Low-Cost 3D-Printed Coupling-Fed Frequency Agile Fluidic Monopole Antenna System

A low-cost 3D-printed frequency agile fluidic monopole antenna system is demonstrated to respond to the increasing demand for reconfigurable antennas, which can operate in a dynamic environment, in this paper. Antennas that can be reconfigured for different operating frequencies, polarizations, or radiation patterns are attracting attention. Traditional reconfigurable antennas using a metallic radiating element with electronic switches are limited by their pre-defined physical geometries. As conductive fluid, either liquid metal or ionized fluid has no defined shape, so it is possible to create the desired shape of a fluidic antenna to support different wireless environments. The fabrication of the leakage-free containers for fluidic antennas needs special consideration, and stereo-lithography-based 3D-printing technology is a possible option to support the fabrication. Moreover, researchers will have higher design freedom and accuracy to create new container shapes for fluidic antennas. The fluidic monopole antenna proposed is coupling-fed by a ring geometry for separating the electrical and mechanical structures; such an approach enables individual optimization and minimizes mutual disturbances in the system. A parametric study of the proposed coupling-feed geometry and the experimental verification of the antenna prototypes have been performed. Reasonable frequency agility from 3.2 to 5 GHz has been demonstrated, and the peak efficiency is about 80%. A maximum gain of 3.8 dBi is obtained. The radiation patterns of the antenna are stable across the operating bandwidth. The proposed antenna could be useful for the applications in the recent 5G mid-bands operations

Beam-steering Surface Wave Fluid Antennas for MIMO Applications

This paper proposed to use surface wave fluid antennas to realize beam-steering functionality and spatial diversity for MIMO applications. By utilizing the advantage of the non-radiating feature of surface wave propagation, in contrast to the conventional multiple RF input ports approach reported, the proposed design only required one RF input to achieve the spatial diversity. The surface wave fluid antenna is designed to work in the millimeter-wave frequency band from 20 to 26.5 GHz. The preliminary results show that the radiation direction of the antenna can be controlled by changing the position of the fluid metal radiator

Reconfigurable Surface Wave Fluid Antenna for Spatial MIMO Applications

This paper presents the design of a surface wave fluid antenna which can realizes beamshaping and spatial diversity for MIMO applications. The proposed design only required one RF input to achieve spatial diversity when comparing to the conventional multiple RF input ports approaches. The surface wave fluid antenna is designed for the millimeter-wave 5G mobile communications band from 24 to 28 GHz. The simulation results show that the radiation direction of the antenna can be controlled by changing the position of the fluid metal radiator

Performance of Machine Learning Aided Fluid Antenna System with Improved Spatial Correlation Model

Fluid antenna has emerged as a new antenna technology that enables software-controllable position reconfigurability for great diversity and multiplexing benefits. The performance of fluid antenna systems has recently been studied for single and multiuser environments adopting a generalized spatial correlation model that accounts for the channel correlation between the ports of the fluid antenna. The recent work [1] further devised machine learning algorithms to select the best port of fluid antenna in a more practical setting in which only a small number of ports is observable in the selection process, and found that extraordinary outage probability performance can be obtained. However, there is a concern of how the spatial correlation parameters are set to reflect the actual correlation structure for accurately evaluating the system performance. In this paper, the method in [2] is used to set the correlation parameter so that the model can accurately characterize the correlation amongst the ports of a fluid antenna in a given space. This paper revisits the port selection problem for single-user fluid antenna system where learning-based algorithms are employed to select the best port when only a small subset of the channel ports are known. The new results demonstrate that the impact of spatial correlation on the performance becomes more pronounced but the machine learning aided fluid antenna system is still able to match the performance of maximum ratio combining (MRC) system with many uncorrelated antennas

Fluid Antenna Systems

Over the past decades, multiple antenna technologies have appeared in many different forms, most notably as multiple-input multiple-output (MIMO), to transform wireless communications for extraordinary diversity and multiplexing gains. The variety of technologies has been based on placing a number of antennas at fixed locations which dictates the fundamental limit on the achievable performance. By contrast, this paper envisages the scenario where the physical position of an antenna can be switched freely to one of the N positions over a fixed-length line space to pick up the strongest signal in the manner of traditional selection combining. We refer to this system as a fluid antenna system (FAS) for tremendous flexibility in its possible shape and position. The aim of this paper is to study the achievable performance of a single-antenna FAS system with a fixed length and N in arbitrarily correlated Rayleigh fading channels. Our contributions include exact and approximate closed-form expressions for the outage probability of FAS. We also derive an upper bound for the outage probability, from which it is shown that a single-antenna FAS given any arbitrarily small space can outperform an L-antenna maximum ratio combining (MRC) system if N is large enough. Our analysis also reveals the minimum required size of the FAS, and how large N is considered enough for the FAS to surpass MRC.Comment: 26 pages, 5 figure

Cost-Efficient Bi-Layer Modeling of Antenna Input Characteristics Using Gradient Kriging Surrogates

Publisher's version (útgefin grein)Over the recent years, surrogate modeling has been playing an increasing role in the design of antenna structures. The main incentive is to mitigate the issues related to high cost of electromagnetic (EM)-based procedures. Among the various techniques, approximation surrogates are the most popular ones due to their flexibility and easy access. Notwithstanding, data-driven modeling of antenna characteristics is associated with serious practical issues, the primary one being the curse of dimensionality, particularly troublesome due to typically high nonlinearity of antenna responses. This limits applicability of conventional surrogates to simple structures described by a few parameters within narrow ranges thereof, which is grossly insufficient from the point of view of design utility. Many of these issues can be alleviated by the recently proposed constrained modeling techniques that restrict the surrogate domain to regions containing high-quality designs with respect to the relevant performance figures, which are identified using the pre-optimized reference designs at an extra computational effort. This paper proposes a methodology based on gradient-enhanced kriging (GEK). It enables a considerable reduction of the number of reference points required to construct the inverse surrogate (employed in surrogate model definition) by incorporating the sensitivity data into the nested kriging framework. Using two antenna examples, it is demonstrated to yield significant savings in terms of the surrogate model setup cost as compared to both conventional modeling methods and the original nested kriging.The Icelandic Centre for Research (RANNIS) under Grant 206606051, in part by the National Science Centre of Poland under Grant 2017/27/B/ST7/00563, and in part by the Abu-Dhabi Department of Education and Knowledge (ADEK) Award for Research Excellence, in 2019, under Grant AARE19-245."Peer Reviewed

Fluid Antenna Multiple Access

Fluid antenna system represents an emerging technology that enables an antenna to switch its physical location in a predefined space. This paper explores the potential of using a single fluid antenna at each mobile user for multiple access, which we refer to it as fluid antenna multiple access (FAMA). FAMA exploits spatial moments of deep fade suffered by the interference to achieve a favourable channel condition for the desired signal, without requiring sophisticated signal processing. We analyze the FAMA network by first deriving the outage probability of the signal-to-interference ratio (SIR) in a double integral form. We then obtain an outage probability upper bound in closed form and an average outage rate lower bound for the FAMA system, with an arbitrary number of interferers, from which the multiplexing gain of FAMA is characterized. We also estimate how large the number of locations is required to achieve a given multiplexing gain using fluid antennas with a given size. Results show that it is possible for FAMA to support hundreds of users using only one fluid antenna of a few wavelengths of space at each user, giving rise to significant gain in the average network outage rate

MIMO Evolution Beyond 5G Through Reconfigurable Intelligent Surfaces and Fluid Antenna Systems

With massive deployment, multiple-input-multiple-output (MIMO) systems continue to take mobile communications to new heights, but the ever-increasing demands mean that there is a need to look beyond MIMO and pursue the next disruptive wireless technologies. Reconfigurable intelligent surface (RIS) is widely considered a key candidate technology block to provide the next generational leap. The first part of this article provides an updated overview of the conventional reflection-based RIS technology, which complements the existing literature to include active and semiactive RIS, and the synergies with cell-free massive MIMO (CF mMIMO). Then, we widen the scope to discuss the surface-wave-assisted RIS that represents a different design dimension in utilizing metasurface technologies. This goes beyond being a passive reflector and can use the surface as an intelligent propagation medium for superb radio propagation efficiency. The third part of this article turns the attention to the fluid antenna, a novel antenna technology that enables a diverse form of reconfigurability that can combine with RIS for ultrahigh capacity, power efficiency, and scalability. This article concludes with a discussion of the potential synergies that can be exploited between MIMO, RIS, and fluid antennas

Diversified Fluid Antenna Designs for Mobile Communications

In current mobile communications, massive MIMO is an essential technology, especially for mm-wave 5G and future 6G mobile systems. However, implementing MIMO antennas for such applications is challenging due to the physical limitations of mobile devices. To address this issue, this study proposes novel surface wave-based fluid antennas. The proposed antennas achieve radiation pattern reconfigurability with a compact design of 10 mm x 33 mm 5 mm at a frequency range of 24 to 30 GHz, which is small enough for portable equipment. These antennas use only one feeding port, simplifying the feeding mechanism compared to MIMO systems that may require multiple RF chains. The fluid channel can also be easily scaled for different shapes and sizes with the proposed surface wave launcher. The proposed fluid antennas were simulated, fabricated, assembled, and measured within UCL facilities. Results show that these antennas achieve radiation pattern diversity, with an average RPDR (radiation pattern dynamic range) of up to 10 dB in the targeted mm-wave 5G frequency bands from 24 to 30 GHz. Radiation pattern dynamic range is a new indicator used to evaluate the proposed fluid antennas' radiation pattern reconfigurability. The proposed antennas offer several notable contributions. Firstly, they demonstrate the successful development of fluid antennas with radiation pattern reconfigurability. Secondly, the antennas feature a relatively simple structure, utilizing a 3D-printed container and PCB board, which enables cost-effective manufacturing and makes the antennas accessible to a wider range of users. Thirdly, the proposed fluid antenna incorporates a fluid control system and a comprehensive measurement setup specifically tailored for fluid antennas. These additions enhance the overall viability and practicality of the antenna design. Lastly, the introduction of the RPDR indicator provides a valuable tool for analyzing the radiation pattern reconfigurability of similar antennas. This indicator facilitates performance comparisons and aids in the refinement of future antenna designs