Real Antenna Research Articles

Noise test of an electromagnetic antenna for low frequency scattered gravitational waves

Abstract Gravitational waves (GW) proved hard to detect experimentally and yet carry high energy fluxes. Conversely the technology for electromagnetic waves (EMW) is sophisticated, easily available and highly sensitive. Various proposals have been made to use the conversion of a gravitational wave into an electromagnetic wave to generate signals that could be detected. We present test results from a novel electromagnetic antenna, efficient at the very low frequencies needed to explore the signals from supermassive black holes mergers. These will eventually be studied by the Laser Interferometric Space Antenna (LISA) at wavelengths between 108 and 1011 m. Common forms of electromagnetic antennae are only efficient when the ratio of wavelength, λ, to antenna length, L, is roughly between 0.1 and 10. This paper proposes a scheme for a realistic ground-based electromagnetic antenna , ”the resistive antenna”, which operates efficiently at a ratio $\frac{\lambda }{L}$ of more than 106. The first estimates of ambient noise at these low frequencies from field trials of such a device are presented. The measured levels of ambient noise result in this detection scheme having a sensitivity much worse than LISA. The antenna design described in this communication may also have application in other fields.

Self-consistent modelling of radio frequency sheath in 3D with realistic ICRF antennas

Abstract Ion Cyclotron Resonant Frequency (ICRF) induced impurity production has raised many concerns since ITER proposed to change the first wall material from beryllium to tungsten. Enhanced DC plasma potential (VDC) due to RF sheath rectification is well known as one of the most important mechanisms behind the RF induced impurities. Our previous work (L. Lu et.al, Plasma Phys. Control. Fusion 60 (2018) 035003) considered the impact of both the slow wave and the fast wave on the RF sheath rectification in a 2D geometry. It can barely recover the double-hump structure of the VDC poloidal distribution observed in various machines when only the slow wave is modelled using the multi-2D approach which intrinsically assumes the poloidal wavenumber kz is zero. The fast wave on the other hand is found to be more sensitive to a finite kz and may need to be tackled in 3D. This work reports our recent progress on the 3D RF sheath modelling. In this new code, the latest RF sheath boundary conditions (J. R. Myra, J. Plasma Phys. 87 (2021) 905870504) and the realistic 3D ICRF antennas are implemented. Compared to the 2D results, the 3D code could well recover the double-hump poloidal distribution of VDC even with the fast wave included, which confirms our speculation on the necessity of treating the fast wave in 3D. While the double-hump pattern is robust in the simulation, the amplitude of VDC is found to be affected by the magnetic tilt angle and the antenna geometry. This emphasizes the importance of adopting a realistic antenna geometry in the RF sheath modelling. The double-hump VDC poloidal structure breaks as the magnetic tilt angle increases. This is explained by the gyrotropic property of the cold plasma dielectric tensor. The spatial proximity effect we identified in the previous 2D simulations is still valid in 3D. Finally, simulation shows the slow wave dominates the RF sheath excitation in the private SOL, while the fast wave gradually takes over when moving to the far SOL region. This code could be a new tool to provide numerical support for ITER impurity assessment and ICRF antenna design.

Dynamic SNR, Spectral Efficiency, and Rate Characterization in 5G/6G mmWave/sub-THz Systems with Macro- and Micro-Mobilities

The performance of 5G/6G cellular systems operating in millimeter wave (mmWave, 30–100 GHz) and sub-terahertz (sub-THz, 100–300 GHz) bands is conventionally assessed by utilizing the static distributions of user locations. The rationale is that the use of the beam tracking procedure allows for keeping the beams of a base station (BS) and user equipment (UE) aligned at all times. However, by introducing 3GPP Reduced Capability (RedCap) UEs utilizing the Radio Resource Management (RRM) Relaxation procedure, this may no longer be the case, as UEs are allowed to skip synchronization signal blocks (SSB) to improve energy efficiency. Thus, to characterize the performance of such UEs, methods explicitly accounting for UE mobility are needed. In this paper, we will utilize the tools of the stochastic geometry and random walk theory to derive signal-to-noise ratio (SNR), spectral efficiency, and rate as an explicit function of time by accounting for mmWave/sub-THZ specifics, including realistic directional antenna radiation patterns and micro- and macro-mobilities causing dynamic antenna misalignment. Different from other studies in the field that consider time-averaged performance measures, these metrics are obtained as an explicit function of time. Our numerical results illustrate that the macro-mobility specifies the overall trend of the time-dependent spectral efficiency, while local dynamics at 1–3 s scales are mainly governed by micro-mobility. The difference between spectral efficiency corresponding to perfectly synchronized UE and BS antennas and time-dependent spectral efficiency in a completely desynchronized system is rather negligible for realistic cell coverages and stays within approximately 5–10% for a wide range of system parameters. These conclusions are not affected by the utilized antenna array at the BS side. However, accounting for realistic radiation patterns is critical for a time-dependent performance analysis of 5G/6G mmWave/sub-THz systems.

Multibeam Wideband Transmit Beamforming Using 2D Sparse FIR Trapezoidal Filters

A low-complexity multibeam wideband transmit beamformer using a 2D sparse FIR filter design capable of multiple beams is proposed as a digital building block for fully digital beamformers. The 2D sparse FIR filter has multiple trapezoid-shaped passbands pertaining to wideband beams aimed at particular directions. The proposed multibeam digital beamformer drives a uniform linear array of wideband antenna elements to achieve the wideband multibeam transmit-mode signals desired by the communication system. The 2D sparse FIR filter is designed to be optimal in the minimax sense using convex optimization techniques. Full-wave electromagnetic simulations using real antenna models confirm that the proposed wideband transmit beamformer can achieve multibeam transmission in the 1.3–2.8 GHz frequency range, with more than 70% fractional bandwidth. Furthermore, the adoption of the wideband transmit multibeam beamformer leads to a significant reduction in digital arithmetic (computational) complexity compared with previously reported wideband transmit beamformers of similar transfer function type, without deteriorating beam directionality and causing increases in the side-lobe level. The proposed sparse 2D FIR multibeam beamformer architecture is well-suited for both sub-6 GHz (legacy) band transmit beamforming, frequency range three (FR3) beamforming up to 28 GHz, and mmWave operation for emerging 5G/6G applications.

Research on Azimuth DBF Method of HRWS SPC MAB SAR Imaging Mode with Non-Ideal Antenna Mode

Single-phase center multiple azimuth beam (SPC MAB) mode is an effective method for high-resolution wide-swath (HRWS) SAR imaging. The traditional azimuth spectrum reconstruction method for SPC MAB mode is based on the combination scheme from which fake targets along the azimuth direction arise because the inter-beam interference is not considered. When the real antenna mode is inconsistent with the ideal one, the disadvantages of the combination scheme become more serious. In this paper, based on the basic theory of the low-pass, band-limited, multiple-channel under-sampling and reconstruction, a novel digital beam-forming method is proposed for the SPC MAB imaging mode with ideal antenna mode first. The method analyzes the system functions of the sub-beams, based on which digital beam-forming filters are designed for all the sub-beams. The designed filters can reconstruct the correct wide-bandwidth azimuth spectrum and suppress the inter-beam interference simultaneously. Furthermore, the proposed method is extended to SPC MAB mode with the non-ideal antenna mode. The simulation experiments prove the validities of the proposed method both for azimuth spectral reconstruction and the inter-beams interfering suppressing, no matter that the SPC MAB’s antenna mode is ideal or non-ideal.

DESIGN OF A REFLECTOR ANTENNA IN THE FORM OF A TRUNCATED PARABOLOID

One of the fastest developing areas of radioelectronics are antennas and microwave devices. Antennas are one of the most important functional blocks of different radio engineering systems. Parabolic antennas are the most common unidirectional microwave antennas in radar systems, radio communication and radio astronomy. A parabolic antenna in the form of truncated paraboloid is developed. The antenna is designed, and its characteristics are calculated using one of the most modern software for electrodynamics modeling, FEKO, which represents a new approach to the design of three-dimensional microwave devices. The visualized results of calculations of a parabolic antenna in the form of a truncated paraboloid, which are displayed in the form of graphs. As a radiator for the designed antenna a circular open-ended waveguide is chosen, which consists of two parts – the rectangular and the circular waveguides. For the developed antenna, the radiation patterns in the polar system in E and H planes, and the gain and voltage standing wave ratio (VSWR) are presented, designed in FEKO software. The value of the main lobe of the pattern at half power 〖2θ〗_0,5 and 〖 2φ〗_0,5 is calculated. The structure of the real antenna is shown. The results of comparisons of the values of dependency of VSWR on the frequency and radiation patterns of real and designed antennas are introduced. The parameters of the developed antenna were measured using the NI PXI-5630 network vector analyzer and the NI USRP-2901 radio device. The results of experimental studies have shown their compliance with the results of modeling. The developed antenna operates in the 4.6...6 GHz frequency range.

Fourier metasurface cloaking: unidirectional cloaking of electrically large cylinder under oblique incidence.

The existence of a non-electrically-small scatterer adjacent to the source can severely distort the radiation and lead to a poor electromagnetic compatibility. In this work, we use a conducting hollow cylinder to shield a cylindrical scatterer. The cylinder is shelled with a single dielectric layer enclosed by an electromagnetic metasurface. The relationship between the scattering field and the surface impedance is derived analytically. By optimizing the Fourier expansion coefficients of the surface impedance distribution along ϕ-dimension, the scattering cross-section can be effectively reduced. This unidirectional cloaking method is valid for both TM/TE and non-TM/TE incident field and is not limited to a plane-wave incident field. The accuracy and effectiveness of the method are verified by four cloaking scenarios in microwave regime. We demonstrate that with the surface impedance obtained by the proposed method, a metasurface is designed with physical subwavelength structures. We also show a cloaking scenario under a magnetic dipole radiation, which is closer to the case of a realistic antenna. This method can be further applied to cloaking tasks in terahertz and optical regimes.

An alternative method to mimic mode conversion for ion cyclotron resonance heating

Ion cyclotron range of frequency waves in hot plasmas exhibit spatial dispersion effects and the wave equation takes the integro-differential form. Under the local plasma model assumption, the wave equation can be simplified to the differential form and adapts to the numerical scheme of the finite element method (FEM). Even though direct absorption of fast waves by ions and electrons can be described well by the local plasma model, linear mode conversion associated with non-local effects is absent. To deal with this issue, an alternative method is put forward in this paper where quasi-electrostatic fluid waves based on the multi-fluid warm plasma model are employed to take the place of ion Bernstein waves in mode conversion. On this basis, an interative fluid-kinetics (INTFLUK) code based on the FEM is developed for full-wave simulation in hot plasmas. Derivation of the wave equations as well as benchmarking of the INTFLUK code against other wave simulation codes are carried out. In both one- and two-dimensional cases, the validity of the INTFLUK code was verified by comparison of the wave field distributions and power deposition. As a useful illustration of the INTFLUK code including the scrape-off layer and a realistic antenna, the influence of the poloidal antenna phasing difference on ion cyclotron resonance heating is analyzed. Finally, it should be noted that the method in this paper has the potential to be extended to the three-dimensional case, which will be considered in the near future.

Numerical and experimental study on the dynamic equivalent methodology of a membrane antenna structure and a grid membrane structure

The dynamic equivalent methodology utilizing a grid membrane substitute for a planar membrane for vibration test verification on the ground has been demonstrated in small sizes with simple constraints. The method lacks accuracy and validity for a real complex membrane antenna. This paper thus focuses on the applicability of the equivalence approach to a membrane antenna and the factors affecting its dynamic equivalence to verify whether the grid membrane structure can replace the membrane antenna structure for modal identification on the ground. To this end, an experimental system is developed to conduct vibration tests on the grid membrane structure in air, using the grid membrane model with unidirectional tension as a substitute for the membrane array. The connecting strips attach the grid membrane to thin-walled lenticular booms (TWLBs) to allow for unidirectional tension. A laser displacement sensor array is employed to obtain the vibration data. A combination of the Fast Fourier Transfer (FFT) and Stochastic Subspace Identification (SSI) methods is applied to identify the structural frequencies and mode shapes. Vibration tests on the grid membranes with different added masses and tensile forces are conducted. Meanwhile, the numerical results for the rectangular membrane are chosen as a reference for comparison with the experimental results for the grid membrane. In conclusion, the numerical results for the membrane antenna structure and the experimental results for the grid membrane structure show good agreement in terms of frequency and mode shape. Additionally, both the added masses in the intersection areas of the grid membrane and the tensile force have a significant effect on the dynamic equivalence.

Methods and means for researching microwave devices

This paper is considered to be a continuation of a previous publication devoted to applications of digital transformations and simulation modeling in aerospace engineering and security (IJITS, №3, 2023). The aim of the paper is to present methods and means for conducting microwave measurements and practical learning of real antennas, which are expressed in the design, modeling, and validation of the models and contribute to obtaining reliable simulation results. The theoretical framework of the study is supported by classifications of the main types of microwave devices and technologies used in innovative laboratories.

A general algorithm to build mixed real and virtual antenna functions for higher-order calculations

The antenna-subtraction technique has demonstrated remarkable effectiveness in providing next-to-next-to-leading order in αs (NNLO) predictions for a wide range of processes relevant for the Large Hadron Collider. In a previous paper [1], we demonstrated how to build real-radiation antenna functions for any number of real emissions directly from a specified list of unresolved limits. Here, we extend this procedure to the mixed case of real and virtual radiation, for any number of real and virtual emissions. A novel feature of the algorithm is the requirement to match the antenna constructed with the correct unresolved limits to the other elements of the subtraction scheme. We discuss how this can be achieved and provide a full set of real-virtual NNLO antenna functions (together with their integration over the final-final unresolved phase space). We demonstrate that these antennae can be combined with the real-radiation antennae of ref. [1] to form a consistent NNLO subtraction scheme that cancels all explicit and implicit singularities at NNLO. We anticipate that the improved antenna functions should be more amenable to automation, thereby making the construction of subtraction terms for more complicated processes simpler at NNLO.

Modification of Simple Antenna Pattern Models for Inter-Beam Interference Assessment in Massive Multiple-Input-Multiple-Output Systems.

The occurrence of cross-beam interference in the received signal is one of the main problems that limit the possibilities of massive multiple-input-multiple-output technology (massive-MIMO) in fifth-generation (5G) systems. Thus, the evaluation of the level of this interference is one of the most important procedures in the spatial planning of currently wireless networks. We propose a novel modification of simple antenna pattern models, which is based only on changing the directivity of real antenna system patterns. This approach is independent of the antenna system's type, structure, and analytical description. Based on the developed modification, the original methodology for assessing the signal-to-interference ratio (SIR) from adjacent beams of a common antenna system is presented. The change in the radiation direction and the accompanying change in the complex shape and parameters of the real antenna beam pattern is one of the problems that significantly hinders the evaluation of the analyzed interference. Hence, in the presented methodology, we propose using our modification. In this case, the modification is reduced to a proportional change in the directivity concerning the real antenna system, which results from a change in the beam direction. The simulation studies used a multi-ellipsoidal propagation model and a real massive MIMO antenna pattern description from 3GPP. For the SIR error analysis, the 3GPP pattern is used as a reference. The simulation results show that modifying simple antenna pattern models allows us to obtain an SIR error of no more than 3 dB and 0.1 dB under line-of-sight (LOS) and non-LOS conditions, respectively.

Resonant vibrations produce quantum bridge over high-energy states in heterogeneous antenna.

Photosynthetic light-harvesting complexes usually contain several pools of molecules with a big difference in transition energies, for example, chlorophylls a and b in plant antennas. Some pathways of the excitation energy transfer may include pigments from the low-energy pool separated by a site occupied by a high-energy molecule. We demonstrate that such pathways may be functional if high-frequency intramolecular vibrations fall in resonance with the energy gap between the neighboring molecules belonging to different pools. In this case, a vibration-assisted mixing of the excited states can produce delocalized vibronic states playing a role of 'quantum bridge' that facilitates a passage over high-energy barrier. We perform calculations of the excitation dynamics in the model three-state system with the parameters emerging from our previous studies of real antennas. Simulation of the dynamics in an explicit electron-vibrational basis demonstrates that the rate of transfer between the two chlorophylls a through the chlorophyll b intermediate is increased by a factor of 1.7-2 in the presence of resonant vibration. A possible influence of energetic disorder and other (non-resonant) vibrations on this effect is discussed.

Features of the trajectory signal processing in the distributed radar when rotating the joint set of transmitting and receiving antennas

Increasing the resolution of ground survey radar systems (radars) makes it possible to obtain images of ground objects and the observed surface with high quality. At the same time, as it is known, the most difficult is to provide high resolution radar by angular coordinate. The method based on synthesis of artificial aperture allows to increase significantly the angular resolution of airborne radar. The capabilities of a radar station with synthesis of antenna aperture (SAR) in angular resolution are determined by the structure of the spatial and temporal trajectory signal formed in the process of synthesis. In this case, the resolution is determined by the angular size of the synthesized aperture. The purpose of this article is to consider the features of the trajectory signal structure and its processing during synthesis of an artificial antenna aperture in a distributed radar station consisting of a set of two receiving and one receiving-transmitting modules rotating in a circle. It is required to analyze the trajectory signal structure and evaluate the potentially achievable angular resolution capabilities of a distributed radar station when synthesizing an artificial antenna aperture under conditions of rotation of a spatially spaced set of phase centers of real antennas. To analyze the structure of the trajectory signal generated in a distributed radar station, we have considered the geometry of the problem, because it determines the change in the current distance between the phase center of the antennas and the observation object and is the main generating factor of the arising modulation of this signal. An informative tool for analyzing the characteristics of radar systems with synthesis of antenna aperture by potential resolution, is the analysis of the output response of the optimal trajectory signal processing system. The direct convolution method has been used to obtain the responses. Evaluation of the efficiency of coherent processing of the trajectory signals formed at the separated reception points has been carried out by computer simulation. From the simulation results presented in the figures in the article, it can be seen that the coherent processing of the trajectory signal formed at the separated receiving points during rotation of the phase center of real antennas, allows to increase the azimuth resolution of the radar. Thus, the results presented in the article show that rotation of the separated phase centers of the antennas of the receiving and receiving and transmitting modules within a range of up to 120 degrees provides the formation of a synthesized aperture when processing the trajectory signal from the observed target at each receiving point. The best azimuth resolution is obtained by processing the trajectory signal at the location of the transceiver module antenna. When coherent processing of trajectory signals formed at separated receiving points is performed together, the azimuth resolution of the radar station increases by about two times compared to the case of their separate handling.

Coherent information accumulation from virtual MIMO radars with multiple increase of interelement distances in the real MIMO radar

To reduce the number of air carriers when using MIMO radars, it is advisable to reduce the number of transmitting and receiving elements (TLE and RTE) of real MIMO radars, as well as the use of virtual MIMO radars. The reduction in the number of TLE and RTE can be achieved by increasing the distances between them to values significantly exceeding the average radiation wavelength. In this case, it is necessary to theoretically estimate the spatial resolution and accuracy of the measured coordinates in the selected system of virtual MIMO radars corresponding to real MIMO radars with spatially highly rarefied TLE and RTE. For short-range MIMO radars, using theoretical expressions for the generalized uncertainty function (GUF) in the case of a fixed point target, two-dimensional and one-dimensional sections of GUF in the “range–azimuth” plane are determined, which are compared for variants of moderate and highly rarefied two-dimensional arrangements of TLE and RTE of real and virtual MIMO antennas. The proposed mathematical technique allows you to quickly evaluate the resolution in range and azimuth in the development and creation of real and virtual MIMO radars with increased inter-element distances.

Discontinuous Galerkin Integral Equation Approach for Electromagnetic Modeling of Realistic and Complex Radiating Systems

An electric field integral equation (EFIE) discontinuous Galerkin (DG) formulation for the electromagnetic radiation analysis of realistic antennas is presented. Radiation problems are known to be computationally challenging, involving complex multiscale geometries often made up of a collection of closed and open surfaces. This complexity points to the convenience of separately building and meshing parts with different characteristics, either physical or geometric. This piecewise modelling approach is also desirable in the context of design optimization processes. The proposed formulation fits perfectly into this context by enabling the assembly of independently-meshed surfaces, yet without the need to enforce mesh conformity along the junction contours. The continuity of the normal components of the equivalent current at junctions is enforced using the interior penalty (IP) concept, which is extended to multiple conducting surfaces meeting at a junction.

Downlink Interference Analysis of UAV-Based mmWave Fronthaul for Small Cell Networks

In this paper, an unmanned aerial vehicles (UAV)-based heterogeneous network is studied to solve the problem of transferring massive traffic of distributed small cells to the core network. First, a detailed three-dimensional (3D) model of the downlink channel is characterized by taking into account the real antenna pattern, UAVs' vibrations, random distribution of small cell base stations (SBSs), and the position of UAVs in 3D space. Then, a rigorous analysis of interference is performed for two types of interference: intra-cell interference and inter-cell interference. The interference analysis results are then used to derive an upper bound of outage probability on the considered system. Using numerical results show that the analytical and simulation results match one another. The results show that, in the presence of UAV's fluctuations, optimizing radiation pattern shape requires balancing an inherent tradeoff between increasing pattern gain to reduce the interference as well as to compensate large path loss at mmWave frequencies and decreasing it to alleviate the adverse effect of a UAV's vibrations.

A Self-Replicating Single-Shape Tiling Technique for the Design of Highly Modular Planar Phased Arrays—The Case of L-Shaped Rep-Tiles

The design of irregular planar phased arrays (PAs) characterized by a highly-modular architecture is addressed. By exploiting the property of self-replicating tile shapes, also known as rep-tiles, the arising array layouts consist of tiles having different sizes, but equal shape, all being generated by assembling a finite number of smaller and congruent copies of a single elementary building-block. Towards this end, a deterministic optimization strategy is used so that the arising rep-tile arrangement of the planar PA is an optimal trade-off between complexity, costs, and fitting of user-defined requirements on the radiated power pattern, while guaranteeing the complete overlay of the array aperture. As a representative instance, such a synthesis method is applied to tile rectangular apertures with L-shaped tromino tiles. A set of representative results, concerned with ideal and real antenna models, as well, is reported for validation purposes, but also to point out the possibility/effectiveness of the proposed approach, unlike state-of-the-art tiling techniques, to reliably handle large-size array apertures.

The Meta Distribution of SINR in UAV-Assisted Cellular Networks

Mounting compact and lightweight base stations on unmanned aerial vehicles (UAVs) is a cost-effective and flexible solution to provide seamless coverage on the existing terrestrial networks. While the coverage probability in UAV-assisted cellular networks has been widely investigated, it provides only the first-order statistic of signal-to-interference-plus-noise ratio (SINR). In this paper, to analyze high-order statistics of SINR and characterize the disparity among individual links, we provide a meta distribution (MD)-based analytical framework for UAV-assisted cellular networks, in which the probabilistic line-of-sight channel and realistic antenna pattern are taken into account for air-to-ground transmissions. To accurately characterize the interference from UAVs, we relax the widely applied uniform off-boresight angle (OBA) assumption and derive the exact distribution of OBA. Using stochastic geometry, for both steerable and vertical antenna scenarios, we obtain mathematical expressions for the moments of condition success probability, the SINR MD, and the mean local delay. Moreover, we study the asymptotic behavior of the moments as network density approaches infinity. Numerical results validate the tightness of the theoretical results and show that the uniform OBA assumption underestimates the network performance, especially in the regime of moderate altitude of UAV. We also show that when UAVs are equipped with steerable antennas, the network coverage and user fairness can be optimized simultaneously by carefully adjusting the UAV parameters.

Semi-analytical and Full Wave Solutionfor the FMCW-signal Path of a Radar for the Metal Rod in a Concrete Medium Detection

This article describes the systematic development of an analytical and full wave model of a radio channel, which may be included in the operation algorithm of detecting metal structures in a concrete medium for the radar device. The analytical model is based on the geometric formulation and solution of an inverse problem to find the required refraction angle to accurately target incidence. In the full wave model, which was developed in CAD Altair Feko, it is possible to take into account both the real antenna or antenna array, which is used in the device, and the real signal reflection object, which is located in the concrete medium. It is important to note that the analytical model takes into account the dispersion effect of electromagnetic waves propagating in the medium. This fact turns out to be especially relevant for the forming of the radar complex based on chirp signals (or FMCW) in a certain frequency range. In this paper, an algorithm is developed for the frequency range of 0.8–5 GHz, however, if necessary, the band boundaries may be changed. The algorithm is established created for its use in radar devices for detecting metal structures in a concrete medium. A measuring module of restoring the actual material parameters may be included in the complex of the radar device for a posteriori accounting of the electrophysical parameters of the concrete.