With the demanding system requirements for the fifth-generation (5G) wireless communications and the severe spectrum shortage at conventional cellular frequencies, multibeam antenna systems operating in the millimeter-wave frequency bands have attracted a lot of research interest and have been actively investigated. They represent the key antenna technology for supporting a high data transmission rate, an improved signal-to-interference-plus-noise ratio, an increased spectral and energy efficiency, and versatile beam shaping, thereby holding a great promise in serving as the critical infrastructure for enabling beamforming and massive multiple-input multiple-output (MIMO) that boost the 5G. This paper provides an overview of the existing multibeam antenna technologies which include the passive multibeam antennas (MBAs) based on quasi-optical components and beamforming circuits, multibeam phased-array antennas enabled by various phase-shifting methods, and digital MBAs with different system architectures. Specifically, their principles of operation, design, and implementation, as well as a number of illustrative application examples are reviewed. Finally, the suitability of these MBAs for the future 5G massive MIMO wireless systems as well as the associated challenges is discussed.

Multibeam Antenna Technologies for 5G Wireless Communications

Reconfigurable antennas, with the ability to radiate more than one pattern at different frequencies and polarizations, are necessary in modern telecommunication systems. The requirements for increased functionality (e.g., direction finding, beam steering, radar, control, and command) within a confined volume place a greater burden on today's transmitting and receiving systems. Reconfigurable antennas are a solution to this problem. This paper discusses the different reconfigurable components that can be used in an antenna to modify its structure and function. These reconfiguration techniques are either based on the integration of radio-frequency microelectromechanical systems (RF-MEMS), PIN diodes, varactors, photoconductive elements, or on the physical alteration of the antenna radiating structure, or on the use of smart materials such as ferrites and liquid crystals. Various activation mechanisms that can be used in each different reconfigurable implementation to achieve optimum performance are presented and discussed. Several examples of reconfigurable antennas for both terrestrial and space applications are highlighted, such as cognitive radio, multiple-input-multiple-output (MIMO) systems, and satellite communication.

Reconfigurable Antennas for Wireless and Space Applications

Satellite communications (SatComs) have recently entered a period of renewed interest motivated by technological advances and nurtured through private investment and ventures. The present survey aims at capturing the state of the art in SatComs, while highlighting the most promising open research topics. Firstly, the main innovation drivers are motivated, such as new constellation types, on-board processing capabilities, non-terrestrial networks and space-based data collection/processing. Secondly, the most promising applications are described, i.e., 5G integration, space communications, Earth observation, aeronautical and maritime tracking and communication. Subsequently, an in-depth literature review is provided across five axes: i) system aspects, ii) air interface, iii) medium access, iv) networking, v) testbeds & prototyping. Finally, a number of future challenges and the respective open research topics are described.

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Satellite Communications in the New Space Era: A Survey and Future Challenges

Communication is one of the most essential activities of mankind and there is no doubt that satellite communications have made a tremendous stride in this matter. The goal has been to create uninterrupted, seamless, high throughput connectivity no matter where. The fact that this is all possible is because of the existence of electromagnetic waves: Antennas play a pivotal role in advanced functionality, efficient usage of the bandwidth, and cost effective deployment of this technology. The trends of the technological development of antennas for a wide range of commercial satellite communication services and the challenges faced in their development are chronologically reviewed. Various antenna concepts are summarized and future challenges are projected. A rather comprehensive list of references is included to assist the reader with further reading beyond this paper.

Technology Trends and Challenges of Antennas for Satellite Communication Systems

Due to the dramatic increase in high data rate services and in order to meet the demands of the fifth-generation (5G) networks, researchers from both academia and industry are exploring advanced transmission techniques, new network architectures and new frequency spectrum such as the visible light spectra. Visible light communication (VLC) particularly is an emerging technology that has been introduced as a promising solution for 5G and beyond. Although VLC systems are more immune against interference and less susceptible to security vulnerabilities since light does not penetrate through walls, security issues arise naturally in VLC channels due to their open and broadcasting nature, compared to fiber-optic systems. In addition, since VLC is considered to be an enabling technology for 5G, and security is one of the 5G fundamental requirements, security issues should be carefully addressed and resolved in the VLC context. On the other hand, due to the success of physical layer security (PLS) in improving the security of radio-frequency (RF) wireless networks, extending such PLS techniques to VLC systems has been of great interest. Only two survey papers on security in VLC have been published in the literature. However, a comparative and unified survey on PLS for VLC from information theoretic and signal processing point of views is still missing. This paper covers almost all aspects of PLS for VLC, including different channel models, input distributions, network configurations, precoding/signaling strategies, and secrecy capacity and information rates. Furthermore, we propose a number of timely and open research directions for PLS-VLC systems, including the application of measurement-based indoor and outdoor channel models, incorporating user mobility and device orientation into the channel model, and combining VLC and RF systems to realize the potential of such technologies.

Physical Layer Security for Visible Light Communication Systems: A Survey

This paper addresses some of the recent developments at LMCSS in the area of multiple beam and reconfigurable beam antennas for communication satellite payloads. These advancements include (a) multiple aperture dual-band reflector antennas, (b) high efficiency horns covering 50% bandwidth, (c) a novel ?stepped-reflector antenna? (SRA) technology, and (d) reconfigurable beam antennas for HIEO and GEO satellites. It is shown that by combining the reflector improvements through the use of SRA with the feed improvements through the use of dual-band high efficiency horns (DBHEH), significant improvements in EIRP, G/T, and co-polar isolation (C/I) can be achieved. The SRA system produces ?flat-top? radiation patterns for receive beams and highly efficient Gaussian patterns for transmit beams over a geographic coverage as seen by the satellite. The DBHEH designs employ ?slope-discontinuities? to generate desired higher order modes over both transmit and receive bands. By employing a ?frequency-dependant? horn design for the DBHEH, it is shown that the step size can be significantly reduced and can be easily blended into the reflector surface for ease of fabrication. Detailed design of a K/Ka band MBA with about 68 spot beams is presented. The RF performance of this novel MBA has been evaluated and shows significant improvements in EIRP, G/T, and C/I in comparison with a conventional MBA. Comparison results of the advanced MBA with conventional MBA are presented in the paper. Design examples for both FSS and DBS satellites are discussed. A novel reconfigurable antenna suitable for HIEO and GEO satellites has been developed at LMCSS. It employs a non-focused reflector (NFR) antenna using a shaped mesh-reflector, and a small active feed array located in the focal-plane of the NFR in order to continuously reconfigure the beam(s), as the satellite goes through the HIEO orbit. The NFR approach has the advantages of reducing the number of feed array elements significantly while achieving the desired beam flexibility. Feed technology advancement for FSS and BSS satellites that includes high efficiency horns, trifurcated horns, feed networks, and trends in high power TVAC testing are briefly discussed.

Advanced antenna technologies for satellite communication payloads

This paper presents a novel antenna system that employs a "non- focused reflector" (NFR) to reconfigure the beams of communications payloads of HIEO (highly inclined elliptical orbit) and GEO (geo-stationary) satellites. The key advantages of the NFR are that it minimizes the number of feed array elements for a given coverage, has better scan performance, and has reduced complexity. Design examples for both HlEO and GEO satellites are shown indicating that the beams are fully reconfigurable on-orbit using the NFR with a small active array feed.

Reconfigurable antenna system for satellite communications

This paper presents an advanced dual-band antenna system suitable for broadband satellites that is capable of providing higher EIRP, higher G/T, and improved copolar isolation among frequency reuse beams The antenna system employs a hybrid-cell frequency reuse scheme instead of conventional fixed cell reuse (4-cell or 7-cell) in order to efficiently use spectrum based on traffic demands It is shown that the advanced antenna employing high-efficiency horns and shaped reflectors provide about 10 dB EIRP improvement, 20 dB G/T improvement, and 30 dB improvement in C/I when compared to conventional antennas

Dual-Band Multiple Beam Antenna System Using Hybrid-Cell Reuse Scheme for Non-Uniform Satellite Communications Traffic

This paper presents a novel "Stepped-Reflector Antenna" (SRA) suitable for multiple beam dual-band satellite communications. The SRA generates "flat-top" receive beams and highly efficient transmit beams over a geographic coverage region as seen by the satellite. It combines the reflector improvements through the use of stepped-regions with the feed horn advancements through the use of dual-band high efficiency horns (DBHEH) [1,2] in order to realize an efficient multiple beam antenna (MBA) system supporting both uplink and downlink frequencies simultaneously. It is shown that the SRA provides a congruent set of spot beams at both frequency bands with the benefits of significantly improved edge-of-coverage (EOC) gain, improved copolar isolation (C/I) among re-use beams, receive beam patterns that are less sensitive to pointing errors, and reduced number of reflector antennas when compared to conventional MBAs.

Minh Tang

Papers

Advanced antenna technologies for satellite communication payloads

Reconfigurable antenna system for satellite communications

Dual-Band Multiple Beam Antenna System Using Hybrid-Cell Reuse Scheme for Non-Uniform Satellite Communications Traffic

Stepped-Reflector Antenna for Dual-Band Satellite Communications Payloads

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