Broadband communication satellites in Ka-band commonly use four reflector antennas to generate a multispot coverage. In this paper, four different multibeam antenna farms are proposed to generate the complete multispot coverage using only two multibeam reflectarrays, making it possible to halve the number of required antennas onboard the satellite. The proposed solutions include flat and curved reflectarrays with single or dual band operation, the operating principles of which have been experimentally validated. The designed multibeam reflectarrays for each antenna farm have been analyzed to evaluate their agreement with the antenna requirements for real satellite scenarios in Ka-band. The results show that the proposed configurations have the potential to reduce the number of antennas and feed-chains onboard the satellite, from four reflectors to two reflectarrays, enabling a significant reduction in cost, mass, and volume of the payload, which provides a considerable benefit for satellite operators.

This article presents a physical optics-based simulator for the analysis of terahertz (THz) imaging systems. The simulation starts by calculating the electromagnetic interactions inside the multireflector system and the incident field that the focusing system creates on the target under inspection. In a second step, the electric field that the modeled target scatters back to the system receiver, is also calculated. This allows to predict the imaging behavior of the system for different targets before manufacturing. The simulator results are validated by using measurements from an existing 300-GHz standoffimaging system. This contribution aims to help in the development of better imaging systems for security applications in the near future.

This study introduces an innovative optimization method to identify the optimal configuration of a sparse symmetric 2D array for applications in security, particularly multistatic imaging. Utilizing genetic algorithms (GAs) in a sophisticated optimization process, the research focuses on achieving the most favorable antenna distribution while mitigating the common issue of secondary lobes in sparse arrays. The main objective is to determine the ideal configuration from specific design parameters, including hardware specifications such as number of radiating elements, minimum spacing, operating frequency range, and image separation distance. The study employed a cost function based on the the point spread function (PSF), the system response to a point source, with the goal of minimizing the secondary lobe levels and maximizing their separation from the main lobe. Advanced simulation algorithms based on physical optics (PO) were used to validate the presented methodology and results.

Recent advances in millimeter-wave multiple-input multiple-output (MIMO) radar architectures have enabled security screening systems capable of detecting concealed threats, including nonmetallic hazardous objects. However, these systems often face challenges related to the distribution of high-frequency signals and bulky external antennas, increasing the complexity and cost of the system. In this work, we present a D-band MIMO radar where high-frequency signals are generated locally at each element of the array. The proposed design leverages commercially available monolithic microwave integrated circuits (MMICs) with on-chip antennas, ensuring a compact and scalable solution. By integrating a horizontal 1-D MIMO array with a mechanical aperture, our system achieves 3-D imaging with subcentimeter cross-range resolution at distances below 3 m.

This paper presents a novel approach to synthesizing curved reflectarrays using Geometrical Optics (GO). It introduces the concepts of virtual normal and path length shift, which enable a vector-based formulation of the problem that can be solved using ray tracing techniques. The formulation is applied for the design of two different versions of a Dual Bifocal Reflectarray with a parabolic main surface and a flat subreflectarray. The first version aims to enhance the performance of the multibeam antenna by providing a focal ring located at the feed cluster plane. The second version focuses on improving the scanning characteristics of the antenna in the horizontal plane by incorporating two foci. The synthesis procedure yields samples of the path length shift or its derivatives. To reconstruct the phase distribution, an interpolation scheme is employed and described in this paper. Numerical results are presented for both the focal-ring and two-foci configurations, demonstrating the feasibility of this solution for multibeam or scanning satellite antennas operating in the Ka.