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.)
This paper explores the impact of varying infill densities for various infill patterns on the effective relative permittivity of 3D printed waveguide slabs. Previous studies have highlighted the substantial influence of infill patterns on the relative permittivity of substrates. The study aims to investigate the disparities in effective relative permittivity when diverse infill patterns are employed at various infill densities for multiple antenna substrates printed with identical parameters. Furthermore, this study examines the relationship between effective permittivities and infill densities for various infill patterns to identify suitable patterns for accurately estimating permittivity at lower densities. To accomplish this objective, dielectric slabs were 3D printed with a range of infill patterns and densities while maintaining consistent manufacturing parameters. The relationship between infill density and effective permittivity was analyzed for samples without the use of solid layers. The results revealed a linear behavior when solid layers were omitted during manufacturing. These findings underscore the critical role of infill pattern selection in determining material density and permittivity for antenna design and related applications.
Sampling of the probe signal first-order spatial derivative, in addition to the probe signal itself, enables the sampling step to be increased to twice that of the standard sampling criterion. In this work, we investigate – theoretically, numerically, and experimentally - the potential of using probe signal derivatives for spherical near-field antenna measurements with the aim of reducing the measurement time. We present a closed-form Fourier coefficient formula and a closed-form interpolation formula based on signal and signal derivative samples. We validate these new formulas using experimental measurement data and thus demonstrate the feasibility of doubling the sampling step in practice. We discuss different principles for determining the probe signal derivative; and we demonstrate the use of probe signal derivatives, in addition to probe signals themselves, for a full-sphere near-field antenna measurement skipping every second full-circle scan.
This paper introduces an innovative testing system designed for the characterization and calibration of W-band active phased array antennas utilizing antenna-in-package (AiP) technology. The proposed system is a multi-axis scanner with nine degrees of freedom, used to perform near-field and farfield measurements with same setup. The multi-axis system allows precise positioning of the antenna and the probe, allowing accurate measurements of the antenna radiation patterns in both near-field (NF) and far-field (FF) regions. Experimental results show that the proposed hybrid multi-axis scanner significantly improves the calibration accuracy of the antennas on-chip at 77 GHz compared to traditional far-field systems. Using the hybrid scanned (near-field and far-field) provides a versatile and effective test procedure to even characterize additional electromagnetic artifacts that may be present during the test. The proposed system enables accurate calibration and measurements by providing precise control over the positioning of the antenna and probe, while minimizing the effects of interference from the surrounding environment. Excellent agreement between the antenna array pattern measured in the near-field and far-field is achieved post-calibration. Moreover, the suggested system supports both automated and manual calibration, rendering it versatile and adaptable across various applications.
Consolidated methodologies have long been established to assess measurement uncertainties in near-field antenna measurements. More recently, similar detailed approaches have been developed for compact ranges and adopted as standard practice. However, currently there is no analogous methodology for outdoor far field measurement facilities. This paper presents a framework for assessing the measurement uncertainties on an outdoor far-field elevated range. Various sources of uncertainty in an outdoor far-field range are identified, using the industry standard 18 term analysis for nearfield range assessment as a baseline. An example analysis based on an actual outdoor far-field range is presented. The uncertainty terms are quantified by analysis, observation, or measurement, and finally combined by the root sum squared method to arrive at the gain uncertainty and the -30 dB sidelobe level uncertainty.
This paper presents the design of an ultrawideband (UWB) open-boundary dual-polarized quad-ridged horn antenna (QRHA) having an impressive 3-decades bandwidth from 1 to 32 GHz, making it an ideal choice for a wide range of applications in radars and communication systems. Its unprecedented bandwidth performance in a single and compact antenna geometry covers various frequency bands including L, S, C, X, Ku, and K. The ridge tapering profile of the proposed QRHA ensures excellent impedance matching, while the aperture matching prevents any phase distortion. The back-cavity design as well as cavity flaring is carefully optimized to achieve wideband performance along with no presence of pattern degradation specifically at the higher end of the frequency band. The antenna design exhibits a favorable impedance matching below -10 dB, well-matched copolar antenna patterns in the principal planes, and good crosspolarization (exceeding -20 dB) over a 3-decades bandwidth.
This paper discusses the novel development of a lightweight RF front-end system aimed at enhancing airborne antenna measurements in the far-field. The proposed system leverages advancements in software-defined radio (SDR) technology and high-performance RF front-end systems. While there are instances of SDR applications in UAS measurements, these systems are predominantly designed for anti-UAS and communication purposes, lacking focus on antenna and radar characterization. In contrast, the proposed system is purposefully tailored for RF applications, completely self-contained and airborne, possessing both RX and TX capabilities, and minimizing reliance on ground-based components. The system facilitates transmission and reception in both H- and V-polarization, employing two independent channels. Consequently, it allows for the simultaneous measurement of antenna or radar properties in both copolar (Cp) and cross-polar (Xp) orientations. The comparison between antenna measurements conducted within an anechoic chamber and those carried out utilizing the proposed UAS system demonstrates a substantial level of agreement.
Compact Ranges are widely used for antenna measurements across wide frequency ranges spanning frequencies as low as 350MHz to as high as 60GHz and above. Advances in electromagnetic (EM) simulations have significantly improved the design process for compact ranges, resulting in reduced costs. Characterizing compact range including the anechoic chamber is computationally very challenging in terms of computer memory and time. In this paper, we will present the full wave method, MLFMM for characterizing compact range without the chamber and application of asymptotic method, RL-GO to characterize the compact range inside the anechoic chamber.
This paper describes two reflection methods to measure highly conductive coatings at VHF frequencies: 1) a resonant method based on eddy-current sensing at HF and VHF frequencies, and 2) a wideband method at VHF and UHF frequencies, based on a shorted transmission line combined with and computational electromagnetic (CEM) simulations to invert surface impedance. In both cases, the methods are able to determine surface impedances with sensitivities of a small fraction of an ohm. Both methods have strengths and weaknesses with respect to ease of calibration, sensitivity, frequency range, and use on non-flat surfaces. This paper describes both approaches and presents measurements on a variety of conducting materials and coatings. The resulting properties are also compared with DC conductivity measurements collected with a four-point probe system. The predicted accuracy for both methods is presented based on simulated data and empirical measurements.
Wireless devices supporting global navigation satellite systems (GNSS) services have become an essential tool in different areas of technology such as agriculture, construction, automotive, etc. Therefore the performance and reliability of such devices are important aspects that need to be addressed in the testing stage during the development of the units. The integration of the Over-the-Air (OTA) testing method with the 3D Wave Field Synthesis (3DWFS) technique offer not only the benefit of having tests under controllable and repeatable conditions but also the ability to recreate complex and realistic scenarios in a controlled environment with full polarimetric support for the testing of wireless devices. This contribution applies this technology to emulate a GNSS scenario within an anechoic chamber. For the results validation, a realistic GNSS outdoor scenario was recorded and compared with the emulated scenario where 3DWFS was applied for each individual satellite. This represents a significant step for the GNSS community and also for the future development and testing of wireless devices.
The existing IEEE-STD 1128 on “Recommended Practice for RF Absorber Evaluation in the Range of 30 MHz to 5 GHz” was published in 1998. The standard has been referenced frequently and used as a guide for RF absorber evaluations. The document has several aspects which need updating, including the frequency range of coverage, requirements for newer test equipment, advances in test methodologies and material property evaluation, measurement uncertainty considerations, and absorber high power handling and fire testing requirements. The working group is divided into task groups and is in the final stage of collecting inputs from these subgroups. The next step is to consolidate the inputs and produce a draft standard for a wider distribution before being submitted for balloting. The subgroup contributions can be found on the IEEE imeetcentral website (https://ieeesa. imeetcentral.com/p1128). The sections which have received substantive updates include bulk material measurements, instrumentation, absorber reflectivity measurements, and power handling test. In this paper, we will provide some detailed discussions on the planned updates from these contributions. For areas which did not receive sufficient input, the working group plan to table those topics for future considerations.
This paper addresses the circularly-polarized (CP) gain uncertainty when using linearly-polarized feeds to obtain circular polarization in Compact Antenna Test Ranges. In particular, our emphasis is placed on quantifying the inaccuracy caused by deviations in amplitude and in phase of the two orthogonal linear measurements. This is of paramount importance especially for highly directive CP antennas operating at high frequencies in that the CP gain will be adversely impacted even by a small deviation from an ideal 90- degree rotation, as well as by a situation when the rotation may cause a slight boresight misalignment. To characterize the gain uncertainty, we look at ratio differences between the peak amplitude of the linear measurements, as well as cases when the phase shift of the two orthogonal linear measurements is no longer 90 degrees. The former is done through mechanical and electrical boresighting technique in the initial setting. The latter, which is the focus of this paper, is carried out through several case studies in practice mimicking some non-ideal 90- degree rotation settings.
Absorber treatment for an anechoic range is designed to attenuate the potential reflections from the walls, ceiling, and floor and to keep a certain level below the direct path between the range antenna (or probe) and the quiet zone (or minimum radiated sphere for spherical near-field ranges). There are, however, some antenna measurement systems where the range changes or moves as the data is acquired. In some cases, the probe moves around the antenna-under-test (AUT) along a section of circle supported by an arch or a gantry. In other ranges, the multiple probes are switched on and off; these probes are supported by an arch. Because the direction of the range moves with respect to the walls, ceiling, and floor, it is a bit more complex to arrive to an optimal absorber layout, as well as locating the preferred placements for the instrument rack, door, and vents in the range. In this paper, a higher-order-basis-function method of moments approach is used to model a gantry-supported probe as it moves around the location of the AUT. The power density at the walls as the probe moves is analyzed to arrive to an optimal absorber layout that will provide adequate levels of reflections for measuring an antenna. The paper looks at a gantry that moves from +135° to -135° with the AUT rotating 180° and for a gantry that moves from 0° to +135° with the AUT rotating 360°. The latter will require a smaller range with one of the walls closer to the location of the antenna under test. A series of recommendations based on the electrical size of the absorber at different areas of the range are provided.
Frequency band requirements for satcom applications in certain cases overlap two conventional microwave frequency bands. Characterizing antennas using near field techniques over such bands require two separate probes resulting in substantial increase in measurement time. This work is motivated by providing solution to such requirements of overlapping bands (K and Ka-band) and wideband operation over an octave frequency from 17-33 GHz. We propose a new WR-38 band and present the design and development of WR-38 waveguide probe realized using 3D metal printing. Impact of higher order modes on operational bandwidth of waveguide, 3D metal printing surface roughness and fabrication tolerances is investigated. Fabricated probe is characterized using planar near field (PNF) and measured results are presented. Performance comparison is done by characterizing SGH-1800 (18-26.5 GHz) and SGH-2200 (22-33 GHz) with 3D printed WR-38 probe and commercial WR-42 and WR-34 probes.
A new general formulation for the asymptotic expansion of electromagnetic fields radiated by an arbitrary antenna is introduced and demonstrated. The presented approach is based on an extended application of the method of stationary phase, updating a methodology proposed by Jones and Kline in 1956. Explicit formulas are derived up to the sixth order (sixth power of the inverse of the distance to a chosen antenna reference point), where coefficients of the spatial field expansion are obtained as linear combinations of even partial-derivatives of the plane-wave spectrum. Provided equations are verified by application to canonical cases of a Hertzian dipole and a 12 × 4 dipole array. An example how these findings could be leveraged in realistic use cases is delivered, using measured data from the antenna array of a 5G radio base station.
Additive Manufacturing (AM), or 3D printing, has gathered increased interest for radio frequency (RF) applications in recent years due to its ability to easily fabricate complex shapes at a low cost. One such application of interest is additive manufacturing of dielectric materials. Through varying the percent fill volume of a print, the bulk material properties can be changed. One method of altering the percent fill volume is through the use of lattice structures, or repeating geometric patterns, through a volume. The lattice is appropriately designed to result in a sample with a specific percent fill volume. This percent fill volume defines the ratio of material to air which in turn defines the bulk dielectric constant of the sample. This paper demonstrates the use of AM and lattice structures to alter the bulk material properties. The latticed material designs are validated through simulated and measured samples. These results are compared to common dielectric mixing approximations to gauge the accuracy of these approximations for latticed AM materials. Included is a parametric study of commonly used lattice structures at different percent fill volumes which is analyzed for variations on bulk dielectric constant due to geometry variations. Theoretically, the bulk dielectric constant should not change so long as the lattice unit cells are sufficiently smaller than the wavelength of the frequency of operation. Additionally, since many 3D printing materials are not well characterized, or do not provide, the necessary material properties critical for RF design, like dielectric constant and losses through the material, a free space lens system is utilized to initially characterize and compare some common 3D printing materials.
Luneburg lenses are popular antenna apertures for applications requiring a wide field of view and beam steering capability as they are a lower cost alternative to phased array apertures with straightforward beam-switching. Traditionally, Luneburg lenses are fabricated by layering shells of different dielectric constants to approximate a theoretically continuous dielectric gradient. Recent developments in additive manufacturing (AM) for radio frequency (RF) applications have led to advances in AM Luneburg lenses. AM enables functional dielectric printing where the dielectric properties can vary spatially within a print. Lenses manufactured using AM can continuously vary the dielectric constant through the material based on the theoretical Luneburg lens dielectric gradient; these AM lenses more accurately match the dielectric gradient of the theoretical Luneburg lens. Additionally, the integration of transformational optics (TO) to AM Luneburg lenses allows for physical reshaping of the lens structure while maintaining the same electrical properties. TO allows reshaping of the focal surface, which enables lateral translations of the feed location to steer the beam instead of radial rotations. This lowers the complexity of the feed arrangement without loosing the beam steering capability. This paper presents the results and analysis of a simulation and measurement study including performance comparisons between three Luneburg lens fabrication methods: traditionally manufactured, AM, and TO-AM.
When numerically simulating antenna problems, the accuracy of the antenna representation is crucial to improve the reliability of the results. Integrating the measured near-field (NF) model of the antenna into Computational Electromagnetic (CEM) tools opens new horizons in solving such problems. This approach has been studied for complex and/or large scenarios, antenna placement, scattering issues, and EMC applications [1- 3]. Another appealing use of merging measurements and simulations is the evaluation of antenna coupling [4-6]. Previous investigations regarded an array of three identical cavity-backed cross-dipole antennas [7-8]. In all the experiments the coupling between elements was evaluated only between an NF source and an antenna represented by its full-wave model and fed by ports. In this new study, following on the heels already presented in the publication [9] in which coupling between multiple simulated NF sources was illustrated using the commercial EM simulation tool Altair Feko [10], we want to show how antenna coupling between NF sources both coming from measurements can be evaluated in numerical simulations. The validation will be done combining two identical NF sources of MVG SMC2200 monocone antennas flush mounted on a rectangular plate. An additional demonstration will be shown on three NF sources of the same monocone on a rotorcraft model.
The reduction of acquisition time in planar near field systems is a high interest topic when active arrays or multi beam antennas are measured. Different solutions have been provided in the last years: multi-probe measurements systems and the PlanarWide Mesh (PWM) methodology, which implements a non redundant sampling scheme that reduces the number of samples required for the far-field transformation, are two of the most well known techniques. This paper proposes the combination of both approaches to derive a multi-probe PWM grid which reduces the measurement times to the minimum. The method is based on treating the near-field to far-field transformation as an inverse source problem. The multi probe PWM is designed with a global optimization process which finds the best measurement locations of the probe array that guarantee a numerically stable inversion of the problem. A simulated measurement example with the VAST12 antenna is presented where the total number of samples is reduced by a factor of 100 using a 4×4 probe array
Piezoelectric transmitters operating at acoustical resonance have been shown to radiate effectively in the Very Low Frequency (3 kHz to 30 kHz) and Low Frequency (30 kHz to 300 kHz) regimes. Such transmitters make use of the inverse piezoelectric effect to couple electrical signals into mechanical vibrations, resulting in near field radiation. This new class of electrically small antennas, known as mechanical antennas or ‘mechtennas’ can provide several orders of magnitude higher efficiency than similarly sized electrically small conventional dipoles. Measuring the dipole-like near field pattern of such piezoelectric field emitters in the Very Low Frequency and Low Frequency range using conventional techniques is not possible. To address this limitation, a simple capacitor plate-based setup is presented that enables the measurement and plotting of the near field patterns of such transmitters. Design and simulation of the capacitor plates to model the fields along with electric field pattern measurements of a Y 36◦ cut Lithium Niobate transmitter having longitudinal mode resonance at 82 kHz are presented.
Mode filtering has been shown to be very effective in suppressing spurious reflections in antenna measurements. Specifically, it has been well documented that in the quasi-far-field, the two polarizations are decoupled, making it possible to apply standard cylindrical near-field theory on the amplitude and phase data acquired from a single polarization measurement on a great circle cut [1]. The method was further extended to allow data collected from an unequally spaced angular abscissa by formulating the solution as a pseudo-inversion of the Fourier matrix [2]. This formulation, however, can be prone to spectral leakage because of nonorthogonality of the Fourier basis on an irregularly sampled grid, especially when the positions deviate significantly from the regular grid [2]. In this paper, we propose to use Compressed Sensing (CS) to compute the Cylindrical Mode Coefficients (CMCs), which improves the signal to noise ratio, allowing more accurate recovery of the prominent modes. The CS recovery is tenable because with the coordinate translation of the measurement pattern to the rotation center, the Maximum Radial Extent (MRE) of the antenna under test is greatly reduced, making CMCs quite sparse in the mode domain. The novel application of CS presented in this paper further expands the generality of the mode filtering method, which is now applicable to under-sampled data (at below the Nyquist rate) acquired on positions that grossly deviate from the equally-spaced regular grid.