Min Zhou

This paper presents the design, manufacturing, testing, and validation of the MASKARA (Multiple Apertures for high-resolution SAR based on Ka-band Reflectarray) Breadboard Model (BBM), a large Ka-band reflectarray antenna developed for Synthetic Aperture Radar (SAR) applications. The BBM features a dual-offset antenna configuration intended for a high-resolution, wide-swath SAR instrument. At the core of the system is a 1.5 m × 0.55 m reflectarray operating between 35.5–36.0 GHz in the Ka-band. To our knowledge, this is the first demonstration of a reflectarray antenna designed to support two distinct modes of operation, exploiting the inherent advantages of reflectarrays—such as reduced cost and compact stowage—over traditional solutions. The antenna provides a high-resolution mode requiring a higher-gain beam in one polarization and a low-resolution mode covering a larger swath with broader beam coverage in the orthogonal polarization. The design process follows a holistic, multidisciplinary approach, integrating RF and thermomechanical considerations through iterative and concurrent design reviews. The BBM has been successfully manufactured and experimentally tested, and the measurement results show good agreement with simulations, confirming the validity of the proposed concept and demonstrating its potential for future high-performance SAR missions.

An antenna solution for broadband communication satellite applications is presented. The proposed antenna design provides a full dual-band (Tx/Rx) four-color multibeam coverage of Europe in K/Ka-band while utilizing only a single main reflector aperture, of interest for smaller platforms and secondary payloads. The antenna system consists of an offset Cassegrain antenna combining two multiple-feed-per-beam feed clusters and a doubly curved modulated frequency selective surface (FSS) sub-reflector, which is the key enabling technology validated in this work. By utilizing a modulated FSS design the antenna system fulfils all RF requirements that were specified on the antenna coverage parameters. An engineering model of the doubly curved FSS sub-reflector has been designed and fabricated. Its RF performance was characterized experimentally, and good agreement has been observed between simulations and measurements, thus validating the proposed concept.

The Higher-Order Array Decomposition Method (HO-ADM) is extended to handle fully populated or thinned finite array antennas and scatterers which can be modeled as arrays with connected elements lying on a regular lattice. The Discontinuous Galerkin Method (DGM) is employed to retain the multi-level block-Toeplitz Method of Moments (MoM) matrix structure even for connected elements. Moreover, by zeroing a selected subset of unknowns in the iterative solution process, thinned arrays can be handled as well. The presented method yields more than an order of magnitude shorter solution times for both a 32×32-element square- and a 793-element circular-thinned array with a memory consumption comparable to existing fast methods such as MLFMM.

The design, manufacturing, and testing of a 0.65-meters doubly curved polarization selective reflectarray for dual-band multiple spot beam communication satellites in Kaband is presented. The configuration is based on a single-offset reflectarray consisting of rotated split hexagonal-loop dipole elements printed on a single-layer substrate. For RHCP, the reflectarray scans the reflected beam half a beamwidth in one direction, and for LHCP, the reflectarray scans the reflected beam half a beamwidth in the opposite direction. This is achieved in both Tx (17.7-20.2 GHz) and Rx (27.5-29.3 GHz) frequency bands. Using a feeding array with 22 feeds, 41 beams over the Earth can be generated, permitting to cover the entire Earth coverage from a geostationary satellite employing the 4-color frequency/polarization re-use scheme using only two reflectarrays while maintaining single-feed-per-beam operation. The reflectarray has been manufactured and measured, and an excellent agreement between simulated and measured patterns is obtained, thus validating the proposed concept.

We present recent advances in the RF modeling of electrically large antennas and platforms, with an emphasis on reflector antennas and satellite platforms. The Higher-Order Multilevel Fast Multipole Method (HO MLFMM) was introduced recently in the commercial software tool GRASP, and this algorithm is employed in this paper due to the very low memory requirements and the need for very high accuracy. We show that the memory distribution of HO MLFMM is different from the typical low-order MLFMM, thereby enabling a more efficient out-of-core solution which allows very large problems to be solved with modest memory requirements. We also investigate the challenging problem of MLFMM-based computation of waveguide scattering parameters when several horn feeds are mounted on large satellite platforms. We show that the use of a Block GMRES method provides a faster and/or more accurate solution than the standard GMRES solution method.