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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.
Radar Cross Section (RCS) computation plays a critical role in the design and analysis of scattering objects in both civilian and military applications. Reliable and efficient simulation tools enable RCS minimization during the design phase, reducing reliance on measurements to the final stages of development. Two main classes of techniques are typically used for RCS prediction: high-frequency asymptotic methods and full-wave numerical methods. Unlike high-frequency approximations, full-wave methods such as the Method of Moments (MoM) provide highly accurate results by rigorously solving Maxwell’s equations removing any approximation. However, their application to electrically large problems is limited by high computational and memory cost. In this paper we present results from an efficient and accurate full-wave solver when computing the mono-static RCS of electrically large structures. The solver employs higher-order basis functions to reduce the number of unknowns and the Multilevel Fast Multipole Method (MLFMM) to significantly lower memory usage and computational time. Additionally a new so-called Fast Direct Solver (FDS) is utilized for a smaller selection of these RCS calculations. After a brief description of the implementation, several application cases are presented and validated against measurements and benchmarks, demonstrating the capability to handle complex scenarios with short simulation times and cost-effective hardware.
Accurate determination of the far-field distance is essential for characterizing antenna performance. The Fraunhofer distance is widely used to estimate the far-field distance of antennas; however, the true far-field distance is often quite different from the Fraunhofer distance depending on antenna type and size. This study presents a comprehensive simulation framework to investigate the far-field distance of dielectric lens antennas operating in the sub-THz band. Using the HFSS SBR+ solver, the framework replicates a direct antenna measurement setup, enabling efficient and accurate analysis of electrically large problems. The far-field distance is defined based on gain saturation, and a new formula is derived through extensive parametric simulations, accounting for lens diameters and operating frequencies. Experimental validation is conducted using a modular anechoic chamber, demonstrating strong agreement between measured and simulated results. The findings confirm the reliability of the proposed framework and the derived formula, offering a practical tool for designing compact antenna test setups. This work advances the understanding of far-field criteria for lens antennas and provides a foundation for future research in antenna measurement systems.
The rapid evolution of Intelligent Transportation Systems (ITS) and the emergence of autonomous vehicles have intensified the need for high-data-rate, low-latency communication systems. In this paper, a novel millimeter-wave (mmWave) Multiple-Input Multiple-Output (MIMO) array antenna is designed and analyzed for integrated 5G and Dedicated Short Range Communications (DSRC) applications in automotive Vehicle-to-Everything (V2X) scenarios. Operating at 5.9 GHz and 28 GHz, the antenna leverages dual-band performance to ensure backward compatibility with DSRC while harnessing the enhanced throughput of 5G mmWave. A compact 2×2 patch MIMO configuration is proposed, utilizing U-shaped elements with a defected ground structure (DGS) and via holes for mutual coupling suppression. The antenna achieves a peak gain of 8.2 dBi at 28 GHz and 6.4 dBi at 5.9 GHz, with S11 values below –10 dB across both bands. Beam steering capability of ±30° and envelope correlation coefficient (ECC) below 0.01 confirm the design’s suitability for automotive MIMO systems. Simulations were conducted using HFSS for full-wave and post-processing evaluations. The proposed design presents an efficient, low-profile solution capable of supporting reliable, real-time vehicular communications, making it a strong candidate for integration into next-generation autonomous driving and connected vehicle platforms.
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.
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.
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.
There are many antennas and microwave analysis and modeling software packages available, each with its preferred computational approach. Sometimes some of the available packages can use different numerical techniques. It is always gratifying if the solutions are consistent. Conventionally at NSI-MI compact range (CR) performance is evaluated with a proprietary software tool that drives two different approaches depending on the type of edge treatment. Serrated edge reflectors are handled using a well-known commercial package based on Asymptotic methods such as Geometrical (GO), Physical Optics (PO) and Geometrical Theory of Diffraction (GTD). For rolled blended-edge reflectors, the tool calls on a GO and modified unified theory of diffraction (UTD) introduced by Ellingson, Gupta and Burnside [1]. UTD used the method introduced by. Recently, NSI-MI has been using a commercial package based on the Method of Moments (MoM) using higher order basis functions. This tool showed correlation with the GO and m-UTD approach introduced in [1]. The results were presented in [2]. While the Asymptotic methods are faster and can be used for quick optimization of the design, they are not suited for analysis of the feed fence interaction, the reflector absorber skirt that hides the support structure or the interaction with the antenna under test (AUT) positioner. The MoM based approach allows for these types of analysis [3,4]. The MoM package leverages techniques like high- order basis functions (HOBFs), and sophisticated reduction methods. In this software a CR dish is modeled though the import of a CAD file that is used in the manufacture of the CR dish or is modeled within the software package GUI using its native CAD functionality. In this paper the quiet zone (QZ) performances predicted by the commercial package using asymptotic techniques and those predicted by the MoM-HOBF package are compared for a typical serrated CR dish. The QZ performance is determined by a set of metrics driven by amplitude and phase flatness along one- dimensional cuts across two lateral and orthogonal axes centered at the center of the QZ as recommended in [5]. The results show that with the proper meshing constraints the performances modeled by the asymptotic approach and the MoM-HOBF are consistent and comparable for the cases presented in this. The long history of predictions that match the measured results upon implementation on the field of reflector designed by the asymptotic technique means that the MoM results can be used to accurately predict the performance of ranges while analyzing the effects of fences, skirts and the absorber on the AUT positioners that the MoM tool allows.
Advanced Driver Assistance Systems (ADAS) rely heavily on Vehicle-to-Everything (V2X) communication, where radar antennas play a pivotal role. This paper presents the design of a radar antenna operating in the W-band at 77 GHz, achieving a VSWR < 2 and a peak gain of 8 dBi. The optimal placement of this antenna on an electric bike is investigated using the 3D Computational Electromagnetic (CEM) solver, Altair FEKO. Furthermore, Altair WinProp is utilized to analyze wave propagation in dynamic environments, considering pitch, yaw, and roll effects for Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communications. By integrating transmitting and receiving antennas on the vehicle, realistic drive-test scenarios are simulated to compute field strength, delay, and Doppler effects for each propagation path. Case studies highlight improved radar reliability and enhanced communication capabilities, particularly for two-wheeler applications, emphasizing the system’s adaptability to real-world vehicular environments.
The MIMO radar technique enables high angular resolution by virtually synthesizing a larger number of receiving antennas [1]. This paper leverages this technique to generate reliable point cloud data of an outdoor space, by applying a series of radar processing techniques and a point cloud denoising function. This work provides a comprehensive explanation of our methodology, from calibration and measurements to data processing and plotting. Our strategy is validated through real-world measurements conducted using the cascaded TI AWR2243 radar, highlighting the potential of mmWave MIMO radars in static 3D mapping scenarios and offering insight into practical implementation challenges.
Time-varying metasurfaces, also known as reconfigurable intelligent surfaces (RISs) or smart surfaces, offer new opportunities and applications, where fast-time modulation of the biasing conditions of individual elements enables beam- steering, frequency shifting, information encoding, and more. The unexplored potential offered by these modulated surfaces is matched by a number of challenges in the characterization of their performance. This work highlights ongoing efforts at GTRI to develop standard techniques for the characterization of these surfaces, with an emphasis on those designed for frequency conversion. First, the complex reflection response must be obtained for the entire range of static DC biasing conditions in order to compute the phase-voltage relationship required to design modulation waveforms. We present a three-standard offset short calibration method to perform static characterization of surface phase versus DC bias conditions in the free-space focused beam system, avoiding phase errors that are introduced by over- constrained time gating of resonant structures with two-standard calibrations. Second, the metasurface must be characterized over frequency under various modulation conditions.
The sampling of the field first-order spatial derivative, in addition to the field itself, enables an increase of the sampling step to twice that of the standard sampling criterion – and thus facilitates a reduction of the measurement time. Here, we investigate so-called derivative probes and their usage for spherical near-field antenna measurements.
Larger low-observable targets are being mounted onto RCS pylons. In many cases not only Azimuth rotation of the target, but a degree of movement in elevation is desired. This requires in many cases a large number of positioning cables to run from the base of the pylon to the tip where the rotator is placed. At the same time the low-observable qualities of the target call for pylon ogives with higher ratios to minimize the background RCS of the pylon that supports the target. The higher ratios call for very thin structures that cannot handle the weight of the rotator or have not enough space for the control and power cable to be fed to the rotator. A way of solving this problem is to have a variable ratio pylon, where the ogive at the tip is different from the ogive on the main body of the pylon. To analyze these pylons a higher-order basis-function method of moments (HOBFMoM) approach has been used in the past [1]. To conform the quadrilateral flat patches to the round geometry of the pylon, patches smaller than 0.3λ were used. While this was still an advantage over the typical 0.1to 0.05λ patches it placed limits on the highest frequencies that could be analyzed give the available computational resources. In this paper the authors present an approach to the meshing of the structure that allows for computing the monostatic RCS at frequencies in the x-band for a 2.4 m tall pylon. In addition, the effects of the non- physical absorber terminations are further analyzed.
We present a bench top demonstration of dropped-channel polarimetric compressive sensing to recover range profiles of a simple scene. Four antennas (H and V transmit and H and V receive) are connected to an arbitrary waveform generator and digital oscilloscope with programmable attenuators and phase shifters inline to control crosstalk. Range profiles of the scene are generated for three measured channels; the fourth is reconstructed from information imbedded in crosstalk using basis pursuit denoising. Reconstructed range profiles are shown to agree with measurements of all channels obtained without crosstalk contamination. Thus, the bench top setup demonstrates the potential use of dropped-channel polarimetric compressive sensing to reduce data storage and transmission burden while preserving full pol information.
We report a new class of wearable loop sensors for monitoring human kinematics (particularly, joint flexion angles) while overcoming limitations in the state-of-the-art. Previous studies have demonstrated the feasibility of these loop sensors using tethered connections to a network analyzer. In this work, we take a major step forward to demonstrate untethered operation for the sensor. To this end, transmitter and receiver boards are designed and integrated into the loops. The transmitter board sends a Radio-Frequency (RF) power of 5.68 dBm at 34 MHz upon a 50 Ω load, while the receiver board detects the power level and transmits the data to a nearby personal computer (PC) via Bluetooth. Flexion tests are conducted upon a tissue-emulating phantom to validate the setup. To quantify performance, we calculate the root mean square error (RMSE) between the estimated angle from our sensor and the gold-standard angle from a marker-based motion capture camera system, as well as Pearson’s correlation coefficient (ρ). The proposed sensor shows outstanding performance with an average RMSE of 0.670° and an average ρ of 0.99966. Overall, our sensor outperforms state-of-the-art wearable kinematic technologies by being highly accurate, seamless, lightweight, unobtrusive to natural motion, and reliable over time.
This paper extends the authors prior studies to develop a more flexible definition for the shape of a blended rolled edge compact antenna test range (CATR). This is accomplished by utilising a more sophisticated definition for the junction contour. This definition ensures the reflector surface is smooth and provides additional parameters that can be used to optimise the performance of the CATR enabling wall illumination and quiet-zone performance to be managed and balanced. As with the authors prior work, a novel, parallel, physical optics based, genetic optimisation is performed that, over subsequent generations, breeds optimal designs for each test case selecting the preferred design from many thousands of potential mutated candidates. Results are presented and discussed for several CATR designs that illustrate the concept and achievable performance highlighting the utility of a hybrid serrated blended rolled edge CATR reflector.
In modern integrated radar systems conventional antenna measurements are often impractical due to the lack of access to the antenna feed points. For frequency modulated continuous wave radars, the two-way radiation pattern can be characterized with a reflector while utilizing the integrated transmit and receive module. However, some post-processing steps are required for this measurement method to obtain the frequency-resolved radiation characteristic. This paper takes a closer look at the fast Fourier transform (FFT) and inverse FFT with the associated window functions and the necessary range gating including zero-padding based on simulations. A sufficiently wide range gating is necessary to reconstruct the frequency resolution of the antennas correctly. Yet a trade-off between the required wide range and the filtering of mutual coupling and reflections from the environment has to be made in the case of real measurements. Moreover, depending on whether a frequency in the center or at the edge of the chirp is to be reconstructed, different window functions provide the most accurate result.
The standard Near-Field antenna characterization allows to reconstruct the Far-Field pattern over the whole visible domain, even if, in many cases, the partial characterization of the Far-Field pattern just along some cuts can be sufficient, and becomes preferred if realized in shorter measurement time with respect to the standard case. A method for Partial Characterization has been proposed. The approach provides a general framework and defines the optimal distribution of the near-field samples required to reconstruct the Far-Field pattern along the cut of interest. The main features of the method are presented, and the performance is verified, experimentally, for two test cases.
It is well-known that any structure in the proximity of a radiating antenna will affect its radiation pattern. This is one of the reasons that a vehicle-mounted antenna tends to be tested while mounted onto the actual vehicle. There is a current discussion regarding how the vehicle should be tested. Traditionally, metallic turntables are used, with the tested vehicle resting on this conductive half-space. Several new spherical near field (SNF) ranges elevate the vehicle over a floor treated with RF absorber to obtain a quasi-free-space pattern. Discussions regarding which method is better are on-going. One of the arguments in favor of the free-space SNF range approach is that, using computational methods, the equivalent radiating currents that radiate the measured near fields, be it over a spherical surface or a non-canonical surface, can be computed. The equivalent radiating currents computed on a triangular element mesh are then imported onto a quadrilateral element mesh on a higher order basis function method of moments (HOBF-MoM) package. Once imported into the HOBF-MoM these currents can be used as excitations to obtain the far field. Within the HOBF-MoMit it is possible to place these equivalent currents in the presence of a metallic (PEC) using symmetry. A new development that allows for the use of an arbitrary Green’s function hence it is possible to get the far field from the computed equivalent currents in the presence of a dielectric half-space. Thus, the theoretical radiation pattern of the vehicle mounted antenna can be computed when the vehicle is on concrete, dirt, or even salt water. In this paper the authors present the latest work performed using this approach to place free space measured antennas over a PEC or dielectric half-space. Results show the potential of this approach. The higher order basis functions allow for the modeling of large structures with reduced number of unknowns. Thus, the antenna under test can be then placed in proximity to not only various half-space materials, but also to towers, buildings, or spacecraft.
Measuring radar cross-section (RCS) in high-noise environments remains a challenge. This paper presents an advanced signal processing framework that uses statistical dimensionality reduction to effectively separate the signal of interest from environmental noise. The proposed technique consists of two main steps. First, background subtraction and a gating technique are used to preprocess the measured data, separating and extracting the target’s reflectivity distribution from unwanted room contributions. Then, principal component analysis (PCA) is employed to analyze the target’s scattering image and localize its main scattering centers. To validate the proposed algorithm, a perfectly electrically conductive (PEC) scaled UAV model is manufactured and tested. The analysis of the experimental results demonstrates that the suggested technique effectively removes background and clutter, providing reliable RCS measurements in noisy environments.