Space-Air-Ground Integrated 6G Wireless Communication Networks: A Review of Antenna Technologies and Application Scenarios

A review of technological solutions and advances in the framework of a Vertical Heterogeneous Network (VHetNet) integrating satellite, airborne and terrestrial networks is presented. The disruptive features and challenges offered by a fruitful cooperation among these segments within a ubiquitous and seamless wireless connectivity are described. The available technologies and the key research directions for achieving global wireless coverage by considering all these layers are thoroughly discussed. Emphasis is placed on the available antenna systems in satellite, airborne and ground layers by highlighting strengths and weakness and by providing some interesting trends in research. A summary of the most suitable applicative scenarios for future 6G wireless communications are finally illustrated

Linear-to-Circular Polarization Transmission Converter Exploiting Meandered Metallic Slots

A novel wideband linear-to-circular polarization transmission converter composed by a cascade of two identical fully-metallic Frequency Selective Surfaces (FSSs) separated by an air gap is presented. The adoption of meandered slots patterned on a metallic layer, along with an interwoven FSS unit cell geometry, allows achieving up to 25 % of 3 dB Axial Ratio (AR) bandwidth for a normally impinging plane wave. Moreover, by exploiting the FSS unit cell compactness, the converter provides a prominent robustness to oblique incidence, and it is therefore suitable to be employed in radomes and dichroics. As a proof of concept, a prototype of the proposed converter is manufactured and tested for assessing the design approach

Compact Reconfigurable Antenna for Nanosatellites

A novel compact S-band antenna concept hosted on a 1U form factor CubeSat platform is presented. Non-resonant radiators are designed to exploit the resonant current modes excitable on the platform. The effect of the satellite platform on the radiated performances (efficiency, band, gain) is intrinsically taken into account by the proposed design approach. A great saving of space and weight is achieved and the robustness of the solution to different platform setup is verified. Measurements assess the achievement of the expected radiation performance

Design of a Transmission-Type Polarization-Insensitive and Angularly Stable Polarization Rotator by Using Characteristic Modes Theory

A novel design strategy for realizing a transmission-type polarization rotator of linearly polarized (LP) plane waves by exploiting the characteristic modes (CMs) theory is described. Design guidelines for the excitation of two current modes on a frequency selective surface (FSS), both exhibiting a circularly polarized (CP) radiated field, are provided to obtain the polarization rotation. The proposed converter exhibits remarkable performance also in the case of oblique incidence and a polarization-insensitive response thanks to the FSS unit cell compactness along with its fourfold rotational symmetry. Specifically, it provides a 3 dB cross-polar transmission percentage bandwidth up to 16.5% with a minimum insertion loss (IL) of 0.1 dB for a normally impinging plane wave whereas in case of an incidence angle of 60° the 3 dB cross-polar transmission percentage bandwidth turns out to be around 14% with a minimum IL of 0.7 dB. Measurements on a realized prototype are in good agreement with simulations, confirming the reliability of the proposed theoretical study

Low Profile 3-D Printed Transmitarray for Future 6G Wireless Communications

A preliminary investigation of the possibility to exploit three-dimensional (3D) printing technology for the fabrication of a transmitarray (TA) is addressed. More in detail, both dielectric and metallic unit cells are designed with the purpose of providing a non-uniform phase profile of the TA panel to collimate the main beam at broadside direction (θ=0°)

Characteristic Modes Analysis for Circularly Polarized 1-Bit Dual-Layer Transmitarray Design

A novel approach for designing a circularly polarized (CP) transmitarray (TA) by resorting to the characteristic modes analysis (CMA) is presented. Two miniaturized dual-layer polarization-insensitive unit cells are tailored to provide the two copolar transmission coefficient phase states that act as a 1-bit spatial phase shifter in the TA. The exploitation of a pair of characteristic modes (CMs), radiating either right-handed CP (RHCP) or left-handed CP (LHCP) scattered field, is at the basis of the TA operation. The TA provides a forward CP scattered field ensuring a low copolar insertion loss (IL) as well as a copolar transmission phase difference of 0° or 180°. To validate the proposed CMA-inspired theoretical study, a CP 1-bit TA has been designed, simulated, fabricated and tested. Measurements assess a good agreement with simulations, showing a maximum TA gain of 21.8 dBic with a remarkable 3 dB gain bandwidth of 15.22% (7.77 GHz -9.05 GHz), a peak aperture efficiency of 28.5% and a very low profile

A Compact CubeSat Antenna with Beamsteering Capability and Polarization Agility: Characteristic Modes Theory for Breakthrough Antenna Design

In this article, we propose a novel compact radiating system for a 1 U CubeSat. The designed antenna benefits from characteristic modes theory (CMT), which provides guidelines to advantageously exploit the hosting platform as part of the radiating system. The effect of the small satellite on the resonance frequency and pattern shape is therefore intrinsically taken into account. The employed inductive-coupling exciters are nonresonant half-loops that offer a huge saving in terms of space and weight requests. Additionally, the proposed S-band antenna provides the remarkable feature of scan-beam capability, in circular polarization (CP) as well as linear polarization (LP), which is not found in any other compact radiator. The overall angular coverage spans more than 90° with an axial ratio (AR) lower than 3 dB and within the half-power beamwidth (HPBW), and therefore a 360° angular coverage is guaranteed if four of these minimally invasive radiators are placed on the small satellite. Measurements are in positive agreement with simulations and confirm the estimated good performance of this innovative solution

Characteristic Mode Analysis for the Design of Metasurface-Based Space Antennas

A novel metasurface is proposed as a superstrate for the design of circularly polarized antennas. A square loop is considered as the unit cell of the metasurface that has to be excited by a linearly polarized source. The use of stubs is investigated toward the excitation of orthogonal radiated fields with the necessary 90-degree phase shift without resorting to a different periodicity of the employed metasurface

Low Profile Dual Linearly Polarized 1-bit Transmitarray Exploiting Two Metallic Layers

A novel azimuth-independent dual linearly polarized (LP) transmitarray (TA) based on a polarization rotator is presented. The exploitation of either right-handed circularly polarized (RHCP) or left-handed CP (LHCP) scattered field is at the basis of the proposed TA. The employed unit cell guarantees a low insertion loss as well as a crosspolar transmission phase difference of 0 or 180. The TA unit cell response is insensitive to any angular rotation of the panel, or the primary feed, along . The conceived dualpolarized 1-bit TA allows achieving up to 16.5 % of 3 dB gain bandwidth (BW3dB) with a maximum gain around 22 dBi and a peak aperture efficiency of 30.4 %. Unlike the previously reported dual-polarized TAs, this novel structure consists of a very thin dielectric layer, namely 0.08 0 at central frequency, comprising only two metallic layers making it a cost-effective solution as well as compliant with the increasingly strict profile requirements imposed by many of the future terrestrial and non-terrestrial wireless communication paradigms such as vehicular communications or SatCom systems. As a proof of concept, a prototype of the proposed dual-polarized 1-bit TA is manufactured and tested for assessing the benefits of this design approach

Improving the Spectral Efficiency of Array for 5G Massive MIMO by Exploiting a Triangular Lattice

The benefits of exploiting a triangular-lattice arrays employed in massive MIMO systems is addressed. Performance comparison with respect to a square lattice planar array has been carried out within 5G NR n257 and n258 frequency band. Particular attention is paid to illustrate the effect of the array lattice at the system level by evaluating significant figure of merits such as the Sum Spectral Efficiency (SSE), Signal to Interference Ratio (SIR) and array gain. The observed advantages offered by the triangular arrangement of antenna elements in terms of improved gain and SSE as well as the thermal aspect make it appealing for massive MIMO 5G applications