Ultra-wideband (UWB) technology is known to have a high data rate in wireless communications due to its broad frequency range and low power consumption. Its flexibility enables a wide range of applications, including multiple-input multiple-output (MIMO) systems, suited for advanced wireless communication systems. In this manuscript a novel meandered MIMO antenna, designed explicitly for UWB applications, is proposed and studied. The antenna features meandered strips arranged in a circular pattern, resembling a sunflower. The antenna structure is built on an FR4 with 24 × 24 × 1.6 mm3 size for a single element and 48 × 48 × 1.6 mm3 for the MIMO configuration. The antenna operates over a wide frequency range between 2.9 and 20 GHz, achieving a fractional bandwidth of 151%. In the MIMO configuration, it maintains good isolation, exceeding 15 dB across the entire operating band. The measured efficiency of the antenna surpasses 75%, with a peak gain of 5.9 dBi. Additionally, key parameters for MIMO performance include an envelope correlation coefficient (ECC) below 0.002, mean effective gain (MEG) less than −3 dB, channel capacity loss (CCL) under 0.25 bps/Hz, and a total active reflection coefficient (TARC) below −20 dB.
The design of isolators to reduce mutual coupling in large two-dimensional antenna arrays is complex and requires significant computational effort. This work attempts to alleviate this problem by applying different types of planar isolators in different orientations and experimenting first with two-element microstrip antenna arrays. A U-shaped planar transmission line isolator, a U-shaped planar transmission line-based destructive ground structure, and a planar neutralization line structure are designed to reduce E-plane or H-plane coupling in two-element microstrip antenna arrays. A mutual coupling reduction of approximately 6 dB is achieved. Four combinations of these planar isolators are compared and analyzed in a four-element microstrip antenna array. An optimal combination is then obtained by using two reversely placed U-shaped line isolators, which reduce the mutual coupling by more than 6.1 dB. The study is also extended to a 5 × 5 antenna array. Similar results of mutual coupling reduction are obtained. In addition to simulation, both two-element and 25-element microstrip antennas have been constructed and tested. The agreement of the simulation results with the measured results confirms the effectiveness of the decoupling structures.
Poonam Tiwari, Vishant Gahlaut, Meenu Kaushik
et al.
The review focuses on the emergence of 5G wireless communication and the need for multiple-input multiple-output antennas to support high-speed communication systems. The article discusses the advantages of MIMO antennas, including increased channel capacity and the ability to focus radio frequency energy on specific users. However, the challenges of creating compact MIMO antennas with ideal isolation are addressed, including short wavelengths, connection losses, constrained bandwidth, and path losses in the millimeter-wave range. Design techniques and methods to enhance the performance of conventional antennas for 5G applications are discussed, along with potential solutions for upcoming challenges. The article provides an overview of MIMO antennas for 5G applications, covering frequency bands, system architecture, advantages, challenges, advancements, performance enhancement techniques, design techniques, and state-of-the-art developments.
This paper studies the optimal detection performance of the standard frequency diverse array (FDA) radar and FDA multi-input multioutput (FDA-MIMO) radar in Gaussian clutter and noise. Array signal processing scheme at the receiver is firstly designed to obtain the array steering vector containing range, azimuth, and frequency increment. For the two array configurations, namely, collocated transmit-receive and collocated transmit distributed receive, the likelihood ratio test statistics and the test statistic distributions are derived in the Neyman–Pearson sense. It is then investigated how the number of array elements influences the detection performance of various radar systems at low signal-to-noise ratio (SNR). Several numerical simulations are carried out to demonstrate that the performance improvement is hard for MIMO and FDA-MIMO by only increasing the number of transmit elements, while it is achievable for the FDA. The paper finally makes a comparative analysis for detection performances of five radar configurations under different SNRs.
When designing printed wide-slot antennas, the shape or profile of the tuning stub is a key geometric structure that affects the impedance bandwidth of the antenna. This article introduces a new process for designing tuning stub shapes, which are the blended results of a diamond and a circle. By using different geometry shapes, the design could generate a series of bandwidths with a regular trend. Detailed investigations and analysis were conducted on some key geometry parameters to explore their impact on the impedance bandwidth of the antenna. To certify the new design method, several prototypes were simulated, developed, and measured. The experimental and simulated results showed good agreement with each other. The results indicate that by properly selecting various blended shapes, a BW range from 80.1 to 117.3% for a VSWR of less than 2 could be obtained, which provides a convenient model for a wideband antenna design.
Coding metamaterials are the new technology where the aperture coding provides the hardware foundation for the miniaturization of the devices. As a synthetic 2-D plane, metamaterial antennas are composed of subwavelength resonant particles. It can realize real-time control of electromagnetic wave and build multifunction radar array system. We make a detailed explanation of its array structure, working principle, and hardware system. However, it is usually difficult to synthesize flexible beams because the phase value is very limited in this antenna. Two methods are proposed in this paper to demonstrate the beam synthesis based on repetitive coding and convolution, and the distribution of beam pointings is analysed on the basis of this mechanism. Experiments that measure the radiation pattern of this antenna are carried out to verify the simulated results using only 1-bit coding metasurface in a radar system, whose phase value is controlled by pin diode on the surface.
This paper proposes a low-complexity estimation algorithm for weighted subspace fitting (WSF) based on the Genetic Algorithm (GA) in the problem of narrow-band direction-of-arrival (DOA) finding. Among various solving techniques for DOA, WSF is one of the highest estimation accuracy algorithms. However, its criteria is a multimodal nonlinear multivariate optimization problem. As a result, the computational complexity of WSF is very high, which prevents its application to real systems. The Genetic Algorithm (GA) is considered as an effective algorithm for finding the global solution of WSF. However, conventional GA usually needs a big population size to cover the whole searching space and a large number of generations for convergence, which means that the computational complexity is still high. To reduce the computational complexity of WSF, this paper proposes an improved Genetic algorithm. Firstly a hypothesis technique is used for a rough DOA estimation for WSF. Then, a dynamic initialization space is formed around this value with an empirical function. Within this space, a smaller population size and smaller amount of generations are required. Consequently, the computational complexity is reduced. Simulation results show the efficiency of the proposed algorithm in comparison to many existing algorithms.
This paper investigates the attenuation by a human body and trees as well as material penetration loss at 26 and 39 GHz by measurements and theoretical modeling work. The measurements were carried out at a large restaurant and a university campus by using a time domain channel sounder. Meanwhile, the knife-edge (KE) model and one-cylinder and two-cylinder models based on uniform theory of diffraction (UTD) are applied to model the shape of a human body and predict its attenuation in theory. The ITU (International Telecommunication Union) and its modified models are used to predict the attenuation by trees. The results show that the upper bound of the KE model is better to predict the attenuation by a human body compared with UTD one-cylinder and two-cylinder models at both 26 and 39 GHz. ITU model overestimates the attenuation by willow trees, and a modified attenuation model by trees is proposed based on our measurements at 26 GHz. Penetration loss for materials such as wood and glass with different types and thicknesses is measured as well. The measurement and modeling results in this paper are significant and necessary for simulation and planning of fifth-generation (5G) mm-wave radio systems in ITU recommended frequency bands at 26 and 39 GHz.
A pair of ultrahigh-frequency (UHF) radars system for measuring the two-dimensional river flow patterns is presented. The system consists of two all-digital UHF radars with exactly the same hardware structure, operating separately at 329–339 MHz and 341–351 MHz. The adoption of direct radio frequency (RF) sampling technique and digital pulse compression simplifies the structure of radar system and eliminates the distortion introduced by the analog mixer, which improves the SNR and dynamic range of the radar. The field experiment was conducted at Hanjiang River, Hubei province, China. Over a period of several weeks, the radar-derived surface velocity has been very highly correlated with the measurements of EKZ-I, with a correlation coefficient of 0.958 and a mean square error of 0.084 m/s.
GNSS’s orbit determinations always rely on ground station or intersatellite links (ISL). In the emergency of satellite-to-ground links and ISL break-off, BeiDou navigation satellite system (BDS) satellites cannot determine their orbits. In this paper, we propose to add a spaceborne annular beam antenna for receiving the global positioning system (GPS) and global navigation satellite system (GLONASS) signals; therefore, the BDS satellites may be capable of determining their orbits by GPS/GLONASS signals. Firstly, the spectrum selection, the power isolation, the range of Doppler frequency shift, and changing rate are taken into account for the feasibility. Specifically, the L2 band signals are chosen for receiving and processing in order to prevent the overlapping of the receiving and transmitting signals. Secondly, the minimum number of visible satellites (MNVS), carrier-to-noise ratio (C/N0), dilution of precision (GDOP), and geometric distance root-mean-square (gdrms) are evaluated for acquiring the effective receiving antennas’ coverage ranges. Finally, the scheme of deploying 3 receiving antennas is proved to be optimal by analysis and simulations over the middle earth orbit (MEO), geostationary earth orbit (GEO), and the inclined geosynchronous satellite orbit (IGSO). The antennas’ structures and patterns are designed to draw a conclusion that installing GPS and GLONASS receivers on BDS satellites for emergent orbits determination is cost-effective.
The secure communication that multiple OFDMA-based cell-edge mobile stations (MS) can only transmit confidential messages to base station (BS) through an untrusted intermediate relay (UR) is discussed. Specifically, with the destination-based jamming (DBJ) scheme and fixed MS transmission power assumption, our focus is on the joint BS and US power allocation to maximize system sum secrecy rate. We
first analyze the challenges in solving this problem. The result indicates that our nonconvex joint power allocation is equivalent to a joint MS access control and power allocation. Then, by problem relaxation and the alternating optimization approach, two suboptimal joint MS access control and power allocation algorithms are proposed. These algorithms alternatively solve the subproblem of joint BS and UR power allocation and the subproblem of MS selection until system sum secrecy rate is nonincreasing. In addition, the convergence and computational complexity of the proposed algorithms are analyzed. Finally, simulations results are presented to demonstrate the performance of our proposed algorithms.
A design of dual broadband antenna is proposed in this paper; it consists of one low frequency unit and two high frequency units. The low frequency unit consists of a pair of printing vibrators; the high frequency unit consists of a pair of printing oscillators, which is bent at its end, and high frequency unit and low frequency unit are set on the same dielectric substrate. Through adding a parasitic unit on antenna, it can enhance frequency bandwidth without affecting the bandwidth. In the high frequency unit, it adopts gap-coupled microstrip line feeding method in order to get enough bandwidth. Through the test of dual broadband antenna, it can be found that, in the low frequency part, the antenna covers 20% bandwidth of the total bandwidth, and it covers the frequency from 800 MHz to 980 MHz. In the high frequency, the antenna covers 60% of total bandwidth and its frequency is from 1540 MHz to 2860 MHz, so the designed antenna can satisfy the frequency requirements of 2G/3G/LTE (4G) communication system.
A compact (8 × 62 × 5 mm3; 2.48 cc) frequency reconfigurable antenna that uses electrical switching with PIN diodes is proposed for the low frequency LTE band (699 MHz–862 MHz), high frequency LTE band (2496 MHz–2690 MHz), GSM850/900 bands (824 MHz–960 MHz), and DCS/PCS/WCDMA bands (1710 MHz–2170 MHz). The penta-band PIFA is first designed for GSM850/900/DCS/PCS/WCDMA bands by using two slits and ground pins within a limited antenna volume (8 × 54.6 × 5 mm3; 2.18 cc). The frequency reconfigurable antenna based on this penta-band PIFA is thus proposed to additionally cover all LTE bands. The proposed antenna has two PIN diodes with an optimal location. For State 1 (PIN diode 1: ON state, PIN diode 2: OFF state), the proposed antenna covers the low frequency LTE band, DCS/PCS/WCDMA bands, and high frequency LTE band. For State 2 (PIN diode 1: OFF state, PIN diode 2: ON state), the antenna covers the GSM850/900 bands. Simulated and measured results show that the total efficiency of the proposed antenna was greater than 40% for all operating frequency bands.
Multi-input multioutput (MIMO) is a novel technique to achieve high-resolution as well as wide swath in synthetic aperture radar (SAR) systems. Channel imbalance is inevitable in multichannel systems that it declines the imaging quality. Generally, the imbalance cannot be fully compensated by simple internal calibration in a MIMO-SAR system. In this paper, a new algorithm based on raw data is presented to remove the channel phase error. Based on the error source, this approach models the phase error as two parts: the transmit phase error and the receive phase error. The receive phase error is removed using cost function at the azimuth processing stage, whereas the transmit phase error is estimated with correlation. Point target simulations confirm the influence of channel phase error and the validation of the proposed approach. Besides, the performance is also investigated.