Francesco Alessio Dicandia

A mechanically reconfigurable transmitarray (TA) to support point-to-multipoint (PtM) communications via simultaneous dual-beam radiation is presented. The architecture employs two independently rotating flat dielectric TAs whose transmitting element permittivity values are rigorously synthesized to transform the feeder spherical wavefront into concurrent multiple beams, thereby enabling simultaneous dual-beam scanning in both elevation and azimuth. The numerical analysis and full-wave simulations demonstrate that the proposed design strategy can achieve a maximum dual-beam elevation scan of 55° with a 3 dB dual-beam gain bandwidth larger than 18%. A prototype comprising two flat dielectric TAs operating at 35 GHz and producing a mechanically scanned dual-beam has been manufactured using an additive manufacturing process. The measurements are in good agreement with the expected outcomes and confirm the effectiveness of the proposed synthesis strategy.

An innovative synthesis approach for realizing a single-feed simultaneous multibeam transmitarray (SMBTA) based on fully-dielectric unit cells is presented. The proposed methodology provides independent control of both amplitude and phase of the transmitted electromagnetic field by a proper tailoring of each dielectric unit cell response, representing a novel tapering method different from those based on lossy materials, multilayer metallic architectures or involving active components. In fact, the proposed design strategy exploits the different degree of reflection from each dielectric unit cell to obtain both the required amplitude and phase profile. Different SMBTA examples are provided to validate the adopted synthesis whereas a dual beam dielectric transmitarray is designed, fabricated and measured to assess the reliability of the design flow.

A synergic cooperation between terrestrial and non-terrestrial networks is a pivotal feature for achieving global wireless coverage. In this framework, the satellite swarm-based massive array represents one of the most promising key enabling technologies in coping with the ever-increasing system requirements for beyond 5G (B5G) and 6G systems. In this paper, a novel strategy for the synthesis of satellite massive arrays with reconfigurable antenna units (SMART-U) is presented. The radiative performance of the proposed configuration are analysed for low-earth and geostationary orbiting satellites and assess a remarkable robustness and flexibility of the new synthesis architecture. A remarkable scanning range improvement and peak side lobe level (PSLL) lowering of the addressed concentric ring array (CRA) is achieved by exploiting a multiobjective optimization based on the Pareto front. The proposed SMART-U phased array can efficiently cope with adverse satellite attitudes by tailoring the circularly polarized (CP) field radiated by each unit offering a clear advantage with respect to conventional swarm-based arrays with a static antenna element factor.

A novel design strategy for improving the radiative performance of simultaneous multibeam (SMB) phased arrays is addressed. The proposed scheme relies on the adoption of mixed and multiple antenna element factors with a dynamic selection of their radiation patterns whose choice depends on the desired SMB pointing directions. In addition, a Penrose-inspired clustering technique is also employed for reducing the array feed points. Compared with traditional phased arrays based on a single antenna element factor, the novel array architecture allows the scan angle range to be widened by improving the minimum array gain as well as reducing the peak side lobe level (PSLL). The superior radiative performance of the proposed approach with respect to the clustered phased arrays with a single-mode element factor is assessed in SMB scenarios comprising two and three main lobe peaks. The notable SMB radiative improvement has been also confirmed from a statistical point of view by considering up to four and five concurrent main lobes. The remarkable radiative improvements confirm the effectiveness of the proposed solution, which also represents an appealing candidate for its exploitation in multiuser and multibeam communications.

A novel design methodology for improving the radiative performance of single-feed simultaneous multibeam transmitarrays (SMBTAs) is presented. Concurrent multibeam scanning is achieved by a linear displacement of the feeder along a line parallel to the TA surface. The proposed synthesis of the passive TA phase distribution relies on an analytical multifocal scheme exploiting the minimum mean square error algorithm. A thorough numerical investigation that examines different TA sizes proves the benefits offered by the investigated strategy. Remarkable performance enhancement in terms of scan loss and peak side lobe level (PSLL) are achieved with respect to the conventional single focus phase correction approach. Furthermore, a detailed statistical analysis verifies the robustness of the adopted solution. Finally, two dielectric-based TAs radiating a simultaneous dual-main beam at 28 GHz are manufactured and tested to assess the reliability of the proposed methodology.

A novel strategy for the design and optimization of large-scan phased arrays is proposed. Active electronically beam-scanning antennas offer an unparalleled set of degrees of freedom, but they can be expensive, require complex radiofrequency frontends, a suitable thermal management and generally undergo a loss in directivity due to the pattern shape of the unit radiating element. A solution to these problems can be offered by an approach that reduces the number of transmit/receive modules (TRMs) and phase shifters (PSs) by a simple and fast clustering strategy based on Penrose tessellation that operates on the regular lattice of the radiating elements. More importantly, the proposed scheme adopts a mixed-mode element factor that proves to be effective in guaranteeing a remarkable scan efficiency and robustness with respect to array elements failures. The optimization process aims to maximize the minimum gain along the main beam during the scan as well as minimizing the peak sidelobe level (PSLL), while reducing the number of TRMs.

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 novel design strategy for realizing a transmission-type polarization rotator of linearly polarized (LP) plane waves by exploiting the characteristic modes 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 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 a good agreement with simulations, confirming the reliability of the proposed theoretical study.