In recent years, multiple-input-multiple-output (MIMO) antennas with the ability to radiate waves in more than one pattern and polarization play a great role in modern telecommunication systems. This ...paper provides a theoretical review of different mutual coupling reduction techniques in MIMO antenna systems. The increase in the mutual coupling can affect the antenna characteristics drastically and therefore degrades the performance of the MIMO systems. It is possible to improve the performance partially by calibrating the mutual coupling in the digital domain. However, the simple and effective approach is to use the techniques, such as defected ground structure, parasitic or slot element, complementary split ring resonator, and decoupling networks which can overcome the mutual coupling effects by means of physical implementation. An extensive discussion on the basis of different mutual coupling reduction techniques, their examples, and comparative study is still rare in the literature. Therefore, in this paper, different MIMO antenna design techniques and all of their mutual coupling reduction techniques through various structures and mechanisms are presented with multiple examples and characteristics comparison.
Research on path loss in indoor stairwells for 5G networks is currently insufficient. However, the study of path loss in indoor staircases is essential for managing network traffic quality under ...typical and emergency conditions and for localization purpose. This study investigated radio propagation on a staircase where a wall separated the stairs from free space. A horn and an omnidirectional antenna were used to determine path loss. The measured path loss evaluated the close-in-free-space reference distance, alpha-beta model, close-in-free-space reference distance with frequency weighting, and alpha-beta-gamma model. These four models exhibited good compatibility with the measured average path loss. However, comparing the path loss distributions of the projected models revealed that the alpha-beta model exhibited 1.29 dB and 6.48 dB for respectively, at 3.7 GHz and 28 GHz bands. Furthermore, the path loss standard deviations obtained in this study were smaller than those reported in previous studies.
This study presents a simple, miniaturized, and low-profile multiple-input multiple-output (MIMO) antenna operating at 29 GHz with reduced mutual coupling between the antenna elements for futuristic ...5G communication. The proposed design employs two radiating elements with slits in the radiators to produce high isolation among the antenna radiators. The MIMO antenna maintains a compact structure of 11.4 × 5.3 mm
, which is the smallest size compared to previous 5G antennas. Roger's 4350B laminate was employed as a substrate material. At 29 GHz, low mutual coupling of - 36 dB, low envelope correlation coefficient (ECC < 0.001), and high diversity gain (DG > 9.8 dB) are achieved. The proposed design is examined in terms of the S-parameters, diversity gain, radiation pattern, and envelope correlation. Compared to the straight antenna element, an improvement of - 20 dB is observed in the isolation for both the simulated and measured results.
The millimeter-wave (mmWave) frequency is considered a viable radio wave band for fifth-generation (5G) mobile networks, owing to its ability to access a vast spectrum of resources. However, mmWave ...suffers from undesirable characteristics such as increased attenuation during transmission. Therefore, a well-fitted path loss model to a specific environment can help manage optimal power delivery in the receiver and optimal transmitter power in the transmitter in the mmWave band. This study investigates large-scale path loss models in a university hall environment with a real-measured path loss dataset using directional horn antennas in co-polarization (H–H) and tracking antenna systems (TAS) in line-of-sight (LOS) circumstances between the transmitter and receptor at mmWave and centimeter-level bands. Although the centimeter-level band is used in certain industrialized nations, path loss characteristics in a university hall environment have not been well-examined. Consequently, this study aims to bridge this research gap. The results of this study indicate that, in general, the large-scale floating-intercept (FI) model gives a satisfactory performance in fitting the path loss both in the center and wall side links.
In this paper, a wideband polarization conversion metasurface is designed. Additionally, coding and chessboard metasurfaces are specifically tailored for radar cross-section reduction (RCS). ...Initially, a compact unit cell demonstrating exceptional polarization conversion performance is introduced, achieving a polarization conversion ratio (PCR) exceeding 90
across frequencies ranging from 7.9 to 22.7 GHz. The PCR remains effective even when oblique incidence angles of up to 30
are utilized across this frequency band. Roger RT5880, with a thickness of 0.254 mm, serves as the substrate. An airgap is introduced between the substrate and the ground plane to enhance the polarization conversion bandwidth. This unit cell serves as the fundamental building block for subsequent metasurface configurations. To assess the scalability and effectiveness, a 36
36 unit array is assembled, confirming efficient polarization conversion capabilities extending to larger structures. Moreover, a 1-bit coding unit "0" and "1" are formed by the Pancharatnam-Berry phase based on the same-sized meta-atom with 90
orientations. The robustness and practicality of the design are demonstrated by creating 12
12 lattices and evaluating their RCS reduction potential under two distinct scenarios: a chessboard pattern and a coding-based scheme. Notably, its results indicate substantial RCS reduction across a broad frequency spectrum (7.9 to 22.7 GHz) for both configurations. This study demonstrates the wide-ranging applicability of metasurface design, making it a valuable contribution to the fields of microwave engineering, polarization control, and radar stealth technology. Owing to its simplicity, bandwidth, and versatility, this approach offers innovative solutions for diverse real-world applications.
In this paper, a horn-shaped strip antenna exponentially tapered carved on a multilayer dielectric substrate for an indoor body position tracking system is proposed. The performance of the proposed ...antenna was verified by testing it as a tracking state of an indoor resting body position. Among different feeding techniques, the uniplanar T-junction power divider approach is used. The performance verification of the proposed antenna is explained through its compact size and 3D shape, along with a performance comparison of the return loss radiation pattern and the realized gain. The suggested antenna has an 88.88% fractional bandwidth and a return loss between 6 and 15.6 GHz, with a maximum gain of 9.46 dBi in the 9.5 GHz region. Within the intended band, the radiation pattern had an excellent directivity characteristics. The proposed antenna was connected to an NVA-R661 module of Xethru Inc. for sleeping body position tracking. The performance of the antenna is measured through microwave imagining of the state of the resting body in various sleeping positions on the bed using a Recurrent Neural Network (RNN). The predicted outcomes clearly define the antenna's performance and could be used for sensing and prediction purposes.
In this study, a multiple-input multiple-output (MIMO) antenna for wide scanning is designed. By adding slits to the patches, each element is intended to strengthen the isolation between the ...radiating elements. The proposed high isolation and wide scanning antenna combine to achieve the desired phased-array antenna. The array has a main beam pointing to the desired scanning region and a minimum side lobe level (SLL) in the undesired direction. A compact and linear eight-element array with an interelement spacing of λ/2 is designed and analyzed for beam scanning in the E-plane. Considering the worst case, the proposed array has a very low mutual coupling of (S21 = -24 dB), and it realizes a gain of 9.3 dBi and an SLL of 11 dB at a scanning angle of 70∘. The antenna performance was studied in terms of the S-parameter, radiation patterns, beam-scanning performance, envelope correlation coefficient (ECC), diversity gain (DG), peak gain, and efficiency. A close agreement was observed between the simulated and measured results.
In this paper, double slot podal and antipodal ultra-wideband (UWB) microstrip antennas for a fluid property measurement system are proposed. Among different feeding techniques, out of phase ...uni-planner power divider approach is used. The performance verification of the proposed antenna is explained, along with a performance comparison of the antenna bandwidth, feeding, and the realized gain. The suggested podal antenna has an impedance bandwidth from 2.4 to 15.4 GHz, with a maximum gain of 11.3 dBi in the 12 GHz region while the antipodal antenna has a 2.8 GHz to 16 GHz impedance bandwidth, with a maximum gain of 10.4 dBi in the 10 GHz region. Within the intended band, the radiation pattern had an excellent directivity characteristic. The implementation of the proposed antenna is calibrated by measuring the propagated signals response via various liquid specimens using UWB radar, which might be applied for fluid sensing and prediction purposes. The proposed antenna was connected to an NVA-R661 module of Xethru Inc. for measuring the sample delay and peak-to-peak amplitude of the received signals passing through specimens. The measured parameters at a different radar frequency range of transmission are applied by drawing the fluid viscous analogy based on Poiseuille’s law hypothesis, showing clear differentiation between the test specimens.
This article introduces a miniaturized dual-band multiple input multiple output (MIMO) antenna with wide bandwidth and high isolation. The design incorporates ground plane modifications and utilizes ...metamaterials to achieve dual-band operation in the millimeter wave spectrum for 5G applications, specifically operating at the 28/38 GHz frequency bands. The proposed antenna maintains its dual-band functionality despite its compact size of 3.8 Formula: see text 3.7 Formula: see text 0.787 Formula: see text (without the feed line). The antenna is fabricated on a Rogers RT5880 substrate with a thickness of 0.787 mm and with relative permittivity Formula: see text = 2.2. The MIMO system comprises two symmetric radiating elements positioned in close proximity, resulting in mutual coupling levels of Formula: see text 20 dB and Formula: see text 12 dB at 25 GHz and 37 GHz, respectively. Modifications are made to the ground length to enhance the isolation at the higher frequency band while embedding metamaterials effectively reduces the coupling at the lower frequency band. The incorporation of metamaterials leads to an enhanced bandwidth from 3.8 to 4.8 GHz in the desired lower band (24-28.8 GHz) and from 3.8 to 4.2 GHz in the higher band (36.6-40.8 GHz). The proposed system can operate across the 28/38 GHz bands using a compact design, thus offering reasonable isolation, an envelope correlation coefficient below 0.0001, and a significant diversity gain (> 9.99 dB). These attributes emphasize the system's suitability for 5G millimeter-wave cellular communications.
The indoor application of wave propagation in the 5G network is essential to fulfill the increasing demands of network access in an indoor environment. This study investigated the wave propagation ...properties of line-of-sight (LOS) links at two long corridors of Chosun University (CU). We chose wave propagation measurements at 3.7 and 28 GHz, since 3.7 GHz is the closest to the roll-out frequency band of 3.5 GHz in South Korea and 28 GHz is next allocated frequency band for Korean telcos. In addition, 28 GHz is the promising millimeter band adopted by the Federal Communications Commission (FCC) for the 5G network. Thus, the 5G network can use 3.7 and 28 GHz frequencies to achieve the spectrum required for its roll-out frequency band. The results observed were applied to simulate the path loss of the LOS links at extended indoor corridor environments. The minimum mean square error (MMSE) approach was used to evaluate the distance and frequency-dependent optimized coefficients of the close-in (CI) model with a frequency-weighted path loss exponent (CIF), floating-intercept (FI), and alpha–beta–gamma (ABG) models. The outcome shows that the large-scale FI and CI models fitted the measured results at 3.7 and 28 GHz.
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