Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
As the 5G system becomes today’s main wireless communication service, a MIMO(Multiple-In Multiple-Output) configuration has been considered as an essential feature to provide an unprecedented high date-rate transfer for the wireless service users. Therefore, it is a big concern to design best diversity antennas for a mobile station and base station which are supposed to operate in mm-Wave frequency bands. In addition to the diversity antenna design, optimally deploying the 5G radio frequency system consisting of the MIMO configuration is another big concern to the 5G wireless service providers, because the millimeter Wave (mm-Wave) is expected to lose its transmitting power more abruptly than the previous wireless services. In this paper, the deployment parameters related to the base-station antennas are studiedfor better 5G networkperformance by applying machine learning algorithm. At first, MIMO antennas based on a printed dipole pair are designed both for a mobile platform and a base-station platform by taking into account the MIMO performance factors: envelope correlation coefficient (ECC) and mean effective gain (MEG) at one of the 5G frequency bands (26.5~29.5 GHz). Secondly, the designed antennas are deployed into a urban wireless communication scenario mainly composed of mobile stations, base stations, and buildings. In the urban scenario, the 5G system performance are estimated in terms of received power, signal-to-noise-and-interference ratio, and maximum data rate. Finally, the 5G base-station system is studied to aim at the better system performance by using a machine learning technique which especially suggests optimum antenna parameters for the base-station deployment.
In this paper, a 77 GHz microstrip comb-line antenna array for an automotive RADAR application with a low sidelobe level is proposed. The microstrip technology is used for the antenna due to its low fabrication cost, small size, and easy integration with other microwave circuitry. At very high frequencies such as millimeter waves, the gain of a single element patch antenna is not enough to withstand the RADAR application requirements, hence an array of antennae is beneficial. A The Phased array antenna configuration is needed to have a high gain and low sidelobe level of -20 dB and a beam steering mechanism. The design procedure used here is the implementation of a single comb antenna, that is further realized into a 1 x 10 uniform linear array of a comb line array. It has a gain of 14.81 dB and a sidelobe level of -15 dB. The radiation in the comb antenna is primarily due to the open sides with the lengths of the comb serving as transmission lines. The adjacent combs are placed at the distance of λ in order to co-phase the antenna elements at the desired frequency. Additionally, with an aim of reducing the sidelobe level, Taylor amplitude distribution is used, and the tapered array is designed. This methodology helped to achieve a sidelobe level of -20 dB. The gain of an overall array is increased to 20 dB by realizing the array of 4 x 10. Another requirement of the Automotive Radar is beam steering to accurately detect the target. Butler matrix is a beamforming network chosen to feed the phased array antenna. The proposed antenna array is simulated in Ansys HFSS with Rogers RO 3003 substrate of the thickness of 1.27 mm and has an overall dimension of 9 x 14.96 mm2. The goal of the design of this antenna is to acquire an appropriate radiation pattern with a low side lobe level better than -20dB and achieve beam steering using the Butler matrix to have a phased array configuration. Index Terms— RADAR, Antenna array, Comb line array, Butler Matrix, Phased array.
Diagnostic and verification testing of Low Observable (LO) platforms and components requires an Ultra-Wideband (UWB) Inverse Synthetic Aperture Radar (ISAR) imaging capability. A Compact Range (CR) is a test instrument that, when fitted with an instrumentation radar and target positioner, can efficiently produce ISAR images and other Radar Cross Section (RCS) data products required for LO research, design and production programs. Key limiting factors for the instantaneous radar imaging bandwidth of a CR is the feed antenna, where the criteria of a good feed is frequency bandwidth and illumination pattern shape. Maintaining a relatively constant reflector illumination characteristic typically requires several feeds with constant patterns functioning over smaller operating bandwidths, to be mechanically sequenced in the measurements. These feed limitations increase operational costs and complexity for LO measurements, driving a need for improved illumination sources providing constant reflector illumination for UWB collections. Focal Plane Arrays (FPAs) can be utilized to resolve these issues while increasing instantaneous bandwidth and measurement quality while reducing operational costs. This paper presents a procedure for defining complex weights of an FPA aperture to optimize radiation pattern matching to the reflector. A simulated plane wave arriving from the CR quiet-zone impinges on a model of the reflector. The FPA is placed in a region near the focal point and contained within the beam waist envelope, and the FPA weights are computed using a Computed Electromagnetic (CEM) techniques. The computational complexity of CEM simulations of electrically large CRs are usually prohibitive, however this method exploits the large focal lengths of CRs to sparsely model reflectors, and produces a tractable solution even at millimeter wavelengths. Practical aspects of FPA designs are presented and discussed as applied to the large outdoor CR at the US Army, Electronic Proving Ground (EPG), Fort Huachuca, Arizona.
Measurements of antenna prototypes are a critical component of the development cycle for antennas, arrays, and other radiating structures. Benchtop tests to characterize the circuit performance of such devices are generally available to engineers and scientists, but the ability to capture the space (radiating) characteristics is often lesser available. This is not only due to the need for a vector network analyzer but also the necessity for mechanical infrastructure to sample the fields in a scan volume around the antenna (i.e., antenna range). Moreover, the software capable of any data manipulation is needed to obtain the far-fields either directly or from the sampled near-fields. Herein, we describe the initial exploratory development of a low-cost, bench-top, custom spherical range. The system consists of a phi-stage turntable where the antenna under test (AUT) is mounted, a theta-stage swing arm that sweeps the probe antenna in an arc about the center of rotation, and a polarization stage turntable on the probe antenna side. An adjustable scan radius of 30-40 cm is built into the theta-stage. The bulk of the range is fabricated using standard fused deposition modeling (FDM) 3D printing and inexpensive commercial off-the-shelf (COTS) components are used for the motors and controllers to keep cost of the system (excluding the network analyzer and RF cables) to around 500 US dollars, in accordance with the restrictions for an advanced antennas course class project. Development, fabrication, and assembly took place over the course of approximately a month. The drawbacks of the utilized materials, however, primarily manifest in the oscillations of the theta-stage due to the low-infill ratio (~10%) of the 3D printed plastic in conjunction with the weight of the probe antenna. Additionally, a basic spherical near-field to far-field transform code is developed. The measurement results of a wideband horn antenna are performed to validate the range performance and will be shown and discussed at the conference. Thoughts on future development and potential are also shared.
Antennas on airborne platforms are subject to harsh environmental conditions such as rain and hail, as well as a wide range of pressure and temperature conditions. In this work, we propose a low-cost and easy to fabricate combined pressure and temperature test-bench for emulating the antenna performance while airborne. The specific antenna under test (AUT) is a millimeter wave 3d printed helix antenna enclosed in a specifically designed radome and fed with a 2.4mm connector. The entire system is subjected to airspeeds in excess of 200 m/s and operational altitude from the sea level through several kilometers. In the intended application, there are two possible pressure conditions that are considered, specifically open and closed. The open scenario assumes that the interior of the antenna is exposed to the ambient pressure level. In the closed case, the antenna has internal pressure that acts on the radome from inside at the higher altitudes in addition to the outside wind load due to the airspeed. Also, at higher altitudes, the temperature can drop to < -30˚C whereas at low altitudes it can be as high as 50˚C or more. Therefore, the structure needs to maintain its high-quality performance over the 80˚C temperature gradient. Note that both pressure and temperature can affect the antenna RF performance due to the drift of tolerances. To ensure proper operation, it is necessary to test the antenna when it is subjected to the above-discussed conditions, and for that purpose, the cost-effective combined pressure and temperature test bench is engineered for environmental tests of airborne antennas. Test-beds are mainly made of commercial off-the-shelf parts and in-house-made frames with all components integrated into one assembly. The system is developed for antennas having diameters and lengths of 125mm and 200mm, respectively, and occupies a relatively small volume. Experimental results that include live monitoring of VSWR during the variation in temperature from -20˚C to 50˚C and pressure from vacuum of half atmosphere to 20 PSI will be presented. This work is funded by the Office of Naval Research (ONR) grant # N00014-21-1-2641
Currently to determine the basic parameters of shales, namely Maturity (which indicates production potential), geochemical analysis need to be performed. These analyses may take days to weeks, depending on laboratory availability. Moreover, by the time the samples get to the laboratory, they could be damaged or poorly preserved, thus creating a significant source of uncertainty in the measurements. Pyrolysis is a method that introduces a sample of rock, of known mass, into a sealed oven that is programmed to heat the sample according to a prescribed rate of increasing temperatures that terminates at 650°C. During the initial heating, upon reaching a threshold in temperature somewhere around 300-350°C, a significant amount of hydrogen is recorded which is called the “S1” peak. With further increases in temperature beyond 350°C, another threshhold is reached at 550-600°C, where yet more hydrogen is evolved from the rock and the peak recorded at that stage is called “S2”. A microwave heating and testing for geological applications was tested with different shale samples. The system consists of a dual-mode microwave cavity, where heating and measuring is performed simultaneously with two different microwave sources. The cavity has a diameter of 104.92 mm and a height of 85 mm. A small shale sample of 9.8 mm diameter by 15 mm height is introduced in a quartz vial with an inner diameter of 9.8 mm and 120 mm. Depending on the electrical losses, the sample could be heated up to 1200°C. Initial complex permittivity measurements show that the imaginary part exhibits relaxation processes at specific temperatures. These temperatures coincide with the expected temperatures of the S1 and S2 peaks of the pyrolysis method, from which we can compute the vitrinite reflectance of the sample, which is an indicator of Maturity. Thus, allowing for quick estimates of maturity, which allows for real time decisions on the development of unconventional resources.
The precise characterization of the complex permittivity, particularly loss tangent, in low-loss dielectric samples at microwave frequencies usually employs resonant cavity methods, where the quality factor of some resonance is determined by a precisely dimensioned sample of the material placed inside the cavity. In order to characterize materials over a broad set of frequencies, a separate measurement fixture and sample is required for each frequency, a tedious and expensive endeavor. In response, one may turn to a single broadband measurement system, such as the focused beam system, but simple transmission and reflection measurements suffer from poor loss tangent sensitivity. In this work, a hybrid approach is investigated whereby a highly resonant periodic metallic array adjoined to a dielectric sample is measured in a broadband focused beam system. A frequency selective surface (FSS) is designed to be placed against a planar dielectric sample to create a transmission or reflection response that is sensitive to the loss tangent of the material under test. This sandwiched structure is illuminated by the focused beam system to approximate plane-wave-like incidence, and scattering parameters measured. It is shown that the magnitude of response at the resonant frequency is linearly dependent on the loss tangent of the material under test for a certain range of loss tangents, and sources of error that limit sensitivity at lower loss tangents are explored. The effect of various FSS design parameters on loss tangent sensitivity is investigated, including sample thickness, FSS substrate thickness and complex permittivity, and FSS element pattern. Techniques for extracting complex permittivity from the scattering parameters of the focused beam measurement are presented, along with measured permittivity data from the FSS against a variety of well-known materials.
Ultra-Wideband (UWB) calibration of RCS measurement radar systems, particularly outdoor, ground-to-air dynamic signature measurement radars, are conventionally accomplished using calibration devices (CD) attached to static towers, tethered from balloons, dropped from helicopters or other air vehicles, or with active RF repeater systems. These methods all contain errors from background-target interactions, or are operationally compromised, or are expensive. For high accuracy RCS radar calibration, a revolutionary methodology and architecture is mandatory to support demanding new radar metrology requirements. Within this paper, an update of ongoing efforts toward developing an autonomous, airborne drone-based CD is provided. The radar reflectivity of such a device must have a highly reproducible RCS, as manifested by a narrow, well defined probability distribution function (PDF), and should be independent of viewing aspect. Computational electromagnetic simulations were used to predict the RCS of a 60.9-cm diameter autonomous Spherical Passive/Active Calibration Device (SPARCS) with periodic, hexagonal “honeycomb” electromagnetic screens for inlet/outlet ports of the propulsion system. Three methods were used to predict the RCS, including Large Element Physical Optics (LE-PO), Physical Optics (PO) and Method of Moments (MoM) using the Adaptive Cross-Approximation (MoM-ACA). All methods show reduced cross section at angles centered on the periodic hexagonal RF screens. LE-PO resulted in a 30-fold decrease in computational expense relative to PO, but had a higher standard deviation. MoM-ACA calculations are ~57-fold more computationally expensive than PO results, but provide the full wave solution. PDFs determined from UWB RCS measurements have a narrow distribution and show reasonable agreement with calculations. These results validate the RCS signatures of the autonomous, airborne, spherical CD incorporating inlet/outlet RF screens as a valid calibration target.
The Boeing 9-77 Compact Radar Range has utilized low-frequency solutions since the 1990s. However, compact radar ranges have innate challenges when it comes to low-frequency measurements, typically due to facility size limitations. Due to increasing demand for more reliable data across a broad set of frequencies, an upgrade to the existing Ultra High Frequency (UHF) antenna feeds was designed and implemented in July 2020. This antenna was developed with field quality improvements, reliability, repeatability, and maintainability in mind. Unlike the previous design, this antenna was designed as an array with weighted feeds to complement the characteristics of the pre-existing range Gregorian reflector system. This new UHF antenna array leveraged the Weighted Element Method (WEM) along with extensive electromagnetic modeling and trade studies to achieve an efficient design at a minimum size. As a result of these design choices, the new antenna has doubled the efficiency in the band of interest. In addition, the frequency bandwidth of the antenna was improved while also reducing calibration and background drift. Lastly, this array has significantly improved the field quality of the quiet zone compared to the previous antenna system and improved the signal-to-noise ratio. This paper describes the UHF Antenna Array design process and the compact range measurements results to demonstrate the benefit of the WEM for feed arrays in a compact range. Additionally, the authors present an evaluation of methods used to create a digital twin of the UHF Antenna Array and a summary of best practices for future development of weighted antenna arrays for compact radar ranges.
The imaging of the reflectivity of a target from Near-Field (NF) scattered data is nowadays well established. Generally speaking, these techniques require complex data, i.e., amplitude and phase acquisitions. In this paper, the use of only-amplitude acquisitions is investigated. We propose an approach to image the reflectivity profile of a target using only amplitude NF data under a monostatic measurement configuration. To cope with phaseless data, a phase retrieval problem is settled and dealt with as a quadratic inverse one. The phaseless procedure requires two sets of independent squared amplitude measurements of the scattered field, collected on two different scanning surfaces. A solution of the problem is reached by the search for the global minimum of an appropriate quartic functional. A proper representation of unknowns and data, exploiting the available information on the target and on the scanning geometry, allows to improve the reliability and the accuracy of the optimization process. First, a representation of the unknown target reflectivity using Prolate Spheroidal Wave Functions is used. Furthermore, properly acquiring the phaselesss NF requires a significantly high sampling rate when performed with a standard approach. From this point of view, a non-redundant sampling can be employed to drastically reduce the amount of requested NF data. Following the use of the non-redundant sampling, a two-dimensional optimal sampling interpolation expansion can be employed to accurately recover the NF scattered amplitude data on the classical Cartesian grid. Numerical results to assess the effectiveness of the proposed approach will be presented. The approach has proved to be capable, besides imaging the unknown reflectivity, to accurately reconstruct the amplitude and phase NF on a third NF test plane. In the shown example, a reduction of 95% NF amplitude-only samples is achieved.
Hybrid radome-antenna designs can enable novel applications and unique benefits that would be difficult to achieve with standalone radomes and antennas. Examples of such designs are provided which use simple antennas and novel radomes to reduce antenna size and weight, to generate and steer antenna beams without use of complex phased arrays and beam forming networks, and to enable precise direction finding with only two antenna elements.
Free space material measurements at VHF and UHF bands require antennas that are necessarily large and heavy to accommodate the long wavelengths in these bands. Large antennas make measurement less practical and more expensive. This paper presents a new flat lens antenna technology, which enables significant reductions in size and weight compared to conventional wide bandwidth horn antennas. These new antennas utilize artificial dielectric loading combined with lossy materials to give directivities similar to much larger and heavier horns. This paper also presents the direct application of these antennas for free space dielectric material characterization. Example measurements of dielectric specimens are shown with a pair of 200 MHz to 4 GHz antennas.
An antenna’s practical far-field distance can be estimated from the upper bound on the ratio of its gain to quality factor. This upper bound is an infinite series that can be truncated based on the desired accuracy. We investigate the convergence properties of this bounding series. We find that the number of terms required for convergence depends on the antenna’s electrical radius in a way similar to the Wiscombe criterion used in Mie scattering theory. For typical experimental accuracy requirements, such convergence can significantly reduce the effective far-field distance.
In this article, a method is presented which describes how to measure the separate performance parameters of an antenna-receiver system after they have been integrated into one system. The integrated receiver may perform different than the cascaded prediction of the pieces that make up the system due to component interaction. This article develops a method that allows the integrated performance of the individual components (an antenna and a receiver for this discussion) to be measured without disassembly. Using the described method, parameters such as, antenna gain, receiver gain, and receiver effective input noise temperature (correspondingly, receiver noise figure) can be measured. Once the receiver effective input noise temperature is measured, then it is possible to determine the remaining parameters. In the past, the difficulty has been separating out the two noise temperature terms (sky noise and receiver effective input noise). The presented method develops multiple equations which essentially separates out the two terms. Once the two terms have been separated, solving for the others is now possible.
Van Atta Arrays are antennas with uniquely configured beamforming networks (BFNs) that allow for innate retrodirection of incident signals. While useful for a range of applications, their characterization has typically necessitated the use of radar crosssection (RCS) ranges. Our work proposes an alternate method that uses conventional array characterization, specifically element patterns and scattering matrix measurements, to synthesize both bistatic and monostatic RCS patterns for Van Atta arrays. This method is demonstrated theoretically and experimentally first with a cross-polarized dipole array followed by a counterwound octafilar helix antenna array. The benefits of the proposed synthesis method include fast design studies and trades of the Van Atta BFN enabling retrodirective operation. Among other things, this allows for broader access to experimental research on this topic. The significance of the structural radar cross-section is also discussed.
Phased array antennas are often built from sub-arrays with identical or symmetrical layout. At an early project stage, performance verification measurements of the sub-array are valuable to proof the single module design. However, the characteristics of the final antenna are questionable without further processing. This work presents a concept that is based on far-field measurements of a sub-array in a Compact Antenna Test Range (CATR) in conjunction with planar near-field (PNF) processing to synthesize the entire phased array antenna characteristics. The procedure is explained with an example of a dual linear polarized L-band planar phased array antenna for an airborne synthetic aperture radar application. It is shown that the measured sub-array can be complemented by the synthesized twin to evaluate the characteristics of a final antenna that is not yet available in this form. The resulting performance of the synthesized entire phased array is presented and compared with simulations. The presented post-processing method would be beneficial to characterizing radiation patterns of large phased arrays by measuring only sub-arrays in a limited test-zone with any measurement principle.
Unmanned Aerial Systems (UAS), colloquially known as drones, offer unparalleled flexibility and portability for outdoor and in situ antenna measurements, which is especially convenient to assess the performance of systems in their realworld conditions of application. As with any new or emerging measurement technology, it is crucial that the various sources of error must be identified and then estimated. This is especially true here where the sources of error differ from those that are generally encountered with classical antenna measurement systems. This is due to the larger number of mechanical degrees of freedom, and to the potentially less repeatable and controllable environmental conditions. In this paper, the impact of some of these various error terms is estimated as part of an ongoing measurement validation campaign. A mechanically and electrically time invariant reference antenna was characterized at ESAESTEC’s measurement facilities which served here as an independent reference laboratory. The reference results were compared and contrasted with measurements performed outdoors at Quad- SAT’s premises using QuadSAT’s UAS for Antenna Performance Evaluation (UAS-APE). While a direct comparison between the measurement results from ESA-ESTEC and QuadSAT delivers information about the various uncertainties within a UAS-APE system in comparison to classical measurement facilities’ and the validity of such a system for antenna testing, other tests aim at providing an estimation of the impact of each error source on the overall uncertainty budget, thus paving the way towards a standardized uncertainty budget for outdoor UAS-based sites.
The characterization of the radiation performances is a necessary step in the conception of any wireless system. These systems require always more demanding radiation performances that calls for time consuming characterizations. This duration can be reduced by the decrease of the number of field samples. By enclosing the antenna in a Huygens’ surface, we can build a radiation matrix that maps equivalent surface currents to the radiated field. A singular value decomposition of this matrix enables to build a compressed representation of the antenna measurement and more specifically a reduced basis of the radiated fields. By harnessing the outer dimensions of the antenna, the number of field samples can be reduced as compared to spherical wave expansion techniques. This number is shown to be connected to the area of the convex equivalent surface enclosing the AUT, as hinted by previous analytical works for canonical enclosing surfaces. The whole antenna characterization procedure is validated by simulations and experiments.
While the size of the parabolic reflector in general determines the usable area of the quiet zone of a compact antenna test range (CATR) inside which a pseudo plane-wave condition is produced, the reflector edge treatment also plays a significant role in terms of overall quality and electromagnetic field distribution & uniformity, and especially so at mm-wave frequencies. Using modern powerful digital computational simulation technology in combination with genetic optimization, the edge treatment can be evolved for a specific CATR application as part of the design process. This is crucial as it attempts to maximize the performance of a given solution while ensuring efficient use of the available space which correspondingly provides an economical implementation. This is particularly important in 5G production test applications where, in many instances, multiple systems are required to be collocated within a given host building and in which case, the savings become multiplicative. In this paper the novel design methodology is introduced for the genetic optimization (GO) of blended rolled edge single offset reflector CATRs. Several edge blends and treatments are considered with the genetically optimized design parameter. For each variation the quiet-zone performances are compared and contrasted.
Robust and repeatable electromagnetic interference and compliance (EMI/C) measurements require specialized test equipment and adherence to a rigorous set of procedures corresponding to the necessary standard. In this work, we describe the EMI/C testing capabilities at the RF Systems Test Facility at MIT Lincoln Laboratory and share the findings from work done in accordance to MIL-STD-461G. Both conducted and radiated emissions were measured on an example RF test artifact in the large near-field anechoic chamber at the facility. CE102, CE106, and RE102 test setups and results are discussed.