Pair Of Antennas Research Articles

A MIMO Channel Prediction Scheme Based on Multi-Task Learning

This paper proposes a multi-input multi-output (MIMO) channel prediction scheme using multi-task learning algorithm. Based on the spatially correlated MIMO channel Channel State Information (CSI) observations, a multi-task least square support vector machine (MTLS-SVM) is trained, where the CSI prediction for each antenna pair can be modeled as one task and jointly learning between these tasks are implemented. Then the future CSI is predicted by this MTLS-SVM. By using the relatedness of the multiple tasks, the spatial correlations between different antenna pairs can fully be exploited and hence better channel prediction performance can be achieved compared with the single task prediction scheme.

Tailoring Antenna Focal Plane Characteristics for a Compact Free-Space Microwave Complex Dielectric Permittivity Measurement Setup

This article presents a compact precision free-space microwave measurement setup with a choice of three dielectric lenses to tailor the antenna focal plane characteristics for extracting complex dielectric permittivity of small samples. Custom designed spot-focusing horn antenna pairs were used to achieve a compact setup with antenna separation distance, 2 f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</sub> :4λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> -8λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and focal spot size, f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> :1λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> -1.5λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is the wavelength at center frequency. Using the compact free-space setup, relative complex permittivity (e' - je'') was extracted over 8-12 GHz for lowand high-loss dielectrics with lateral dimensions, 3.3λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> × 3.3λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and 10λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> × 10λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . For large materials under test (MUTs), i.e., 10λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> × 10λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , measurement accuracy in dielectric constant, Δe'% was <; 0.65% and <; 1.14% for low- and high-loss dielectrics, respectively. For smaller MUTs (3.3λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> × 3.3λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ), Ae'% was <; 0.89% and <; 2.29% for low- and high-loss MUTs, respectively. The error in loss tangent (Δtanδ) varied over 0.002-0.016 and 0.015-0.056 for large (10λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> × 10λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) and small MUTs (3.3λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> × 3.3λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ), respectively. For large MUTs, biconvex lens pair with the smallest f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> (1λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</sub> (4λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) among the three lenses yielded the best accuracy in dielectric constant (e') due to tight field focusing at the focal plane. The plano-convex lens pair yielded the best accuracy in loss tangent (tanδ = e''/e') for large MUTs due to slow variation in the phase of the local plane wave. By tailoring antenna focal plane characteristics, a compact free-space setup that is 6×-10× smaller than the classical setup for handling MUTs that are 1/5th of the size used in classical setup is demonstrated without compromising the measurement accuracy.

User scheduling for full‐duplex non‐orthogonal multiple access systems with reconfiguration antennas

As the promising technologies for providing higher network throughput, full-duplex (FD) communications and non-orthogonal multiple access (NOMA) have attracted wide attention in recent years. In this study, the authors propose a user scheduling algorithm for the full-duplex non-orthogonal multiple access system (FD-NOMA) where an FD base station equipped with a pair of reconfigurable antennas serves multiple half-duplex downlink (DL) and uplink (UL) users simultaneously. Firstly, they formulate a user scheduling problem to maximise the sum rate of the FD-NOMA system. Then, they eliminate the inter-user interference from caused by the UL users to the DL users through the blind interference alignment based on reconfigurable antennas and decouple the user scheduling problem into a DL user scheduling problem and a UL user scheduling problem. Next, for the DL and UL user scheduling subproblems, they pair the users aligned with the same directions based on the channel correlation metric. Finally, they employ the exhausting search and iterative power allocation algorithm to solve the subproblems. Simulation results show that the proposed FD-NOMA system can achieve up to 233 of gain in the average sum rate compared with the existing baseline schemes.

A new approach to map lightning channels based on low-frequency interferometry

A purely interferometric algorithm, named imaging algorithm, has been developed for mapping lightning in the low-frequency band. The imaging algorithm locates a lightning source by computing the three-dimensional correlation of the lightning signals arriving at a pair of lightning sensors, and then summing the correlations of all antenna pairs. This algorithm does not locate the source by solving the non-linear time-of-arrival (TOA) equations, instead the source is located at the global maxima of the total correlation. The lightning map produced by the imaging algorithm for one intracloud flash was compared with that of the hybrid interferometric-TOA algorithm. The imaging algorithm can locate more sources than the hybrid algorithm and produce more complete lightning maps. We also demonstrated that the imaging algorithm can locate multiple concurrent lightning sources even though the recorded signals from the pulses overlap in time at some stations, which is not possible with a traditional TOA-based technique.

Sub-6 GHz Dual-Band 8 × 8 MIMO Antenna for 5G Smartphones

In this letter, a dual-band 8x8 MIMO antenna that operates in the sub-6 GHz spectrum for future 5G multiple-input multiple-output (MIMO) smartphone applications is presented. The design consists of a fully grounded plane with closely spaced orthogonal pairs of antennas placed symmetrically along the long edges and on the corners of the smartphone. The orthogonal pairs are connected by a 7.8 mm short neutral line for mutual coupling reduction at both bands. Each antenna element consists of a folded monopole with dimensions 17.85 x 5mm2 and can operate in 3100-3850 MHz for the low band and 4800-6000 MHz for the high band ([S11] ˂ -10dB). The fabricated antenna prototype is tested and offers good performance in terms of Envelope Correlation Coefficient (ECC), Mean Effective Gain (MEG), total efficiency and channel capacity. Finally, the user effects on the antenna and the Specific Absorption Rate (SAR) are also presented.

A Self-Decoupled Antenna Array Using Inductive and Capacitive Couplings Cancellation

The concept of a self-decoupled antenna array using the cancellation of two opposite couplings is proposed in this article. A pair of such antennas can be closely placed with inherent high isolation without using an extra decoupling structure between the antennas. A pertinent equivalent circuit model is presented to illustrate the physical mechanism of this new concept. It is found that the inductive and capacitive couplings between the antennas can be well canceled out with each other by properly adjusting the antenna dimensions. A demonstrating antenna array with a spacing of 0.024λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> at the working frequency of 3.5 GHz and its counterpart array are first studied. The measured results show that although the proposed antenna array occupies a slightly larger size than its counterpart array, it presents better performance compared with its counterpart antenna array in port isolation (from 10 to 20 dB), total efficiency (from 68% to 80%), and envelope correlation coefficient (ECC) (from 0.14 to 0.04) throughout the desired frequency band of 3.3-3.8 GHz. A 3-D self-decoupled antenna array is designed to show that the proposed antenna can be in a compact form factor. Another self-decoupled array and its counterpart working at 2.14 GHz (long-term evolution (LTE) band 1) are studied through multi-input multi-output (MIMO) over-the-air (OTA) test when the arrays are integrated with an LTE module, showing significant improvement on the data throughput.

Image Distortion Characterization due to Equivalent Monostatic Approximation in Near-Field Bistatic SAR Imaging

The $\omega $ – $k$ synthetic aperture radar (SAR) algorithm is a computationally efficient algorithm for near-field 3-D monostatic SAR imaging in nondestructive testing (NDT) applications. However, bistatic measurements are preferred in order to obtain high dynamic range, in particular when real-time imaging arrays are used. This article investigates the image distortion caused by using an equivalent monostatic imaging algorithm for bistatic measurements. Simulations and measurements at millimeter-wave frequencies in the Ka-band (26.5–40 GHz) are used to investigate the resultant image distortion. Furthermore, the image distortion is quantified through the root-mean-square (rms) error, which is calculated as a function of the bistatic transmitter–receiver separation distance, range, and noise power. Simulations and measurements are conducted for imaging using the raster scanning of a pair of antennas and for nonuniform imaging arrays. In addition, an approximate method for phase compensation is introduced to improve the image error from the monostatic approximation of bistatic measurement.

Lightning observations using broadband VHF interferometer and electric field measurements

A broadband radio interferometer for locating lightning emissions was built and deployed at the high-altitude research station on Mount Aragats (Armenia). The instrument operates in the frequency range from 24 to 78 MHz and employs three identical broadband flat-plate antennas which are located in the horizontal plane and form two orthogonal baselines of 13 m length. The time differences of arrival of the signals at pairs of antennas determined from the peak of the cross-correlation function are used to measure the azimuth and elevation angles of the radiation source as a function of time. This paper describes the operation of the interferometer and reports observations of lightning flashes complemented by synchronous measurements of fast wideband electric field waveforms and changes in the near-surface electrostatic field. Combined analysis of these data makes it possible to identify the type of lightning discharge. The capability of the system to classify lightning types is demonstrated by example observations of an intracloud and a cloud-to-ground lightning flashes.

Asymmetric Excitation of Surface Plasmon Polaritons via Paired Slot Antennas for Angstrom Displacement Sensing.

Optical antennas enable efficient coupling between propagating light and bonding electromagnetic waves like surface plasmon polaritons (SPPs). Under the illumination of inhomogeneous optical fields, propagating SPPs mediated by multimode antennas could be spatially asymmetric and the asymmetry strongly depends on the position of the antennas relative to the illumination field. Here we develop such asymmetric excitation of SPPs through illuminating a pair of slot antennas with the (1,0) mode Hermite-Gaussian beam. The physical scenario of the interaction between the illumination optical field and the paired slot antennas are elaborated by full-wave electromagnetic simulations. We also carry out experiments to monitor the asymmetric SPPs propagation with a back-focal plane imaging technique. By retrieving the asymmetric intensity ratio of the SPP pattern in the back-focal plane image, lateral displacement of the antennas down to angstrom level is demonstrated.

Dual‐band decoupling and wideband harmonic suppression for asymmetric antenna pair by using filtering structures

AbstractIn this letter, a new method is proposed to achieve high port isolation and wideband harmonic suppression for two closely placed asymmetric antennas by using integrated filtering structures cascaded on the feeding microstrip lines. The proposed asymmetric antenna pair operates normally at 2.34 to 2.6 GHz and 3.31 to 3.69 GHz, respectively, containing the WLAN band (2.4‐2.484 GHz) and the fifth generation (5G) bands of China Telecom (3.4‐3.5 GHz) and China Unicom (3.5‐3.6 GHz). Compared to the reference antenna pair, the proposed antenna pair has an enhancement in isolation of 40.8 and 38.1 dB at 2.45 and 3.5 GHz individually, and the higher harmonics of up to 18 GHz generated by the reference antenna pair can be suppressed. The gain of the proposed antenna pair decreases by an average of 8.8 dB in the higher harmonic frequency bands. The measured results of the manufactured antenna pair agree well with the simulated results, indicating that the designed antenna pair has good dual‐band decoupling and wideband harmonic suppression characteristics. This method particularly reduces the complexity of the decoupling antenna design and is suitable for the future multi‐functional terminals.

A High Precision Direction-Finding Method Based on Multi-Baseline for Target Rescue

Target rescue is an important application in the Internet of Things (IoT), and the direction-finding (DF) is an essential technology for the target rescue. The DF technology based on the phase comparison method is widely used in target rescue. However, due to the phase ambiguity, the phase comparison method is difficult to meet the needs of high precision DF. The long and short baseline method can eliminate the phase ambiguity in a certain angle range, but it cannot accurately direction in all directions. In this article, we propose a high precision DF method based on the multi-baseline and multi-antenna for target rescue. Firstly, the performance of the proposed method in eliminating the inhomogeneity and azimuth ambiguity in single antenna pairs is analyzed theoretically. Then, a measurement system configured of a cycle array with eight antennas is presented to validate the practicability of the proposed method. Finally, the measurement system is verified by experiments conducted in both anechoic chamber and the out-field scenarios. The experiment results demonstrate that the error of the proposed DF method is within 2° in the anechoic chamber and within 5° in out-field. Therefore, the proposed multi-baseline and multi-antenna method can be used for high precision DF for the target rescue.

Design of planar inverted‐F antenna pair with reflectors for near‐field power transfer

AbstractIn this article, a planar inverted‐F antenna (PIFA) pair with reflectors for near‐field power transfer at a frequency of 2.45 GHz is proposed. In order to enhance efficiency of power transmission and reduce electromagnetic wave leaked to free space due to the power transmission, the reflectors are installed around the transmitting and receiving antenna pair except on the open side. The transmitting antenna is designed with high impedance characteristics to prevent the radiated electromagnetic wave to free space when the antenna is waiting for the power transmission. The receiving antenna is designed for Wi‐Fi and also functions as an antenna for energy harvesting at a frequency of 2.4 GHz when the antenna operates solely. Furthermore, the L‐shaped slot is added on the FR‐4 substrate of the receiving antenna as a harmonic rejection filter (HRF) used to suppress reradiation of the higher order harmonics and improve the conversion efficiency. The conversion efficiency of the proposed transmitting and receiving antenna pair is 79.4% when the input RF power is 23 dBm.

Compact Decoupled Antenna Pairs for 5G Applications

Compact Decoupled Antenna Pairs for 5G Applications

Self-Decoupled MIMO Antenna Pair With Shared Radiator for 5G Smartphones

In this article, a novel self-decoupled multiple-input multiple-output (MIMO) antenna pair with a shared radiator is proposed for fifth-generation (5G) smartphones. In our approach, a radiator is directly excited by two feeding ports, and interestingly, the two ports are naturally isolated across a wide bandwidth without using any extra decoupling structures. To offer a deep physical insight of the self-decoupling mechanism, a mode-cancellation method based on the synthesis of common and differential modes is developed for the first time. The proposed self-decoupled antenna pair shows a good isolation of better than 11.5 dB across the 5G N77 band (3.3-4.2 GHz) with a radiation pattern diversity property. Based on the self-decoupled antenna pair, an 8 × 8 MIMO antenna system, constituted by four sets of antenna pairs, is simulated, fabricated, and measured to validate the concept. The experimental results demonstrate that the proposed 8 × 8 MIMO system can offer an isolation of better than 10.5 dB between all ports and a high total efficiency of 63.1%-85.1% across 3.3-4.2 GHz. With the advantages of self-decoupling, shared radiator, simple structure, wide bandwidth, and high efficiency, the proposed design scheme exhibits promising potential for the future highly integrated MIMO antennas for 5G smartphones.

Calculation of Site Attenuation for Calculable Dipole Antennas

This paper presents a method for calculating the site attenuation (SA) of an open-area test site (OATS) for a pair of calculable dipole antennas with a 3-dB hybrid balun in the frequency range of 30 MHz to 1 GHz. The SA was directly derived using the concept of power mismatch and dissipative loss from the SA measurement system instead of the concept of substitution loss. Two types of SA formulas using the power loss concept on the treatment of the OATS are presented. The first is the SA formula related to knowing only the value of the SA. The other is the SA formula that analyzed the effects of each part of the SA. Additionally, the constituent losses of the SA measurement system are discussed using the derived SA formula. The analysis of the results showed that the SA could be successfully characterized individually from the loss of the OATS. It also showed that SA is expressed as two kinds of losses: the balanced portmismatch losses of transmit and receive baluns and the half-space dissipative loss. The resultant SA showed good agreement with the results calculated from the S-parameters as well as with the measured results.

Analysis of the Envelope Correlation Coefficient of MIMO Antennas Connected with Suspended Lines

Inserting a suspended line is a widely used technique to reduce the envelope correlation coefficients (ECC) of multiple-input multiple-output (MIMO) antennas, but its ECC reduction mechanism has not been carefully investigated so far. In this paper, MIMO antenna pairs connected with different suspended lines were evaluated using a full-wave simulation and measurement results. We calculated the surface current density at the center of the suspended line inserted between the antenna elements and found that the derivative of the surface current density was closely related to the ECC values. Furthermore, parametric studies showed that the suspended line length determines the ECC reduction bandwidth of the MIMO antenna, and the antenna length controls the ECC minimum frequency point. These guidelines provide useful insights into designing a low ECC MIMO antenna employing a suspended line.

Time-Domain Mixed-Mode Site Attenuation Measurement

The mixed-mode S -parameters have become widely used for transmission line measurements on printed circuit boards. In this article, the mixed-mode S -parameter measurement is applied to the site attenuation measurement using a pair of dipole antennas. The proposed method requires no balance–unbalance transformer (balun) for the balancing antenna measurement and is free from the limitation of the antenna operating frequency caused by the balun. Compared with conventional methods, 20-dB smaller site attenuation between the dipole antenna pair was obtained. This results in expansion of the measurement frequency and enables us to carry out time-domain measurements with higher time resolution. Since no additional circuit, such as a matching circuit is necessary for the proposed method, the ring-down time of the main response is much shorter. These characteristics lead to significant advantages in carrying out precision measurements.

Ultra-Wideband Diversity MIMO Antenna System for Future Mobile Handsets.

A new ultra-wideband (UWB) multiple-input/multiple-output (MIMO) antenna system is proposed for future smartphones. The structure of the design comprises four identical pairs of compact microstrip-fed slot antennas with polarization diversity function that are placed symmetrically at different edge corners of the smartphone mainboard. Each antenna pair consists of an open-ended circular-ring slot radiator fed by two independently semi-arc-shaped microstrip-feeding lines exhibiting the polarization diversity characteristic. Therefore, in total, the proposed smartphone antenna design contains four horizontally-polarized and four vertically-polarized elements. The characteristics of the single-element dual-polarized UWB antenna and the proposed UWB-MIMO smartphone antenna are examined while using both experimental and simulated results. An impedance bandwidth of 2.5–10.2 GHz with 121% fractional bandwidth (FBW) is achieved for each element. However, for S11 ≤ −6 dB, this value is more than 130% (2.2–11 GHz). The proposed UWB-MIMO smartphone antenna system offers good isolation, dual-polarized function, full radiation coverage, and sufficient efficiency. Besides, the calculated diversity performances of the design in terms of the envelope correlation coefficient (ECC) and total active reflection coefficient (TARC) are very low over the entire operating band.

Investigation of turbulence rotation in the SOL and plasma edge of W7-X for different magnetic configurations

The W7-X stellarator is optimized with respect to neoclassical transport. Therefore turbulent transport plays an important role. It is equipped with an inertial cooled graphite divertor which intersects the island chain at the plasma edge depending on the magnetic configuration. Additional control coils and the plasma current modify the iota profile at the plasma edge and shift the position of the island chain. To monitor the effects on the poloidal propagation velocity in the scrape-off layer (SOL) and the plasma edge, an O-mode Poloidal Correlation Reflectometer (PCR) is used which simultaneously monitors the propagation of low-k turbulence. Operating in the density range of 0.6 × 1019 m−3 to 2 × 1019 m−3 it covers a large part of the SOL and the plasma edge and allows for the experimental determination in the last closed flux surface (LCFS) and the associated shear layer in low to mid-density discharges. In this paper it is shown that the propagation in the shear layer and its vicinity is determined best, when based on an elliptical model. Different magnetic configurations with magnetic edge topology of five independent islands for ι = 1 and six linked islands for ι = 0.81 are investigated. Also the effects of the plasma current and additional control coils on the edge magnetic topology are studied. The coherence spectra of antenna pairs for different poloidal separations is investigated. Using a decomposition method for the measured coherence spectra the characterization of turbulence spectra is possible with respect to e.g. broad band turbulence and quasi coherent modes. A strong reduction of the broad band turbulence is observed in the vicinity of the LCFS which is evidence for the suppression of low-k turbulence at the shear layer.

Design and Fabrication of Metamaterial Absorbers Used for RF-ID

Radio frequency identification (RF-ID) uses electromagnetic fields to automatically identify and track tags attached to objects. In response to the need to suppress the electromagnetic interference between adjacent RF-ID equipment or systems, this study aims to achieve a thin and multi-resonance absorber using metamaterials composed of patterned grids on a grounded dielectric substrate in the frequency region of UHF and microwaves. A computational tool (ANSYS HFSS) was used to model and estimate the reflection coefficient and surface current distribution. The samples used to measure reflection loss were fabricated by the printed circuit board (PCB) method in which a copper film was deposited on both sides of a photosensitized board. The reflection loss was measured using a free space measurement system, composed of a pair of horn antennas and network analyzer. The grid-patterned metamaterial absorbers exhibited dual-band absorption peaks at 0.88 GHz and 2.45 GHz with a small substrate thickness (about 3.7 mm) that can be usefully applied to electromagnetic compatibility in RF-ID system. Magnetic coupling is achieved via antiparallel currents in the grid conductor on the top layer and the ground conductor on the bottom layer. Since the magnetic response is influenced by the dimension of the resonators, it is possible to achieve two resonances by scaling the resonating structures. The metamaterial absorbers also exhibited good oblique incidence performance. A high level of absorption (above 10 dB) was maintained at up to 30 degrees of incidence angle for both TE and TM polarization.