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This paper presents the design, simulation, and experimental validation of a compact full-polarimetric antenna module for short-range radar sensors. Existing radar modules often use same-polarized antennas, potentially missing cross-polarized signals. While polarimetric radar systems offer superior polarization diversity, they are typically costly and complex. Research on radar polarimetry for short-range radar sensors is limited, and a compact antenna design is desirable for seamless integration and flexible placement in modern sensors. Additionally, collecting full-polarimetric data with a small sensor is crucial for developing realistic channel model tailored to short-range sensors. Developing a radar sensor with full-polarimetric operation is challenging due to size limitations and design complexity. This study introduces a 24-GHz full-polarimetric radar system utilizing a novel compact antenna module that captures both co- and cross-polarized signals. The well-designed antenna module, combined with generalized calibration techniques (GCT) demostrated outstanding performance in simulations and experimental validation. Both results closely aligned with ideal target scattering matrices. The proposed module's accuracy and reliability were confirmed through the successful characterization of various targets. These findings highlight the potential of the proposed antenna module for advanced radar sensors applications.
Free space material measurements illuminate a material or component with wave propagating through space. Algorithms for inverting intrinsic properties or thickness from free space measurements usually assume an ideal plane wave. This is an approximation because a typical incident beam is finite in extent and comes from a nearby aperture. In reality, the beam consists of a distribution of plane waves around the propagation direction. Typically, the illumination spot is minimized to measure different areas of a material and characterize homogeneity, or because the component itself is limited in size. A smaller spot leads to a wider distribution of plane-waves, which causes an effect called space loss, where the illuminating beam spreads as it travels. An ideal plane wave does not have space loss, so the plane-wave assumption results in systematic error when space loss is present. This paper derives a correction for the space loss phenomenon and applies it to thickness inversions used in microwave spot probe measurements. The correction is demonstrated on commercial microwave probes and quantified with a series of computational electromagnetic simulations. These calculations are discussed in terms of microwave mapping of radomes to measure performance and establish their compliance with design specifications.
This paper presents an analysis of the truncation errors of co-pol and cross-pol data by comparing a far-field pattern obtained from simulation, with different patterns obtained from the near-field to far-field transformation for different scan area sizes. It is shown how these errors are reduced when the scan area is larger, the reason being that more significant fields are being captured by the probe; however, the improvement comes at the expense of longer measurement time. From this problem, a new method is proposed where the system makes sure to measure all the significant fields and avoid the insignificant ones, reducing the measurement time and increasing the accuracy.
Non-terrestrial networks (NTNs), including satellites, high-altitude platforms (HAPS), and unmanned aerial vehicles (UAVs), operate above the Earth’s surface. Along with ground base stations, they often require the implementation of beamforming and beam tracking techniques to achieve high-speed, low-latency transmission, thereby ensuring seamless coverage. Consequently, diagnosing the functionality of the radio units (RUs) in those network devices and verifying their beamforming patterns are critical for the effective applications of this technology. This paper presents the 3D far-field pattern measurements and calibrations of the RF carrier EIRP levels for millimeter-wave beamforming testing suites that emulate RU operations. This is achieved using a combination of the planar near-field (PNF) and compact antenna test range (CATR) measurement systems at Taiwan Tech. A side-deployed PNF scanner is used in over-the-air (OTA) scan mode for 3D antenna pattern measurement and aperture diagnosis of the RU devices in transmit mode, utilizing controlled scan beams of single-tone and modulated RF carriers. Additionally, a compact range (CR) mode is employed to calibrate the RF EIRP in the peak direction of each RU-scanned beam. Beamforming patterns obtained from the near-field measurements in the OTA scan mode demonstrate good agreements with conventional near-field tests and show reliable EIRP values at 28 GHz for 5G FR2 radio units.
The IEEE Std 149-2021TM recommended practice for antenna measurements was recently revised by the IEEE Antennas and Propagation Standards Committee (APS/SC), sponsored by the IEEE Antennas and Propagation Society (AP-S). The document represents a major revision of IEEE Std 149-1977TM. It describes the procedure for the measurement of the transmitting and receiving properties of an antenna that is assumed to be a passive, linear, and reciprocal device. Among different topics addressed, it provides guidance about the antenna range design and evaluation. To complement this document, an international antenna measurement campaign was launched in an aim to provide an example of measurement that may be expected when applying this standard. A 5G New Radio (NR) ultrawide band (UWB) antenna was selected for this measurement campaign.
The feasibility and radiation properties of the nullifier-based monopole array antenna are studied and analyzed. Since this antenna does not require grounding, arrays of this antenna are less prone to mutual coupling, at least to the part stemming from mixing currents in a common ground plane. Simulations results for the performance of a 2-element array of the nullifier-based monopole antenna and the mutual coupling between the elements are presented and compared with those of a similar array of conventional monopole. The proposed array of nullifier-based monopole can be used in wireless communication systems such as RADAR and IoT applications.
Industrial robotic arms offering high speed, precise positioning repeatability, and a high degree of freedom in motion, are an attractive alternative positioning solution for supporting a wide variety of scan geometries using a single antenna measurement system. For multi-function and production antenna measurement applications, this makes them a cost-effective solution compared to custom designed positioner stack-ups. However, motion is not the only consideration when implementing a multi-functional measurement system. The RF system design needs to be equally flexible to accommodate different measurement topologies and operating modes. Ideally, the solution should be flexible enough to also provide a clear upgrade path to accommodate future requirements. This paper discusses the use of commercial modular multi-port Vector Network Analyzer products in the implementation of a distributed RF system for a 14-axis robotic antenna measurement system that supports multiple antenna measurement geometries with minimal manual reconfiguration. This novel RF system design has the capability of simultaneously measuring multiple antenna test ports and can be easily reconfigured to support a variety of measurement configurations and other applications.
This paper presents antenna design and measurements for wireless audio applications in the 470-600 MHz frequency range. Simulation and measurement results show that going from an external whip antenna to an internal helix antenna, realized gain was reduced between 2-4 dB across the desired frequency band, agreeing with or better than theoretical maximum gain calculations.
A free-space material measurement for a small dielectric plate using a truncated Gaussian beam whose beam width is smaller than the material under test (MUT) is described. Measurement results of two glass plates of different thicknesses at W-band (75-110 GHz) show its validity and the minimum beam width of the truncated Gaussian beam for the reliable material property measurement of a small planar MUT.
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.
In this paper, the full-wave computational electromagnetic simulation of the production test, measurement, and calibration of a 5G, 24 elements, C-band, active, planar array antenna together with a representative open-ended rectangular waveguide probe with, and without, absorber collar were evaluated using a large computing cluster and a proprietary full-wave solver. In this way, various components within the measurement could be carefully and precisely examined providing a framework for further measurement optimization. Particular attention has been paid to the presence of the standing waves in the simulated near-field measurement. This is a crucial feature of most practical measurements, but is omitted from the vast majority of simulations due to the computational effort required to evaluate it, and which is absent from the standard near-field theory. Here, the presence and impact of this phenomenon has been carefully examined with a range of intensive simulations being harnessed to quantify their impact, as well as enabling various methods for their minimization to be explored in a convenient and highly controlled fashion.
In the 2013 revision of the IEEE Standard for Definitions of Terms for Antennas [1], multiple new terms were added to describe active antenna systems. One such term is receiving efficiency, which was added to describe the behavior of either a passive receiving antenna or an active receiving antenna system. The definition of receiving efficiency contains other new terms such as isotropic noise response and isotropic noise response of a noiseless antenna. These new terms and definitions may cause some confusion for individuals responsible for antenna design and measurement. We attempt to demystify a few of the terms added to IEEE Std 145-2013, especially those terms that relate to receiving efficiency. In addition, we propose a measurement technique for measuring the receiving efficiency of an active receiving antenna system.