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This letter shows a comparative analysis between the conventional and reverberation chamber (RC) measurements of error vector magnitude (EVM). The conventional methods, including direct link (DL) and anechoic chamber (AC), have been used to measure EVM for several years. However, the over-the-air testing of devices under test (DUT) is emphasized, and the EVM measurement in RC is a difficult question. For mass production testing, instead of using two chambers (RC and AC), it is expected to integrate EVM testing into the existing RC measurement system to give a pass/fail conclusion quickly. Hence, we measured EVM in 2 GHz (2412 MHz) and 5 GHz (5180 MHz) using RC, AC, and DL methods. From the measurement results, we find that the measured EVM is repeatable, stable, and insensitive to the location of DUT. Besides, the measured EVMs obtained from all scenarios deteriorate with the decrease of received power. Comparing the results from RC with that from the conventional methods, it could be concluded that with the reduction of multipath effect, the measured EVMs approach to the ideal values measured in AC. The differences among the methods could be used to calibrate the measured EVMs and give a pass/fail conclusion efficiently for mass production. [ABSTRACT FROM AUTHOR]

The scanning rate of a composite right/left-handed (CRLH) leaky-wave antenna (LWA) is usually determined by the dispersive behavior of the corresponding CRLH unit cell. In this letter, a novel CRLH unit cell with high dispersive behavior is proposed and investigated. The unit cell is formed by four stubs embedded in a rectangular ring patch, which is grounded with several metal vias. The right-handed characteristic is enhanced by the ring patch, while the left-handed characteristic is reduced by the vias and the gaps between the patch and the stubs. Then, the unit cell is applied to design an LWA with high scanning rate. The measured result shows that the seamless scanning angle of the antenna prototype is 130° (−65° to +65°) within a frequency range from 9.3 to 9.93 GHz (i.e., 6.6% for fractional bandwidth). Therefore, the proposed LWA antenna is with a high scanning rate up to 19.7°/%BW. [ABSTRACT FROM AUTHOR]

This letter presents a single-layer, wide-angle, low-cost frequency beam scanning leaky-wave antenna (LWA) based on spoof surface plasmon polaritons (SSPPs). Here, two rows of Sierpinski prefractal parasitic patches are placed near an ultrathin planar SSPP waveguide, which can achieve continuous backfire to nearly endfire beam scanning with increasing frequency. The overall width of the proposed antenna is only 0.75 $\lambda _{\text{0}}$ (with $\lambda _{\text{0}}$ being the wavelength of the lowest operating frequency). This SSPP LWA provides high-performance backfire and broadside radiations due to applying prefractal units. Simulated results show that the proposed SSPP LWA achieves a wide scanning range from −90 $^{\circ }$ to +58 $^{\circ }$ within the frequency range of 3–8 GHz. The average gain and radiation efficiency of the antenna are 10.9 dBi and 88%, respectively. An antenna prototype is fabricated and measured. The measured results agree reasonably well with the simulated ones. [ABSTRACT FROM AUTHOR]

For fifth-generation (5G) millimeter-wave (mmWave) beamforming, a fully planar 2 × 2 2-D multibeam antenna operating at 24–28 GHz is proposed. The proposed antenna is fed by a compact dual-layer 4 × 4 Butler matrix in substrate-integrated waveguide (SIW). In this fully planar and compact configuration, SIW coupling slot is used to facilitate the output ports of the Butler matrix on the same planar layer, and the via-based phase shifters are designed to generate wideband phase performance with compact size. The measured impedance bandwidth is 15.4%, and the measured maximum beam pointing angle is 55°. These results are in good agreement with simulation. The proposed configuration can be extended with more radiating elements for higher gain, and it is promising for beamforming scenarios, including communications. [ABSTRACT FROM AUTHOR]

This article investigates practical implementation aspects of a novel hybrid chamber concept that has been recently introduced for over-the-air (OTA) testing of wireless devices. The chamber allows to synthesize a spectrum of plane waves (PWs) incident on a device under test (DUT) from a wide range of angles of arrival (AoAs) through exploiting multiple field scattering inside the overmoded waveguide (WG) chamber. An optimal design approach for the plane wave spectrum generator (PWSG) array inside the chamber is presented considering: 1) array antenna impedance matching for the desired test zone (TZ) quality and AoAs’ range; 2) an operational frequency bandwidth of the test environment and an instantaneous signal bandwidth; and 3) the impact of PWSG excitation errors. A robust linearly constrained minimum variance (LCMV) beamformer is formulated to realize the desired test environment over a wide frequency band, while accounting for the varying number of the WG propagating modes as excited by PWSG array. Numerical simulations and measurements with the first prototype of the hybrid chamber for FR1 frequency band (~3.5 GHz) are presented. This prototype includes a ${7\times 7}$ bowtie antenna element PWSG array, a 1.00 m $\times1.25$ m $\times1.75$ m metal WG chamber, an off-line optimal array beamforming setup, and a planar scanner for TZ characterization. [ABSTRACT FROM AUTHOR]

Large-scale propagation characterization for multiple measurements in a micro-cell scenario is carried out at 5G frequency (3.8 GHz). Distance-based path loss is computed for routes with line-of-sight, non-line-of-sight and obstructed-line-of-sight conditions, assuming a simple power law model. Path Loss exponents are computed for the whole routes, giving an effective understanding of the propagation environment. Empirical shadowing distribution is fitted to red Gaussian and non-Gaussian probability distributions. All previous propagation parameters are also found assuming measurements with similar transmitter locations come from the same channel conditions. This assumption is tested. Finally, although frequently absent in standard channel models, and useful for statistical ensemble average approximations, stationary regions are computed for all the routes. [ABSTRACT FROM AUTHOR]

In this work, a simple method is proposed to simultaneously reduce the size and cross-polarization level (XPL) of quarter-wave microstrip antennas by reconstructing the magnetic currents along the radiation edges. A design example of five shorted elements is given with a comparison of the quarter-wave microstrip antennas at 1.88 GHz. Measured results show an over 64% size reduction and 17-dB cross-polarization suppression enhancement for the proposed scheme as compared with the conventional one. Moreover, the proposed scheme exhibits good broadside radiation patterns with a gain of 5.4 dBi and the half-power beamwidths of about 104° in the E-plane and 84° in the H-plane. [ABSTRACT FROM AUTHOR]

This article presents a radio propagation model for macrocell coverage predictions in built-up areas for sub-6-GHz frequency band. The proposed two-ray model is a combination of various individual propagation models available in the literature, namely the discrete mixed Fourier transform split-step parabolic-equation (DMFT-SSPE) to characterize reflection and diffraction phenomena due to the presence of buildings and terrain irregularities, the building-transmission model (BTM) to account for the signal attenuation through the nearby buildings and the International Telecommunication Union of Radio-communications (ITU-R) model for attenuation in vegetation to weight the excess attenuation caused by the surrounding vegetation. The performance of the proposed modeling approach was assessed against measurement results obtained from an extensive measurement campaign conducted in Rio de Janeiro, Brazil. The receiver (RX) antenna was assembled on an automotive van, and it was made to travel around the city recording the received signal level. Several drive tests were conducted, including different transmitter (TX) locations and scenarios, and at various frequencies foreseen for 5G systems, namely 750 MHz, 2.5 GHz, and 3.5 GHz. [ABSTRACT FROM AUTHOR]

This article presents the degradation effects of long-term use of a dual vibrating intrinsic reverberation chamber (dual VIRC) for shielding effectiveness (SE) measurements. At the beginning with a new fresh dual VIRC setup it is possible to achieve a very high dynamic range (DR) but the DR degrades due to long-term use of the dual VIRC. The effect of 10 years use of the dual VIRC on the DR is shown as function of usage time. Also, the effect on the DR of a new dual VIRC with better conductive cloth has been presented. [ABSTRACT FROM AUTHOR]

This article highlights the specific application of two standardized test methods for the characterization of the shielding effectiveness of conductive gaskets, in the extended frequency range from 30 MHz up to 40 GHz. Each method is discussed with respect to its specific characteristics including advantages and disadvantages. Furthermore, two nonstandardized setups are also analyzed. Two different types of gaskets under recommended compression rates have been used to show the difference between the various test methodologies in relationship with their measuring setup, theory, and observations. Regarding the standard MIL DTL 83528G, the effects of both the antenna radiation patterns and the impinging angle of the fields are analyzed. Following the specific shielding effectiveness measuring results, recommendations are given for the choice of the test method corresponding the best to the real implementation in practice. It is also stated that the nonstandardized methods can easily be used for small samples of gaskets during development and/or for production control. [ABSTRACT FROM AUTHOR]

In this article, a method for removing the return loss effect during shielding effectiveness (SE) measurements for a shielding enclosure is proposed. According to the IEEE 299.1 standard, a receiving antenna is located inside the enclosure to be measured, and this antenna measures the signal loss after passing through the enclosure. The receiving antenna experiences the return loss at its input, and this return loss increases the SE because the occurrence of the return loss is equivalent to the increasing loss when passing through the enclosure. The IEEE 299.1 standard provides a method for removing the return loss effect. The return-loss removal is only effective, however, when the receiving antenna has an input impedance that does not significantly change, remaining almost constant at the adjacent frequencies. The proposed method generalizes the return-loss removal, and thus the return loss effect can be removed irrespective of the input impedance condition of the receiving antenna. As the return loss is removed for any type of the receiving antenna, the SE can be accurately measured to prevent an overestimation of the SE. [ABSTRACT FROM AUTHOR]

This article presents a novel and cost-effective vector network analyzer (VNA)-based phase-compensated channel sounder operating in the frequency range of 10–50 GHz using radio-over-fiber (RoF) techniques, which can support multilink/channel long-range phase-coherent measurements. The optical cable enables long-range channel measurements with a dynamic range of 115.7 dB at 30 GHz (for the back-to-back connection). The phase compensation scheme is utilized for stabilizing the inherent phase variations introduced by the optical fiber of the channel sounder to enable its application in multichannel/antenna measurements. A novel optical delay line and combiner scheme is proposed and implemented to separate the signals, thereby saving the port resource on the VNA for multilink/channel measurements. The proposed channel sounder is validated in back-to-back measurements under two optical cable conditions, i.e., with the presence of thermal changes and mechanical stress. The phase change could be maintained within 3° at 10–30 GHz and 7° in 30–50 GHz compared to the over 80° phase variation introduced by the cable effects at 10–50 GHz, demonstrating the robustness and effectiveness of the developed channel sounder in practice. With the proposed optical delay line and combiner scheme, multiple channels can be measured simultaneously with minimal VNA ports, significantly reducing the measurement cost and time for multilink channel measurements. Two multilink indoor channel measurements are conducted and analyzed using a virtual uniform rectangular array (URA) at 28-GHz bands. The results demonstrate the capability of the proposed channel sounder to perform high-fidelity long-range ultrawideband multilink channel measurements. [ABSTRACT FROM AUTHOR]

We propose a low-profile hexagonal patch antenna pair with pattern diversity by using a single shared radiator. More specifically, both equivalent circuit and full wave simulation results show that the common mode and the differential mode of the grounded hexagonal patch could be excited with similar resonant frequencies, and then the coupling-feed method is employed to extend the impedance bandwidth. Simulation and measurement results demonstrate that such antenna pair, featuring a better decoupling performance, could be capable of generating both of the apple-shaped radiation pattern and the broadside radiation pattern in a wide band with the shared patch size of 0.2 $ \lambda _{0}$ $ \times\, 0.37\, \lambda _{0}$ and the profile height of 0.05  $ \lambda _{0}$. The proposed design should pave the way for the development of more compact multiple-input–multiple-output (MIMO) systems. [ABSTRACT FROM AUTHOR]

This letter presents an analysis of channel characteristics for an outdoor scenario at the frequency band of 28–30 GHz. A geometry-based clustering algorithm is proposed to group the measured multipath components (MPCs) from the interaction points on the surrounding walls or objects according to ray-tracing three-dimensional (3-D) simulations, giving results that are more physically interpretable than the traditional clustering algorithms. The cluster-level characteristics at 15 positions along a predefined route covering both line-of-sight (LoS) and non-LoS (NLoS) scenarios are investigated. Moreover, power contributions of MPCs with multiple bounces (up to seven bounces in NLoS scenario) from the interaction objects are also investigated. [ABSTRACT FROM AUTHOR]

This letter presents a combined model for appropriate radio coverage of mission-critical push-to-talk communications in mountainous vegetated terrains. The proposed model uses the irregular terrain model (ITM) with the detailed information of the ground topography to predict the excess loss caused by the terrain irregularities, along with the Lateral International Telecommunications Union of Radio model, to account for the excess loss caused by the presence of vegetation in the radio path. The performance of the proposed combined model was assessed against experimental results obtained from a measurement campaign conducted along unpaved paths and trails, usually taken by firefighters during firefighting procedures, in mountainous terrains with dense vegetation. The acquired experimental data was assessed against experimental results obtained from a measurement campaign conducted along unpaved paths and trails. [ABSTRACT FROM AUTHOR]

This letter presents a wideband three-dimensional (3-D)-printed circularly polarized (CP) ultrathin dielectric slab waveguide (DSW) Luneburg lens (LL) with multibeam application in X-band. The characteristic that DSW supports TE0 and TM0 waves to pass through with different phase constants is used to generate 90° phase difference to compose CP wave for the proposed structure. To prove the point, the prototype antenna is fabricated by 3-D printing and measured. The results show that the proposed LL supports multibeam application with 11 beams covering ±60° range in azimuth plane, and the 3 dB axial ratio bandwidth for multibeam antenna is 23.5% with reflection coefficient lower than −10 dB and gain higher than 13.7 dBi. The measured results show good coincidence with simulated ones. [ABSTRACT FROM AUTHOR]

This letter introduces a method for implementing a frequency-reconfigurable Fabry–Pérot cavity (FPC) antenna utilizing polarization standing waves (PSWs). The PSW is supported by two metasurfaces (MSs) at cavity ends. The resonant condition allows the antenna to have frequency-reconfigurable characteristic by mechanically rotating the top MS around the center and relative to the bottom MS, without adjusting the physical dimension. The antenna is prototyped at 60 GHz for millimeter-wave applications. Simulated and measured results demonstrate that a tunable frequency range of 60.8–66.2 GHz with a maximum boresight gain of around 22.2 dBi can be attained, verifying the antenna concept. [ABSTRACT FROM AUTHOR]

This letter presents 60 GHz radio measurements and channel characterization for wireless rack area network (WRAN) application within a networking enclosure, commonly known as a server rack. The propagation characterization is conducted with wideband and narrowband measurements to characterize the propagation phenomena and investigate the feasibility of a reflected non-line-of-sight (RNLoS) link. The impact of obstruction by networking cables and a human hand is also investigated to extract the fading depth, fading rate, and the time varying shadowing. The implications on WRAN system design are accordingly deduced. It is found that optimal RNLoS channel response is characterized by a clustering effect with a 7.82 dB reflection loss. The obstruction by networking cables introduces significant channel dispersion and contributes to significant fading depth and fading rate values. [ABSTRACT FROM AUTHOR]

Over the past decade, spectrum sharing has evolved into viable commercial systems poised to meet the ever-increasing spectrum demand from service providers and end users. The key to the success of these systems is accurate and reliable propagation models that will simultaneously maximize the number of users able to access the spectrum and minimize the interference to incumbent or protected users. The classical propagation models currently utilized by these systems—the irregular terrain model (ITM) and extended hata (eHata)—do not account for features, such as foliage or endpoint clutter that can have a large impact on propagation loss. This article presents a measurement-based framework for updating these classical models and proposes a new integrated terrain and clutter model using publicly available geographic information system datasets. Over 400 000 path loss measurements were recorded in nine diverse locations across the United States at 1.7 and 3.5 GHz. Our updates improved the rms difference between measurements and model by 3–7 dB for ITM and 3–14 dB for eHata. In addition, we demonstrate several integrated terrain and clutter models that have rms differences ranging from 9.5 to 17.8 dB. Finally, cross validation was used to demonstrate the generalizability of our models to a wide variety of propagation environments. [ABSTRACT FROM AUTHOR]

Channel predictions are important to achieve high spectral efficiency for high-mobility vehicles. Channel extrapolation, used by many prediction methods, suffers from a limited prediction horizon in difficult radio environments. The predictor antenna (PA) concept provides the prediction horizons required for efficient transmission to fast-moving vehicles by measuring the channel ahead of time with an extra antenna placed on the vehicle. This paper presents a general framework that addresses the practical signal processing challenges of the PA concept. It is adaptable to a vast variety of vehicular deployment, mobility, and communication scenarios. A new theoretical prediction normalized mean-squared error (NMSE) expression is derived based on the presented framework. The framework is demonstrated by applying it to extensive channel measurements and comparing the PA predictions to Kalman-based channel predictions and outdated channel estimates. By studying the impact of vehicular velocity and radio environment on the prediction performance, it is shown that PA prediction is weaker at low velocities, where Kalman prediction methods are sufficient, but is uncontested at high velocities in environments without a dominating path. At high velocities in dominating path environments, the Kalman predictor provides usable predictions, but it is still outperformed by the PA predictions. [ABSTRACT FROM AUTHOR]

We report the design, fabrication, and prototype demonstration of a 200-GHz polarization-resolved quasi-optical detector employing monolithically integrated zero-bias heterostructure backward diodes (HBDs). In this design, polarization resolution is achieved by orthogonally integrating the detectors with a planar dual-polarization annular-slot antenna. The detector chip was fabricated and mounted on an extended hemispherical Si lens to enhance antenna efficiency in the millimeter-wave to terahertz region. The responsivity and radiation patterns of the detector were characterized experimentally; good agreement with theoretical calculations was obtained. By measuring the outputs of two orthogonal HBDs as a function of the polarization angle of the incident wave, the planar detector detects intensity and resolves polarization. On the basis of the polarimetric measurement, we further demonstrate the polarization imaging capability of the proposed detector by using it as an imaging system. The detector is promising for developing terahertz polarimetric sensors and imaging arrays in chemical sensing, biomedical imaging, and radio astronomy applications. [ABSTRACT FROM AUTHOR]

This letter presents a simple method to design the wideband circularly polarized spherical multibeam Luneburg lens (LL) antenna by using three-dimensional (3-D)-printing. The conventional 3-D-printed spherical LL is divided into many cells and each cell is filled by the unit cell with different filling ratios, which breaks the circular symmetry of the LL. The proposed method divides the LL into many layers, and the profile surface equation of each layer is calculated by the ordinary least square method to keep the rotation symmetry of the LL. Then, according to the proposed circularly polarized implement method, the transformation of linear polarization to circular polarization can be realized by selecting a proper radius of LL. The simulated and measured results show that the axial ratios of the proposed multibeam LL antenna are less than 3 dB with good impedance performance and more than 13.8 dBi gain in a relative bandwidth of 31.6%, which demonstrates the validity and simplicity of the presented method. [ABSTRACT FROM AUTHOR]

This letter proposes a unified initial preprocessing technique to address phaseless characterization of a compact antenna test range (CATR) system within millimeter-wave range. With the aid of phase retrieval algorithm, the missing phase information of quiet zone (QZ) can be reconstructed by only two amplitude-only measurements. Here, the initial complex information consists of two parts: back propagation of measurements in QZ as initial amplitude and Zernike-Fourier expansion as initial phase. To further validate the superiority and robustness of the proposed approach, we conduct extensive simulations over the state-of-the-art phase retrieval algorithms under different operating frequencies and compare it to different initial preprocessing methods. In addition to be readily available in practical applications, the proposed technique is also verified under experimental conditions. In a nutshell, this letter paves the way toward the applications of phaseless characterization in CATR system. [ABSTRACT FROM AUTHOR]

An X-band, free-space microwave sensor consisting of 30 radial spokes connected in a central hub with a gap region was designed, fabricated and tested. The sensor structure results in an electric dipole at 10 GHz with a split circular disc capacitor at the center. Viruses, dust, and soot particles in the gap region change the sensor’s impedance and its reflection coefficient monitored by a horn antenna and a network analyzer. The sensor sensitivity was 85.02 MHz/microliter for deionized water, 89.5 MHz/microliter for uninfected saliva, and 94.6 MHz/microliter for SARS-COV-2 infected saliva with 103 viruses/ $\mu \text{L}$. Its sensitivity to a dielectric sample ($\varepsilon _{\rho }\sim 5.84$) was 3.23 MHz/mm3, and for iron particles was 16.25 MHz/mm3. All these samples were smaller than $\lambda $ /30 at 10 GHz and could not be detected on uniform dielectric or metallic substrates without the spoke structure. A $2\times 2$ array of spoke sensors was also constructed and tested as a feasibility study for designing larger metamaterial (MTM) periodic arrays. [ABSTRACT FROM AUTHOR]

A novel self-decoupling tri-port antenna is proposed. The three ports of the proposed antenna simultaneously excite a radiator printed on the inner surface of the smartphone frame. Based on the mode cancellation method and active reflection coefficient theory, the self-decoupling mechanism of the proposed antenna is investigated. The results reveal that the three ports remain well isolated and no decoupling structure is required. The simulated results illustrate that the isolation of the proposed tri-port antenna is higher than 11 dB in the LTE 42 band, and the envelope correlation coefficients (ECCs) are less than 0.14. A $12\times12$ multiple-input–multiple-output (MIMO) antenna system consisting of four tri-port antennas is designed, manufactured, and measured. The measured results show that the isolation among the 12 ports is better than 10 dB, and the ECCs are less than 0.14. The total efficiency of all ports is 51%–71%. The calculated channel capacity ranges from 57.98 to 59.87 bps/Hz when the signal-to-noise ratio (SNR) is 20 dB. [ABSTRACT FROM AUTHOR]

Using a new propagation measurement set-up, which produces a high number of data, enabling a proper statistical analysis, and resulting in very concise results, propagation measurements were performed and analyzed at 16 residential locations in The Netherlands in the frequency range from 1.8 to 28 MHz. In the whole frequency range the propagation loss appears to be higher than might be expected according the International Telecommunication Union ground-wave propagation model. Also typical characteristics of that model are not present, but instead the propagation shows a constant roll-off in dBs per decade, with a slope increasing with frequency. A regression curve could be established, and constants filled in. This statistical information may be used for building an accumulation model to lay a causality between source powers, source densities, and local man-made noise levels. [ABSTRACT FROM AUTHOR]

Due to the great demand of throughput and reliability for multimedia applications in Fifth Generation (5G) networks, many broadcasting systems adopt the Millimeter Wave (mmWave) technology to address the lack of the spectrum resources. As one of 5G-PPP projects, Internet of Radio Light (IoRL) project adopts 40GHz mmWave band to support a high-speed and stable Ultra-High-Definition (UHD) television broadcasting service in the indoor environment. Because of the high frequency property, mmWave bands usually suffers from the high path loss and the penetration loss. Thus, in order to overcome these issues, directional antennas are employed to provide additional power gain while increasing transmission distance. However, the mmWave with directional antennas brings additional problems, such as limited transmission angle and more multipath effects. Therefore, in this paper, for better understanding of impact factors on the signal quality and transmission coverage of the directional 40GHz mmWave band in the indoor environment, a measurement campaign is introduced in detail and the channel characteristics are measured and analysed in varying cases. The mainly concerned characteristics are path loss, shadow fading, average Power Delay Profile (PDP), Root-Mean-Square (RMS) delay spread, arrival rate and coherence bandwidth. All Measured characteristic values are summarised in three tables at the end of this paper. Besides of these, as a reference of channel analysis and a metric of signal quality and effective coverage, Error Vector Magnitude (EVM) of received signal in each case is measured and discussed. Moreover, a simulation is performed based on a statistical channel model to validate the measured results. [ABSTRACT FROM AUTHOR]

Agriculture 4.0 represents a considerable increase in the number of sensors, as well as the appearance of new wireless technologies, which will meet the need to efficiently plan radio communication systems in agricultural environments. In this letter, a simplified model for path loss estimation in citrus plantations is proposed. The model assumes that, for long distances, the physical mechanism is a parallel transmission path over the treetops that can be modeled by multiple-knife-edge diffraction. In our scenario, where the height of the transmitter is above the height of the trees, we proposed to estimate the multiple-knife-edge diffraction contribution by the settled field defined by Walfisch and Bertoni. In this way, the propagation losses estimated by the model have been compared with measurements carried out at 3.5 GHz in a lemon plantation before and after the fruit were collected. It has been observed that the slope of the regression line of the measurements yields values of 3.6 (with fruit) and 3.7 (without fruit), which are close to the value estimated by the model (3.8). The standard deviation of the prediction error given by the difference of the observed and estimated values is 4.5 dB (with fruit) and 3.2 dB (without fruit). [ABSTRACT FROM AUTHOR]

The clinical use of microwave tomography (MT) requires addressing the significant mismatch between simulated environment, which is used in the forward solver, and real-life system. To alleviate this mismatch, a calibrated tomography, which uses two homogeneous calibration phantoms and a modified distorted Born iterative method (DBIM), is presented. The two phantoms are used to derive a linear model that matches the forward solver to real-life measurements. Moreover, experimental observations indicate that signal quality at different frequencies varies between different antennas due to inevitably inconsistent manufacturing tolerance and variances in radio-frequency chains. An optimum frequency, at which the simulated and measured signals of the antenna present maximum similarity when irradiating the calibrated phantoms, is thus calculated for each antenna. A frequency-division DBIM (FD-DBIM), in which different antennas in the array transmit their corresponding optimum frequencies, is subsequently developed. A clinical brain scanner is then used to assess performance of the algorithm in lab and healthy volunteers’ tests. The linear calibration model is first used to calibrate the measured data. After that FD-DBIM is used to solve the problem and map the dielectric properties of the imaged domain. The simulated and experimental results confirm validity of the presented approach and its superiority to other tomographic method. [ABSTRACT FROM AUTHOR]

Wireless in-body devices are those in which a medical sensor is introduced–implanted or ingested– inside the human body and communicates with a remote node. Some in-body applications demand high data rates, so ultrawideband (UWB) spectrum has been proposed as a good candidate because of its large bandwidth available. Besides, breathing can lead to internal movement of the torso and consequently, of devices installed in this area. Thus, the radio channel performance can be affected by such movement leading to a malfunction of the radio interface of the medical device. This work aims at analyzing the effect of breathing on the propagation channel by means of in vivo measurements in living animal models. Continuous wave (CW) measurements have been carried out for five different frequencies in the lower part of the UWB band, and the effects of breathing on the relative received power (module and phase) are analyzed and discussed. [ABSTRACT FROM AUTHOR]

This article presents a contactless measurement method for antenna radiation efficiency estimation within reverberation chambers (RCs). This method does not require to connect any analyzer to the antenna under test (AUT). The AUT radiation efficiency is obtained from the differential measurement of the RC composite ${Q}$ -factor estimated for two AUT load conditions, namely an open circuit and a 50 $\Omega$ load. Remotely controlled RF switches are used in order to keep the setup identical for both measurements. The method is experimentally validated in two RCs of different volumes (1 m $\mathbf {^3}$ and 19 m $\mathbf {^3}$) with a wideband patch antenna in the 1.8 GHz to 2.8 GHz frequency range. The estimated efficiency is found to be in a very good agreement with the one obtained through a conventional invasive RC measurement technique. This new method is suitable for miniature and buried antenna characterization without access to its port. [ABSTRACT FROM AUTHOR]

This letter presents a spherical helix antenna. Its specific shape allows broadband operation within the usual satellite S-band telemetry, tracking, and control frequency bands ($2.025\!-\!2.29$ GHz). The antenna radiates right-handed polarization over a wide beamwidth. Axial ratio is better than 6 dB until roughly $80^{\circ }$ elevation. Almost all external parts are composed of metal, which makes this antenna well-suited for harsh space environment such as geostationary orbit or deep-space missions. Overall dimensions are $\text{94}\times \text{94}\times \text{48}$ mm $^3$ (with connector). [ABSTRACT FROM AUTHOR]

Low-altitude communication has attracted lots of attention in recent years, and it is very important to obtain an accurate clutter loss model for evaluating and designing such a communication system. For this purpose, we have conducted a channel measurement campaign at 5.8 GHz for suburban low-altitude scenario. Based on the measured pathloss, we extract and analyze the clutter loss for different link distances and elevation angles between the transceiver. The measured clutter loss is validated by the ITU clutter loss model with respect to the link distance. Moreover, inspired by the measured clutter loss and the unavailability of the low-frequency band in the ITU model with respect to the elevation angle, and thus, we propose a new clutter loss model based on the ITU model and a pathloss model with respect to the elevation angle factor for the C-band frequencies around 5.8 GHz in the suburban low-altitude scenario. [ABSTRACT FROM AUTHOR]

This letter proposes a novel leaky-wave antenna (LWA) based on low profile substrate integrated waveguide (SIW), which can operate in either left-handed circular-polarization (LHCP) or right-handed circular-polarization (RHCP) mode. Different from other kinds of literature, the proposed SIW LWA is capable of CP state switching without introducing multiple LWA elements, phase-correct couplers or polarization converter, which is a single LWA element with a simple coaxial feeding/matching structure. Specially, the periodic slots on its radiation aperture are Archimedean spiral slots which are curved slots with curl property. These curled slots can excite vortex fields in the waveguide channel of SIW, and the generated vortex field is capable of changing vortex direction by selectively exciting the port of LWA, making the CP features flexible. The final Archimedean spiral slotted SIW LWA realizes LHCP or RHCP (AR < 3 dB) in the wide CP band of 27.7–34.6 GHz (BW = 22%), and the LHCP scanning range is from −51° to −10° while the RHCP beam scans from 10° to 50°. [ABSTRACT FROM AUTHOR]

A novel design method of harmonic suppression and size reduction of a circularly polarized (CP) microstrip patch antenna (MPA) is presented by using nondegenerate modes. Based on a circular MPA, a pair of orthogonal modes could be generated between these undesired resonant modes. Then, by loading the shorting pins in a quarter fan-shaped patch, all these undesirable high-order modes could be suppressed between them. After that, the higher and lower modes are moved closer to each other by cutting a long slot at the angle bisector of the fan-shaped patch, providing the CP radiation pattern. Finally, a prototype of this proposed antenna has been designed, produced, and measured to verify the design concept. The experimental results show that the proposed antenna has an impedance bandwidth of 286 MHz (13 774–14 060 MHz), axial ratio bandwidth of 80 MHz (13 900–13 980 MHz), and a left-hand CP peak gain of around 4.8 dBi. Most importantly, the CP antenna has realized the harmonic suppression of about 15 GHz, which has an obvious advantage as compared to the traditional CP MPA. Moreover, the antenna still holds the primary low-profile, single-radiator, simple structure, and high-efficiency simultaneously. [ABSTRACT FROM AUTHOR]

In this letter, an ultrawideband (UWB) antipodal tapered slot antenna with reflectionless notched band is proposed and investigated. The proposed antenna uses an integrated absorptive bandstop filter, consisting of two quarter-wavelength open-circuit stubs and a 50 Ω resistor, to form a reflectionless notched band. Consequently, the input energy at the notched frequency is absorbed by the resistor rather than reflected. An antenna prototype is designed and fabricated to validate the design. Both simulated and measured results present that the realized gain drops over 40 dB at 5.5 GHz, and the reflection coefficient is below –10 dB from 3.1 to 10.6 GHz. Besides, a low ringing level of –23.4 dB of the measured reception pulse shows a good time-domain performance. Therefore, the proposed antenna could be applied in UWB short-pulse system to inhibit the 5 GHz WLAN interference. [ABSTRACT FROM AUTHOR]

This article reports on the experimental validation of a method to predict radiated emissions of equipment under test in a reverberation chamber where the multiple monopole sources stirring technique is implemented. The method is validated for three different case studies: a loop, a slot in a metal enclosure, and a realistic device comprised of the chassis of a power supply for a workstation. The reconstruction of the free space electromagnetic emissions starting from measurements in a reverberation chamber is compared with measurements in an anechoic environment. A statistical analysis of the uncertainty due to a positioning error of the field sample measurement points is also proposed. [ABSTRACT FROM AUTHOR]

Cough detection has aroused great interest because the assessment of cough frequency may improve diagnosis accuracy for dealing with several diseases, such as chronic obstructive pulmonary disease (COPD) and the recent COVID-19 global pandemic crisis. Here, we propose and experimentally demonstrate a wireless smart face mask based on a passive harmonic tag for real-time cough monitoring and alert. Our results show that the cough events can be successfully monitored through non-contact track of the received signal strength indicator (RSSI) at the harmonic frequency. Owing to the frequency orthogonality between the launched and backscattered radio-frequency (RF) signals, the harmonic tag-based smart mask can well suppress the electromagnetic interferences, such as clutters and crosstalks in noisy environments. We envision that this zero-power and lightweight wireless wearable device may be beneficial for cough monitoring and the public health condition in terms of tracking potential contagious person and virus-transmissive events. [ABSTRACT FROM AUTHOR]

This article proposes a design optimization method of fast compressive sensing (CS) operators for wideband three-dimensional (3-D) millimeter-wave (mmW) imaging systems. The proposed method consists of two parts: 1) a near-orthogonal 3-D mmW imaging operator design for avoiding large precomputed arrays and 2) a random antenna pattern design (compressive binary sampling matrix) for sparse sampling. The 3-D mmW imaging operator takes the nonlinear wavenumber relationship into account and uses a combination of truncation repair and sampling density compensation to eliminate the reconstruction error caused by truncating $z$ and the nonuniform $k_{z}$ sampling. The compressive binary sampling matrix minimizes grating lobes and suppresses residual grating lobes while maintaining the mainlobe width, by maximizing PeakSLL and maxPSF in the respective frequency range and 2-D measurement aperture. A ${Ka}$ -band (35–45 GHz) experiment utilizes the measurements of a very low sampling rate of 6.25% of fully sampled data to recover a high-resolution image. The result shows that the proposed CS operator reduces the maximum reconstruction error and the mean square error (MSE) between the recovered images from undersampled measurement and from the fully sampled data to $10^{-15}$ and $10^{-3}$ , respectively. Furthermore, the proposed decomposition method enables the soft thresholding in the CS iterative algorithms and simplifies the CS implementation in terms of antenna-array patterns, memory usage, and parallel computing. If the imaging system is implemented by a spatial antenna array, then the 6.25% sampling rate means that the number of antennas is reduced to 25% of the full-sampling system, thus reducing the cost. If the imaging system is implemented by raster scanning, then the CS implementation will reduce the number of spatial points to 25%, thus reducing the scan time. The number of frequency points is also reduced to 25%, which reduces the memory usage. [ABSTRACT FROM AUTHOR]

This letter addresses the effect of the ionosphere on the extremely low-frequency and lower frequency waves excited in the Earth-ionosphere waveguide by a controlled source. The experiment carried out on the Kola Peninsula is described and the results of measurements in the frequency range 0.4–95 Hz are presented. Nonmonotonic behavior of the magnetic field with time is revealed. It is shown that variations in the magnetic field are related to the state of the ionosphere and depend on the geomagnetic activity. The importance of the effect of the topside ionosphere on the structure of the studied field is discussed. [ABSTRACT FROM AUTHOR]

A compact printed-circuit leaky-wave antenna is designed to synthesize frequency-scanned monopulse patterns in the UHF RFID band from 902 to 928 MHz. A high-permittivity ceramic substrate is used to maximize the angular scanning range in such a narrow band. Two operating modes, i.e., narrow-field and wide-field modes, can be chosen by properly selecting the frequency channels and antenna ports. This allows to adapt to different fields of view while maximizing the maximum reading distance, as demonstrated with a fabricated prototype. [ABSTRACT FROM AUTHOR]

This letter presents the design and testing of a novel triple-layer frequency selective surface (FSS) with ultraminiaturization for electromagnetic shielding applications. The proposed unit cell is constructed using meandered lines running along the three layers and they are interconnected using metalized vias to increase the electrical length of FSS. The FSS is designed to offer band stop resonance at L-band frequency with a foot-print of 0.022 λo × 0.022 λowith a thickness of 0.006 λo and it provides at least 38% of miniaturization in comparison with similar literature. To validate the transmission performance, a prototype FSS with a periodicity of 6 mm is fabricated. The FSS consists of 2500 elements arranged in a 50 × 50 square lattice. The transmission performance of the proposed FSS is verified using simulation and experiment. The proposed FSS has rotational symmetry and hence it is polarization insensitive. Furthermore, the FSS offers excellent angular stability up to the maximum incidence angle of 60° under both transverse electric and transverse magnetic modes of operation. The proposed FSS can be used for shielding applications in global positioning systems tracking and aircraft surveillance systems. [ABSTRACT FROM AUTHOR]

Antenna, radio frequency (RF) circuit, algorithm, and system researchers on sub-THz RF are interested in knowing characteristics of corresponding radio channels. Among other things, a relevant question is the number of beams supported by the channel. From wideband directional propagation measurements one can estimate how many significant paths are present in a measurement location, but interpreting that to separable beams is not trivial. In this letter, we introduce three methods to approximate the number of beams that a measured power angular delay profile can support. We show also example evaluations and distribution functions of beam numbers, estimated from indoor D-band measurement data. [ABSTRACT FROM AUTHOR]

This article presents a multiwideband monopole antenna for automotive application in the long-term evolution (LTE) and 5G systems that covers the frequency range from 617 MHz to 5 GHz with reasonable rejection on the L1/L2/L5 GNSS bands. The antenna is suitable for placement on a car roof within a shark-fin radome due to its physical dimensions and performance. The antenna is simulated using software and then fabricated and measured on a 1 m ground plane and a vehicle roof. The measurement results of the fabricated prototype are presented and plotted in terms of reflection coefficient, radiation patterns, antenna efficiency, and linear average gain (LAG). The proposed antenna shows very good properties that make it suitable for the automotive industry. [ABSTRACT FROM AUTHOR]

An electrically small, planar, frequency-agile, beam-switchable Huygens dipole antenna is investigated in this article. The near-field resonant parasitic (NFRP) design incorporates an Egyptian axe dipole (EAD) and a capacitively loaded loop (CLL) that function as the electric and magnetic NFRP elements, respectively. A varactor diode is integrated into each of these NFRP elements to facilitate simultaneous tuning of its operating frequency and switching its main beam direction. By changing the capacitance values of these two varactor diodes, the antenna realizes two independent, antipodal, unidirectional endfire radiating states with similar realized gain (RG) and front-to-back ratio (FTBR) values within virtually the same frequency-agile ranges. The experimental results demonstrate that the developed antenna exhibits a 5% frequency-agile fractional impedance bandwidth in both of its two oppositely directed endfire states. The antenna is electrically small at the highest frequency of this bandwidth (${ka}_{high} < 0.86$) and has measured relatively high radiation efficiency (RE >67.7%), peak RG (2.1–3.19 dBi), and FTBR (5.61–13.4 dB) values, together with stable and uniform radiation patterns, over this frequency-agile range. [ABSTRACT FROM AUTHOR]

In this work, we show that high antenna frequency selectivity can make it more challenging to accurately measure antenna efficiency in a reverberation chamber (RC) when using the two-antenna method since electronic noise can affect the measured stirred-energy component of the $S$ -parameters. Recognizing whether the measured antenna-efficiency estimate is significantly affected by electronic noise is not trivial. The measured $S$ -parameters used for calculation may have high signal-to-noise ratios (SNRs), but the antenna-efficiency estimate can still show large systematic errors due to noise. We model noise as a component of the measured stirred energy, showing that the measured reflection is much more susceptible to noise than the measured transmission. We do not focus on the origin of the noise, but rather on the effect it has on the measurement. We show the effect of noise on the overestimation of the stirred energy components of the $S$ -parameters, which affects the two-antenna formulation more significantly than the three-antenna method one. We show that this overestimation can cause efficiency estimates calculated with the two- and three-antenna methods to be significantly over- or under-estimated and we show that uncertainties increase as well. Finally, we provide clear steps to recognize and reduce noise effects in antenna efficiency measurements. [ABSTRACT FROM AUTHOR]

Future cellular systems will make use of millimeter-wave (mm-wave) frequency bands. Many users in these bands are located indoors, i.e., inside buildings, homes, and offices. The typical building material attenuations in these high-frequency ranges are of interest for link budget calculations. In this article, we report on a collaborative measurement campaign to find the attenuation of several typical building materials in three potential mm-wave bands (28, 73, and 91 GHz). Using directional antennas, we took multiple measurements at multiple locations using narrow-band and wideband signals and averaged out residual small-scale fading effects. The materials include clear glass, drywall (plasterboard), plywood, acoustic ceiling tile, and cinder blocks. The specific attenuations range from approximately 0.5 dB/cm for ceiling tile at 28 GHz to approximately 19 dB/cm for clear glass at 91 GHz. [ABSTRACT FROM AUTHOR]

In this communication, a low-profile single-layered duplex-filtenna scheme is proposed by using two feeds, and a common substrate integrated waveguide (SIW) cavity. A rectangular slot is carved on the top of the cavity along the narrower side of the SIW, which splits the cavity into two unequal parts. Each part behaves as a half-mode SIW (HMSIW) resonator which radiates with the help of an additional longitudinal slot and open-end of HMSIW when excited with corresponding feed. Also, two vias have been loaded along the broad side of the transverse slot to tune the impedance bandwidth and improve the selectivity in the passbands. The working process of both HMSIW resonators is similar, thus similar type of electrical performance is expected. By properly optimizing the locations of these vias and transverse-slot dimensions, high isolation between input ports is realized. To validate the proposed concept, design has been fabricated and measured. The measured results show good agreement with the simulated counterparts. The measured result shows that the design exhibits impedance bandwidths of around 3.0% (8.63–8.88 GHz) and 4.2% (9.26 $ - $ 9.66 GHz) for lower and upper-frequency pass channel, respectively. The measured average realized gains in the broadside direction are 3.51 and 4.10 dBi, respectively. [ABSTRACT FROM AUTHOR]

A wearable tri-band half-mode substrate integrated waveguide (HMSIW) antenna is proposed for wireless body area network (WBAN) applications. The lower frequency band is generated by combining the TE010 and TE110 modes of the HMSIW cavity, whereas the middle and upper bands are achieved with the stubs and the slot. Simulated and measured results show that the antenna can cover the three frequency bands, i.e., 2.36–2.5, 3.32–3.54, and 5.61–6.12 GHz with broadside radiation patterns. The antenna performance is evaluated on the human tissue model. Owing to the isolation characteristic of the cavity structure, the performance of the antenna on the body will not degenerate significantly compared to the results in free space. Due to the advantages of tri-band operation, simple topology, low back radiation, and low specific absorption ratio values, the proposed antenna is a competitive candidate for WBAN applications. [ABSTRACT FROM AUTHOR]

A highly efficient air-filled multiband antenna is presented for unobtrusive integration into smart surfaces. By introducing a capacitive loading ridge in the cavity formed by two coupled eighth-mode resonators, the higher order modes are judiciously manipulated. A supplementary slot-mode resonance is provided by a resonant U-slot in the first resonator. These measures yield dual-band impedance matching, covering the SRD860 (863–870 MHz), 2.4 GHz ISM (2.4–2.4835 GHz), and LTE-7 (2.5–2.69 GHz) standards. The antenna, fully realized in low-cost FR-4 substrate layers, complies with standard printed circuit board manufacturing. Measurements on a prototype reveal an impedance bandwidth of 51.8 MHz (6.1%) and 428.6 MHz (17.0%) in the lower and upper frequency band, respectively. Furthermore, a total efficiency and peak gain of 86.1% and 3.8 dBi at 866 MHz, 75.2% and 9.0 dBi at 2.45 GHz, and 70.1% and 8.1 dBi at 2.6 GHz were obtained in standalone conditions. At 2.4 GHz, a measured total efficiency and gain of 73.9% and 8.9 dBi are reported for the antenna covered by a cork superstrate, and 73.6% and 6.6 dBi for the antenna inside a drywall construction. [ABSTRACT FROM AUTHOR]