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

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

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

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

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

Exploitation of Triangular Lattice Arrays for Improved Spectral Efficiency in Massive MIMO 5G Systems

A thorough analysis of the performance of planar arrays with a regular periodic lattice is carried out and applied to massive multiple-input-multiple-output (MIMO) systems operating within 5G NR n257 and n258 frequency band. It is shown that, among different arrangements with uniform spacing, a triangular lattice guarantees the reduction of the Average Side Lobe Level (ASLL), a better angular scan resolution of the main beam within a predefined angular sector and a lower mutual coupling level among elements. Moreover, single beam and multibeam application scenarios are considered for the performance comparison and both cases assess the remarkable features offered by a triangular arrangement. Particular attention is paid to illustrate, for different propagation channel scenarios, the effects of the array lattice on overall system performance including average gain as well as Signal-to-Interference plus Noise Ratio (SINR) and Sum Spectral Efficiency (SSE). The obtained results prove that a regular and periodic triangular lattice is appealing for arrays to be adopted in massive MIMO 5G systems

Negative capacitor for electrically small antennas

Electrically small antennas (ESAs) are more and more necessary in a lot of communication system where available space is limited. This includes commercial mobile wireless antennas, military handheld, body-wearable radios and aircraft antennas. However, because of their compact size, ESAs are generally not efficient radiators and they have narrow bandwidths, as expressed by the fundamental limit individuated by Wheeler, Chu and Harrington. In other words, the input impedance of ESA is characterized by a high reactive part Xa and a small radiation resistance Rr; for this reason, there is a strong mismatch between the antenna and transmission line which it is connected. In transmit application, most of the incident power is reflected by the antenna with a decrease the radiated power that forces the transceiver to increase the power in order to compensate the reduction. This leads to an increase of the power consumption, lower battery life and transmission quality deterioration. Instead, in receive application; this impedance mismatch leads in poor signal-to-noise ratio (SNR). For this reason it is necessary add an external matching network to increase the power transfer between the generator and antenna in both transmit and receive application. However, if we use a passive matching network (also known as Foster circuits), the achievable matching bandwidth is limited by another fundamental gain-bandwidth limitation derived by Bode and Fano. A possible way to overcome the fundamental gain-bandwidth limit is the use of active components in the antenna or in the matching network. On this basis, the employment of non-Foster circuits (NFCs) in the matching network of antennas has been proposed in order to achieve a broadband ESA for high-data-rate applications. These NFCs do not follow Foster's reactance theorem, indeed it provide a negative slope reactance X versus frequency f (dX/df<0). This property, on the Smith chart, is transformed in a counterclockwise motion of the reflection coefficient Γ and the phase increases with the frequency. Negative capacitor and negative inductor are example of non-Foster elements. These NFCs can be implemented by used of 2-port active circuit, called negative impedance converter (NIC) or negative impedance inverter (NII), that contain a feedback circuits that convert a passive capacitor or inductor to a negative capacitor or inductor. In general, the input impedance can be scaled by a k factor as well. In recent years, some published paper, used this NFCs to broaden the bandwidth of parasitic arrays or enhance the bandwidth of artificial magnetic conductors (AMCs). Moreover, when transmission line are periodically loaded with negative capacitor or inductor, fast low-dispersion transmission lines can be obtained; afterwards these fast transmission lines have been suggested for squint-free broadband leaky-wave antenna application. Although NFCs can be very useful, there are many issues involved in the design of these circuits, such stability, losses and linearity. At first it was designed a variable negative capacitor with a Linvill's open circuit stable (OCS) NIC to match the model of electrically small printed monopole antenna (single capacitor). Moreover, several prototypes with different sizes have been designed and investigated. The topology of these circuits comprises two back to back n-p-n bipolar-junction transistors (BJTs), a variable capacitor CL connected between two collectors with the base of one transistor connected to the collector of the other one (feedback circuits). The evaluation of the linearity and the level of the distortion introduced by the active matching network is currently under study

Characteristic Mode Analysis for the Design of Nanosatellite Reconfigurable Antennas

A novel S-band antenna concept hosted on a 1U form factor CubeSat platform is designed by exploiting the Characteristic Modes Theory (CMT). The innovative strategy provides useful design guidelines to transform the external platform into an efficient radiator by stimulating an optimal current distribution on its conductive surface. The effect of the satellite platform on the radiated performances (efficiency, band, gain) is intrinsically taken into account and profitably exploited to realize an efficient radiation system. The minimally invasive radiators, strategically collocated on the platform thanks the CMT, allow achieving a great saving of space and an optimal modal current excitation able to provide excellent radiation performance

Spectral efficiency improvement of 5G massive MIMO systems for high-altitude platform stations by using triangular lattice arrays

The beneficial effects of adopting a triangular lattice on phased arrays with regular and periodic grids for high-altitude platform station (HAPS) systems are presented in the scenario of massive MIMO communications operating within the 5G NR n257 and n258 frequency bands. Assessment of a planar array with 64 elements (8 × 8) is provided for both a triangular lattice and a square one in terms of array gain, average sidelobe level (ASLL), and mutual coupling. Particular attention is devoted to illustrating the impact of the antenna array lattice at the system level by evaluating its significant merits, such as its spectral efficiency (SE) and signal-to-interference ratio (SIR). The better performance exhibited by the triangular lattice array in comparison to the square one makes it appealing for the 5G massive MIMO paradigm

Smart Antennas Mounted on Complex Platforms by Using Phase-Shifted Characteristic Modes

A preliminary investigation of the modal excitation purity effect on a three dimensional platform is presented. A novel Balanced Inductive Exciter (BIE)is proposed for improving the modal excitation in the considered scenario. The Modal Weighing Coefficient (MWC)and radiated power (P r ) have been accurately investigated in order to assess the performance of the new exciters when compared to previously adopted solutions