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An Upper Bound for the Envelope Correlation Coefficient of Antenna Clusters
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The intensive research in the fifth generation (5G) technology is a clear indication of technological revolution to meet the ever-increasing demand and needs for high speed communication as well as Internet of Thing (IoT) based applications. The timely upgradation in 5G technology standards is released by third generation partnership project (3GPP) which enables the researchers to refine the research objectives and contribute towards the development. The 5G technology will be supported by not only smartphones but also different IoT devices to provide different services like smart building, smart city, and many more which will require a 5G antenna with low latency, low path loss, and stable radiation pattern. This paper provides a comprehensive study of different antenna designs considering various 5G antenna design aspects like compactness, efficiency, isolation, etc. This review paper elaborates the state-of-the-art research on the different types of antennas with their performance enhancement techniques for 5G technology in recent years. Also, this paper precisely covers 5G specifications and categorization of antennas followed by a comparative analysis of different antenna designs. Till now, many 5G antenna designs have been proposed by the different researchers, but an exhaustive review of different types of 5G antenna with their performance enhancement method is not yet done. So, in this paper, we have attempted to explore the different types of 5G antenna designs, their performance enhancement techniques, comparison, and future breakthroughs in a holistic way.
Realising capacity demands of future wireless communications require improved spectral efficiency in the sub‐6 GHz frequency bands. This study proposes a novel eight‐element multiple‐input–multiple‐output (MIMO) antenna that can be tuned from 1.7 to 6 GHz. The design is based on the antenna cluster concept, where weighted feeding of multiple antenna elements is used to modify the operating frequency. This study extends the theory of the concept to account for multiple separate clusters, thus enabling it to be used for MIMO. The proposed antenna achieves over 60% efficiency at frequencies above 3 GHz, and the system exceeds the ergodic capacity of the ideal 7 × 7 MIMO in that band.
Employing characteristic mode theory (CMT), a shape-first feed-next design methodology for compact planar antennas is proposed, which facilitates rapid and systematic design of self-matched, multi-port antennas with optimal bandwidth and high isolation. First, the optimal antenna shape with multiple self-resonant modes is synthesized using a binary genetic algorithm. Then, the optimal feed positions that provide good input matching and high isolation between the excitation ports are specified using a virtual probe modeling technique. A two-port microstrip antenna with an electrical size of 0.45λd × 0.297λd is designed, fabricated and measured. The measured operating frequency is within 1% of the full wave simulation, and the overall S parameter characteristics and far field patterns agree well with the simulation result, validating our design methodology. Mutual coupling S21 < −35 dB at the center frequency is achieved in this design.
A novel pattern-reconfigurable two-port multi-ple-input multiple-output (MIMO) antenna system at WIFI band has been designed by resorting to characteristic modes analysis (CMA). The design method of the proposed MIMO antenna array is based on selective excitation of three orthogonal characteristic modes. The selective excitation is achieved by integrating two pairs of capacitive coupling elements (CCEs) on the same plane with the ground. Two feeding networks related to two ports have been designed for achieving a good impedance matching and providing the feeding to the CCEs. By switching the p-i-n diodes in each feeding network, the selective excitation mode of the two ports can be varied, thus leading to the reconfigurable patterns. Three operating states can be obtained for the proposed antenna design. Simulation results demonstrate that the envelope correla-tion coefficients (ECC) of the proposed MIMO antenna array are far less than 0.5 due to the orthogonality of radiation patterns between the characteristic modes in each of the three states. Measured S-parameters and radiation patterns of a realized prototype are in good agreement with simulation ones confirming the reliability of the design method.
A simple internal antenna design for WWAN/LTE operations is investigated, and it can be incorporated into a mobile phone that has an unbroken metal rim of height 5 mm. The proposed antenna is mainly composed of two parallel slots (dual-loop) embedded on the system ground, and by feeding them with an L-shaped coupled feedline with matching networks, good excitation of multiple loop resonant modes can be obtained, which is capable of covering the GSM850/900 (824–960 MHz), DCS/PCS/UMTS2100 and LTE2300/2500 (1710–2690 MHz) operating bands. In addition, the feasibility of realizing decoupled multi-antennas (2 ×2 MIMO antenna system) is also demonstrated and its performances are acceptable for smartphone applications.
The use of multiple-input-multiple-output (MIMO) antenna systems will be required by next generation wireless systems to achieve their high throughput data transmissions. In this work, the authors present the design and fabrication of a 2 - 2 MIMO antenna system for the 700-MHz band of the long-term evolution (LTE) wireless standard. The MIMO antenna system is based on a novel 4-shaped antenna geometry that is compact in size and covers two bands of operation. The dual-band 2 - 2 MIMO antenna system covers the 734-790-MHz and the 2307-2475-MHz LTE and industrial, scientific and medical (ISM) bands. It occupies an FR-4 material substrate size of 58-110-1.56-mm3. The antenna has frequency tuning capabilities without changing the over all size of the MIMO system substrate. Several isolation enhancements methods were investigated, and the values of the correlation coefficient (|ρ|max) were within the LTE requirements. The maximum obtained gain for a single operating antenna at 770 and 2380 MHz was 5 and 4.5 dBi, respectively.
A simple and intuitive metric of multiplexing efficiency is proposed for evaluating the performance of multiple-input-multiple-output (MIMO) antennas in the spatial multiplexing mode of operation. Apart from gaining valuable insights into the impact of antenna efficiency, efficiency imbalance, and correlation on multiplexing performance, the metric is particularly useful for antenna engineers whose goal is to achieve the optimum antenna system design. Experimental results involving prototype mobile terminals highlight the effectiveness of our proposal.
A simple formulation to compute the envelope correlation of an antenna diversity system is derived. It is shown how to compute the envelope correlation from the S-parameter description of the antenna system. This approach has the advantage that it does not require the computation nor the measurement of the radiation pattern of the antenna system. It also offers the advantage of providing a clear understanding of the effects of mutual coupling and input match on the diversity performance of the antenna system.
MIMO systems are characterized by their maximum available capacity, which is reduced if there is correlation between the signals on different channels. The correlation is primarily caused by mutual coupling between the elements of the antenna arrays on both the receiving and transmitting sides. Similarly, diversity antennas can be characterized by a diversity gain that also is affected by mutual coupling between the antennas. We explain how such MIMO and diversity antennas with mutual coupling can be analyzed by classical embedded element patterns that can be computed by standard computer codes. In the MIMO example under investigation, the mutual coupling reduces both correlation, which increases the capacity, and radiation efficiency, which decreases it, and the combined effect is a net capacity reduction. We also explain how the radiation efficiency, diversity gain, correlation, and channel capacity can be measured in a reverberation chamber. The measurements show good agreement with simulations.
The presented paper proposes a theory for the optimization of multiple-input-multiple-output antenna performance by assessing feeding coefficients. Antenna clusters with multiple feeding ports are utilized, which brings additional degrees of freedom and improves the performance. This work considers fixed shape and matching networks. The method is based on quadratic programming and maximizes total efficiency constrained by channel correlation and channel power distribution. The formulation provided in the paper enables establishing trade-offs between all mentioned metrics. Evaluating the performance in this manner provides comprehensive information about the chosen geometry and port placement. Selected examples demonstrate how efficiency and channel correlation can be both in agreement but also in significant conflict. The effect of frequency dispersion on feeding is also investigated.
Optimal inverse design, including topology optimization and evaluation of fundamental bounds on performance, which was introduced in Part 1, is applied to various antenna design problems. A memetic scheme for topology optimization combines local and global techniques to accelerate convergence and maintain robustness. Method-of-moments matrices are used to evaluate objective functions and allow to determine fundamental bounds on performance. By applying the Shermann-Morrison-Woodbury identity, the repetitively performed structural update is inversion-free yet full-wave. The technique can easily be combined with additional features often required in practice,
e.g
., only a part of the structure is controllable, or evaluation of an objective function is required in a subdomain only. The memetic framework supports multi-frequency and multi-port optimization and offers many other advantages, such as an actual shape being known at every moment of the optimization. The performance of the method is assessed, including its convergence and computational cost.
A memetic framework for optimal inverse design is proposed by combining a local gradient-based procedure and a robust global scheme. The procedure is based on method-of-moments matrices and does not demand full inversion of a system matrix. Fundamental bounds are evaluated for all optimized metrics in the same manner, providing natural stopping criteria and quality measures for realized devices. Compared to density-based topology optimization, the proposed routine does not require filtering or thresholding. Compared to commonly used heuristics, the technique is significantly faster, still preserving a high level of versatility and robustness. This is a two-part paper in which the first part is devoted to the theoretical background and properties, and the second part applies the method to examples of varying complexity.
Optimal performance of antennas used in MIMO systems is addressed in this paper with optimality being expressed in terms of the power radiated which is subject to realistic, yet unknown, excitation and fixed, however arbitrarily complicated, matching. It is shown that if excitation is not specified, the optimality of a MIMO radiating system has to be understood differently as compared to the case of a specified excitation. Consequently, two important figures of merits – transducer and radiation efficiency figures – are adopted to measure the quality of the MIMO radiating systems. The communication is accompanied by examples illustrating the theoretical concepts.
We derive some general properties of generalized Rayleigh ratios, and use these properties to present a detailed theory of two efficiency metrics relevant to a specified excitation of a multiport antenna array (MAA) by a linear time-invariant (LTI) multiport generator. These efficiency metrics are the transducer efficiency and the radiation efficiency. To define the excitation and compute the transducer efficiency and the radiation efficiency, we consider six different variables. We then define and study four new efficiency metrics relevant to unspecified excitations: the minimum transducer efficiency, the transducer efficiency figure, the minimum radiation efficiency, and the radiation efficiency figure. We also look at their connection with the minimum power transfer ratio during emission and the power match figure. We discuss the relevance of the theory presented in this article to the design of an MAA, and to an actual configuration comprising a transmitter, the antenna outputs of which need not behave like an LTI multiport.
A numerically effective description of the total active reflection coefficient and realized gain are studied for multi-port antennas. Material losses are fully considered. The description is based on operators represented in an entire-domain port-mode basis, i.e., on matrices with favorably small dimensions. Optimal performance is investigated and conditions on optimal excitation and matching are derived. The solution to the combinatorial problem of optimal ports’ placement and optimal feeding synthesis is also accomplished. Four examples of various complexity are numerically studied, demonstrating the advantages of the proposed method. The final formulas can easily be implemented in existing electromagnetic simulators using integral equation solver.
This paper describes a low-profile
multi-input multi-output (MIMO) antenna system that is fully functional over the entire long-term evolution (LTE) spectrum 699–960 MHz (lower frequency spectrum) and 1710–2690 MHz (higher frequency spectrum) that is applicable to real-life metallic smartphone platforms. The presented methodology entails utilizing the longitudinal edges of the ground plane amid an extremely narrow ground clearance of 2 mm. The metallic frame of the smartphone is utilized along with a stub network to devise a reconfigurable coupled loop antenna topology. The proposed
MIMO antenna configuration is measured and confirmed to exhibit efficient envelope correlation coefficient (<0.5) and one of the highest radiation efficiencies to be reported in the literature across the entire LTE spectrum.
The upcoming standards of wireless communications result in additional and more stringent requirements for antennas in mobile phones. In this paper, we present a frequencyreconfigurable antenna that could potentially be suited for future mobile devices. Frequency reconfigurability is achieved through a cluster of mutually coupled antenna elements that is excited with frequency-dependent weights using a multichannel transceiver. We report a mobile handset antenna cluster measuring 15 × 15 × 1.6 mm
3
that covers the frequency bands of 1.7-2.7, 3.3-4.5, and 5.475-6.425 GHz with an antenna efficiency better than 90%. The operation of the antenna cluster is experimentally verified by feeding all the antenna elements with proper weights using tailor-made power splitters that represent a multichannel transceiver with adjustable amplitude and phase in each branch. The results obtained with the feed networks suggest the feasibility of the reconfigurability concept and pave way for codesign of the antenna and the transceiver.
Everything readers need to implement and support a wireless point-to-point communications environment In order to cope with the tremendous explosion of the telecommunications market, the field of wireless communications has greatly expanded in the past fifty years, especially in the domains of microwave radio systems including line-of-sight, satellites, and tropospheric-scatter. Now, Microwave Engineering: Land & Space Radio- communications answers the growing worldwide demand for an authoritative book on this important and emerging subject area. In five succinct chapters, the book introduces students and practicing engineers to the main propagation phenomena that are encountered and that must be considered in the design and planning for any given system type and frequency of operation: Electromagnetic wave propagation-An introduction to the fundamentaltheory of radiation and propagation of electromagnetic waves, polarization, antenna properties, free space attenuation, atmospheric refractivity, diffraction, reflection, multipath and scattering mechanisms, hydrometeor effects, and probability distributions Principles of digital communication systems-Modulation techniques, signal processing, error probability, spectral characteristics, spectrum efficiency, thermal noise, intermodulation, jamming, and interference Microwave line-of-sight systems-Path profile, flat fading and frequency-selective fading, interferometric method for space and frequency diversity techniques, International Standards and ITU Recommendations, optimization of the frequency-plan resource, link budget, quality, reliability, and availability Microwave transhorizon systems-Design of beyond-the-horizon communication systems, properties of scattering and diffraction modes, multipath statistical relations, long-term and short-term field strength variations, quality of service, optimization of antenna alignment, and experimental analysis of various diversity and combining methods Satellite communications-Design of satellite communications systems, orbital parameters, Earth-satellite geometry, uplink and downlink budgets for both space and Earth segments, and total system noise temperature Microwave Engineering: Land & Space Radiocommunications is suitable for engineers involved in wireless telecommunications, as well as for students and members of various seminars and workshops.
In this study, the authors present a systematic design method of a three-port multiple-input-multiple-output antenna system for small terminals, such as smart phones based on the selective excitation of orthogonal chassis modes. The underlying idea is based on the theory of characteristic modes (TCM). Selective excitation of these modes is realised by sets of nonresonant inductive coupling elements integrated at predefined positions into the printed circuit board (PCB) layout. Stripline feed networks also integrated within the multi-layer PCB layout care for a good impedance match to 50 O. The design method of this antenna system is a straight forward application of the TCM and is therefore of general interest for the design of small terminal antennas. Furthermore, owing to the electrically small couplers that require only limited area at the outer edge of the PCB the method represents an interesting solution with the clear potential to be extended to more ports. The realised prototype resembles the predicted performance very well and therefore proves the applicability of the proposed method.
In this letter, a disk-shaped ultra-compact three-port planar multiple-input–multiple-output (MIMO) antenna is proposed and fabricated. The antenna is designed for the 2.4-GHz WLAN band, the radius of which is only 16 mm (0.13lambda ). Three microstrip-fed T-shaped open-ended slots are used as radiating elements, whose edge-to-edge separation is only 0.006lambda. They are rotationally symmetric and generate directional patterns that aim at 0 , 120 , and 240 , respectively. The peak gain of these patterns is 2.3 dBi, and the pattern correlation coefficient is below 0.03, which provides good pattern diversity for an MIMO system. Meanwhile, the 3-dB beamwidth of these patterns is 105 , which can realize nearly full azimuth coverage with its three beams. By introducing a newly designed neutralization network, the isolation between elements reaches 24 dB at the resonant frequency. Moreover, the proposed antenna is manufactured on the FR-4 substrate, which is cost-effective and easy to be implemented in a size-limited MIMO application.
A compact dual-port, multiple input-multiple output (MIMO) antenna array for handheld devices is introduced. The antenna structure consists of two quarter wavelength monopole slots etched on the ground plane of a printed circuit board (PCB) and a meandered slot cut between them. The meandered slot not only reduces the coupling between the two slot antennas, but also improves the bandwidth and efficiency of the array by acting as a radiating parasitic element. Simulated and measured results show that the meandered isolating slot allows the antennas to achieve wider bandwidth, higher efficiency, higher isolation and better diversity performance, compared to other types of isolating slots.
Mutual coupling is an inevitable phenomenon in multiantenna systems, usually reducing the system performance. Numerous works have focused on the reduction of this effect. The aim is maintaining the mutual coupling suppressing structure as simple as possible while having a high amount of mutual coupling reduction. This letter presents a novel structure suppressing the mutual coupling between nearby patches. It is composed of only a simple U-shaped microstrip, which reduces the mutual coupling considerably. The structure has been constructed and tested. The measurement results prove the high efficiency of this configuration.
If N ports are defined on the moment method model of a radiating structure, so-called characteristic port modes may be computed, using the moment method operator matrix, with respect to these ports. This results in N port excitation vectors (each of length N ). Each vector excites a radiated field which is orthogonal to the fields excited by any of the other N excitation vectors. It is shown that this may be usefully employed in the design of antennas for multiple-input multiple-output (MIMO) communications, and that recent multimodal/multipolar approaches for MIMO antenna design may be interpreted in terms of such port modes.
A compact decoupling network for enhancing the port isolation between two closely spaced antennas is proposed in this paper. In the network, we first connect two transmission lines (TLs) individually to the input ports of two strongly coupled antennas. The length of the TLs is designed so that the trans-admittance between ports changes from a complex one at the antenna inputs to a pure imaginary one. A shunt reactive component is then attached in between the TL ends to cancel the resultant imaginary trans-admittance. Finally, a simple lumped-element circuit is added to each port for input impedance matching. The even-odd mode analysis is adopted to investigate the currents excited on the antennas for predicting the radiation pattern of the two-element antenna array. Two examples of printed antennas at 2.45 GHz are tackled by using the proposed decoupling structure. The measurement results agree quite well with the simulation ones. High antenna isolation and good input return loss are simultaneously achieved in both cases, which demonstrates the feasibility of the structure. The decoupled antenna array in each example radiates, as prediction, toward different but complementary directions when the input power is fed in turn to the two input ports. The array efficiency is estimated better than 75% in each example. This pattern diversity effect is helpful for reducing the channel correlation in a multiple-input multiple-output (MIMO) communication system.
From the Publisher:
"An IEEE reprinting of this classic 1968 edition, FIELD COMPUTATION BY MOMENT METHODS is the first book to explore the computation of electromagnetic fields by the most popular method for the numerical solution to electromagnetic field problems. It presents a unified approach to moment methods by employing the concepts of linear spaces and functional analysis. Written especially for those who have a minimal amount of experience in electromagnetic theory, this book illustrates theoretical and mathematical concepts to prepare all readers with the skills they need to apply the method of moments to new, engineering-related problems.Written especially for those who have a minimal amount of experience in electromagnetic theory, theoretical and mathematical concepts are illustrated by examples that prepare all readers with the skills they need to apply the method of moments to new, engineering-related problems."
In general, the beam patterns of a multiple-beam antenna system may overlap. The degree of overlap is usefully defined by a cross-correlation type of integral which includes phase factors as well as polar diagrams in the description of the beams. It is shown that when beam overlap exists, conservation of energy implies the unavoidable existence of cross couplings between the feed lines, and a related limitation on the radiation efficiency (or correspending receiving cross section) of any single beam. Quantitative relationships are derived describing these limitations, and examples given. The implied character of the scattering matrix, comprised of the array of cross-coupling factors, is also discussed with especial emphasis on lossless, reciprocal systems.
A relationship between the scattering parameters of a set of antennas and the correlation between the signals received by them is derived. This relationship is valid for an arbitrary number of ports and antenna elements under the assumption that the environment is completely uniform with respect to incidence angles and polarisation state.
The conditions for antenna diversity action are investigated. In terms of the fields, a condition is shown to be that the incident field and the far field of the diversity antenna should obey (or nearly obey) an orthogonality relationship. The role of mutual coupling is central, and it is different from that in a conventional array antenna. In terms of antenna parameters, a sufficient condition for diversity action for a certain class of high gain antennas at the mobile, which approximates most practical mobile antennas, is shown to be zero (or low) mutual resistance between elements. This is not the case at the base station, where the condition is necessary only. The mutual resistance condition offers a powerful design tool, and examples of new mobile diversity antennas are discussed along with some existing designs.
Microwave Engineering
Optimal inverse design based on memetic algorithms - part 1: Theory and implementation
- M Capek
- M Gustafsson
- L Jelinek
- P Kadlec