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Over-the-air (OTA) measurement is mandatory for 5G mm-wave wireless devices. The compact antenna test range (CATR) is the baseline method in the current version of TR 38.810 in 3rd generation partnership project (3GPP) and cellular telecommunications industry association (CTIA) millimeter-wave (mm-Wave) test plan. For CATR, both amplitude and phase variations inside the quiet zone (QZ) could affect the final OTA results significantly and hence need to be characterized carefully. Especially in the phase validation of QZ, even slight misalignments between sampling plane and incident plane wavefront due to the limited precision of the positioner or tolerance in antenna fixture could result in large phase variations, which is not the true phase property of QZ. This letter presents a method to remove the effect of the angular error due to misalignment when measuring the phase variation inside QZ. By adopting the proposed method to the measured phase data, any angular error due to misalignment with respect to the incident plane wavefront will be eliminated mathematically, leaving the true phase variations of QZ only. In the meanwhile, the proposed method can alleviate the requirements of fixture manufacture and alignment precision and reduce the test cost.

In this letter, a single-layer bandpass frequency selective surface (FSS) working at 2.6 GHz is proposed to decrease the interference to communication systems and the cost of processing based on a multimode resonator. A metasurface unit cell is adopted to suppress the grating lobe and achieve miniaturization. Therefore, the performance of the proposed FSS can remain stable under a large oblique incidence. The surface current distribution and equivalent circuit model at each design step are extracted to explain its working principle. Good agreement between the experimental results and the simulated response verifies the feasibility of the proposed FSS.

A broadband, electrically controlled, reconfigurable, circularly polarized reflective metasurface is presented. The chirality of the metasurface structure is changed by switching active elements, which benefits from the tunable current distributions generated by the elaborately designed structure under x-polarized and y-polarized waves. Notably, the proposed metasurface unit cell maintains a good circular-polarization efficiency in a broadband range of 6.82-9.96 GHz (fractional bandwidth of 37%) with a phase difference of π between the two states. As a demonstration, a reconfigurable circularly polarized metasurface containing 8 × 8 elements was simulated and measured. The results verify that the proposed metasurface can flexibly control circularly polarized waves in a broadband, realizing beam splitting, mirror reflection, and other beam manipulations from 7.4 GHz to 9.9 GHz (fractional bandwidth of 28.9%) by simply adjusting the loaded active elements. The proposed reconfigurable metasurface may offer a promising approach to electromagnetic wave manipulation or communication systems.

All of the test cases in the current version of TR 38.810 in 3GPP and CTIA millimeter-Wave (mm- Wave) test plan are limited to the free space configuration. However, the truly free-space condition does not exist for mm-Wave testing of 5G user equipment since no device can float in the air. Mounting fixtures and supporting structures are needed to fix the device under test (DUT) and move it in two axes. The influence of mounting fixture on 5G mm-Wave wireless device performance is analyzed in this paper. First, a common 4×1 patch array at 28 GHz is simulated as the performance baseline. Various mounting fixture thickness & various spacing between the DUT and the mounting fixture are simulated to get a quick understanding of the mounting fixture’s influence on DUT performance. In different configurations, the working frequency of the antenna would have different degrees of deviation, while the gain could decrease or increase accordingly. Then, to explain these phenomena, an equivalent circuit is extracted utilizing the transmission line theory. Finally, according to the findings, it is recommended that the thickness of the mounting structure should be equal to an integer time of 0.5 λg to minimize the impact of the fixture for practical mounting structure design.

An optical transparent metasurface for dual-band Wi-Fi shielding is presented in this paper. The unit cell of the proposed metasurface is composed of a hexagonal ring and a three-petal oval flower which resonate at 2.4 and 5.5 GHz, respectively. The corresponding equivalent circuit is modelled to better understand the physical phenomena of electromagnetic shielding. Based on transmission line theory and curve fitting technique, a convenient and efficient method for extracting permittivity of substrate is presented. Simulation results show that the proposed metasurface is insensitive to the polarization of incoming wave under normal incidence and offers excellent angular stability. For verifying the design, two prototypes are fabricated using different manufacturing technologies, flexible printed circuit and ink-jet printing of silver nano-particles. The measured results are in good agreement with the simulated ones. The proposed metasurface has potential applications of electromagnetic wave suppression and information security in indoor environments.

A planar metasurface is designed to replace the traditional three-dimensional axicon lens to generate a nondiffraction in normal direction at first. Then, to generate Bessel beams that can be tilte...

This article proposes a novel wideband single-layer coplanar waveguide (CPW)-fed antenna element and multiple-input, multiple-output (MIMO) antenna based on a multimode resonator. Equivalent circuits of the multimode resonator are analyzed by adopting the odd- and even-mode analysis approach. To prove the effectiveness of the equivalent circuit, scattering (S)-parameters of the equivalent circuit are simulated in Advanced Design System (ADS). Additionally, transmission coefficients are studied under the weakly coupling condition. The first and second resonant points are introduced by even and odd modes, respectively, whereas the third resonance is caused by the embedded stepped impedance resonator (ESIR). The CPW-fed antenna element is designed based on the proposed resonator. CPW fed not only excites the multimode resonator but also generates an extra resonance between the odd mode and ESIR resonant frequencies. Furthermore, the odd-mode resonance creates the lower cutoff frequency, and the resonance caused by ESIR forms the higher cutoff frequency. Hence, a filteringlike operating frequency band is achieved without introducing an extra filtering circuit. The filtering characteristic is favorable for the system to realize high sensitivity and reduce outof-band interferences simultaneously.

This paper reports a dual-polarized graphene-based multi-functional device which could switch between rasorber and absorber flexibly. The only difference between rasorber and absorber is that rasorber has a transmission window with low loss. Therefore, a wideband absorber is proposed at the first step. Then, four split-ring resonators (SRRs) are introduced to the absorber, which makes the electromagnetic (EM) energy could be reflected at the certain frequency band. The state (on/off) of SRRs and absorber can be controlled by the chemical potential of graphene. To find a new pathway for this part of the reflected energy, metal ground of the absorber is replaced by a reconfigurable graphene-based frequency selective surface (FSS). The proposed FSS could be switched between FSS and metal plate by controlling the chemical potential of graphene ring embedded in the bottom metal layer. Therefore, the proposed multi-functional device could be obtained by combing the absorber with SRRs and reconfigurable FSS. When the proposed device serves as a rasorber, it has an absorption-transmission-absorption response with superior selectivity. When it performs as an absorber, it has wideband performance with high absorptive rate. It is an attractive candidate for stealth applications.

A novel bandpass frequency selective surface (FSS) working at 2.4 GHz is proposed in this paper based on metasurface with independent-polarization, wide rejection band and good angular stability. The 10-dB upper stopband could cover 3.35-9.4 GHz with a fractional bandwidth of 94.9%. In addition, the filtering response could remain stable under different polarizations and incidence angles. Parameter analysis and equivalent circuit model are illustrated to explain the resonance behavior of the proposed FSS. It is demonstrated that the lower resonant point in the stopband could be tuned independently by changing the length of small rectangular patches in the top layer. While the higher resonant point could be changeable independently by adjusting the diameter of circular gap in the bottom layer. A prototype of the proposed FSS is fabricated and its simulated results are coincided with measurements.

For Multiple-input, multiple-output (MIMO) user equipment (UE), over-the-air (OTA) testing of radiated multi-antenna reception performance is crucial to guarantee actual network performance and is mandatory in North America, Europe and China. For 5G MIMO OTA, 3GPP has specified the clustered delay line (CDL) channel models as the reference channel models, which present higher order and directivity than those of 4G. Therefore, which kinds of performance metrics and environmental conditions are feasible and necessary to better characterize the MIMO performance should be studied. In this paper, MIMO OTA measurement results of different figures of merits (FoMs) under both UE noise-limited and interference-limited environmental conditions have been compared and discussed, respectively. In addition, the impact of different channel models on MIMO OTA throughput performance as well as the variance per azimuth are compared. Based on the analysis, Peak-Null can better reflect the difference between the 12 azimuth positions than Variance. Total Radiated Multi-antenna Sensitivity (TRMS) under both channel models presents nearly the same performance trends at different thresholds. On the contrary, MIMO Average Radiated SIR Sensitivity (MARSS) exhibits a high dependence on channel models. The MARSS under UMi channel model shows a much smaller performance variation between UEs than UMa channel model. TRMS under 3GPP UE noise-limited environmental condition exhibits a stronger ability to distinguish between good and bad performing devices than that of MARSS under CTIA interference-limited environmental condition. The discrepancy can reach 4 dB at most. This discrepancy does not come from different average manners between TRMS and MARSS, but originates from environmental condition itself. Therefore, it is proposed to adopt TRMS under UE noise-limited environmental condition as the unique or baseline test condition in 5G FR1 MIMO OTA. Peak-Null can be considered as a secondary FoM to characterize the variance per azimuth.

In this work, an ultrawideband and high-efficient polarization conversion metasurface (PCM) is proposed, which can efficiently convert linearly polarized waves into cross-polarized waves in an ultra-wide frequency range. The unit cell of the proposed PCM is composed of two pairs of L-shaped metallic patches covered by a dielectric superstrate and an air-based substrate attached with a metallic ground. The PCM has an operating band from 3.37 to 22.07 GHz with the polarization conversion ratio (PCR) over 90% under the normal incidence, which the ratio bandwidth (fH/fL) is 6.5:1. The PCR can achieve 100% at seven resonant frequencies. The equivalent circuit model is analyzed to explain the fundamental cause of the PCM’s multi-resonance and polarization conversion behaviors. In addition, all possible near-field interactions among the resonator, the superstrate, and the ground sheet can be accurately calculated using interference theory, which reveals the underlying physical mechanisms of the multi-resonance metasurface. The theoretical calculated, numerically simulated, and measured results are in good agreement. Compared to other PCMs, the proposed PCM has a simple geometry structure but an ultrawideband and high PCR property.

A frequency selective absorber (FSA) with two tunable notch bands is presented in this paper. The proposed FSA is composed of an ultra-wideband absorber at the top layer to achieve an absorption band from 4.4 to 18.67 GHz and two resonators at both sides of the bottom layer to realize two tunable notch bands with about 8 GHz and 4 GHz tunable range, respectively. The biasing grids are also used at the bottom layer and metal ground to adjust the voltage of the varactors, which makes notch band tunable. In order to achieve polarization insensitive, four varactors are used on one side of the bottom layer. The simulation results show that the proposed FSA has an ultrawide absorption band and two tunable notch bands.

This paper proposes a frequency-selective absorber (FSA) with ultra-wide absorption band and adjustable notch band. The top layer of the structure is a lossy layer, which uses a traditional ring structure with lumped resistors inserted in the four sides and round metal patches on the four corners. A notch resonator is placed on the top of bottom substrate as the lossless layer instead of the metal plane used in traditional absorber. The structure of this paper realizes the adjustment of the notch band by modifying the value of the capacitors in the lossless layer without reducing the absorption performance. The proposed FSA has a simple structure and an ultra-wide absorption band of 5-22 GHz, which has good stealth performance and application prospects.

This paper reports a novel differentially driven circularly polarized metasurface-based antenna with symmetrical and unidirectional radiation pattern. The introduction of metasurface could generate...

Here, the differential macromolecular evolutions and the structural defects in various TDCs (tectonically deformed coals) were profoundly investigated utilizing the 13C NMR, FTIR, Raman, and DFT (density function theory) calculations. The increasing aromatics provides evidences for advance evolution for aromatic clusters induced by dynamic metamorphism. The variations of fal∗ (non-protonated carbons) and falH ( CH or CH2) indicates that the brittle could promote the aliphatic carbon diversifications while ductile deformation could significantly promote the loss of aliphatic carbons. The I2 (=A900–700/A3000–2800) gradually increases while the I3 (=A1703+1745/A1618) decreases. The comparisons of the D1 peak in TDCs with those in perfect- and defective graphene indicated the existences of the structural defects in TDCs. The ductile TDCs have the lowest D1 peak positions, indicating that ductile deformation can promote the macromolecular disorder degrees to the maximum extent. The gradual increase of ID1/IG and the good linear relationship (R2 = 0.90) between ID1/IG and AD1/AG indicated the gradual increasing content of structural defects with the enhancement of the tectonic deformation. The geological conditions and the Raman results indicated the existences of the Stone-Wales defect (SW) and vacancy-like defects, including the single vacancy (SV), double vacancies (DV), and multi vacancies (MV1 and MV2) in TDCs. The evolution paths of DV (formation energy, Ef: 11.68 eV) → MV1 (Ef: 9.74 eV) → MV2 (Ef: 18.34 eV) and initial structures → SW defects have witnessed the increasing defects and disorder degrees with the enhancement of the tectonic deformation without damaging the continuity of coal matrix structures, which macroscopically manifests as ductile deformation. However, the evolution paths of initial structure → DV (Ef: 11.68 eV) and initial structure → SV (Ef: 9.08 eV) have damaged the continuity by missing carbons, which are consistent with the brittle TDCs.

This paper reports a dual-polarized frequency-selective rasorber that has a transmission window with low insertion loss and two absorption bands at both sides of the passband. Equivalent circuit and simple design guidelines for rasorber design are further developed. First, the notch structure with high Q is used to make the absorber realize the notch characteristic. Then, a frequency selective surface is utilized to replace the ground of the absorber. Note that the center frequency of the passband is consistent with the notch frequency. Therefore, the incident power is allowed to penetrate the proposed rasorber with a low insertion loss and transmissive behavior of the proposed rasorber is realized by this way. In addition, it is found that the main transmission band and lower absorption bands almost maintain stable performances in the angular range of 0° to 35°, while the upper absorption bands get slightly worse as angular range increases for both the TE and TM incidences. A rasorber prototype has been fabricated to experimentally validate the principle and design approach. The measurements agree reasonably with the simulated ones. Finally, a broadband and high-selectivity rasorber is achieved simultaneously.

Mounted locations and the ground plane structure have remarkable influences on the performance of roof-mounted automotive antennas. To distinguish this influence in radiation, figure of merits (FoMs), including total radiated power (TRP), near-horizontal part radiated power (NHPRP), and cumulative distribution function (CDF), are studied in this paper. It is proved that TRPs are almost the same with different mounting configurations. Because the radiation toward the horizon is a critical performance metric for automotive antennas, NHPRP is analyzed within certain degrees near the horizon. Even though a bigger deviation has been observed in NHPRP, the discrimination between different mounted scenarios is still not enough. Different from TPR and NHPRP, which are efficiency-based FoMs, CDF combines the gain values and the pattern shape together, achieving a comprehensive and intuitive insight into the antenna performance. It is more predictive and distinguishable in terms of the radiation pattern than NHPRP and TRP. Therefore, CDF can be utilized as a good supplement to existing metrics and can better distinguish the radiation performance of different antenna mounting configurations.

Aiming at the application of high-overload projectiles, this letter proposes a new type of miniaturized conical conformal Beidou antenna with right-hand circular polarization (RHCP) characteristic. The radiation patch and the ground plane of the proposed antenna are printed on the outer and inner surface of a hollow conical substrate. The inner wall of the substrate is metallized as the ground plane, so that the antenna performance will not be affected by the equipment installed in the internal space. The introduction of short ring and substrate with high dielectric constant makes the proposed antenna achieve miniaturization feature. Experimental results demonstrate that the proposed antenna can receive signals from eight satellites and provide stable signal reception.

This paper reports a novel wideband differential antenna based on metasurface. It consists of a differential slot coupled antenna and a planar metasurface. Planar metasurface is composed of 4 × 4 elements, and a rectangular slot is embedded on the ground plane to couple energy between the differential feeding lines and metasurface. The feeding line employs the three-line coupled lines which could provide wideband filter-integrated feature. The lower and upper resonant frequencies of the proposed antenna can be adjusted independently by tuning the distance of the metasurface units and the length of the rectangular slot in metallic ground, respectively. Moreover, a differential dielectric resonator antenna is simulated for performance comparison. It is concluded that the proposed antenna has many advantages, such as low profile (0.08λ0 at 5 GHz), frequency independent, high-gain, and symmetrical radiation pattern, comparing with the differential dielectric resonator antenna. Furthermore, a differential metasurface-based antenna prototype has been fabricated to experimentally validate the principle and design approach. The measured impedance bandwidth with odd mode reflection coefficient below − 10 dB is 19.35% from 4.76 to 5.78 GHz. Meanwhile, the measured boresight gain at 5 GHz is 6.4 dB, and low cross-polarization level could be achieved.

A novel frequency-independent printed quadrifilar helix antenna with wideband performance is presented in this paper. The proposed antenna utilizes four simple gradient microstrip lines as radiators, which are wrapped around a thin cylindrical dielectric substrate. Each microstrip line has etched two slots. The introduction of the slots results in a reduced frequency interval between two resonances, making the proposed antenna achieve a wideband characteristic. In addition, the input impedance of the proposed antenna is extracted for parametric analysis. The change rule of the real and imaginary parts of the input impedance indicates that the position of the slot at below (top) could control the lower (upper) resonance point independently. A prototype is simulated, fabricated, and measured for demonstration. The measured impedance bandwidth of the proposed antenna is 42.6% from 1.09 to 1.68 GHz. Moreover, a feeding network adopting a chip balun and two chip hybrid couplers is designed to measure the radiation pattern and axial ratio of the proposed antenna. Finally, the wideband, frequency-independent, wide half-power beamwidth, and excellent circularly-polarized characteristics make the proposed antenna become a competitive candidate in the satellite communication and navigation and positioning systems.

Accurately predicting the power load in certain areas is of great importance for grid management and power dispatching. A great deal of research has been conducted within the smart grid system community in developing an assortment of different algorithms that seek to increase the accuracy of these predictions. However, these predictions suffer from various sources of error, such as the variations in weather conditions, calendar effects, economic indicators, and many other sources, which are caused by the inherent stochastic and nonlinear characteristics of power demand. In order to quantify the uncertainty in load forecasting effectively, this paper proposes a comprehensive probability density forecasting method employing Gaussian process quantile regression (GPQR). GPQR is a type of Bayesian non-parametric method which can handle the uncertainties in power load data in a principled manner. Consequently, the probabilistic distribution of power load data can be statistically formulated. The effectiveness of the proposed method for short-term load forecasting has been assessed adopting the real dataset provided by American PJM electric power company. Numerical results demonstrate that the uncertainties in power load data can be effectively acquired based on the proposed method. Meanwhile, the competitive predictive performance could be yielded with respect to the conventional adopted methods.