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1.	Abbas, Taimoor, et al. (author) Simulation and Measurement Based Vehicle-to-Vehicle Channel Characterization: Accuracy and Constraint Analysis 2015 In: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 63:7, s. 3208-3218 Journal article (peer-reviewed)
2.	Abenius, Erik, et al. (author) Thin Sheet Modeling Using Shell Elements in the Finite-Element Time-Domain Method 2006 In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 54, s. 28-34 Journal article (peer-reviewed)
3.	Adeogun, Ramoni, et al. (author) Polarimetric Wireless Indoor Channel Modeling Based on Propagation Graph 2019 In: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 67:10, s. 6585-6595 Journal article (peer-reviewed)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. (author) A new compact wideband MIMO antenna – the double-sided tapered self-grounded monopole array 2014 In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 62:6, s. 3365 - 3369 Journal article (peer-reviewed)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. (author) Impact of Scattering Within a Multipath Simulator Antenna Array on the Ricean Fading Distribution Parameters in OTA Testing 2014 In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 62:6, s. 3257-3269 Journal article (peer-reviewed)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. (author) On the Physical Limitations of the Interaction of a Spherical Aperture and a Random Field 2011 In: IEEE Transactions on Antennas and Propagation. - : IEEE. - 0018-926X .- 1558-2221. ; 59:1, s. 119-128 Journal article (peer-reviewed)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. (author) Spherical Vector Wave Expansion of Gaussian Electromagnetic Fields for Antenna-Channel Interaction Analysis 2009 In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 57:7, s. 2055-2067 Journal article (peer-reviewed)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. (author) Dispersion Analysis of Periodic Structures in Anisotropic Media : Application to Liquid Crystals 2022 In: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 70:4, s. 2811-2821 Journal article (peer-reviewed)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. (author) Dual-Polarized Highly Folded Bowtie Antenna with Slotted Self-Grounded Structure for Sub-6 GHz 5G Applications 2022 In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 70:4, s. 3028-3033 Journal article (peer-reviewed)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. (author) Sparse Array Synthesis Including Mutual Coupling for MU-MIMO Average Capacity Maximization 2022 In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 70:8, s. 6617-6626 Journal article (peer-reviewed)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. (author) Simultaneous Transmit and Receive Self-Duplexing Antenna for Head Implants 2023 In: IEEE Transactions on Antennas and Propagation. - Piscataway, NJ : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 71:11, s. 8592-8601 Journal article (peer-reviewed)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 (author) Moment-method calculations on apertures using basis singular functions 1993 In: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X. ; 41:12, s. 16-1709 Journal article (peer-reviewed)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. (author) Ultrawideband Conical Log-Spiral Circularly Polarized Feed for Radio Astronomy 2020 In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 68:3, s. 1995-2007 Journal article (peer-reviewed)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. (author) A 16 × 16 45° Slant-Polarized Gapwaveguide Phased Array With 65-dBm EIRP at 28 GHz 2023 In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 71:2, s. 1319-1329 Journal article (peer-reviewed)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. (author) A Cost-Effective Wideband Switched Beam Antenna System for a Small Cell Base Station 2018 In: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers Inc.. - 0018-926X .- 1558-2221. ; 66:12, s. 6851-6861 Journal article (peer-reviewed)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. (author) Synthesis of Maximally Sparse Arrays Using Compressive Sensing and Full-Wave Analysis for Global Earth Coverage Applications 2016 In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 64:11, s. 4872-4877 Journal article (peer-reviewed)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 (author) Bandwidth Limitations for Scattering of Higher Order Electromagnetic Spherical Waves with Implications for the Antenna Scattering Matrix 2012 In: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 60:9, s. 4345-4353 Journal article (peer-reviewed)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. (author) Modal-Based Design of a Wideband Quadruple-Ridged Flared Horn Antenna 2016 In: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 64:5, s. 1615-1626 Journal article (peer-reviewed)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. (author) Delay insensitive signal-injection calibration for large antenna arrays using passive hierarchical networks 2017 In: IEEE Transactions on Antennas and Propagation. - : IEEE. - 0018-926X .- 1558-2221. ; 65:1, s. 190-195 Journal article (peer-reviewed)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. (author) Efficient Analysis of Aperture Antennas on Generally Shaped Convex Multilayered Surfaces Using a Hybrid SD-UTD Method 2009 In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 57:5, s. 1420-1431 Journal article (peer-reviewed)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. (author) Simple Boundary Condition for Canonical EBG Surface: PMC-Backed Uniaxial Medium 2016 In: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 64:2, s. 785-U550 Journal article (peer-reviewed)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. (author) Evaluation of antenna diversity performance for mobile handsets using 3-D measurement data 1999 In: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 47:11, s. 1736-1738 Journal article (peer-reviewed)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. (author) Measuring Array Mutual Impedances Using Embedded Element Patterns 2023 In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 71:1, s. 606-611 Journal article (peer-reviewed)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. (author) A Switched Array Sounder for Dynamic Millimeter-Wave Channel Characterization: Design, Implementation and Measurements 2024 In: IEEE Transactions on Antennas and Propagation. - 0018-926X. Journal article (peer-reviewed)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. (author) Dynamic mmWave Channel Emulation in a Cost-Effective MPAC with Dominant-Cluster Concept 2021 In: IEEE Transactions on Antennas and Propagation. - 0018-926X. Journal article (peer-reviewed)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.

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