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1.	Abbas, Taimoor, et al. (författare) Simulation and Measurement Based Vehicle-to-Vehicle Channel Characterization: Accuracy and Constraint Analysis 2015 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 63:7, s. 3208-3218 Tidskriftsartikel (refereegranskat)
2.	Abenius, Erik, et al. (författare) Thin Sheet Modeling Using Shell Elements in the Finite-Element Time-Domain Method 2006 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 54, s. 28-34 Tidskriftsartikel (refereegranskat)
3.	Adeogun, Ramoni, et al. (författare) Polarimetric Wireless Indoor Channel Modeling Based on Propagation Graph 2019 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 67:10, s. 6585-6595 Tidskriftsartikel (refereegranskat)abstract This paper generalizes a propagation graph model to polarized indoor wireless channels. In the original contribution, the channel is modeled as a propagation graph in which vertices represent transmitters, receivers, and scatterers, while edges represent the propagation conditions between vertices. Each edge is characterized by an edge transfer function accounting for the attenuation, delay spread, and the phase shift on the edge. In this contribution, we extend this modeling formalism to polarized channels by incorporating depolarization effects into the edge transfer functions and hence, the channel transfer matrix. We derive closed form expressions for the polarimetric power delay spectrum and cross-polarization ratio of the indoor channel. The expressions are derived considering average signal propagation in a graph and relate these statistics to model parameters, thereby providing a useful approach to investigate the averaged effect of these parameters on the channel statistics. Furthermore, we present a procedure for calibrating the model based on method of moments. Simulations were performed to validate the proposed model and the derived approximate expressions using both synthetic data and channel measurements at 15 GHz and 60 GHz. We observe that the model and approximate expressions provide good fit to the measurement data.
4.	Al-Rawi, Ali, 1985, et al. (författare) A new compact wideband MIMO antenna – the double-sided tapered self-grounded monopole array 2014 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 62:6, s. 3365 - 3369 Tidskriftsartikel (refereegranskat)abstract We present a new compact wideband multiple input multiple output (MIMO) antenna—the double-sided 4-port arm-tapered self-grounded monopole array, briefly referred to as the butterfly antenna, in the communication. The antenna is very compact with low correlation between ports and high diversity gain. The genetic algorithm optimization scheme has been employed in the design. Simulation results have been verified against measurements. The measured reflection coefficients at all ports are below -7 dB over 0.5–9 GHz and below -4.5 dB over 0.4–0.5 GHz and 9–15 GHz. The measured correlation coefficients are below 0.4 over 0.4–15 GHz and lower than 0.1 in most of the frequency band. This new MIMO antenna is developed as a transmit antenna in reverberation chambers, and we believe that it will find more applications in other systems, such as micro base station antennas in wireless communication systems.
5.	Alayon Glazunov, Andres, et al. (författare) Impact of Scattering Within a Multipath Simulator Antenna Array on the Ricean Fading Distribution Parameters in OTA Testing 2014 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 62:6, s. 3257-3269 Tidskriftsartikel (refereegranskat)abstract In this paper, we investigate the unwanted scattering that exists within the multipath simulator (MPS) array antennas employed in over the air (OTA) testing of mobile terminals. The impact of scattering is evaluated in terms of the measurement uncertainty of the average received power and the Ricean K-factor. The maximum ratio combining diversity is investigated for a generic device under test comprising two half-wavelength dipole antennas. We provide closed-form expressions for the uncertainties of the average received power and the Ricean K-factor for a uniform circular array of MPS antennas and a 2-D uniformly distributed angle-of-arrival spectrum. We also derive the maximum number of MPS antennas and the minimum ring radius of the MPS system as a function of the separation between the most distant antenna elements if the device under test employs a uniform linear array. As a result, we provide design guidelines for MPS array in terms of the number antennas, the radius of the MPS array and the wavelength of the carrier frequency.
6.	Alayon Glazunov, Andres, et al. (författare) On the Physical Limitations of the Interaction of a Spherical Aperture and a Random Field 2011 Ingår i: IEEE Transactions on Antennas and Propagation. - : IEEE. - 0018-926X .- 1558-2221. ; 59:1, s. 119-128 Tidskriftsartikel (refereegranskat)abstract This paper derives physical limitations on the interactions of antennas exciting TM or TE modes (but not both) and wireless propagation channels. The derivation is based on the spherical vector wave expansion of the electromagnetic field outside a sphere circumscribing the antennas. The result is an extension of the seminal work of Chu on the classical limitations on maximum antenna gain and radiation Q. Rather than maximizing antenna gain in a single direction we obtain physical limitations on the antenna gain pattern, which is directly translated to more condensed parameters, i.e., the instantaneous effective gain G(i) and the mean effective gain G(e) if instantaneous realizations or correlation statistics of the expansion coefficients of the electromagnetic field are known, spectively. The obtained limitations are on the maximum of G(i)/Q and G(e)/Q, which establish a trade-off between link gain and Q.
7.	Alayon Glazunov, Andres, et al. (författare) Spherical Vector Wave Expansion of Gaussian Electromagnetic Fields for Antenna-Channel Interaction Analysis 2009 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 57:7, s. 2055-2067 Tidskriftsartikel (refereegranskat)abstract In this paper, we introduce an approach to analyze the interaction between antennas and the propagation channel. We study both the antennas and the propagation channel by means of the spherical vector wave mode expansion of the electromagnetic field. Then we use the expansion coefficients to study some properties of general antennas in thosefields by means of the antenna scattering matrix. The focus is on the spatio-polar characterization of antennas, channels and their interactions. We provide closed form expressions for the covariance of the field multimodes as function of the power angle spectrum (PAS) and the channel cross-polarization ratio (XPR). A new interpretation of the mean effective gains (MEG) of antennas is also provided. The maximum MEG is obtained by conjugate mode matching between the antennas and the channel; we also prove the (intuitive) results that the optimum decorrelation of the antenna signals is obtained by the excitation of orthogonal spherical vector modes.
8.	Alex-Amor, Antonio, et al. (författare) Dispersion Analysis of Periodic Structures in Anisotropic Media : Application to Liquid Crystals 2022 Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 70:4, s. 2811-2821 Tidskriftsartikel (refereegranskat)abstract This article presents an efficient method to compute the dispersion diagram of periodic and uniform structures with generic anisotropic media. The method takes advantage of the ability of full-wave commercial simulators to deal with finite structures having anisotropic media. In particular, the proposed method extends the possibilities of commercial eigenmode solvers in the following ways: 1) anisotropic materials with nondiagonal permittivity and permeability tensors can be analyzed; 2) the attenuation constant can easily be computed in both propagating and stopband regions, and lossy materials can be included in the simulation; and 3) unbounded and radiating structures, such as leaky-wave antennas (LWAs), can be treated. The latter feature may be considered the most remarkable since the structures must be forcefully bounded with electric/magnetic walls in the eigensolvers of most commercial simulators. In this work, the proposed method is particularized for the study of liquid crystals (LCs) in microwave and antenna devices. Thus, the dispersion properties of a great variety of LC-based configurations are analyzed, from canonical structures, such as waveguide and microstrip, to complex reconfigurable phase shifters in ridge gap-waveguide technology and LWAs. Our results have been validated with previously reported works in the literature and with commercial software CST and HFSS.
9.	Alibakhshikenari, Mohammad, et al. (författare) Dual-Polarized Highly Folded Bowtie Antenna with Slotted Self-Grounded Structure for Sub-6 GHz 5G Applications 2022 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 70:4, s. 3028-3033 Tidskriftsartikel (refereegranskat)abstract In this paper, a novel dual-polarized highly-folded self-grounded Bowtie antenna that is excited through I-shaped slots is proposed for applications in sub-6GHz 5G multiple-input-multiple-output (MIMO) antenna systems. The antenna consists of two pairs of folded radiation petals whose base is embedded in a double layer of FR-4 substrate with a common ground-plane which is sandwiched between the two substrate layers. The ground-plane is defected with two I-shaped slots located under the radiation elements. Each pair of radiation elements are excited through a microstrip line on the top layer with RF signal that is 180° out of phase with respect to each other. The RF signal is coupled to the pair of feedlines on the top layer through the I-shaped slots from the two microstrip feedlines on the underside of the second substrate. The proposed feed mechanism gets rid of the otherwise bulky balun. The Bowtie antenna is a compact solution with dimensions of 32 32 33.8 mm3. Measured results have verified that the antenna operates over a frequency range of 3.1–5 GHz and exhibits an average gain and antenna efficiency in the vertical and horizontal polarizations of 7.5 dBi and 82.6%, respectively.
10.	Amani, Navid, 1985, et al. (författare) Sparse Array Synthesis Including Mutual Coupling for MU-MIMO Average Capacity Maximization 2022 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 70:8, s. 6617-6626 Tidskriftsartikel (refereegranskat)abstract A hybrid optimization algorithm including mutual coupling (MC) is proposed to synthesize an irregular sparse array (ISA) for average capacity maximization in a multi-user multiple-input multiple-output (MU-MIMO) system. The hybrid approach is composed of two phases to sub-optimally determine the location of a fixed number of omni-directional thin dipole antennas in an arbitrary sparse aperture via a diagonal antenna selection matrix. In Phase I, the problem is relaxed to a convex optimization by ignoring the MC and weakening the constraints. The output of Phase I is accounted as a reliable initial guess for the genetic algorithm (GA) in Phase II, which incorporates the MC effects through the coupling matrix and avoids the convex relaxation technique. The proposed approach outperforms the conventional GA with a random initial population, while it avoids trying several starting positions. Meanwhile, the undesirable appearance of grating lobes, due to the under-sampling, and the degrading MC effects are suppressed by aperiodicity. It is observed that, doubling the conventional inter-element spacing (half-wavelength) and finding the location of eight dipoles in a sparse aperture by the proposed method improves the average capacity by 3.27-11.9% when the number of users varies from two to eight and the signal-to-noise ratio (SNR) is 30dB.
11.	Amjad, Iqbal, Universitetslektor, 1994-, et al. (författare) Simultaneous Transmit and Receive Self-Duplexing Antenna for Head Implants 2023 Ingår i: IEEE Transactions on Antennas and Propagation. - Piscataway, NJ : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 71:11, s. 8592-8601 Tidskriftsartikel (refereegranskat)abstract A novel dual-port, dual-band self-duplexing implantable antenna for head implants is presented in this article. It operates at 915 MHz Industrial, Scientific, and Medical (ISM) band (when Port 1 is active) and 1420 MHz Wireless Medical Telemetry Service (WMTS) band (when Port2 is active). The proposed antenna is kept inside a flat device and simulated in a human head model. The miniaturization of the proposed antenna is achieved using a high dielectric substrate, shorted pins, and multiple capacitive slots. Consequently, it occupies a compact volume of 7.13 x 8.9 x 0.13 = 8.24 mm(3). The coupling between both radiators is enhanced by printing it on a thin substrate and placing vias between them. As a result, an isolation level better than 31.4 dB is achieved. It has peak realized gains of -18.94 and -17.06 dBi at 915 and 1420 MHz, respectively. The link budget analysis and specific absorption rate (SAR) are performed, showing promising results. The proposed concept is practically validated by measuring its performance inside the minced pork meat. Furthermore, the simultaneous transmit and receive concept is practically verified with the aid of software-defined radio (SDR). The main advantages of this antenna are its compact size, low coupling level, independently controllable bands, and simultaneous transmission and reception of signals without using a multiplexer circuit. © 2023 IEEE.
12.	Andersson, Tommy (författare) Moment-method calculations on apertures using basis singular functions 1993 Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X. ; 41:12, s. 16-1709 Tidskriftsartikel (refereegranskat)abstract The transmission properties of perforated perfectly conducting screens are of practical interest. The treatment of nonperiodical structures by numerical techniques, such as the method of moments, is very computer intensive. In this paper it is shown that using basis functions that incorporate the edge as well as the corner singularities, the number of unknowns can be drastically reduced. The advantages and limitations of the method are discussed. Numerical results are presented illustrating the transmission properties of arrays of square and rectangular apertures
13.	Atia Abdalmalak, Kerlos, et al. (författare) Ultrawideband Conical Log-Spiral Circularly Polarized Feed for Radio Astronomy 2020 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 68:3, s. 1995-2007 Tidskriftsartikel (refereegranskat)abstract In order to meet the requirements of the new generation of radio telescopes, we have developed a new topology called DYQSA, which stands for DYson Quad-Spiral Array. The design exhibits dual circular polarization contrary to dual linear polarization of state-of-the-art feeds. It covers the required ultrawideband (UWB) from 2 to 14 GHz with an almost constant and real input impedance which facilitates the design of the feeding structure and the low-noise amplifiers (LNAs). Different versions are investigated for enhancing feed performance, ensuring higher aperture efficiencies and mechanical stability. The simulation results of the reflector loaded by the proposed feed show an aperture efficiency of 65%±5% with a noise antenna temperature around 14 K and a system equivalent flux density (SEFD) of about 1300 Jy, both averaged over the required bandwidth at zenith. Measurements of the single-element and the four-element feeds are presented. Comparisons with other state-of-the-art feeds are shown in terms of total aperture efficiencies, design adaptability to different reflectors, calibration signal injection, and the required number of LNAs per feed, cost, and physical volume.
14.	Bagheri, Alireza, et al. (författare) A 16 × 16 45° Slant-Polarized Gapwaveguide Phased Array With 65-dBm EIRP at 28 GHz 2023 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 71:2, s. 1319-1329 Tidskriftsartikel (refereegranskat)abstract A high equivalent isotropic radiated power (EIRP) active phased array antenna is proposed for fifth-generation (5G) communication systems at 28 GHz. The numerical design, measurements of a fabricated prototype, and performance analysis are presented. The antenna design is based on the gapwaveguide technology and consists of $16 \times 16$ single 45° slant-polarized elements. The proposed design uses a low complexity printed circuit board (PCB) structure with only six layers, i.e., a half of the existing wideband solutions. The array antenna incorporates up/downconverter integrated circuits (UDCs) and $1 \times 4$ transceiver beamformer integrated circuits (BFICs). Moreover, a compact and highly efficient transition at the end of each channel of the BFICs has been designed to interconnect the antenna elements with the PCB. The antenna's front-end loss, which includes the feed line, mismatch, and ohmic losses, is only 1.3 dB. The array covers the scanning range of ±60° in the azimuth plane and ±10° in the elevation plane. The $S_{11} < -10$ dB frequency bandwidth is from 26.5 to 29.5 GHz. The maximum EIRP of the antenna is 65.5 dBm at saturation point. The presented design offers a compact, robust, and low-loss performance solution meeting the high transmission power requirements of 5G applications.
15.	Bantavis, P. I., et al. (författare) A Cost-Effective Wideband Switched Beam Antenna System for a Small Cell Base Station 2018 Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers Inc.. - 0018-926X .- 1558-2221. ; 66:12, s. 6851-6861 Tidskriftsartikel (refereegranskat)abstract A wideband switched beam antenna array system operating from 2 to 5 GHz is presented. It is comprised of a 4 × 1 Vivaldi antenna elements and a 4 × 4 Butler matrix beamformer driven by a digitally controlled double-pole four-throw RF switch. The Butler matrix is implemented on a multilayer structure, using 90° hybrid couplers and 45° phase shifters. For the design of the coupler and phase shifter, we propose a unified methodology applied, but not limited, to elliptically shaped geometries. The multilayer realization enables us to avoid microstrip crossing and supports wideband operation of the beamforming network. To realize the Butler matrix, we introduce a step-by-step and stage-by-stage design methodology that enables accurate balance of the output weights at the antenna ports to achieve a stable beamforming performance. In this paper, we use a Vivaldi antenna element in a linear four-element array, since such element supports wideband and wide-scan angle operation. A soft condition in the form of corrugations is implemented around the periphery of the array, in order to reduce the edge effects. This technique improved the gain, the sidelobes, and helped to obtain back radiation suppression. Finally, impedance loading was also utilized in the two edge elements of the array to improve the active impedance. The proposed system of the Butler matrix in conjunction with the constructed array can be utilized as a common RF front end in a wideband air interface for a small cell 5G application and beyond as it is capable to simultaneously cover all the commercial bands from 2 to 5 GHz.
16.	Bencivenni, Carlo, 1986, et al. (författare) Synthesis of Maximally Sparse Arrays Using Compressive Sensing and Full-Wave Analysis for Global Earth Coverage Applications 2016 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 64:11, s. 4872-4877 Tidskriftsartikel (refereegranskat)abstract Global optimization methods can be employed to design aperiodic array antennas that accurately account for their electromagnetic (EM) behavior and complex performance specifications. However, they are computationally expensive and, therefore, limited to small to midsized array problems. On the other hand, analytical methods do not suffer from this problem, but often assume idealized antenna elements and fully adjustable excitation controls, thereby excluding beam degradation effects caused, e.g., by mutual coupling (MC) and quantized phase shifters. We present a fast design method for large maximally sparse arrays that is capable of handling the aforementioned limitations. It is based on the previously published combined EM-Compressive Sensing approach, which has been herein generalized for multibeam optimization, and where we also exploit array symmetry in order to reduce the design complexity. Results are obtained for a circular array ( 100 λ diameter) of horn antennas operating in a multibeam SATCOM scenario, and demonstrate that even weak MC effects and small phase quantization are important when very demanding sidelobe and cross-polarization levels are required.
17.	Bernland, Anders (författare) Bandwidth Limitations for Scattering of Higher Order Electromagnetic Spherical Waves with Implications for the Antenna Scattering Matrix 2012 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 60:9, s. 4345-4353 Tidskriftsartikel (refereegranskat)abstract Various physical limitations in electromagnetic theory and antenna theory have received considerable attention recently. However, there are no previous limitations on the scattering of higher order electromagnetic vector spherical waves, despite the widespread use of spherical wave decompositions. In the present paper, bandwidth limitations on the scattering matrix are derived for a wide class of heterogeneous objects, in terms of their electrical size, shape and static material properties. In particular, it is seen that the order of the dominating term in the Rayleigh limit increases with the order of the spherical wave. Furthermore, it is shown how the limitations place bounds on the antenna scattering matrix, thus introducing a new approach to physical limitations on antennas. Comparisons to other types of antenna limitations are given, and numerical simulations for two folded spherical helix antennas and a directive Yagi-Uda antenna are included to illuminate and validate the theory. The results in this paper are derived using a general approach to derive limitations for passive systems: First, the low-frequency asymptotic expansion of the scattering matrix of a general scatterer is derived. This gives a set of sum rules, from which the limitations follow.
18.	Beukman, T. S., et al. (författare) Modal-Based Design of a Wideband Quadruple-Ridged Flared Horn Antenna 2016 Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 64:5, s. 1615-1626 Tidskriftsartikel (refereegranskat)abstract In this paper, a systematic design technique for quadruple-ridged flared horn antennas is presented, to enhance the radiation properties through the profiling of the ridge taper. The technique relies on control of the cutoff frequencies of specific modes inside the horn, instead of brute-force optimization. This is used to design a prototype antenna as a feed for an offset Gregorian reflector system, such as considered for the Square Kilometer Array (SKA) radio telescope, to achieve an optimized aperture efficiency from 2 to 12 GHz. The antenna is employed with a quadraxial feeding network that allows the excitation of the fundamental TE11 mode, while suppressing all other modes that causes phase errors in the aperture. Measured results confirm the validity of this approach, where good agreement is found with the simulated results.
19.	Borg, Johan, et al. (författare) Delay insensitive signal-injection calibration for large antenna arrays using passive hierarchical networks 2017 Ingår i: IEEE Transactions on Antennas and Propagation. - : IEEE. - 0018-926X .- 1558-2221. ; 65:1, s. 190-195 Tidskriftsartikel (refereegranskat)abstract Efficient beamforming of phased-array antennas requires that the phase delay of each channel is accurately known. One technique for achieving this is to distribute a calibration or local-oscillator reference signal through a delay-insensitive signal distribution network. In this paper, we propose using passive hierarchical signal distribution networks to distribute such signals, a method that scales significantly better with the size of the array than existing signal distribution methods. We analyze the impact of impedance variations within the network on the phase accuracy and propose a calibration front-end architecture. This front end also enables the return loss and coupling between antennas to be monitored for diagnostic purposes. We present an implementation of this front end that was applied to a small prototype antenna array, and show that this implementation exhibited low sensitivity to delays within the calibration network, reduced the temperature-dependent phase error of the front ends substantially, and can be used for performing antenna return-loss measurements
20.	Bosiljevac, Marko, et al. (författare) Efficient Analysis of Aperture Antennas on Generally Shaped Convex Multilayered Surfaces Using a Hybrid SD-UTD Method 2009 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 57:5, s. 1420-1431 Tidskriftsartikel (refereegranskat)abstract A novel hybrid method is described for analyzing convex multilayered conformal array antennas. The hybrid method is based on the spectral domain approach in combination with the ray-based uniform theory of diffraction (UTD) method. The analysis is divided in two parts. First, the spectral domain approach is accelerated by using an asymptotic extraction technique where the extracted term of the Green's function is calculated using UTD. It is shown that this new approach results in significant acceleration of the existing spectral domain algorithm without losing accuracy. The modified spectral domain method is then used in the second part where generally shaped convex multilayered surfaces are analyzed by using sets of canonically shaped surfaces (spheres and/or circular cylinders). Their radii are obtained using the UTD formulation, which contains important information such as distance and curvature of the generally shaped surface along each geodesic. The results obtained using the new algorithm are compared to the available results (calculated and measured) for different conformal antennas, showing very good agreement.
21.	Bosiljevac, M., et al. (författare) Simple Boundary Condition for Canonical EBG Surface: PMC-Backed Uniaxial Medium 2016 Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 64:2, s. 785-U550 Tidskriftsartikel (refereegranskat)abstract A simple-to-use replacement model for isotropic electromagnetic bandgap (EBG) surfaces such as mushroom surfaces is investigated. Properties of EBG surfaces strongly depend on the incidence angle of the incoming plane wave. The suggested model takes this behavior into account and actually represents the ideal EBG surface. The model is based on uniaxial representation of a thin DB layer backed by a perfect magnetic conductor (PMC) plate. We investigate how this model behaves in comparison with a realistic mushroom surface, and when it can be applied. The results show that the proposed model can be used for both far field calculations and antenna coupling evaluation.
22.	Braun, Christian, et al. (författare) Evaluation of antenna diversity performance for mobile handsets using 3-D measurement data 1999 Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 47:11, s. 1736-1738 Tidskriftsartikel (refereegranskat)abstract An evaluation of two-branch antenna diversity on mobile telephones is performed in the presence of head and hand phantoms to model the influence of the user. Two mobile telephone prototypes for the 1800-MHz band are considered. The evaluation is done by measuring the three-dimensional (3-D) complex radiation patterns from each antenna with the prototypes positioned near the phantom head and hand (i.e., in talk position) and calculating the diversity performance for three different scenarios of the incoming field. The two-branch antenna setups on both prototypes produce a calculated diversity gain of about 9 dB for selection diversity at the 99% reliability level.
23.	Buck, David, et al. (författare) Measuring Array Mutual Impedances Using Embedded Element Patterns 2023 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 71:1, s. 606-611 Tidskriftsartikel (refereegranskat)abstract The radiation pattern of an antenna element embedded in a multiport antenna such as a phased array depends on the loads connected to the array element ports. If the embedded element patterns are measured using at least two known loading conditions, the patterns can be used to determine the array mutual impedance matrix. In previous work, this result has been derived with the simplifying assumption that the impedance of the source connected to the driven element changes along with the load impedances connected to the nondriven elements. In a practical test configuration, the source impedance cannot be readily changed. We analyze the case of EEPs measured with a fixed source impedance and changing impedances on the nondriven elements. The transformation from one set of EEPs to another with fixed source impedance is more complex than in the case of a source impedance that changes with the load impedances. The transformation depends on the coupling between elements and is only weakly sensitive to the element self-impedances. With measured EEPs for an array of identical elements, the impedance matrix can be found up to a scale factor. We demonstrate the method experimentally by measuring the patterns of an antenna array terminated with one loading condition and repeating the pattern measurements with a different loading condition. The mutual impedance matrix extracted from the pattern measurements compared to network analyzer mutual impedance measurements is accurate to within 1–2 Ω for most of the mutual impedances.
24.	Cai, Xuesong, et al. (författare) A Switched Array Sounder for Dynamic Millimeter-Wave Channel Characterization: Design, Implementation and Measurements 2024 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. Tidskriftsartikel (refereegranskat)abstract A prerequisite for the design and evaluation of wireless systems is the understanding of propagation channels. While abundant propagation knowledge exists for bands below 6 GHz, the same is not true for millimeter-wave frequencies. In this paper, we present the design, implementation and measurement-based verification of a re-configurable 27.5-29.5 GHz channel sounder. Based on the switched array principle, our design is capable of characterizing 128×256 dynamic double-directional dual-polarized channels with snapshot times of around 600 ms. This is in sharp contrast to measurement times on the order of tens-of-minutes of sounders by rotating horn antennas. The antenna arrays at both link ends are calibrated in an anechoic chamber with high angular sampling intervals of 3 degrees in azimuth and elevation domains, which enables de-embedding the system responses of the sounder from the propagation channels. This is complemented with a bandwidth of up to 2 GHz, i.e., nanosecond-level delay resolution. The short measurement times and stable radio frequency design facilitate real-time processing of the received wavefronts to enhance measurement dynamic range. After disclosing the sounder design and implementation, we demonstrate its capabilities by presenting a measurement campaign at 28 GHz in an indoor lab environment.
25.	Cai, Xuesong, et al. (författare) Dynamic mmWave Channel Emulation in a Cost-Effective MPAC with Dominant-Cluster Concept 2021 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. Tidskriftsartikel (refereegranskat)abstract Millimeter-Wave (mmWave) massive multiple-input multiple-output (MIMO) has been considered as a key enabler for the fifth-generation (5G) communications. It is essential to design and test mmWave 5G devices under various realisticscenarios since the radio propagation channels pose intrinsic limitations on the performance. This requires emulating realistic dynamic mmWave channels in a reproducible manner in laboratories, which is the goal of this paper. In this contribution, we first illustrate the dominant-cluster(s) concept, where thenon-dominant clusters in the mmWave channels are pruned, for mmWave 5G devices applying massive MIMO beamforming. This demonstrates the importance and necessity to accurately emulate the mmWave channels at a cluster level rather than the composite-channel level. Thus, an over-the-air (OTA) emulationstrategy for dynamic mmWave channels is proposed based on the concept of dominant-cluster(s) in a sectored multiprobe anechoic chamber (SMPAC). The key design parameters including the probe number and the angular spacing of probes are investigated through comprehensive simulations. A cost-effective switch circuit is also designed for this purpose and validated in the simulation. Furthermore, a dynamic mmWave channel measured in an indoor scenario at 28-30 GHz is presented, where the proposed emulation strategy is also validated by reproducing the measured reality.
26.	Cai, Xuesong, et al. (författare) Enhanced Effective Aperture Distribution Function for Characterizing Large-Scale Antenna Arrays 2023 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 71:8, s. 6869-6877 Tidskriftsartikel (refereegranskat)abstract Accurate characterization of large-scale antenna arrays is growing in importance and complexity for the fifth-generation (5G) and beyond systems, as they feature more antenna elements and require increased overall performance. The full 3D patterns of all antenna elements in the array need to be characterized because they are in general different due to construction inaccuracy, coupling, antenna array's asymmetry, etc. The effective aperture distribution function (EADF) can provide an analytic description of an antenna array based on a full-sphere measurement of the array in an anechoic chamber. However, as the array aperture increases, denser spatial samples are needed for EADF due to large distance offsets of array elements from the reference point in the anechoic chamber, leading to a prohibitive measurement time and increased complexity of EADF. In this paper, we present the EADF applied to large-scale arrays and highlight issues caused by the large array aperture. To overcome the issues, an enhanced EADF is proposed with a low complexity that is intrinsically determined by the characteristic of each array element rather than the array aperture. The enhanced EADF is validated using experimental measurements conducted at 27-30 GHz frequency band with a relatively large planar array.
27.	Capek, Miloslav, et al. (författare) Characteristic Mode Decomposition Using the Scattering Dyadic in Arbitrary Full-Wave Solvers 2023 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 71:1, s. 830-839 Tidskriftsartikel (refereegranskat)abstract Characteristic modes are formulated using the scattering dyadic, which maps incident plane waves to scattered far fields generated by an object of arbitrary material composition. Numerical construction of the scattering dyadic using arbitrary full-wave electromagnetic solvers is demonstrated in examples involving a variety of dielectric and magnetic materials. Wrapper functions for computing characteristic modes in method-of-moments, finite-difference time domain, and finite element solvers are provided as supplementary material.
28.	Capek, Miloslav, et al. (författare) Minimization of Antenna Quality Factor 2017 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 65:8, s. 4115-4123 Tidskriftsartikel (refereegranskat)abstract Optimal currents on arbitrarily shaped radiators with respect to the minimum quality factor are found using a simple and efficient procedure. The solution starts with a reformulation of the problem of minimizing quality factor Q as an alternative, so-called dual, problem. Taking advantage of modal decomposition and group theory, it is shown that the dual problem can easily be solved and always results in minimal quality factor Q. Moreover, the optimization procedure is generalized to minimize quality factor Q for embedded antennas, with respect to the arbitrarily weighted radiation patterns, or with prescribed magnitude of the electric and magnetic near-fields. The obtained numerical results are compatible with previous results based on composition of modal currents, convex optimization, and quasistatic approximations; however, using the methodology in this paper, the class of solvable problems is significantly extended.
29.	Capek, Miloslav, et al. (författare) Optimal Inverse Design Based on Memetic Algorithms - Part 1 : Theory and Implementation 2023 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 71:11, s. 8806-8816 Tidskriftsartikel (refereegranskat)abstract A memetic framework for optimal inverse design is proposed by combining a local gradient-based procedure and a robust global scheme. The procedure is based on method-of-moments matrices and does not demand full inversion of a system matrix. Fundamental bounds are evaluated for all optimized metrics in the same manner, providing natural stopping criteria and quality measures for realized devices. Compared to density-based topology optimization, the proposed routine does not require filtering or thresholding. Compared to commonly used heuristics, the technique is significantly faster, still preserving a high level of versatility and robustness. This is a two-part paper in which the first part is devoted to the theoretical background and properties, and the second part applies the method to examples of varying complexity.
30.	Capek, Miloslav, et al. (författare) Optimal Inverse Design Based on Memetic Algorithms - Part II : Examples and Properties 2023 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 71:11, s. 8817-8829 Tidskriftsartikel (refereegranskat)abstract Optimal inverse design, including topology optimization and evaluation of fundamental bounds on performance, which was introduced in Part 1, is applied to various antenna design problems. A memetic scheme for topology optimization combines local and global techniques to accelerate convergence and maintain robustness. Method-of-moments (MoMs) matrices are used to evaluate objective functions and allow determination of fundamental bounds on performance. By applying the Shermann-Morrison-Woodbury identity, the repetitively performed structural update is inversion-free yet full-wave. The technique can easily be combined with additional features often required in practice, e.g., only a part of the structure is controllable, or evaluation of an objective function is required in a subdomain only. The memetic framework supports multifrequency and multiport optimization and offers many other advantages, such as an actual shape being known at every moment of the optimization. The performance of the method is assessed, including its convergence and computational cost.
31.	Capek, Miloslav, et al. (författare) Shape Synthesis Based on Topology Sensitivity 2019 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 67:6, s. 3889-3901 Tidskriftsartikel (refereegranskat)abstract A method evaluating the sensitivity of a given parameter to topological changes is proposed within the method of moments paradigm. The basis functions are used as degrees of freedom which, when compared to the classical pixeling technique, provide important advantages, one of them being impedance matrix inversion free evaluation of the sensitivity. The devised procedure utilizes port modes and their superposition which, together with only a single evaluation of all matrix operators, leads to a computationally effective procedure. The proposed method is approximately 100 times faster than the contemporary approaches, which allows the investigation of the sensitivity and the modification of shapes in real time. The method is compared with the known approaches and its validity and effectiveness are verified using a series of examples. The procedure can be implemented in up-to-date electromagnetic (EM) simulators in a straightforward manner. It is shown that the iterative repetition of the topology sensitivity evaluation can be used for gradient-based topology synthesis. This technique can also be employed as a local step in global optimizers.
32.	Capek, Miloslav, et al. (författare) Validating the Characteristic Modes Solvers 2017 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 65:8, s. 4134-4145 Tidskriftsartikel (refereegranskat)abstract Characteristic modes (CMs) of a spherical shell are found analytically as spherical harmonics normalized to radiate unitary power and to fulfill specific boundary conditions. The presented closed-form formulas lead to a proposal of precise synthetic benchmarks that can be utilized to validate the method-of-moments matrix or performance of CM decomposition. Dependence on the mesh size, electrical size, and other parameters can systematically be studied, including the performance of various mode tracking algorithms. A notable advantage is the independence on feeding models. Both theoretical and numerical aspects of CM decomposition are discussed and illustrated by examples. The performance of state-of-the-art commercial simulators and academic packages having been investigated, we can conclude that all contemporary implementations are capable of identifying the first dominant modes while having severe difficulties with higher order modes. Surprisingly poor performance of the tracking routines is observed notwithstanding the recent ambitious development.
33.	Carozzi, Tobia, 1966, et al. (författare) A Fundamental Figure of Merit for Radio Polarimeters 2011 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 59:6, s. 2058-2065 Tidskriftsartikel (refereegranskat)abstract Many modern radio applications, such as astronomy and remote sensing, require high-precision polarimetry. These applications put exacting demands on radio polarimeters (antenna systems that can measure the state of polarization of radio sources), and in order to assess their polarimetric performance, a figure of merit (FoM) would be desirable. Unfortunately, we find that the parameter commonly used for this purpose, the cross-polarization ratio, is not suitable as a polarimetry FoM unless it is given in an appropriate coordinate system. This is because although the cross-polarization ratio is relevant for raw, uncalibrated polarimetry, in general it is not relevant to the quality of the polarimetry after polarimetric calibration. However, a cross-polarization ratio can be constructed from invariants of the Jones matrix (the matrix that describes the polarimetric response of a polarimeter) that quantifies polarimetric performance even after calibration. We call this cross-polarization ratio the intrinsic cross-polarization ratio (IXR) and conclude that it is a fundamental FoM for polarimeters. We then extend the IXR concept from the Jones calculus to the Mueller calculus and also to interferometers, and we give numerical examples of these parameters applied to the Parkes radio telescope, the Westerbork synthesis radio telescope, and the Effelsberg telescope.
34.	Castillo Tapia, Pilar, et al. (författare) Two-Dimensional Beam Steering Using a Stacked Modulated Geodesic Luneburg Lens Array Antenna for 5G and Beyond 2023 Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 71:1, s. 487-496 Tidskriftsartikel (refereegranskat)abstract Antennas for future communication systems are required to be highly directive and steerable to compensate for the high path loss in the millimeter-wave band. In this work, we propose a linear array of modulated geodesic Luneburg lens (the so-called water drop lens) antennas operating at 56-62 GHz. The lens array antenna features 2-D beam scanning with low structural complexity. The lenses are fully metallic and implemented in parallel plate waveguides (PPWs), meaning that they are highly efficient. Each lens is fed with 13 rectangular waveguides surrounded by glide-symmetric holes to suppress leakage. The lenses provide 110? beam coverage in the H-plane with scan losses below 1 dB. In order to scan in the E-plane, we use a feeding network based on a 1:4 power divider and three phase shifters. In this configuration, the array can scan 60? in the E-plane, albeit with higher scanning losses than in the H-plane. The lens array is manufactured and a good agreement between simulated and experimental results is obtained.
35.	Chandra, Rohit, et al. (författare) A Link Loss Model for the On-body Propagation Channel for Binaural Hearing Aids 2013 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 61:12, s. 6180-6190 Tidskriftsartikel (refereegranskat)abstract Binaural hearing aids communicate with each other through a wireless link for synchronization. A propagation model is needed to estimate the ear-to-ear link loss for such binaural hearing aids. The link loss is a critical parameter in a link budget to decide the sensitivity of the transceiver. In this paper, we have presented a model for the deterministic component of the ear-to-ear link loss. The model takes into account the dominant paths having most of the power of the creeping wave from the transceiver in one ear to the transceiver in other ear and the effect of the protruding part of the outer ear called pinna. Simulations are done to validate the model using in-the-ear (ITE) placement of antennas at 2.45 GHz on two heterogeneous phantoms of different age-group and body size. The model agrees with the simulations. The ear-to-ear link loss between the antennas for the binaural hearing aids in the homogeneous SAM phantom is compared with a heterogeneous phantom. It is found that the absence of the pinna and the lossless shell in the SAM phantom underestimate the link loss. This is verified by the measurements on a phantom where we have included the pinnas fabricated by 3D-printing.
36.	Chen, Ming Zheng, et al. (författare) Geodesic H-Plane Horn Antennas 2023 Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 71:8, s. 6329-6339 Tidskriftsartikel (refereegranskat)abstract This article describes a detailed procedure that allows for a time-efficient design of fully metallic geodesic H-plane horn antennas using an in-house ray-tracing method together with an optimization algorithm. With all the propagation in the air, geodesic H-plane horn antennas are of low loss and highly efficient. The proposed geodesic H-plane horn antennas provide a new degree of freedom, the height profile, to alleviate phase errors, realizing high gains and aperture efficiencies. Optimizations are implemented to design the height profile for a given target, enabled by the highly accurate and time-efficient in-house ray-tracing model. To demonstrate the correctness and versatility of the proposed design procedure, two prototypes are manufactured with computerized numerical control (CNC) machining and compared to their planar counterparts, with the aim of a high increased gain and aperture efficiency, respectively. The prototypes maintain good frequency stability from 26 to 33GHz, with sidelobe levels lower than -15dB and return loss better than 15dB. The first prototype improves the realized gain by over 5dB compared to the reference horn, while the second prototype achieves an aperture efficiency of around 65% within the operating frequency band.
37.	Chen, Ming Zheng, et al. (författare) Ray-Tracing and Physical-Optics Model for Planar Mikaelian Lens Antennas 2024 Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 72:2, s. 1735-1744 Tidskriftsartikel (refereegranskat)abstract This article proposes a ray-tracing and physical-optics (RT-PO) model that allows for an accurate and time-efficient evaluation of planar Mikaelian lens antennas implemented by parallel plate waveguides (PPWs). With an intrinsic flat shape and axis-symmetry of refractive-index distribution characteristics, the planar Mikaelian lens antennas are easy to fabricate and integrate into standard planar feeds. A numerical computation of the ray paths based on Snell's law describes the phase of the electric field in the lens aperture, while the ray-tube power conservation theory is employed to evaluate the amplitude. The field equivalence principle is then used to calculate the far-field of the lens antenna. The information on far-field directivity, gain, and dielectric efficiency is further obtained, considering a small loss in the dielectric materials. Our approach is validated by comparing the results of a particular Mikaelian lens antenna with those computed using a commercial full-wave simulator, demonstrating high accuracy and a significant reduction in computation resources and times.
38.	Chen, Qiao, et al. (författare) Efficient Leaky-Lens Antenna at 60 GHz Based on a Substrate-Integrated-Holey Metasurface 2020 Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 68:12, s. 7777-7784 Tidskriftsartikel (refereegranskat)abstract We propose a low-cost implementation of a low-dispersive leaky-wave antenna (LWA) at 60 GHz for point-to-point 5G communications. The LWA is implemented with glide-symmetric holes in gap-waveguide technology. The radiation is produced through a slit and controlled with glide-symmetric holes. The low dispersion is achieved thanks to the use of a dispersive prism that compensates the frequency dependence of the radiation through the slit. The main innovation of our proposed design is the use of substrate integrated holes (SIHs) to implement the dispersive prism. This implementation significantly enhances the bandwidth and improves the robustness to manufacturing tolerances. Also, this implementation reduces the cost of the antenna while maintaining low losses since the majority of the propagation inside the prism is in air. Additionally, we demonstrate that the use of glide-symmetric holes in the slit allows for a better control of the amount of radiation (attenuation constant) when compared with conventional holes. The differences in the attenuation constant between conventional and glide-symmetric holes have been studied with a multimodal analysis. Apart from giving a convenient physical insight, this method also expedites the design process.
39.	Chen, Qiao, et al. (författare) Glide-Symmetric Holey Leaky-Wave Antenna With Low Dispersion for 60 GHz Point-to-Point Communications 2020 Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 68:3, s. 1925-1936 Tidskriftsartikel (refereegranskat)abstract In this article, two novel efficient leaky-wave antennas (LWAs) with stable radiation patterns operating in the 60 GHz band are proposed. The LWAs are implemented in groove-gap waveguide (GGW) technology. To mitigate the beam squint due to the dispersive nature of LWAs, complementary-dispersive prisms are coupled to the LWA radiation aperture. The antennas are implemented in fully metallic purely holey periodic structures, resulting in a more cost-effective and robust manufacturing process compared to previously reported pin-based structures. Two prisms are proposed, one with mirror symmetry and one with glide symmetry. When the prism possesses a glide symmetry, much fewer holes are required while maintaining a similar performance, which even further decreases the fabrication costs. The complex propagation constant is optimized for low sidelobe levels (SLLs) with tailored hole diameters and waveguide dimensions, thus for the first time demonstrating the capability of using glide-symmetric holes to control the leakage rate. Two prototypes with mirror- and glide-symmetric prisms are theoretically synthesized and validated by the simulated and experimental results. A frequency bandwidth of 11% is achieved for both prototypes with the beam squint within +/- 0.9 degrees (mirror) and +/- 1.7 degrees (glide), SLLs below -15 dB (mirror) and -13 dB (glide), total efficiency almost 90%, and realized gain of 17 +/- 0.5 dB at a fixed observing angle. The developed antennas are intended for mm-wave point-to-point communications.
40.	Chen, Zihao, et al. (författare) A Multi-Port Microstrip Grid Array Structure 2016 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 64:11, s. 4953-4958 Tidskriftsartikel (refereegranskat)abstract This paper presents a multi-port microstrip grid array structure, which gives the flexibility to use it as a single antenna or multiple antennas. To realize such a structure, the key challenges are impedance matching and port isolation. It is shown that impedance matching can be made with stepped-impedance lines and port isolation can be enhanced from the defected ground plane. A particular example of 145 radiating elements with 4 ports is implemented in RT/duroid 5880 substrate for 24-GHz applications. Simulated and measured results are compared, which verifies the design, analysis, and versatility of the structure.
41.	Cheng, Shi, et al. (författare) 79 GHz Slot Antennas Based on Substrate Integrated Waveguides (SIW) in a Flexible Printed Circuit Board 2009 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 57:1, s. 64-71 Tidskriftsartikel (refereegranskat)abstract The design, fabrication and characterization of 79 GHz slot antennas based on substrate integrated waveguides (SIW) are presented in this paper. All the prototypes are fabricated in a polyimide flex foil using printed circuit board (PCB) fabrication processes. A novel concept is used to minimize the leakage losses of the SlWs at millimeter wave frequencies. Different losses in the SlWs are analyzed. SIW-based single slot antenna, longitudinal and four-by-four slot array antennas are numerically and experimentally studied. Measurements of the antennas show approximately 4.7%, 5.4% and 10.7% impedance bandwidth (S-11 = -10 dB) with 2.8 dBi, 6.0 dBi and 11.0 dBi maximum antenna gain around 79 GHz, respectively. The measured results are in good agreement with the numerical simulations.
42.	Cheng, Shi, et al. (författare) Foldable and stretchable liquid metal planar inverted cone antenna 2009 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 57:12, s. 3765-3771 Tidskriftsartikel (refereegranskat)abstract A mechanically flexible planar inverted cone antenna (PICA) for ultrawideband (UWB) applications is presented. It can be both folded and stretched significantly without permanent damage or loss of electrical functionality. The antenna is manufactured with a process in which conductors are realized by injecting room temperature liquid metal alloy into micro-structured channels in an elastic dielectric material. The elastic dielectric material together with the liquid metal enables bending with a very small radius, twisting, and stretching along any direction. Port impedance and radiation characteristics of the non-stretched and stretched antenna are studied in simulations and experiments. The presented antenna has a return loss better than 10 dB within 3-11 GHz and a radiation efficiency of > 70% over 3-10 GHz, also when stretched. Tests verify that stretching up to 40% is possible with maintained electrical performance. The presented antenna is useful for example for body-worn antennas and in applications in harsh environments where mechanical flexibility helps improve durability.
43.	Chepala, Anil, et al. (författare) Beamspace Modulated Circular Array 2019 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 67:5, s. 3496-3499 Tidskriftsartikel (refereegranskat)abstract In this paper, we show how each independent spatial mode of a circular array can be individually encoded and collimated to yield high ergodic spectral sum efficiency of an uplink mobile communication system. We show that every mode generated with the help of Rotman Lens is orthogonal to every other mode. This reduces the spatial cross-coupling and thereby enhances data throughput.We also show that unlike other phased arrays, the circular array has the ability to detect direction of arrival (DOA) from the backward half-space of the array to advantage. Furthermore, we show that because of its symmetry, the array can unlike linear arrays, create beam that can be scanned over 360° in azimuth scan plane. A proof of principle multi-mode circular array (MMCA) for the purpose defined above is designed, simulated and tested.
44.	Cismasu, Marius, et al. (författare) Antenna Bandwidth Optimization with Single Frequency Simulation 2014 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 62:3, s. 1304-1311 Tidskriftsartikel (refereegranskat)abstract A method to compute antenna Q using an electromagnetic simulation at a single frequency is described. This method can easily be integrated into global optimization algorithms. In this way the optimization time of some antenna parameters, e.g., bandwidth, may be significantly reduced. The method is validated by direct comparison with the physical bound of the analyzed structure. Numerical examples for rectangular antennas and antennas with a rectangular ground plane illustrate the integration of the method into a genetic algorithm. The results predicted by optimization agree very well with those obtained using a commercial electromagnetic solver. These results suggest that the method can be used to yield antennas with Q factors within 20% of their corresponding physical bound.
45.	Claesson, Ingvar, et al. (författare) A Spatial Filtering Approach to Robust Adaptive Beamforming 1992 Ingår i: IEEE Transactions on Antennas and Propagation. - New York : Institute of electrical and electronics engineers. - 0018-926X. ; 40:9, s. 1093-1096 Tidskriftsartikel (refereegranskat)abstract This communication treats the problem of controlling the superresolution in adaptive beamformers. A straightforward method is presented that works for both narrow-band and broad-band arrays. The method is based on forming the blocking matrix in a general sidelobe canceller (GSC) structure using a spatial FIR filter. The suppression of this spatial filter and the implicit noise of the leaky (LMS) algorithm together determine the beamformer.
46.	Cooray, Vernon (författare) On the accuracy of several approximate theories used in quantifying the propagation effects on lightning generated electromagnetic fields 2008 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 56:7, s. 1960-1967 Tidskriftsartikel (refereegranskat)abstract The effect of finitely conducting ground on the signature of lightning generated vertical electric fields at ground level was evaluated by numerical solution of Sommerfeld's integrals. Results are presented for distances between 10 m to 1 km from the lightning channel and for ground conductivities in the range of 0.01 and 0.001 S/m. The results obtained from the exact theory are compared with the predictions of several approximate theories available in the literature. Based on that comparison the limits of validity of these approximate theories are obtained.
47.	Cooray, Vernon, et al. (författare) Pulse propagation along transmission lines in the presence of corona and their implication to lightning return strokes 2008 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 56:7, s. 1948-1959 Tidskriftsartikel (refereegranskat)abstract Transmission line equations in air in the presence of corona are derived. The analysis shows that the corona caused by a voltage or a current pulse propagating along a transmission line can be represented by a series of corona current sources distributed along the line. Corona has two effects on the voltage or current pulses propagating along a transmission line. First, it will clamp down the pulse amplitude at the front of the pulse to the corona threshold. Second, it will cause the portion of the pulse whose amplitude is larger than the corona threshold to travel with a speed less than the speed of light. The effects of corona on the voltage or current pulses propagating along a transmission line can also be evaluated by introducing a time varying capacitance and a conductance into the transmission line. If the time varying capacitance is assumed to be proportional to the ratio between the corona charge and the applied voltage then one requires both this and the time varying conductance to represent the corona effects more accurately. Analysis of the return stroke as a current pulse propagating along a transmission line undergoing corona shows that the corona effects may explain the reason why the measured return stroke speeds are considerably less than the speed of light. Moreover, based on the effects of corona, a physical justification for the concepts used in the current generation type return stroke models is provided.
48.	Cuesta, F. S., et al. (författare) Planar Broadband Huygens' Metasurfaces for Wave Manipulations 2018 Ingår i: Ieee Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 66:12, s. 7117-7127 Tidskriftsartikel (refereegranskat)abstract Electrically thin and effectively 2-D material composites, metasurfaces, have been widely exploited for the manipulation of electromagnetic waves. For many applications, it is desired to transform incident waves of a specific frequency range keeping the metasurface invisible at other frequencies. Such a frequency-selective response can be achieved based on subwavelength Huygens' inclusions. However, their fabrication requires sophisticated processes due to the 3-D geometry. Here, we propose a planar Huygens' meta-atom with the goal to open a way to realize broadband invisible metasurfaces with topologies suitable for the conventional printed circuit board fabrication technology. We synthesize and analyze, both numerically and experimentally, three different metasurfaces capable of polarization and amplitude transformations of incident waves.
49.	Dahlberg, Oskar, et al. (författare) Low-Dispersive Leaky-Wave Antennas for mmWave Point-to-Point High-Throughput Communications 2020 Ingår i: IEEE Transactions on Antennas and Propagation. - : IEEE. - 0018-926X .- 1558-2221. ; 68:3, s. 1322-1331 Tidskriftsartikel (refereegranskat)abstract In this article, we present two efficient leaky-wave antennas (LWAs) with stable radiation pattern, operating at 60 GHz. Both antennas exhibit attractive properties such as significantly reduced beam-squint, low loss, low sidelobes, high directivity, and simple manufacturing. The beam-squint of conventional LWAs is reduced by refracting the leaked waves in a dispersive lens and the low sidelobe levels are achieved by tapering the leakage rate along the aperture. Since the antennas are implemented in groove gap waveguide technology, the losses are low. The two antennas are different in terms of their asymmetric/symmetric leakage tapering with respect to the broadside direction. Both designs are optimized for low sidelobes, but since symmetry is enforced in one, the resulting performance in terms of sidelobes is suboptimal. However, in the symmetric design, multiple stable beams can be obtained, simultaneously or independently. Twenty percent bandwidth is obtained with less than +/- 0.5 degrees beam-squint. In this frequency range, the gain is stable at 17 and 15 dBi for the asymmetric and symmetric designs, respectively. The designs are intended for point-to-point links in mmWave communication networks where low losses, directive beams, and low sidelobes are expected to be key features.
50.	Djounidi, Justine, et al. (författare) Low-Profile Fully Metallic Multiple-Ridge Luneburg Lens Antenna 2024 Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 72:6, s. 4852-4861 Tidskriftsartikel (refereegranskat)abstract The geodesic Luneburg lens has been revisited as a suitable solution for applications requiring directive beams in the millimeter waveband. Among its advantages, its rotational symmetry and high efficiency stand out. However, one of its drawbacks is the need for a certain height to produce the desired focusing properties of the lens. Here, we propose a low-profile solution based on rotationally symmetric ridges that mimic, similar to geodesic lenses, the effective refractive index of a Luneburg lens. Moreover, we show that both rectangular and trapezoidal ridges perform similarly, opening the possibility for other manufacturing techniques. We demonstrate this concept with a prototype that is fully metallic and provides a scanning range of +/- 62 degrees over a broadband of operation, from 24 to 34 GHz. In this prototype, the height of the lens is 18 times more compact than the original Rinehart-Luneburg lens, allowing the lens to be vertically stacked, which is beneficial, for example, for producing linear arrays. This technique could be used to produce other type of lenses.

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