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.)
Reliable in-flight Wi-Fi is an essential service in modern aviation, requiring efficient planning to ensure consistent coverage with minimal infrastructure. This paper presents a simulation-driven approach to optimize the placement of Wi-Fi access points (APs) inside an aircraft fuselage, aiming to achieve maximum signal coverage with a minimum number of APs while maintaining a signal strength threshold of -30 dBm. A detailed 3D model of a typical aircraft cabin is constructed, incorporating structural elements, seating layouts, and material-specific electromagnetic properties, including the presence of passengers. Signal propagation is simulated using Altair WinProp and Feko, which account for reflection, diffraction, and material attenuation. The optimization is carried out using Altair HyperStudy, leveraging the Global Response Surface Method (GRSM) to explore the large design space and converge on an effective solution. The results show that strategic placement of as few as three access points can provide over 75% cabin coverage, demonstrating the effectiveness of the combined simulation and optimization workflow. This methodology enables efficient Wi-Fi network planning in confined, complex environments such as aircraft cabins and can be extended to other transportation systems like trains and buses.
The first mention of a Robot for near-field measurements of antennas appears is by Jeff Snow in [1]. This was a simple robotic arm to do planar measurements. About 7 years later, the use of off-the-shelf industrial robotic arms for doing antenna measurements is introduced [2]. Since then, industrial- robot-arm based antenna measurement systems have become increasingly popular due to their flexibility to measure over different surfaces allowing the system to do planar, spherical and cylindrical. The use of other methods to perform the transform, by numerically compute the currents on an arbitrary surface from the measured fields has helped in the growing popularity of robotic systems. This is related that the measurement surface does no longer have to be a canonical surface but can be any shape. However, the flexibility of the robots may be limited by the RF absorber coverage used in treating them. In this paper, the authors explore the potential scattering from the robotic arm in different positions and its effect on the probe illuminations. This is an area of research on the use of absorber that has not been explored until recently [3]. Numerical experiments are conducted to explore the effects of RF absorbers in the 300 MHz to 3 GHz range. Open ended waveguides (OEWG) as well as dual ridged horns (see Figure 1) are used as the probes. The results suggest that some areas of the arm need to be treated while others can be left bare. The analyses performed suggest that optimized treatment of robotic arms to maintain the flexibility of the technique while also reducing effects on the probe illuminations are possible.
In recent times, we have become familiar with the use of commercial software for designing our antennas and microwave devices. This is very common since it is easy to find high-performance desktop computers at affordable prices in our daily lives. The use of general-purpose commercial software is widespread because it allows for the simulation of any arbitrary configuration. However, many of us have experienced, given the ease of using commercial software, trying to simulate electrically large electromagnetic devices which take days or, in some cases, cannot be completed at all. While it is true that we now have very powerful simulation tools, by making a few simple assumptions, we can significantly reduce computational time without sacrificing accuracy. In this talk, I will introduce a simple ray-tracing technique that can be used, in combination with physical optics, to calculate the radiation pattern of antennas, as well as directivity, gain, mutual coupling, and even early-time response in complex configurations. The results are not only faster than those produced by conventional commercial software, but also more accurate, as they avoid many of the numerical errors that typically arise when computing electrically large structures.
This paper presents the design and simulation-based evaluation of a high-resolution millimeter-wave (mmWave) MIMO (Multiple-Input Multiple-Output) antenna array system for non-invasive medical diagnostics. The system is specifically optimized for applications such as early-stage tumor detection and soft tissue anomaly mapping, where high spatial resolution and tissue penetration are crucial. A 4×4 MIMO antenna array operating in the 28–40 GHz frequency band is proposed, leveraging the inherent advantages of mmWave frequencies— namely, shorter wavelengths for finer imaging resolution and wide bandwidth for enhanced contrast.The MIMO antenna array is designed using Rogers RT5880 substrate with a dielectric constant of 2.2 and a thickness of 0.787 mm to ensure minimal dielectric loss and mechanical stability. High-fidelity electromagnetic simulations were conducted using ANSYS HFSS to validate the antenna design. The resulting 3D radiation patterns confirm the beam directivity and uniform power distribution across all elements. The array was then integrated into a synthetic aperture radar (SAR)-based imaging model in MATLAB, where point- spread function (PSF) analysis revealed a lateral resolution of 3.2 mm and an axial resolution of 2.5 mm at 35 GHz. Imaging simulations on a multilayer human tissue-equivalent phantom model—comprising skin, fat, and muscle layers—demonstrated the system’s ability to resolve dielectric contrasts simulating benign and malignant tissue anomalies. The proposed MIMO antenna array enables real-time, contactless, and radiation-free imaging, positioning it as a cost-effective alternative to traditional imaging modalities such as X-ray or MRI for preliminary screening and continuous monitoring. The fully simulated results validate the concept’s feasibility and effectiveness for non-invasive medical diagnostics, particularly in point-of-care settings.
One of the most important key performance indicators of Reconfigurable Intelligent Surfaces (RISs) represents the RIS reflection or bistatic RIS Radar Cross Section (RCS) pattern, which needs to be evaluated under Far-Field (FF) conditions. Since a bistatic setup that fulfills FF conditions is mechanically complex, expensive and results in a large setup footprint, the measurement of RIS reflection patterns within a monostatic setup is proposed. Subsequently, the monostatic pattern results are transformed into bistatic patterns using a Monostatic to Bistatic Equivalence Theorem (MBET). This approach reduces the total measurement time tremendously. However, the state- of-the art MBET proposed for RIS measurements, is limited to 1-D pattern application, where the illumination-/transmit- and the probing-/measurement- antennas are located in the same plane. As RIS can also be configured to reflect off-the-plane, the evaluation of 2-D scenarios is crucial. With the state-of-the-art 1-D MBET such scenarios cannot be investigated. To close this gap, this paper derives a novel 2-D MBET well suited for RIS measurements. The novel MBET is validated with an analytical metal plate reflection model, by comparing the resulting 2-D MBET transformed monostatic pattern with the bistatic reference pattern. This procedure is repeated for measurement and simulation data of two different RIS prototypes designed for the mmWave frequency range. The deviation of the resulting patterns after applying the novel derived MBET from the bistatic reference patterns is analyzed based on the pattern difference metric. This difference metric evaluated in the main cuts exhibits a worst case mean value of –24dB which proves the suitability of this novel MBET for 2-D RIS measurements.
This paper explores a Phase Retrieval (PR) method for automotive Over-The-Air (OTA) spherical Near-Field (NF) measurements. Two signals are acquired phase-coherently: one from a fixed reference antenna attached to the vehicle, and the other from a conventional NF probe. The phase information is retrieved from the relationship between the two signals. An off-the-shelf Software-Defined Radio (SDR) two-channel receiver module is used. This setup enables one-step NF OTA measurements, potentially improving time- and cost-efficiency. Moreover, it solves the inaccessibility of antenna connectors. This approach has been tested on a vehicle in an actual automotive OTA measurement setup with a modulated signal centered at 810 MHz, which presents a challenging and realistic scenario. This work demonstrates that phase retrieval is feasible with the proposed setup. Moreover, good agreement with a reference measurement taken using a Vector Network Analyzer (VNA) is achieved at high Signal-to-Noise Ratio (SNR) levels. E.g., phase errors with respect to the reference measurement in the NF of less than 10° at 90% of the angular sampling points can be obtained with an SNR of at least 27 dB. The corresponding transformed Far-Field (FF) EIRP shows also good agreement between the PR and VNA measurements, with an Equivalent Noise Level (ENL) of -32 dB. In the evaluated example, the direct OTA measurement in the NF yields a much less similar pattern to the reference FF than with the proposed method.
Near-Field (NF) antenna measurement ranges have evolved as an alternative to Far-Field (FF) ranges to be the prominent method for pattern estimation from measurement. This is because NF ranges are more convenient to use and require much less space in laboratories [1]. The Microwave Vision Group (MVG) StarGate series, such as the legacy Satimo StarGate 64 (SG64), employs an array of multiplexed probes to perform measurements, sampling across a synthetic aperture created by moving the test antenna with respect to the probe array. This example of a commercial system does not use a Vector Network Analyzer (VNA), and was not designed to be updated. This means that it cannot benefit from improvements made in RF measurement equipment, requiring instead that a new system be purchased, which is unrealistic for many users. This work describes the initial process of updating a legacy SG64 to use a VNA. It includes characterization of the control signals, the transmit and receive paths, as well as the potential improvements to performance and lifetime that upgrading the legacy system to a VNA-based configuration offers.
We have newly developed a four-antenna array type antenna-coupled electrode electro-optic phase modulator for the 80 GHz band to be used as an electric field sensor. The receiving antenna arrays of the EO sensor are fabricated on a z-cut LiNbO3 film on a base substrate of SiO2 glass. The EO sensor can measure the electric field in the 80 GHz frequency band in both the frequency and time domains. In this paper, we show the receiving pattern of the EO sensor around 80 GHz. We demonstrate the possibility of measuring the vector radiation pattern of a standard gain horn antenna in the time domain and the frequency domain.
The primary role of an anechoic chamber is to provide a reflection free environment that can be used for electro-magnetic measurements, with antenna pattern being one of the most prominent measurements utilizing anechoic chambers. Real world anechoic chambers, however, rarely provide a reflection free environment. Reflections in an anechoic chamber can arise from a mismatch between the absorber size and the frequency used, the angle of incidence between the absorbers and the wave front, various metallic objects inside the chamber and more. As reflections can introduce impairments in the measurements, it is highly desirable to measure an anechoic chamber for reflections and reduce these reflections as much as possible (especially in the designated “quiet zone”). This paper introduces an innovative reflection evaluation method that harnesses both communication processing and radar processing to localize reflection sources in an anechoic chamber. The chamber setup consists of a probe and an antenna under test (AUT). The probe emits a signal, which is directly received by the AUT along with reflections within the anechoic chamber. Employing either a frequency modulated continuous-wave (FMCW) or stepped-frequency signal, the indirect path length is estimated, resulting in a ellipsoid representing potential reflection points. By intersecting multiple ellipsoids generated through relocating the probe and projecting the intersection onto the chamber, the reflection location is determined. The method’s efficiency has been demonstrated through implementation and validation in an anechoic chamber, with the paper presenting real measurement results for validation purposes.
A low-cost drone kit is demonstrated for measurement of HF antenna radiation patterns. An RTL-SDR V3 serves as the receiver on the drone and is controlled by a Raspberry Pi 4. The PixHawk 6X flight controller navigates the drone to programmed waypoints and triggers data collection by the Raspberry Pi and RTL-SDR. A GPS real-time kinematic (RTK) system is used to increase positioning accuracy to less than 10 cm. The antenna-under-test (AUT) is a cylindrical folded helix, derived from the spherical folded helix antenna. It has three arms with 1.5 turns each and is integrated into a spring-loaded collapsible leaf-basket. Dimensions are 0.64 and 0.54 meters tall and diameter, respectively, for a ka of 0.41 at 28 MHz. 36 5.1-meter radial ground wires are attached to the antenna when deployed. Measurements of the radiation pattern are taken between 45 and 50 meters away and show good agreement with simulations. Horizontal position is accurately achieved and the source of increased error in vertical position is described.
This paper presents a study aimed at developing guidelines for generating accurate Huygens Boxes from low-frequency antenna measurements, particularly in the VHF/UHF range, for antenna placement analysis. In flush-mounted scenarios, it is standard practice to measure the source antenna on a finite ground plane and apply a pre-processing step, known as the Infinite Plane Boundary Condition (IPBC), to emulate the response over an infinite ground plane. For the first time, a simulation-based approach is used to quantify far-field reconstruction errors arising from three key limitations in applying IPBC at low frequencies, namely: the size of the Huygens Box, the dimensions of the ground plane, and the truncation of the scanning area. Among these, scanning area truncation is particularly critical, as IPBC requires radiation pattern data from both the upper and the lower hemispheres to effectively mitigate edge diffraction effects. While a ground plane of 5–7 wavelengths is typically recommended, such dimensions are often impractical at VHF due to physical constraints. This study investigates the impact of using a reduced ground plane down to one wavelength and less. Additionally, the influence of varying Huygens box sizes is examined to determine the necessary margin between the antenna and the box boundary. The overall analysis is conducted using two RF sources: a single blade antenna and a 2-element blade antenna array. The accuracy of the IPBC method is evaluated in both free-space conditions and in a realistic aircraft model scenario.
A novel Ku-band antenna system has been specifically developed for supporting passive positioning and navigation operations using Ku-band signals of opportunities (SoOP) transmitted from low Earth orbit (LEO) satellites. This 7- element antenna design is compact, inexpensive, and easily to fabricate. Its gain pattern has been optimized to achieve stable signal-to-noise ratio (SNR) of the received LEO satellite signals over the most sky region above 25 degrees of elevation, and thus enabling longer and more stable PPN operations without actively tracking a fast-moving LEO satellite using complex beam steering electronics. Its pattern was also designed to have low reception at low elevations for rejecting interferences from ground emitters. This antenna design can also be easily scaled to using different LEO constellations in different frequency band. This paper discusses about the antenna design approaches, operating principles, prototype fabrication method, and measurement validations.
This paper presents an extended uncertainty analysis of a multiprobe antenna measurement system developed for large platform testing across the 64 MHz to 6 GHz frequency range. Installed at the Pulsaart by AGC facility in Belgium, the system enables fast and accurate characterization of complex structures integrating multiple antennas. Building on previous studies, the analysis expands the uncertainty budget by including a broader set of antennas, such as monocones operating down to 50 MHz, and evaluating key figures of merit including radiation pattern, gain, efficiency, and cross-polarization. Particular emphasis is placed on reflectivity-related uncertainty, which is a dominant factor at lower frequencies due to chamber electrical size and absorber limitations. The methodology incorporates modal filtering and spatial displacement of antennas to isolate the environmental effects. The results offer detailed insights into antenna-dependent uncertainties and, for the first time, provide complete uncertainty estimations for the aforementioned metrics across the full operating frequency range.
A commonly employed technique in the field of phaseless antenna measurements is the two-sphere method, wherein complex spherical mode coefficients are reconstructed from amplitude-only near-field measurements taken on two spheres that are separated by a specific distance. Recent numerical studies have indicated that the second sphere can also be substituted with a polyhedral surface. However, traditional positioning systems are incapable of measuring such configurations. This work demonstrates that a robotic antenna measurement system can efficiently measure the near-field on the surface of an octahedron. Two approaches for scanning a spiral grid with a robot are presented. It is shown that the additional degrees of freedom offered by the robot can reduce measurement time by up to 15 % compared to conventional spiral measurements. Furthermore, the far-field pattern derived from the complex near-field data on an octahedron produces highly accurate results, achieving an average equivalent error signal of −56.6 dB when compared to standard spherical measurements. A comparison between phaseless reconstruction using two spheres and a combination of a sphere and an octahedron reveals that both methods yield comparable accuracy.
This paper examines the uncertainty contributions associated with the spherical Near-Field to Far-Field (NF/FF) transformation process when applied to electrically large antennas. The transformation is based on the Spherical Wave Expansion (SWE) and implemented through the Transmission Formula (TXF), which provides a mathematically rigorous and computationally efficient framework. The TXF supports multiple levels of Probe Correction (PC), each with varying complexity and accuracy. However, applying the TXF to electrically large antennas (e.g. larger than 500 wavelengths) present significant computational challenges. The large number of spherical harmonics required increases the processing burden, and the accurate evaluation of the rotation and translation operators becomes critical. These operators must be computed using suitable recurrence relations to avoid instabilities. Additionally, the use of probes with arbitrary patterns can further complicate the probe correction process, potentially introducing numerical instabilities that must be carefully controlled. This work investigates the accuracy of the NF/FF transformation for electrically large antennas by considering both idealized cases without PC, and more realistic scenarios with full PC. The ability to compensate for large tapering effect introduced by the probe will be addressed for the first time.
NASA has commissioned a 10 m × 10 m Horizontal Planar Near-Field (HPNF) measurement facility to ad- vance the precision characterization of spaceborne antennas for aerospace and defense applications. Developed by MVG-OATI and NASA Glenn Research Center, the system accommodates diverse antenna types, including active electronically scanned arrays (AESAs) and parabolic reflectors, across a 1–110 GHz frequency range. It employs planar near-field techniques to measure gain, directivity, 3D radiation patterns, sidelobe levels, and advanced metrics like effective isotropic radiated power (EIRP), gain-to-noise-temperature (G/T), intermodulation distortion (IMD), and gain compression. The horizontal orientation simplifies installation and mitigates gravity-induced distortions, critical for zero-gravity space environments. A laser tracker ensures precise alignment and surface measurements, enhancing millimeter-wave accuracy. This paper provides an overview of the facility’s design, measurement methodology, and preliminary performance, highlighting its role in next-generation antenna testing.
This paper presents the results of an extensive numerical investigation into the spherical mode filtering method and the application of Compressed Sensing (CS) for near- or far- field two-dimensional antenna pattern measurements. This study is an extension of the authors’ prior work [1, 2] that expands the findings to the generalized case. When measuring an antenna pattern at a near-, intermediate, or true far-field distance, spherical mode filtering of an intentional offset antenna very effectively removes parasitically coupled multipath reflections from the test environment. The CS algorithm further enhances this technique by allowing the data to be sampled on an irregularly spaced spherical grid comprising only a few percent of the measurement points required by a conventional equiangular, Nyquist sampled, spherical acquisition. This investigation uses full-wave three-dimensional computational electromagnetic simulated data to examine the spherical mode filtering technique, addressing questions about the mechanism of modal separation, i.e. the mode orthogonalization, and sparsification facilitated by the translation of origins of the measured antenna pattern to the measurement rotation center. Additionally, the paper discusses potential limitations of the approach, identifying scenarios where modal filtering may be less effective—issues previously noted for one-dimensional cylindrical mode filtering but not yet documented in existing open literature for the analogous 2-D spherical case.
This paper presents a compact lens-integrated metasurface antenna system for beamwidth reduction and polarization conversion in the sub-THz D-band. The proposed metasurface achieves a circular polarization (CP) bandwidth of 2.86GHz (2.12%) within the 133.41-136.27 GHz band and has an axial ratio < 3 dB. A 3D-printed graded-index (GRIN) dielectric lens is integrated with the metasurface to provide beamwidth reduction and gain enhancement in both E-and H-planes. Moreover the proposed GRIN lens helps in achieving pattern symmetry and improved side-lobe levels. The lens-integrated metasurface configuration has a compact overall structure and provides efficient linear-to-circular polarization (LP–CP) conversion and beamwidth reduction. The proposed design can be a strong candidate for the future sub-THz 6G wireless and satellite communication (SatCom) systems.
The Free Space Voltage Standing Wave Ratio (FSVSWR) method has been the de facto standard for assessing anechoic chamber performance for more than fifty years. However, it depends on specialized linear scanning hardware and can take several days to complete a full data sweep. In this paper, a circular scan approach is introduced where the receive antenna is mounted at the quiet-zone boundary on a standard turntable or multi-axis positioner and then rotated through 360° to obtain a single-cut radiation pattern. We apply three data-processing techniques, namely plane wave decomposition, matched filtering and matched filtering with spectral filter, to extract the chamber’s plane wave spectrum and to locate reflections. To ensure accurate energy recovery for each reflection, we incorporate an anti-leakage compensation step into the spectrally filtered matched filtering process. The proposed methods are validated through numerical simulations and measurements in a fully anechoic chamber.
This work presents an integrated 3D-printed ultra-wideband (UWB) graded-index (GRIN) lens antenna that offers a simple, efficient, and cost-effective solution to the inherent wide beamwidth and asymmetric radiation problems of the commercial wideband antenna probes. The integration of the proposed antenna enables the effective use of these wideband probes on UAV/UAS platforms, which was previously not feasible due to the aforementioned problems. The proposed integrated antenna system covers a wide range of frequencies from 3 to 32 GHz, enabling the use of a single probe antenna for in-situ UAV-based calibration of maritime, weather, surveillance, and airborne radars. The proposed GRIN lens provides symmetric radiation patterns and reduced half-power beamwidth performance, especially in the lower part of the frequency band between 3 to 7 GHz, where the commercial UWB ridged-horn probes have significantly wider beamwidth values. Measured results show that the integration of the GRIN lens achieves a relatively constant beamwidth as well as an average beamwidth reduction of around 68% in both E- and H-planes, meeting the probe antenna performance requirements for radar characterization using UAVs/UAS.