic Safety Administration is in process of mandating a vehicle to vehicle (V2V) communications system operating at 5.9 GHz for all new ve hicles to be implemented in the mid 2020's. A key safety feature of this system is to provide alerts allowing the driver time to take evasive action, including situations with obstructed views whe re LIDAR or other line-of-sight based safety systems will not have adequate performance. The safety feature is implemented by e ach vehicle broadcasting a basic safety message (BSM) to all surrounding vehicles out to 300 meters in all directions. The refore, the antenna system shall be capable of transmitting and receiving the BSMs in all directions around the vehicle, ide ally with no pattern nulls. Due to the realities of antenna placement multiple antennas with transmit and receive diversity are needed to achieve the full 360 degree azimuth coverage. As this is a NHTSA regulated requirement the performance of the V2V antenna system will be certified via test. Un fortunately, passive antenna testing is insufficient to fully validate the antenna system. Moreover, the specific diversity algorithms to be used are not defined by the V2V regulation and often vary from manufacturer to manufacturer. And e ven if all manufacturers are using maximal ratio combining for receive diversity and cyclic delay diversity for transmit diversity, the actual implementation due to differences in digital filters or delays will change the overall performance. The result is that the actual radio performance must be considered when combining the antenna patterns of multiple antennas. This paper discusses a te chnique using a channel emulator and V2V radios to combine antenna gain and determine the realized antenna gain of the combined antenna system after diversity is considered. Using this technique the antenna test engineer can validate the antenna system performance against the V2V required performance.
Testing of automotive antennas are commonly performed in large Spherical Near Field (SNF) ranges [1-3] able to host the entire vehicle to test the effect of the antenna coupling with the structure [3]. The impact of a realistic ground, such as asphalts or soil, on the radiation performance of the vehicle mounted antennas is often a desired information. As long as the free-space response of the vehicle is available, such information can be obtained with fairly good accuracy considering post-processing techniques based on the Image Theory (IT). Automotive systems with absorber material on the floor [3] are thus ideal for estimating such effects because the free-space signature of the vehicle is directly measured and because the radiation pattern is usually available on more than just a hemisphere. In this paper an IT-based technique which allows for the estimation of a realistic ground is proposed and validated with simulations where the measurement setup of a typical multi-probe free-space automotive system is emulated. The impact of the truncation of the scanning area is analyzed in detail showing how advanced post-processing techniques [4-6] can be involved to mitigate the truncation errors and thus obtain a better estimation of the realistic ground effect.
Planar near-field ranges are popular facilities to evaluate far-field antenna patterns. These ranges typically have the scanner plane parallel to the Antenna Under Test (AUT). Having the scanner plane parallel to the AUT can limit the maximum far-field angles that can be properly measured due to the mechanical extents over which the range can accommodate. This paper summarizes a test approach where the AUT is rotated in the near-field such that sufficient energy is concentrated within the range extents, ultimately resulting in an accurate far-field pattern. Measured results will be shown which demonstrate the limitations of the current testing approach, as well as the benefits of the near-field rotation approach.
This paper documents the various elements of the 2017/18 upgrade and presents results from the performance validation measurements with the DTU-ESA 12 GHz Validation Standard antenna conducted before and after the upgrade. The upgrade concerned several major improvements to the building infrastructure, the ventilation system, the antenna positioner, and the probe positioner. The validation measurements involved the averaging of measurements at different distances between the antenna under test and the probe to compensate the multiple reflections between these. This in turn necessitated the investigation of the compensation of the system drift between the measurements and of the sensitivity of the probe calibration to the position of the probe on the probe positioner.
Empirical optimization of software reconfigurable antennas having hundreds of degrees of freedom demands rapid measurement, especially when multiple objectives, e.g. gain at multiple angles and polarizations, are included. This paper describes a measurement technique and process flow for rapid optimization of antenna performance. Previously, such evaluation with mechanical scanning was slow and impractical. The technique is enabled by closed-loop automation of an electronically scanned near field measurement system that determines the hemispherical radiation pattern of a given antenna state in approximately 1 second. In this way thousands of antenna states are evaluated per hour. This paper presents measurements of antenna states optimized using the new technique, and results are compared to measurements of states optimized by the usual far field technique.
Additive manufacturing has become a popular alternative to traditional CAM techniques, as it has reached a suitable maturity and accuracy for microwave applications. The main advantage of the additive technologies is that the manufacturing can be performed directly from the 3D CAD model, available from the numerical simulation of the antenna, without significant modifications. This is a highly desirable feature, in particular for time and cost critical applications such as prototyping and manufacturing of small quantities of antennas. Different 3D-printing/additive manufacturing technologies are available in industry today. The purpose of the paper is an investigation on the accuracy and repeatability of the Selective Laser Melting (SLM) manufacturing technique applied to the construction of a batch of 15 broad band fully metallic chocked horns, operating at X/Ku band, manufactured in parallel. Manufacturing accuracy and repeatability has been evaluated using RF parameters as performance indicators comparing measured data and high accuracy simulations. The radiation patterns have been correlated to the numerical reference using the Equivalent Noise Level, while manufacturing repeatability is quantified on input matching by defining an interference level. These indicators have also been compared to state-of-the-art values commonly found for traditional manufacturing.
NB-IoT (Narrowband Internet of Things) is a narrowband radio technology showing very different characteristics compared with traditional wireless protocols. For the first time based on authors' best knowledge, this paper compares the Over-the-Air (OTA) performance of NB-IoT in the Reverberation Chamber (RC) and Anechoic Chamber (AC), which involves two major RF test environment variations in the OTA test arena. In this paper, the Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS), related to the transmitter and receiver performance of NB-IoT, respectively, are investigated. For TIS test, an early exit algorithm with 95% confidence level based on Chi-Square distribution has been developed to improve the test speed. The test results show a good match (Within CTIA allowed measurement uncertainty) between AC and RC. Our analysis also includes several key parameters, such as test repeatability, measurement uncertainty, and test time, which gives a comprehensive comparison of different aspects between RC and AC for NB-IoT OTA test. It could be noticed as well that the early exit algorithm based on Chi-Square distribution improves the test time performance significantly without compromising the test accuracy.
This paper presents the second phase of the development of a new measurement technique to determine antenna system noise temperature using data acquired from a planar near-field measurement. In the first phase, it was shown that the noise temperature can be obtained using the plane-wave spectrum of the planar near-field data and focusing on the portion of the spectrum in the evanescent region or "imaginary space". Actual evanescent modes are highly attenuated in the latter region and therefore the spectrum in this region must be produced by "errors" in the measured data. Some error sources such as multiple reflections will produce distinct localized lobes in the evanescent region and these are recognized and correctly identified by using a data point spacing of less than /2 to avoid aliasing errors in the far-field pattern. It has been observed that the plane wave spectrum beyond these localized lobes becomes random with a uniform average power. This region of the spectrum must be produced by random noise in the near-field data that is produced by all sources of thermal noise in the electronics and radiated noise sources received by the antenna. By analysing and calibrating this portion of the spectrum in the evanescent region the near-field noise power can be deduced and the corresponding noise temperature determined. In the current phase of tests, planar near-field data has been acquired on a measurement system and the analysis applied to determine the system noise parameters. Measurements have been performed with terminations inserted at three different locations in the RF receiving path: the IF input to the receiver, the input to the mixer and the input to the probe that is transmitting to a centre-fed reflector antenna. The terminations consist of either a load that serves as the "cold" noise source or a noise source with a known noise output for the "hot" noise source.
A new Compact Antenna Test Range (CATR) has been built, as a turnkey facility, with a cubic quiet zone (QZ) of 4.8m x 4.8m x 4.8m in the frequency range 0.9-18 GHz. The CATR has been installed in a new building with an isolated and stable foundation. The dimensions of a traditional CATR for such QZ size becomes impractical and requires a very large chamber. A new, diagonally fed, short focal length reflector has been developed to minimize the chamber size to fit the dimensions of 22 m x 14.5 m x 14.5 m.
In this paper, we present a chip antenna in the 27GHz band, targeting 5G measurements. This antenna can be used as reference in mm-wave measurement systems, such as the MVG µ-Lab, feeding the antenna under test through a micro-probe station. The reference antenna is employed to calibrate in gain through the substitution method. The antenna shown in this paper is an array of four patches, fed through a strip-line beam forming network. A transition strip-line to coplanar waveguide allows the antenna be fed by the micro-probe.
This paper discusses about the design, fabrication and testing of a compact P-band (370 MHz) dual circular polarization (CP) patch antenna. The antenna is intended for reflectometry applications by measuring both direct and ground reflected 370 MHz signals transmitted from a satellite or airborne source. This design adopts quadrature-phase hybrid feeding network for achieving excellent polarization purity and supporting simultaneously LHCP and RHCP measurements. Another novel design aspect is placing the feeding network on top of the patch so that the antenna can be mounted directly on a ground plane. Therefore, the resonant modes inside the patch is excited from the top instead of from ground plane as in conventional designs. High dielectric material (ECCOSTOCK®HiK) with a dielectric constant of 9 and loss tangent of 0.002 was used as the substrate to reduce the antenna size. The final antenna has a dimension of 5.9" x 5.9" x 1.3" (excluding ground plane) and weight of 1620 gram. The measured performance on a 1-foot diameter circular ground plane showed 4.5 dBic gain and 23 dB co-polarization to cross-polarization isolation at the center frequency for both LHCP and RHCP. The 1-dB gain bandwidth is approximately 3.7%.
The fundamental purpose of absorber treatment in an anechoic chamber is to ensure that only the direct-path signal is coupled between the range antenna(s) and the device under test. For many simple and standard geometries, this is readily accomplished with conventional processes and procedures. When the geometry and/or stray-signal requirements deviate from the norm, however, it can be very beneficial to have an easy and reliable way to locate and quantify sources of stray signals. This paper discusses a straightforward algorithm for creating images of those stray signals in a range when a planar scanner and broad-beamed probe are available in the test zone. Measured data from multiple facilities are evaluated, along with absorber-treatment improvements made based on some of the images produced.
This paper presents a time domain antenna measurement technique by using a low cost software defined radio receiver. The technique aims to resolve measurement challenges derived from antennas where the reference signal is not accessible. The phase reconstruction implemented in this work is based on calculating the Fast Fourier Transform of the time domain signal to estimate the power spectrum and the relative phase between measurement points. In order to do that a reference antenna is used to retrieve the phase, providing a full characterization in amplitude and phase of the electric field and allowing source reconstruction. The results demonstrate the potential of this technique for new antenna measurement systems and reveal some of the limitations of the technique to be optimized, like the undesired reflections due to the interactions between the probe and the reference antenna.
This communication provides an experimental assessment of an accurate near-field-far-field (NF-FF) transformation with spherical scan, properly developed to take into account a mounting in offset configuration of a quasi-planar antenna under test (AUT). Such a technique relies on the nonredundant sampling representation of electromagnetic fields and, unlike the classical NF-FF transformation, it allows the reconstruction of the far field radiated by an AUT from a minimum number of NF data, which remains practically the same both when the AUT is mounted in onset and offset configuration, since this number is related only to the surface modeling the AUT. Such a surface has been here chosen coincident with that formed by two circular bowls with the same aperture and eventually different bending radii. Experimental results assessing the validity of such a technique are reported.
The principles of near-field antenna measurements in Cartesian, cylindrical, and spherical coordinates are well established and documented in the literature and in standards used on antenna ranges throughout government, industry, and academia. However the measurement methods used and the mathematics that are applied to compute the gain and radiation of the pattern of the test antenna from the near-field data assume that the antenna is operating in free space. This leaves several questions open when dealing with antennas operating over a lossy ground plane, such as the ocean. In this paper, we shall discuss a possible avenue for addressing this problem : the use of Complex Image Theory (CIT). The CIT approach allows the lossy earth to be removed and an image of each equivalent source point in the space above it to be constructed in the now empty space below it, but where the depth of that image is in general a complex number. While it might appear confusing to define a complex depth, such a depth is merely a mathematical construct that accounts for a magnitude and phase shift that occurs due to the presence of the lossy ground. The depth is computed so that the boundary condition at the surface of the original lossy ground is maintained; in this way, an equivalent problem is formulated. We propose an approach based on CIT that can be applied to the problem of a spherical nearfield antenna measurement taken over seawater. A limiting case of measurements taken over a metal ground plane shall be presented, along with thoughts about some practical concerns involved in the performance of such measurements.
In this paper, we investigate the achievable time savings in planar near-field (PNF) measurement of high gain antennas using a planar wide-mesh scanning (PWMS) approach [1-2]. The PWMS employs at least four times less measurements points than standard scanning without degrading the measurement accuracy leading to an under-sampling factor of four. Such mesh scanning can be implemented on standard planar near-field systems similar to the ESTEC, Hertz PNF scanner [3, 4]. The measurement accuracy vs time-saving for the wide-mesh approach is investigated using the numerical model of a highly-shaped Ku-band reflector antenna. This antenna is a realistic representation of what is currently flying on typical satellites with European coverage such as Eutelsat W [5]. The Near Field to Far Field transformation accuracy is investigated by comparing traditional and PWMS results using the same base data from the antenna model. A discussion on implementation on existing scanners and the relation with measurement time-savings is included. The experimental verification of the technique will be included in the conference presentation.
The performance of a compact antenna test range is evaluated by field-probing measurements of the quiet zone. The comparison between the simulated and measured data, however, is misleading due to the finite measurement accuracy and the limited nature of the numerical model. In order to allow a comparison, the uncertainty terms of the field-probing measurements and the numerical model are identified based on the National Institute of Standards and Technology 18-term uncertainty analysis technique. The individual terms are evaluated with simulations or measurements using the equivalent-stray-signal model. Bearing the differences between the model and the actual measurements in mind, the electrical field can be estimated precisely within the overlapping region of both uncertainty budgets.
In this paper, a novel algorithm for designing 3D-printed shaped inhomogeneous dielectric lens antennas is provided. The synthesis approach is based on a novel combination of Geometrical Optics (GO) and the Particle Swarm Optimization (PSO) method. The GO method can trace rays through inhomogeneous media and calculate the amplitude, phase, and polarization of the electric field. The algorithm is used to design an inhomogeneous lens antenna to produce an electronically scanned revolving conical beam to replace a mechanically scanned parabolic reflector antenna for spaceborne weather radar satellite antenna applications. Two breadboard model on-axis fed lens designs are presented and measured results given to validate the approach. A representative optimum off-axis design is presented which produces the revolving conically scanned beam. Imposition of a Body-of-Revolution restriction allows the optimization to be performed at a single offset feed location. The complex inhomogeneous engineered materials that results from optimization are printed using new 3D printers.