AMTA Paper Archive
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A New Formulation for Three Antenna Polarization Measurements
In this contribution the signal received by an antenna is understood as an inner product built by the polarization vectors of the involved antennas. By using a suitable unitary transformation the polarization efficiency can be straightforwardly calculated without additional assumptions. By solving an eigenvalue problem given by a unitary operator which represents a rotation, a simple and illustrative interpretation is possible. The formulation is applied to derive the well-known relations of the improved three antenna polarization measurement technique given by Allen C. Newell, which is mainly based on the measurement of relative power levels. Some measurement results and the calculation of the achievable measurement accuracy are presented.
Geometric Effects on Radar Echoes from a Corner Reflector
Radar data on the complete polarimetric responses from a 4" dihedral corner reflector from 4 to 18 GHz have been collected and studied. As a function of the azimuth, the vertically suspended object may present itself to the radar as a dihedral, a flat plate, an edge, a wedge, or combinations of these. A two-dimensional method-of-moment (2-D MOM) code is used to model the perfectly electrical conducting (PEC) body, which allows us to closely simulate the radar responses and to provide insight for the data interpretation. Of particular interest are the frequency and angular dependences of the responses which yield information about the downrange separation of the dominant scattering centers, as well as their respective odd-or even-bounce nature. Use of the corner reflector as a calibration target is discussed.
Specular Reflectance and Antenna Property Measurements in 325-500 GHz Frequency Range
Specular reflectance data of indoor interior materials is a prerequisite to analysis of the channel characteristics for new millimeter and submillimeter indoor wireless communications. Antenna property such as gain and radiation pattern is one of the key measurement quantities in electromagnetic wave metrology. This paper describes a specular reflectance and antenna property measurement system and shows measurement results of the specular reflectance of an Acetal plate and the antenna property of a 24 dB horn antenna in 325-500 GHz frequency range.
Equivalent Sources Based Near-Field Far-Field Transformation Above Dielectric Half Space
In order to support near-field measurements of automobile antennas in as realistic as possible environments, an equivalent sources based near-field far-field transformation approach for near-field measurements above a possibly lossy dielectric half-space is presented and evaluated. Different possibilities for considering the half-space influence are discussed, where an approach with an appropriate half-space Green's function is found to be most accurate, as expected. The formulation of the equivalent sources transformation approach with the half-space Green's function and a formulation with free-space Green's function together with equivalent sources representation of the half-space influence are discussed and a variety of results are presented in order to corroborate the feasibility of the various approaches.
Measurement of Active Reflection Coefficient for Co-located MIMO Radar Using Dual Directional Couplers
This paper presents a way to determine mutual coupling effects through analysis of the active voltage standing wave ratio (VSWR) to predict the presence of large reverse power levels in co-located multiple input multiple output (MIMO) radars in transmit mode. The methodology consists of measuring the forward and reverse waves on a dual directional coupler (DDC) to directly obtain the active reflection coefficient on a co-located MIMO radar system. The active VSWR of each individual antenna is computed from measurements of the active reflection coefficient. These results are compared against analytical methodologies.
A General and Effective Mode Filtering Method for the Suppression of Clutter in Far-Field Antenna Measurements
The use of mode filtering to improve the quality of antenna measurements taken in non-anechoic environments is well known, [1, 2, 3, 4, 5]. In the far-field case [6, 7, 8], it has been shown that it is possible to use standard cylindrical near-field theory  to implement the necessary mode filtering using a singularly polarized, great circle, far-field pattern cut consisting of amplitude and phase data. The careful verification of this technique using a compact antenna test range (CATR) was reported in [7, 8] however that implementation had, as a prerequisite, the need to acquire the far-field data on a monotonic and equally spaced pattern abscissa. In many instances this is not convenient or perhaps impossible. This paper presents a recent development which allows data to be processed rigorously when having been acquired using an unequally spaced angular abscissa. This paper sets out the novel, far more sophisticated, algorithm together with results of actual range measurements that were processed using this new technique.
Fully Probe Corrected Spherical Near Field Offset Measurements with Minimum Sampling Using the Translated-SWE Algorithm
The Translated Spherical Wave Expansion (TSWE) has recently been proposed as a very effective Near-Field-to-Far-Field (NF/FF) transformation tool for down-sampled Spherical Near Field (SNF) measurements with offset Antenna Under Test (AUT). In case of electrically small probes and/or small AUT-probe view angles the TSWE can be accurately applied without compensating for the probe effect. Instead, when electrically larger probes and/or larger view angles are considered, the measured signal is affected by an averaging field effect that should be properly compensated to ensure a good accuracy. In this paper the TSWE technique is applied for the first time tacking into account the full effect of the measuring probe. To validate the proposed technique, a standard gain horn intentionally displaced in offset configuration have been measured in SNF geometry with a first order probe and two different wideband higher-order antennas as probe.
Plane Wave Generator for Direct Far-field Over-The-Air Testing of Devices
The Plane Wave Generator (PWG) is an array of elements with suitably optimized complex coefficients, generating a plane wave in the close proximity of the array. Thus, the PWG achieve far-field testing conditions in a Quiet Zone (QZ) at a reduced distance in a manner similar to what is achieved in a Compact Antenna Test Range (CATR) . In this paper, the concept of a high performance, dual polarized PWG supporting up to 10:1 bandwidth is presented for the first time. A prototype of a dual polarized PWG has been designed, manufactured and tested in the 600MHz to 6GHz frequency range. The initial testing results on QZ uniformity and evaluation of possible measurement accuracy are presented.
Some Advantages of Using Bi-directional S-Parameters in Near-Field Measurements 1
The unknown-thru calibration technique is being used to achieve a system level calibration at millimeter wave frequencies (>50 GHz) on the robotic ranges at NIST. This two-port calibration requires the use of a full bi-directional measurement, instead of a traditional single-direction antenna measurement. We explored the value of the additional data acquired. We find that we can use this information to verify antenna/scan alignment, image the scattering from the positioner/facility, and perform a first order correction to the transmission data for uncertainties due to LO cable flexure.
Adapting a Commercial-Off-The-Shelf Amateur Radio Antenna for Use in Small Satellite Ground Station Radio Link
Finding an off the shelf antenna tuned for the operating frequency of a small satellite mission can be difficult, especially when the mission uses an experimental license in a frequency band that is not used for commercial or amateur radio systems. This paper discusses how electromagnetic modeling software can be used to assist adapting commercial-off-the-shelf (COTS) antennas to other operating frequencies than the ones for which they have been originally designed. The discussion is illustrated with a case study outlining how a COTS cross-polarized UHF Yagi amateur radio antenna is adapted for operation in the 400 MHz experimental bands.
Systematic Study: Channel Sounding via Modal Expansion
We present a preliminary study of a modal (partial wave) expansion of the field used to characterize a propagation channel. We assume that the measurements of the scalar, two-dimensional field from which the modal expansion coefficients are obtained, contain Gaussian phase noise with zero mean. Three spatial sampling patterns of the field are considered. We find that the accuracy of the reconstructed field is strongly influenced by the spatial sampling pattern.
Antenna Radiation Pattern Measurements Using a Reverberation Chamber
This paper investigates the use of a reverberation chamber for antenna radiation pattern measurements allowing for significant cost reduction compared to anechoic environments. Our method utilizes averaging of paddle measurements to replicate anechoic data. We discuss both a correlation experiment, to determine how many degrees the reverberation paddle must rotate to create an uncorrelated measurement based on a 0.5 correlation threshold, and a radiation pattern measurement. Two matched horn antennas are used and operated between 1 GHz and 18 GHz. Good agreement is found between our measurements taken in a reverberation chamber and those taken by the manufacturer of the antenna in an anechoic chamber. We find that the main lobe radiation pattern of our antenna can be estimated with more certainty than the back-lobe radiation using a reverberation chamber. The goal is to use this simple and cost-effective method to determine radiation patterns for embedded antennas with unknown patterns, such as those within wireless devices.
Implementation and Numerical Analysis of an Indoor mm-Wave Network
The growth of connected mobile devices in the current network and new applications such as real-time communication, video streaming and others, exponentially increases the throughput demand. The proposed paper presents a numerical and experimental study of propagation and coverage on a 91 m² indoor environment at 24.15 GHz. The numerical analysis has been made with the support of Altair WinProp™ software in order to estimate the environment coverage map. The numerical study is experimentally validated by collecting error vector magnitude (EVM) measurements, in specific positions, of a 160 Mbit/s QAM signal. The transmission is made by a 12-dBi gain omnidirectional slotted waveguide antenna array with approximately 1 GHz of operational bandwidth. Experimental results presented a 40% coverage for EVM below 12%.
Conex Antenna, Radar, and Measurement Equipment Lab
The Conex Antenna, Radar, and Measurement Equipment Lab (CARAMEL) is a ten-element VHF antenna array that operates from 30 MHz-120 MHz with an attached lab space. This array was developed for use in low frequency Radar Cross Section (RCS) measurements. The antenna elements support both vertical and horizontal polarizations. The antenna was designed using a genetic algorithm, employing the fragmented aperture technique; measured and modeled data will be presented. The attached lab space is air conditioned and provisioned for rack mounted equipment. The structure uses a modified 20' Conex shipping container where an entire sidewall has been replaced with a reinforced composite radome for the antennas. The overall mechanical frame design included a Finite Element Analysis to ensure structural integrity. The system is intended for long-term standalone use as an outdoor measurement radar system but can be moved using standard shipping container methods. The structure was shipped using a standard cargo carrier from Atlanta, Georgia to White Sands, New Mexico.
A Novel S-band Two-Layer Dielectric Rod Antenna with High Gain and Very Low Cross-polarization
In this paper, the concept of a new S-band dual-polarized dielectric rod antenna is discussed. The antenna is composed of two concentric dielectric cylinders. The inner dielectric presents high dielectric constant, while the outer has a lower dielectric constant. Given this configuration, the resulting antenna provides high gain, narrow beamwidth, large bandwidth, and very low cross-polarization. In addition, the antenna is lower size in the transversal dimensions, and is predicted to be lighter than other antennas that provide equivalent performance, especially at low frequencies (S-band). An antenna with such an architecture can be 3D-printed, and therefore, the cost for the fabrication are considerable low. Numerical results of the antenna performance are presented and discussed.
A Novel Method for Suppression of Individual Problematic Sidelobes in Phased Array Antennas
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.
Improved Nearfield Gain Measurement of High Gain Antennas Using Directivity and Loss Technique
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.
A Method for Transmit and Receive Antenna Diversity System Characterization for Automotive Vehicle to Vehicle Communications
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.
Estimation of the Realistic Ground Effect in Free-Space Automotive Measurements
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 . 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  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.
Extending the Scan Volume of Planar Near-Field Scanners with AUT Rotation
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.
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