Satellite, fifth generation (5G), and sixth generation (6G) mobile communication systems operating at micro- and millimeter wave frequencies are an essential pillar in advanced network architectures for high-throughput low latency services. The decisive factors for this current development were the significant technological advances accomplished over the last two decades, which meanwhile enable highly integrated, feature-rich, and cost-effective realizations of complete phased array transceiver topologies. Motivated through the today's trend for heterogeneous constellation types to provide truly global coverage, this contribution reviews the current state-of-the-art of electronically steerable antennas for terrestrial and non-terrestrial communication systems up to 100 GHz. First, the potential benefits and limitations of the most relevant technologies are contrasted and put into context with recent system architectures for adaptive beamforming. Their operating principles along with various experimental implementation and achievements providing advanced capabilities such as multi-band/multi-beam operation, polarization agility, and wide-angle scanning are thoroughly presented. Particular emphasis is laid on the review of direct radiating arrays, quasi-optical antenna configurations, and metasurface-based antennas.

The development of a circularly-polarized compact high-gain antenna to be used for the European Student Earth Orbiter small satellite mission is described. The antenna is realized stacking two coaxial shorted annular patches and placing the top one at half a wavelength from the lower one. At variance of other similar configurations proposed in the past, the one presented in this paper has several important features which can be extremely useful for application in the space environment. In particular, it can be easily fabricated employing suspended technology and its radiation characteristics are to some extent controllable by opportunely varying the geometry. In the following, a straightforward design procedure will be presented detailing the criteria to optimize top and bottom radiating elements. Both numerical and measured results will show that the proposed design satisfies the specifications and presents characteristics comparable to other larger and heavier solutions usually more difficult to design. Specifically, it will be shown that with this configuration it is possible to obtain gain values higher than 12 dB using ground plane of moderate size and that a further improvement up to 15dB can be obtained employing larger ground planes

A broadband and wide-angle scanning linear-to-circular polarization converter based on a dual-layer structure is presented. The elementary cell is composed of conventional Jerusalem Crosses (JC). The design procedure is based on transmission line circuit model and on full-wave simulations. The proposed equivalent circuit has been generalized to include the oblique incidence in the model. Simulated results demonstrate a 24% axial ratio bandwidth for an incidence angle θ=±50° in both x-z and y-z planes. The proposed converter provides a unique combination of wide bandwidth, thin profile, and stable response with respect to the angle of incidence. It can be integrated into any linearly polarized antenna system to generate circular polarization without significantly affecting the antenna performances.

A Polarization Rotator based on Substrate Integrated Waveguide (SIW) is proposed in this paper. The rotator is designed as a dual band, single layer, Frequency Selective Surface (FSS) that transmits a wave rotated of 90-degree with respect to the incident one in one of the two bands maintaining unchanged the polarization in the other one. Other than the design and characterization of the rotator, its application to a linear-to-circular dual band polarizer is also investigated. To this purpose, the rotator is coupled to a conventional meander line polarizer generating orthogonal circular polarizations (CP) in the two bands. This configuration is useful in SatCom applications where the required high isolation between TX and RX channels is obtained assigning orthogonal polarizations to the two bands. As a design example, a prototype is designed and experimentally validated in the SatCom K/Ka-bands. Measured performance shows an isolation between the TX and RX channels of more than 35 dB and insertion losses which do not exceed 1.5 dB in the two operating bands.

The demand for wireless communication in biomedical applications is increasing, thereby necessitating the development of reliable and efficient communication systems that can operate within the human body. This study introduces a novel dual-band two-port multiple-input multiple-output (MIMO) implantable antenna for deep tissue purposes with an overall size of 10.8 × 5.6 × 0.254 mm ³ = 15.3 mm ³ . The proposed MIMO antenna operates in the 915 and 2450 MHz industrial scientific medical bands with a measured bandwidth of 82.5, 148.5 MHz (port 1) and 130, 89 MHz (port 2), in addition peak realized gains of -32.15 and -22.2 dBi, respectively, are observed. High-measured port isolation (over 20 dB and 30 dB at 915 and 2450 MHz bands, respectively) was accomplished by means of meandered resonators. The determined specific absorption rate was within the safe limits. The MIMO performance factors, for instance, the envelope correlation coefficient and diversity gain, were also evaluated and determined to be in the acceptable range. According to our knowledge, this is the first dual-band implantable MIMO antenna developed for biomedical applications. The results from the simulations and measurements indicate that the developed antenna holds great promise for enabling effective communication within the human body for biomedical applications.

This paper presents the full-wave characterization of substrate integrated waveguide structures. Substrate integrated circuits are considered as an ensemble of conducting posts placed in a parallel-plate waveguide and are analyzed in terms of the cavities formed by the top and bottom conducting plates and by the walls of the metallic vias. The field inside the parallel-plate waveguide is computed by considering the dyadic Green's function expressed as an expansion in terms of vectorial cylindrical eigenfunctions and considering the scattering from the ensemble of conducting posts. Coaxial or waveguide ports are included in the analysis as equivalent magnetic current distributions. Self-admittance and mutual admittance are calculated in a form that separates the parallel-plate contribution from the field scattered by the posts. Results relevant to structures already presented in literature will be shown and compared with simulations obtained with one of the most used articles of commercial software. It will be shown that an excellent agreement with published results is achieved together with significant improvements both in computational time and memory requirements.