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.

/pdf/satellite-communications-in-the-new-space-era-a-survey-and-13ge69opzh.pdf

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

Advances in reflectarrays and array lenses with electronic beam-forming capabilities are enabling a host of new possibilities for these high-performance, low-cost antenna architectures. This paper reviews enabling technologies and topologies of reconfigurable reflectarray and array lens designs, and surveys a range of experimental implementations and achievements that have been made in this area in recent years. The paper describes the fundamental design approaches employed in realizing reconfigurable designs, and explores advanced capabilities of these nascent architectures, such as multi-band operation, polarization manipulation, frequency agility, and amplification. Finally, the paper concludes by discussing future challenges and possibilities for these antennas.

Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review

The reflectarray has significant promise in applications requiring high-gain, low-profile reflectors. Recent advances in tuning technology have raised the possibility of realizing electronically tunable reflectarrays, which can dynamically adjust their radiation patterns. This paper presents an electronically tunable reflectarray based on elements tuned using varactor diodes. Modeling approaches based on an equivalent circuit representation and computational electromagnetics simulations are presented. Both techniques accurately predict the scattering characteristics of the unit cell as compared to experimental measurements. The development of a unit cell with over 320omicron of phase agility at 5.5 GHz is discussed. Finally, a 70-element electronically tunable reflectarray prototype operating at 5.8 GHz is presented. Radiation pattern measurements with the reflectarray demonstrate its dynamic beam-forming characteristics. Measurements of the gain of the reflectarray correlate well with theoretical expectations.

Modeling and Design of Electronically Tunable Reflectarrays

Surface scattering antennas provide adjustable radiation fields by adjustably coupling scattering elements along a wave-propagating structure. In some approaches, the scattering elements are patch elements. In some approaches, the scattering elements are made adjustable by disposing an electrically adjustable material, such as a liquid crystal, in proximity to the scattering elements. Methods and systems provide control and adjustment of surface scattering antennas for various applications.

Surface scattering antenna improvements

One embodiment describes a reflectarray antenna system. The system includes an antenna feed configured to at least one of transmit and receive a wireless signal occupying a frequency band. The system also includes a reflector comprising a reflectarray. The reflectarray includes a plurality of reflectarray elements, where each of the reflectarray elements includes a dipole element. The dipole element of at least a portion of the plurality of reflectarray elements comprises a crossed-dipole portion and a looped-dipole portion. The plurality of reflectarray elements can be configured to selectively phase-delay the wireless signal to provide the wireless signal as a coherent beam.

Reflectarray antenna system

Communication link and target ranges for satellite communications (SATCOM) and space-based sensors (e.g. radars) vary from approximately 400–1000 km for low earth orbits (LEO) to 35,800 km for geosynchronous orbits (GEO). At these long ranges, large antenna gains are required and most legacy systems use high gain reflectors with beams that are either fixed or mechanically steered. However, for some radio frequency (RF) sensor applications, mechanical beam scanning has inherent limitations.

/pdf/phased-array-fed-reflector-pafr-antenna-architectures-for-gkrdjj7aj1.pdf

Phased Array Fed Reflector (PAFR) antenna architectures for space-based sensors

A full-wave method of moments solution for infinite arrays of stripline-fed tapered slot antennas is described The formulation of the problem is sufficiently general to permit performance evaluation of most of the geometries that have been proposed for stripline-fed antennas as well as of several other types of array antennas Computed results for some well-known antenna arrays are presented to demonstrate the validity and accuracy of the method Excellent agreement with published results has been obtained for scattering from corrugated surfaces and grounded dielectric slabs and for the input impedance of dipole and monopole arrays Catastrophic effects such as scan blindness are accurately predicted A sample result showing the measured and computed input impedance of a stripline-fed tapered slot antenna array is also presented >

Moment method analysis of infinite stripline-fed tapered slot antenna arrays with a ground plane

The analysis of infinite arrays of printed dipoles on finite-height dielectric sheets is described. A full-wave solution is obtained by using a combination of the Green's function-moment method approach and mode matching techniques. Numerical calculations and experimental results validating the theory are shown for the air-dielectric case and for epsilon /sub r/ not=1. Scan blindnesses are identified in arrays with epsilon /sub r/ not=1. Pertinent numerical considerations and issues of convergence are discussed. >

Analysis of infinite arrays of printed dipoles on dielectric sheets perpendicular to a ground plane

The paper describes a novel dipole reflectarray element with variable reflection phase. The element is described and array waveguide simulator measurement data demonstrating its phase shifting properties is presented. The element was developed originally as a mechanism for antenna pattern tuning of a fixed-beam crossed-dipole reflectarray. However, it might also be applied, using small electric motors, to achieve electronic scanning or active beam reshaping. These potential applications are discussed briefly.

Novel reflectarray element with variable phase characteristics

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