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The objective of this special issue is to publish papers related to the basic physics of Electromagnetism in thecontext of radio wave propagation, see editorial of Part I. [ABSTRACT FROM AUTHOR]

The Piergiorgio L. E. Uslenghi Letters Prize Paper Award was established in 2009 to recognize the best contribution published in the IEEE Antennas and Wireless Propagation Letters during the previous year. [ABSTRACT FROM AUTHOR]

The article presents the winners in the Harold A. Wheeler Applications Prize Paper Award for 2017. It highlight the significance of the award which recognizes authors of the best applications paper published in the Institute of Electrical and Electronics Engineers (IEEE) Transactions on Antennas and Propagation. The winners include Dia'aaldin J. Bisharat, Shaowei Liao and Quan Xue.

This paper provides a survey of various experimental data available on the value of the propagation path loss of radio waves in a cellular wireless environment. It is shown starting with the Okumuraet al.’s paper on propagation measurements and other available published experimental data that they all exhibit that the electric field varies as $\rho ^{-1.5}$ within a cellular radius of a few kilometers, where $\rho $ is the radial distance of the receiving antenna from the transmitting one. This decay in the fields is equivalent to a propagation loss of −9 dB/octave or −30 dB for a decade of the distance. This value is independent of the nature of the ground, whether it be composed of rural, urban, suburban, or water. This is the first time it is stated that the propagation path loss due to the presence of ground generates a path loss of 90 dB when the signals travel a distance of 1 km. This value is rather large when compared to a loss of 30–50 dB produced by buildings, trees, and similar artifacts. Therefore, the experimental data indicate that the effect of trees and buildings have a secondary influence on the decay of the electric field with distance, the dominant one is the propagation loss over an imperfect ground. Contemporary propagation models do not acknowledge this fact. Outside the cellular radius of a few kilometers, the path loss appears to be 12 dB/octave or 40 dB/decade of distance. In a companion paper, it will be demonstrated that the values for the path loss can be explained from an analytical standpoint without taking recourse to statistics which involves a lot of assumptions on the functional variation of the variables of interest. [ABSTRACT FROM AUTHOR]

Three main characteristics of massive multiple-input-multiple-output (MIMO) are studied. The widespread use of these characteristics and their lack of validation motivates this paper based in measurements. First, we study the channel hardening when the number of antennas in the base station (BS) increases. Second, we focus on the channel vector orthogonality between two users. Third, we investigate the rank of the spatial covariance matrix. The data used for this paper have been obtained in two measurement campaigns with all real antennas (i.e., neither virtual arrays nor virtual users). The first one has 64 BS elements arranged in 3 configurations, and it serves 8 users with 2 antennas each. The second campaign has 128 BS elements, serving 2 users with 2 antennas each. Both campaigns include line-of-sight and nonline-of-sight scenarios, designed according to the future 5G deployment scenarios. We show the rate of channel hardening when the number of BS elements increases. We evaluate the sum rate of two users at specific distances between them. We observe the large angular spread occupied by the user. [ABSTRACT FROM AUTHOR]

This paper addresses the question of how much information can be transmitted reliably over a wireless channel. It is shown that the limit of this mode of transmission is dictated by the amount of information that an electromagnetic field is capable of carrying. The methodology for the analysis of this problem is along the theory developed by Kolmogorov. This allows one to quantify the amount of information that can be transmitted by a wireless communication system taking into account the physical limitations governed by the laws of electromagnetism. Starting from the results related to the amount of information carried by an electromagnetic field, a novel antenna synthesis technique that simultaneously takes into account the requirements of information and antenna theory is introduced and applied to the synthesis of multiantenna systems. [ABSTRACT FROM AUTHOR]

This paper describes the design and testing of a multiple-in multiple-out (MIMO) antenna for metal-frame smartwatch applications. The antenna operates from 2.4 to 2.49 GHz, which can cover Bluetooth/WiFi band. The design procedure is based on the theory of characteristic modes and it is discussed thoroughly. By employing a pair of degenerated modes to design the MIMO antenna, a high port-to-port isolation can be achieved over the operating frequency band. Simulated and measured results are presented to verify the antenna design. Furthermore, the antenna has a low envelope correlation coefficient and a high effective diversity gain even when it is mounted on the human phantom. Hence, the proposed antenna proves to be a good candidate for smartwatch applications. [ABSTRACT FROM AUTHOR]

We give an overview of recent developments in the modeling of radiowave propagation, based on machine learning (ML) algorithms. We identify the input and output specification and the architecture of the model as the main challenges associated with ML-driven propagation models. Relevant papers are discussed and categorized based on their approach to each of these challenges. Emphasis is given on presenting the prospects and open problems in this promising and rapidly evolving area. [ABSTRACT FROM AUTHOR]

The emerging applications for wearable electronics have experienced enormous growth over the last decade. Antennas, being one of the critical components in modern wireless devices, thus need to be specifically designed to function while being worn and bent. In this paper, we present a systematic investigation of the effects of bending applied on wearable patch antennas over cylindrical surfaces. The resonant frequency variations and radiation pattern variations have been studied by simulating and measuring patch antennas that are bent by different angles. A frequency shift plot with respect to bending radius has been generated to target antennas for various wearable applications. An analytical approach has been presented to study the effect of resonant frequency shifting for both E- and H-planes bending. A lumped element circuit model is used to interpret the E-plane bending from different perspectives. One of the main objectives of this paper is to develop useful design-oriented charts and provide a better understanding of the effects of antenna bending to assist wearable antenna designers. [ABSTRACT FROM PUBLISHER]

In certain radar and wireless communication applications, omnidirectional circularly polarized (CP) antennas are desired but existing solutions have complex 3-D structures and are large in size. In this paper, a compact and low profile CP antenna having omnidirectional pattern on azimuthal plane is demonstrated. The CP waveform is synthesized by combining two linearly polarized and omnidirectional antennas with 90° phase difference on their terminals. The most challenging part of the design is the realization of the horizontally polarized antenna with omnidirectional radiation pattern. This antenna is designed using a novel two-faced slot antenna structure capable of emitting in-phase radiation of equal magnitude on both sides of the antenna. The two faces of the low-profile slot antenna are connected by a thin meander parallel plate waveguide to provide antiparallel field distributions over the two faces of the slot radiators. This special design removes radiation nulls on E-plane that exists on conventional slot antennas, the mechanism of which has been carefully discussed in this paper. The other antenna is a compatible pair of planar inverted-F antennas constructed on the sides of the finite-ground plane two-faced slot antenna for the provision of vertically polarized omnidirectional radiation. A feed network with power splitter and phase shifter is also accommodated on the compact CP antenna. The antenna is designed and fabricated, and its performance is measured against numerical simulations. It is shown that the fabricated antenna at 2.4 GHz can provide measured axial ratio of lower than 1.8 and gain variations of less than ±1.5 dB over all azimuth angles. [ABSTRACT FROM PUBLISHER]

This paper combines a study of human body morphology with physical layer characteristics to introduce a novel biometric identity feature for security in wearable communication applications. The physical layer characteristics of close fitting wearable devices are shown to vary in a unique manner through electromagnetic interactions between the tissue morphology and the antenna. Experimental measurement results demonstrate the new biometric concept using return loss characteristics to identify individuals on multiple body parts. An optimized directional coupler design is implemented with the antenna to optimize the characteristic feature detection range for human identification. Experiments conducted on human subjects using a prototype standalone test-bed and sensing circuitry at 2.45 GHz show that classification accuracies of over 98% are achieved for stationary subjects and 93% for mobile subjects. The new physical layer biometric has the potential to be used for authentication and authorization by using return loss as an indicator for secure user applications, using circuitry already implemented in wireless wearable communication systems. [ABSTRACT FROM AUTHOR]

This paper proposes a method to represent and predict received signal instantaneous polarization states as a function of arbitrary transmit polarization states for time-dispersive channels. The model incorporates frequency-dependent characterizations to represent the polarization dispersion behavior of a received signal across its bandwidth in a multipath channel. The representation takes advantage of signal dispersion features typical of depolarized signals, and employs subbanded characterizations to achieve polarization representations exhibiting high degrees of polarization in each subband. Experiments are conducted that demonstrate the utility of the modeling approach to predict polarization dispersion responses for arbitrary transmit polarizations based on measurements from two orthogonal transmit polarizations. [ABSTRACT FROM AUTHOR]

This paper presents a low-profile coplanar dual-polarized dual-band base station antenna array. A slotted patch antenna operating from 0.82 to 0.99 GHz with four shorting strips is proposed and analyzed. The four shorting strips are employed not only to improve the impedance matching in the lower band but also to remove the center part of the patch, thus making room for higher band dipoles operating from 1.68 to 2.86 GHz. The height of the proposed array is nearly half of the conventional base station array while other performances are guaranteed. The measured results show that the proposed antenna array has wide impedance bandwidths of 18.7% (0.82–0.99 GHz) and 57.9% (1.68–2.86 GHz) (VSWR < 2) with a low profile ($0.109\lambda _{0}$ at 820 MHz). The measured gains are 13.8±0.5 dB and 16.7 ± 1 dB in lower and upper bands. Large front-to-back ratio (>24.6 dB) and high isolations (>30 and >25 dB in lower and upper bands, respectively) are achieved. The proposed antenna can be easily built with printed circuit board fabrication technique and applied in low profile multiband base stations for 2G/3G/4G and the next-generation systems. [ABSTRACT FROM AUTHOR]

This paper presents a simple, compact, and low-power method for generating extremely low-frequency radio signals below ~500 Hz. This paper is motivated by the prohibitively large size and low efficiency of conventional antennas operating in this frequency range. The successful generation of time-varying magnetic fields produced by the physical rotation of a 3 cm3 permanent magnet is demonstrated. Ground plane and receiver orientation effects are analyzed both theoretically and experimentally. Observations as a function of distance from the source indicate that the fields are dominated by the static component, rather than by the radiation component, of the generated field. Based on these observations, the electromagnetic radiation emitted by a spinning magnet source is predicted to be weak. Nevertheless, static magnetic signaling using this technique is proven to be both possible and practical at frequencies below ~500 Hz and at distances in excess of 100 m. [ABSTRACT FROM AUTHOR]

This paper presents a short-term analysis of the radio propagation channels within vegetation media at the most commonly used wireless network frequency bands: 2.4, 3.5, and 5.8 GHz. Fading effects underlying this short-term analysis would determine whether the radio channel could support a stable link or not. The configuration used in this study is a peer-to-peer system, where the transmitter and the receiver are located at low heights inside several vegetation media, including forests and meadows. The distribution function that best fits the received power was determined to be Weibull, and the evolution of its parameters was studied as the distance between transmitter and receiver increases. [ABSTRACT FROM PUBLISHER]

In this paper, metrics for assessing the performance of directional modulation (DM) physical-layer secure wireless systems are discussed. In the paper DM systems are shown to be categorized as static or dynamic. The behavior of each type of system is discussed for QPSK modulation. Besides EVM-like and bit error rate (BER) metrics, secrecy rate as used in information theory community is also derived for the purpose of this QPSK DM system evaluation. [ABSTRACT FROM PUBLISHER]

This paper presents an off-body channel model for body area networks (BANs) in indoor environments. The proposed model, which is based on both simulations and measurements in a realistic environment, consists of three components: mean path loss, body shadowing, and multipath fading. Seven scenarios in a realistic indoor office environment containing typical scatterers have been measured: five were static (three standing and two sitting) and two dynamic (walk in a fixed place and real walk). The measurement equipment and measurement procedures are described. The mean path loss component is modeled as a log function of distance, the path loss exponent being in the range between 0.4 and 1.6, while a statistical perspective is taken for the other two components, i.e., body shadowing is found to be well modeled by a ognormal distribution and multipath fading by Rice or Nakagami- m distributions, depending on body motion characteristics. The correlation between the selected distributions and empirical data is not lower than 0.95, typically being greater than 0.98. The novelty of this model is that it takes the statistical influence of various parameters and features present in BANs into account, such as body influence, placement of the wearable antennas, user orientation in the environment, dynamism of the BAN scenario, and propagation conditions. [ABSTRACT FROM AUTHOR]

Frequency-agile pathloss models for urban street canyons are discussed in this paper. The models are floating intercept (FI), fixed reference (FR), and ITU-R M.2135 urban microcellular (UMi) line-of-sight (LOS) and Manhattan-grid non-LOS (NLOS) models. These models are parameterized based on channel sounding campaigns in three cities covering radio frequencies ranging from 0.8 to 60 GHz. Fitting the models with measured pathloss reveals that the models are usable to cover the considered frequency range. The FI and FR models are equally simple and robust, with a slight advantage of the FI model in accuracy because of the larger number of model parameters. The original M.2135 LOS model is based on a two-ray model that includes a break point (BP). The model is extended for a better fit with measurements by including new model parameters such as a pathloss offset and a BP scaling factor that represent local scattering conditions of surrounding environments. The new model parameters are found frequency dependent in many cases. The original M.2135 model is furthermore simplified in NLOS scenarios while maintaining the model accuracy. The model parameters are derived using maximum likelihood estimation, which also showed that the modified M.2135 model offers up to 50% better accuracy compared to the FI and FR models in terms of the employed log-likelihood function (LLF). The improvement in accuracy is particularly remarkable in NLOS scenarios. A full set of parameters is provided for the models, allowing a choice for any given requirements on accuracy and complexity. Finally, applicability of the proposed models to other street canyons is discussed using independent pathloss measurements. [ABSTRACT FROM PUBLISHER]

This paper presents two end-fed compact Yagi-Uda-type pattern diversity antennas, which use a coplanar-waveguide (CPW)-fed printed pseudomonopole antenna (PPMA) as the driver element. The balun-less driver PPMA behaves like a folded strip dipole and adds to its compactness. A common mode/differential mode (CM/DM) decomposition of antenna current on PPMA is carried out to show that the CM current distribution is similar to the current distribution of an asymmetrically fed dipole. The designed three-element Yagi-Uda antenna operates in the 2.4-GHz band with F/B ratio of about 23 dB and gain of 7.3 dBi. The compact pattern diversity antennas are realized by using two Yagi-Uda antennas separated by a common reflector. Two diversity antennas are realized using two different arrangements of Yagi-Uda antennas. The separation between the constituent PPMAs is varied to study its effect on the isolation and element embedded efficiency. The better of the two diversity antennas has overall footprint area of 65\; \times \;58\;\textmm^2 and the separation between two radiating elements is only 34 mm or 0.272\;\lambda _o. The simulated and measured port isolation (\vert\text S12\vert) between two diversity branches is about 35 and 27 dB, respectively. The signal envelope correlation is 0.018 and the embedded efficiency is about 93%. [ABSTRACT FROM AUTHOR]

Magnetic induction (MI) communication technique has shown great potentials in complex and RF-challenging environments, such as underground and underwater, due to its advantage over EM wave-based techniques in penetrating lossy medium. However, the transmission distance of MI techniques is limited since magnetic field attenuates very fast in the near field. To this end, this paper proposes metamaterial-enhanced magnetic induction (\textM^2\textI) communication mechanism, where an MI coil antenna is enclosed by a metamaterial shell that can enhance the magnetic fields around the MI transceivers. As a result, the \textM^2\textI communication system can achieve tens of meters communication range by using pocket-sized antennas. In this paper, an analytical channel model is developed to explore the fundamentals of the \textM^2\textI mechanism, in the aspects of communication range and channel capacity, and the susceptibility to various hostile and complex environments. The theoretical model is validated through the finite element simulation software, Comsol Multiphysics. Proof-of-concept experiments are also conducted to validate the feasibility of \textM^2\textI. [ABSTRACT FROM PUBLISHER]

Multipolarized antenna systems are able to reduce equipment size while maintaining low interantenna correlation and are thus attractive for mobile-to-mobile (M2M) wireless communications. In this paper, a polarized multiple-input multiple-output (MIMO) channel model is proposed by using a geometrical theory based on a two-cylinder M2M reference model. A geometrical approach is used to model channel depolarization, where the MIMO signal contributions of the scatterers are determined from a greatly simplified ray-tracing method. The modeling method provides a mechanism for computing MIMO-polarized channel impulse responses analytically, and the cross-polarization discrimination (XPD) and MIMO time–frequency function are further derived. The proposed model shows good agreement with measurements and simulation results from the literature and provides insights on the MIMO channel depolarization behavior. In addition, numerical simulations with appropriate modeling parameters are conducted. The XPD is shown to depend on the distribution of scatterers and MIMO subchannel index. Moreover, the co-polar channel is shown to have a higher time–frequency correlation than the cross-polar channel. This should be carefully considered in a multipolarized antenna system design. [ABSTRACT FROM AUTHOR]

The conventional time-modulated arrays (TMAs) have a low radiation efficiency, since each antenna turns off at specific time slots. In this paper, first, the efficiency of TMA is investigated analytically. Next, the optimized switching sequences are proposed to enhance the radiation efficiency of a specific sideband, while preserving the level of the other sidebands. The practical hardware limitations are considered in the switching sequence design. Moreover, a low-cost flexible eight-element printed dipole array operating at 1.2–1.4 GHz is implemented to verify the proposed algorithms. The measured radiation patterns indicate that by applying the proposed sequences, the TMA efficiency improves by 8.3 dB for the fundamental frequency. The efficiency enhancement for the first and second sidebands is 2.9 and 2.95 dB, respectively. In addition, a fast and low-cost setup for TMA measurement using the commercial software defined radio dongle is implemented in this paper. [ABSTRACT FROM AUTHOR]

While conventional antenna array synthesis determines the beamforming weights that create a specified antenna radiation pattern, secure array synthesis formulates the beamforming weights that enhance security for wireless transmission of sensitive data. This paper focuses on creating beamformers that improve the generation of secret encryption keys based on bidirectional estimation of the reciprocal electromagnetic propagation channel between two radios. The technique uses semidefinite programming to determine the array weights that maximize the average secure key rate under a constraint on the total transmit power. The numerical implementation of the technique incorporates array mutual coupling, and the results demonstrate that the technique outperforms a conventional beamforming solution, with the improvement becoming significant for certain channel correlation conditions. [ABSTRACT FROM AUTHOR]

This paper presents a novel and simple ultrawideband printed rectangular monopole antenna for body-centric wireless communications. The design is based on etching a Q-slot on a rectangular radiator and is optimized to produce the largest bandwidth in free space and close to the human body. We analyze the design of the proposed antenna and assess its performance in terms of bandwidth, gain, efficiency, and radiation patterns. We also characterize the antenna in the time-domain by calculating its fidelity factor. Our results show that the Q-slot antenna maintains its bandwidth when placed in close contact with the human body, or in contact with breast-mimicking tissue phantoms. The very good agreement between the calculated and measured antenna performances in free space and on body suggests that the antenna is immune to variations in the human tissue and is also robust to fabrication tolerances. [ABSTRACT FROM PUBLISHER]

A differential microstrip antenna with improved gain for RF energy harvesting is presented in this paper. The developed antenna can be used in either center grounded or differential configuration. The antenna is designed and fabricated for GSM900 band (890–960 MHz). The antenna has a gain of 8.5 dBi at the center frequency and exhibits VSWR \boldsymbol\leq 2 for frequencies between 870 MHz to 1.05 GHz. The efficiency of the antenna is 80%. The developed antenna finds its application in energy harvesting, RFID tags and in wireless communication circuits, where differential inputs/outputs are needed. A complete differential RF energy harvesting system with a peak efficiency of 65.3% for a load of 3 \mathbfk\boldsymbol\Omega is also developed. [ABSTRACT FROM PUBLISHER]

The objective of this presentation is to illustrate the accuracy of the Schelkunoff formulation over the Sommerfeld solution for a vertical electric dipole radiating over an imperfect ground. In an earlier paper, the alternate form of the Sommerfeld Green's function developed by Schelkunoff was presented (Schelkunoff, 1943 and Dyab, 2013). Here we demonstrate the application of this new methodology for two classes of problems. First, the problem of predicting the propagation path loss in a wireless communication environment is illustrated. The second application problem described in this paper deals with the verification of experimental data related to propagation over an Aluminum sheet at THz frequencies. It is seen that the main contribution of the reflected field is due to a specular image point as expected for a metal and the presence of surface waves in the total reflected field is absent, even though the permittivity of the metal is negative at these frequencies. Both theoretical predictions and experimental data demonstrate that there is little contribution to the reflected field due to a surface wave. Also, a clear definition is made to characterize surface waves as there is confusion as to what a surface wave really is. [ABSTRACT FROM PUBLISHER]

A novel transparent ultra-wideband antenna for photovoltaic solar-panel integration and RF energy harvesting is proposed in this paper. Since the approval by the Federal Communications Committee (FCC) in 2002, much research has been undertaken on UWB technology, especially for wireless communications. However, in the last decade, UWB has also been proposed as a power harvester. In this paper, a transparent cone-top-tapered slot antenna covering the frequency range from 2.2 to 12.1 GHz is designed and fabricated to provide UWB communications whilst integrated onto solar panels as well as harvest electromagnetic waves from free space and convert them into electrical energy. The antenna when sandwiched between an a-Si solar panel and glass is able to demonstrate a quasi omni-directional pattern that is characteristic of a UWB. The antenna when connected to a 2.55-GHz rectifier is able to produce 18-mV dc in free space and 4.4-mV dc on glass for an input power of 10 dBm at a distance of 5 cm. Although the antenna presented in this paper is a UWB antenna, only an operating range of 2.49 to 2.58 GHz for power scavenging is possible due to the limitation of the narrowband rectifier used for the study. [ABSTRACT FROM PUBLISHER]

The proposed time-interleaved phased array is a functional integration of a space-time domain filter in antenna arrays and a time-frequency domain filter in mixer arrays. Spatially sampled signals by the antenna arrays will be interleaved in time by the mixer arrays to increase modulation speed while leveraging relatively low-frequency carriers. In M-element time-interleaved arrays, the carriers frequency can be reduced by the factor of M to realize an equivalent functionality as in conventional phased arrays based on fundamental carrier modulations. Depending on the array configuration, the time-interleaved phased array can be categorized as “correlated-noise time-interleaved (CNTI)” array or “uncorrelated-noise time-interleaved (UNTI)” array. In the CNTI-array, both signal and correlated noise will be interleaved resulting in the same filter response for the signal and noise, whereas in the UNTI-array only signal will be interleaved in time domain: uncorrelated noise will not participate in the time-interleaving process. An extensive noise analysis for both array types is provided in the paper. To achieve maximum SNR, noise filtering techniques are proposed and verified through CAD behavioral simulations. In essence, the time-interleaved array architecture is a mix of parallel signal processing at RF and LO domains, which can have an advantage in compensating system performance deficits due to an active device speed limitation at high frequencies at the expense of an endurable system complexity. [ABSTRACT FROM PUBLISHER]

This paper proposes a concept of waveguide-based dual-polarized magnetoelectric (ME) dipole antenna. Based on this concept, two antenna designs with rectangular and triangular-shaped E-dipoles are studied and presented. The former is differentially fed by $four$ probes and the latter by a turnstile junction orthomode transducer feed. Using 3-D printing technique, the corresponding prototypes are fabricated for demonstration. Experimental results show that the rectangular-shaped E-dipole design has a wide impedance bandwidth of 55.1% from 7.5 to 13.2 GHz and a stable gain of 6 ± 1.5 dBi. On the other hand, the triangular-shaped E-dipole design can achieve 62.8% impedance bandwidth from 7 to 13.4 GHz and 5.15 ± 0.95 dBi gain over the operating frequencies. Furthermore, it is found that both antennas have low cross polarization and backlobe radiation, both characteristics of ME dipoles. Due to the waveguide configuration, the proposed antennas have good mechanical and electrical performances. They can be easily implemented and applied for various high power capacity applications. With these advantages, the proposed antennas are good candidates for the satellite and other wireless communication systems. [ABSTRACT FROM AUTHOR]

In this paper, a novel topology of the coplanar waveguide fed truncated octahedron-shaped antenna is proposed. The linearly polarized antenna operates over the triple radio frequency identification technique (RFID) bands of 858–930MHz, 2.4–2.454 GHz, and 5.725–5.875 GHz at ultrahigh frequency (UHF), microwave-, and super high-frequency bands, respectively. In addition, it also supports long-term evolution 4G, TV broadcasting, and 5G bands of the electromagnetic spectrum. The S11 = -10 dB impedance bandwidth is 294 MHz (697–991 MHz), 120 MHz (2.38–2.5 GHz), 310 MHz (3.07–3.35 GHz), and 310 MHz (5.61–5.92 GHz) in the various bands. The antenna is fabricated on a polyguide substrate of 0.3023\lambda L\times 0.209\lambda L \times 0.014\lambda L dimension, where \lambda L is the free-space wavelength at the lowest operating frequency. The antenna’s S11 and the radiation patterns have been measured, and a good agreement between simulated and the measured results has been found. In addition, the proposed antenna is also experimentally verified for the UHF band RFID detection and the global standard for mobile communications 900 band cellular applications. We also propose a system-level schematic to integrate this antenna to other communication standards for the automated RFID applications needed for the Internet of Things. [ABSTRACT FROM AUTHOR]

This paper presents a novel resistance-type sensor based on chipless radio-frequency identification. It consists of a scatterer and the resistor to be detected. The scatterer is designed to be V-shaped. The angle $\theta $ between two arms is used to encode the address data of sensor. The resistor to be detected is loaded in the middle of the two V-shaped arms. The sensor is excited by the plane wave. By measuring the scattered fields in two orthogonal polarization directions, the angle $\theta $ and the value of resistor can be identified. Compared with the normal resistance-type sensor, the novel sensor can transform the resistance value and its address into the wireless signal which can be received directly by the reader. Another advantage of angle-based sensor is that every element can encode multibit data. This is helpful to achieve higher capacity. Also, for different codes of one element, the proposed sensor uses the same spectrum. This is beneficial to improve the efficiency of the spectrum. The realized sensor has the identification errors less than 3° in the angle and less than $1.5~\Omega $ in the resistance value. [ABSTRACT FROM AUTHOR]

The next generation of intelligent vehicle systems will use wireless communication to connect a car and its passengers. It is therefore important to understand the in-cabin propagation characteristics of an automobile. This paper investigates the wireless channel native to these cabin enclosures. We present detailed, polarization dependent field measurements over a plane of interest in the cabin, and show that a simple analytical model gives reasonable agreement with our measurements. [ABSTRACT FROM PUBLISHER]

One of the most important field in array signal processing is direction-of-arrival (DOA) estimation, which is applicable in wireless and mobile communications. We consider the problem of estimating the DOA for reactance-based uniform circular arrays (UCAs). In this paper, a new technique of estimating DOAs is proposed for the reactance-based UCA antenna as well as a method to calculate optimal reactance values. This technique is based on the modified reactance domain MUltiple Signal Classification (MUSIC) algorithm. Simulation results show that DOAs can be estimated by the active ports reactance domain MUSIC (APRD-MUSIC) algorithm for reactance-based UCA antennas. By optimizing the reactance values, the proposed system obtains good performance in estimating DOAs in terms of resolution and error estimation. Simulation and measurement results show that high-resolution DOA estimation can be achieved by using APRD-MUSIC algorithm for Reactance based UCA antennas. [ABSTRACT FROM PUBLISHER]

We present the Bio-Matched Horn antenna: a novel 1.773 cm3 on-body antenna for very low-loss communication with wireless implants across the 1–9 GHz bandwidth. To achieve this unique performance, the Bio-Matched Horn is composed of water-filled holes used to mimic the frequency-dependent permittivity of the underlying tissue over its entire bandwidth. The horn shape further allows the proposed antenna to communicate efficiently through the biological tissue for both subcutaneous and deep-tissue wireless implants. Measurement results at 2.4 GHz are in good agreement with simulations and show a transmission loss of 8.01 dB to a 4 mm-deep implant and 19.21 dB to a 2 cm-deep implant. Compared to the previous designs, this is a remarkable improvement by 14.5 and 10.8 dB for subcutaneous and deep-tissue communication, respectively. In this paper, we discuss the operation principle and design of the Bio-Matched Horn, its performance for subcutaneous and deep-tissue implant telemetry, sensitivity to rotational and positional misalignments, and specific absorption rate performance. [ABSTRACT FROM AUTHOR]

This paper summarizes the lessons learned using a physics-based macromodel in studying electromagnetic wave propagation over an imperfectly conducting ground in cellular wireless communication. First, it has been observed that the path loss exponent is independent of the nature of the ground parameters inside the cell of interest. Second, the electrical parameters of the environment have little effect on the path loss exponent in the cellular band. Third, it is observed that lowering the base station antenna toward the ground provides a stronger signal in the near field within the cell of interest. Furthermore, tilting the transmitting antenna toward the sky enhances the signal strength. Tilting the antenna toward the ground increases the signal strength but, in addition, enhances the interference pattern and, hence, is not a good solution. A typical path loss inside the cell is 30 dB per decade of distance, and outside the cell, it increases to 40 dB per decade. By bringing the antenna closer to the ground and then tilting it toward the sky, a good nonintuitive solution is provided. In such scenarios, a path loss of 20 dB per decade for some components of the field, the lowest possible, can be achieved for certain orientations and deployment of the base station antenna. In addition, it is shown that operating an antenna inside a metallic box eliminates its radiation capabilities and, hence, has no physical meaning even though it is claimed in the contemporary literature that it simulates a rich multipath environment. Finally, a note on the proper interpretation of the term channel capacity and its implications is delineated. [ABSTRACT FROM AUTHOR]

This paper presents a planar omnidirectional multiple-input multiple-output (MIMO) antenna with pattern phase diversity. The profiles of conventional dual-polarized omnidirectional MIMO antennas are too high to be planar integrated due to the limited bandwidth of vertical-polarized element. Therefore, a dual-channel horizontal-polarized MIMO antenna is proposed for the planar integration of omnidirectional MIMO antenna. The antenna is formed with four-element folded dipole array, and a compact feed network with two sets of 90° progressive phases is employed to feed the two channels with shared elements, thus the antenna can be integrated into a sheet of substrate with an ultralow profile of 0.8 mm. Although the polarization and radiation pattern (amplitude) of the two colocated channels are the same with each other, a high isolation is still achieved as a result of the orthogonal pattern phase. A prototype was fabricated to validate the performance. The measured highest isolation between two channels is 31.7 dB, and −10 dB isolated bandwidth is 2.29–2.57 GHz (11.7%) with S11 < −14 dB and envelope correlation coefficient less than 0.05, which shows a good diversity performance. Therefore, the proposed dual-channel antenna gives a feasible solution for the planar integration of the omnidirectional MIMO system. [ABSTRACT FROM AUTHOR]

In this paper, multiband antennas based on a single ring slot are proposed for 4G/5G smartphone applications. The basic structure of the antenna is consisted of a large metal ground and an unbroken metal rim, in which a single 2 mm-wide ring slots is realized between the metal ground and rim. Here, a reconfigurable 4G antenna (820–960 and 1710–2690 MHz) is initially devised by loading multiple grounded stubs and a simple dc controlling circuit with varactor diode into the upper section of the ring slot. To further cover the sub-6 GHz spectrum (3400–3600 MHz) for future 5G communications, a four-element multi-input multi-output (MIMO) slot antennas configuration is designed by utilizing the lower section of the ring slot. A prototype antenna was fabricated, and good agreement is shown between the measured and simulated results. Due to the advantages such as multiband operation, MIMO configuration for 5G communications, high isolation, and compact structure, the proposed antenna design is attractive for 4G/5G smartphones. [ABSTRACT FROM AUTHOR]

In this paper, two different patch antenna geometries are proposed for wireless sensor applications involving electromagnetic propagation from inside the jet engine to our designed relaying antenna at the rim of the inlet. First, an enhanced modified version of our earlier proposed two-element circular patch antenna array is proposed. We follow with a fresh new design based on two-element array of hybrid rectangular circular patch antenna geometry. Both antenna designs are discussed in light of basic governing equations enabling initial design calculations, intuitions behind selecting the design elements based on desired propagation characteristics, simulation results, as well as fabrication and experimental measurements. Because of the environmental constraints, the proposed antennas need to be an extremely low profile and ultrathin. The proposed relaying antennas are designed to have a dual-beam pattern, one of which is directed toward the inside of the jet engine. The antennas are simulated using HFSS as well as fabricated and measured inside an anechoic chamber. Experimental results, which sufficiently agree well with the simulation results, demonstrate the achievement of the desired characteristics by fabricated antennas for deployment on jet engines. [ABSTRACT FROM AUTHOR]

A novel study on monitoring and analysis of the debilitating condition of patients suffering from the neurological disorder is presented. Parkinson’s disease is characterized by limited motor ability of a patient. Freezing of gait is a major nonmotor condition among aging patients and its evaluation can reduce the chances of any secondary disorders. In this paper, amplitude and phase information of the radio signals observed for a fixed period of time are used to differentiate the motor and nonmotor symptoms. The amplitude information is classified using a support vector machine, while the linear transformation is applied to obtain sanitized phase information for detection. The proposed method is very handy with the minimum deployment overhead. The analysis shows that this method also offers a high-accuracy level of around 99% based on the observation of a number of patients. These features make it an attractive solution for real-time patient monitoring systems. [ABSTRACT FROM AUTHOR]

Wide-angle coverage, fine angular resolution, and low-power consumption are the key characteristics of millimeter-wave short-range wireless systems, such as access points in fifth-generation cellular networks and automotive radars. In this paper, we present a 60 GHz switched-beam antenna system addressing all these requirements. It consists of two identical parallel-fed arrays of eight slots, each fed by a passive pillbox beamformer. A switch network comprising four single-pole-multiple-throw switches excites one of the two arrays at a time and selects the radiated beam. The whole system is fully integrated into a multilayer low-temperature cofired ceramic module. The antenna covers a scan range of about ±39° in one plane using 11 beams between 57 and 66 GHz. The proposed architecture enables the simultaneous achievement of continuous coverage (beam crossover levels of about −3 dB) and of low sidelobe levels. Dedicated numerical tools are used for a preliminary design of the antenna. The design procedure, the technological development, and the experimental results are discussed in detail. [ABSTRACT FROM AUTHOR]

Wireless communications are expected to take place in increasingly complicated scenarios, such as dense urban, forest, tunnel, and other cluttered environments. A key emerging challenge is to understand the physics and characteristics of wave propagation in these environments, which is critical for the analysis, design, and application of advanced mobile and wireless communication systems. In this paper, we present a full-wave field-based computational methodology for radio wave propagation in complex urban environments. Both transmitting/receiving antennas and propagation environments are modeled by first-principles calculations. A system-level, large scene analysis is enabled by the scalable, ultraparallel algorithms on the emerging high-performance computing platforms. The proposed computational framework is verified and validated with semianalytical models and representative measurements. [ABSTRACT FROM AUTHOR]

This paper presents a physics-based macro model that can predict with a high degree of accuracy various experimental data available for the propagation path loss of radio waves in a cellular wireless environment. A theoretical macro model based on the classical Sommerfeld formulation can duplicate various experimental data including that of Okumuraet al.carried out in 1968. It is important to point out that there are also many statistical models but they do not conform to the results of the available experimental data. Specifically, there are separate path loss propagation models available in the literature for waves traveling in urban, suburban, rural environments, and the like. However, no such distinction is made in the results obtained from the theoretical analysis and measured experimental data. Based on the analysis using the macro model developed after Sommerfeld’s classic century-old analytical formulation, one can also explain the origin of slow fading which is due to the interference between the direct wave from the base station antenna and the ground wave emanating from the reflections of the direct wave and occurs only in the near field of the transmitting antenna. The so-called height gain occurs in the far field of a base station antenna deployment which falls generally outside the cell of interest, while in the near field, within the cell, there is a height loss of the field strength for observation points near the ground. A physical realization of the propagation mechanism is illustrated through Vander Pol’s exact transformation of the Sommerfeld integrals for the potential to a spatial semiinfinite volume integral and thus illustrates why buildings, trees, and the like have little effects on the propagation mechanism. [ABSTRACT FROM AUTHOR]

Complex scattering targets are often made by structures constituted of wedges that may interact at near field. In this paper, we examine the scattering of a plane electromagnetic wave by two separated arbitrarily oriented perfectly electrically conducting wedges with parallel axes. The procedure to obtain the solution is based on the recently developed semianalytical method known as generalized Wiener–Hopf technique that allows a comprehensive mathematical model of the problem in the spectral domain avoiding multiple steps of interaction among separated objects. The numerical results are presented to validate the procedure in terms of spectral quantities, GTD/uniform theory of diffraction coefficients and total far fields for engineering applications. The structure is of interest in electromagnetic applications, in particular, to accurately predict path loss in propagation with diffraction phenomena. [ABSTRACT FROM AUTHOR]

This paper describes and evaluates a new test facility able to generate different wireless multipath radiocommunication channels. It is used to recreate various electromagnetic (EM) environments, such as those inside vehicles. This test facility, in the form of a moderate volume metallic chamber, contains apertures, left opened or obstructed as required, and a variable quantity of salt water. Both are used to adjust the EM losses and to control smoothly and accurately the delay spread of the communication channel inside the test facility. A frequency range between 2 and 3 GHz is studied. As a first step, the root-mean-square (rms) delay spread is measured inside a vehicle for several locations of the receiving antenna and for different scenarios including different line-of-sight and non-line-of-sight paths. Then, the test facility is introduced, dimensioned, and evaluated, trying to reproduce the rms delay spread of each previous in-vehicle radiocommunication configuration. A comparison between the measurement data performed both in the vehicle and in the configured test facility is presented. This comparison shows a good agreement between these two sets of measurements. It demonstrates that different static wireless in-vehicle multipath channels, corresponding to various transmitting and receiving antenna configurations, can be reproduced inside the proposed prototype test facility. [ABSTRACT FROM AUTHOR]

Crossed-dipole (CD) antennas have been widely employed for dual polarization in wireless communication systems in recent years. In this paper, a novel design concept of dual-polarized shared-dipole (DPSD) antenna is presented. Different from the traditional CD antennas, the arms of the DPSD antenna are shared for two orthogonal polarizations. This design technique leads to significant size reduction and high isolation compared to the traditional CD antennas. The operation principle of the proposed antenna is theoretically analyzed. To validate the presented design concept, two novel DPSD antennas are designed, fabricated, and measured. The first design is a four-port DPSD antenna, which is a straightforward demonstration of the operation principle of the DPSD antenna. The second design is a highly integrated DPSD antenna, which avoids the use of a feed network and provides a simple configuration to design the dual-polarized antenna. Both of the DPSD antennas are designed to operate at 1.7–2.7 GHz for base station applications. The simulated and measured results confirm that the two DPSD antennas have wide bandwidth with VSWR < 1.5 and isolation > 35 dB dB. In addition, stable gain and half-power beamwidth are obtained with the variance less than ±0.55 dB and ±3.5°, respectively. [ABSTRACT FROM AUTHOR]

A circular patch antenna loading symmetrically with some conductive shorting vias can radiate monopolelike pattern in its fundamental mode as well as the higher order modes. As a result, this antenna can be considered as a candidate to replace the conventional large profile monopole antenna in many communication systems. However, no comprehensive analytical study has been presented for it. In this paper, an analytical method based on cavity model and the generalized multipole technique is intended to investigate the antenna. A sample of the antenna is designed and analyzed using the proposed theory. The electromagnetic fields, radiation pattern, input impedance, and return loss of the antenna are analytically expressed. The designed antenna is implemented and measured. The measurement results are compared with the analytical results to justify the analysis. [ABSTRACT FROM AUTHOR]

In this paper, low-profile broadband planar folded transmitarray antennas (FTAs) are proposed and studied based on a novel Fabry–Perot polarizer. A novel element is proposed to carry out high-efficiency transmission, the phase compensation and the 90° polarization rotation at the same time. The element consists of two identical dielectric slabs, sandwiched by three metal layers, and has a thickness of only about $0.1\lambda $. To verify this element, a transmitarray antenna is first designed and its highly efficient radiation performance is demonstrated by both simulations and the experiments. Low-profile FTAs are then designed and studied. The results show that the advantages of broad bandwidth, high gain, lower profile, planar geometry, and ease of integration can be achieved. The experiments of the FTA antenna demonstrate a 3 dB gain bandwidths of 18% and a peak gain of 25.2 dBi. [ABSTRACT FROM AUTHOR]

Electrically small antennas (ESAs) can be passively matched only over very narrow bandwidths and the resulting antennas have low gains. These are the major limiting factors for ESAs used in transmit applications, especially at high-frequency (HF) and lower Very HF frequency bands. This paper discusses the challenges of transmit ESA matching circuit design and the design process of a new non-Foster transmit matching architecture for electrically small monopole antennas that achieves wide bandwidth, high transmission efficiency (transducer power gain), and stability at the same time. The proposed circuit is composed of a current buffer (for high isolation), a transformer (for real-part matching), and a negative impedance converter (for imaginary-part matching). The measured −6 dB (−10 dB) $|S_{11}|$ fractional bandwidth of the proposed non-Foster transmitting system is 110% (39%), while the maximum bandwidth that can be achieved is 0.076% (0.047%) when matched with the conventional passive matching. The transmission efficiency of the system is improved by as much as 34.4 dB compared to the same antenna without the proposed non-Foster matching circuit, and it retains an enhanced efficiency over the entire frequency band of operation (26–89 MHz). The system remains stable within this frequency band. The measurement results of the compact and broadband transmitting antenna prototype verify the design concept. [ABSTRACT FROM AUTHOR]

In this paper, the use of a dispersive prism with a triangular shape is proposed to reduce the dispersive radiation nature of a leaky-wave antenna (LWA) in groove-gap waveguide technology. The operation of gap waveguide technology is based on the use of metallic pins that act as an artificial magnetic conductor, so the electromagnetic fields are confined and guided in the desired directions. To control a leaky-wave radiation of these confined fields is possible by tailoring the height of the pins, its periodicity, and the waveguide width. This radiation, as in any conventional LWA, is dispersive, leading to beam squint as the frequency is varied. Here, we mitigate this beam squint by using a prism made of dispersive pins and choosing appropriately their periodicity and height. With this prism, the leaky-wave radiation is focused into one single direction in a wide frequency band. This concept is demonstrated with a prototype designed to radiate at $\varphi =41^\circ $ with a central frequency of 12 GHz and the high gain of 16.5 dBi. A 22% frequency bandwidth for the 3 dB realized gain at $\varphi =41^\circ $ is achieved, and the main radiating direction, with half-power beamwidth of 5°, steers only ±0.5° from 11.4 to 13.4 GHz. [ABSTRACT FROM AUTHOR]