Hybrid antennas for a maritime satellite communication terminal with simultaneous operation at L- and Ka-band have been investigated. The frequency bands of interest are 1; 525:0 1; 660:5 MHz (RX+TX, RHCP), 19:7 20:2 (RX, LHCP) and 29:5 30:0 GHz (TX, RHCP), which are all part of the Inmarsat BGAN and Inmarsat GX services, respectively. The results of this study are three antenna concepts, which demonstrates high performance at both L- and Ka-band. A combined single/dual-reflector antenna is designed, which presents a favourable way of combining feed antennas for the diverse frequencies. This antenna enables the use of a conventional horn-fed dual-reflector for Ka-band, while a backfire helical antenna is used to form a single-reflector antenna at L-band. Simulations show excellent performance of the L-band backfire helical reflector antenna, due to the utilization of the entire antenna aperture. The Ka-band dual-reflector is inherently a high-gain and low-loss antenna, and investigations show negligible impact of the L-band backfire helical antenna. Therfore, this hybrid single/dual-reflector antenna presents a viable solution to the combined L- and Ka-band antenna. Novel hybrid antennas that use Frequency Selective Surfaces (FSSs) are investigated, such that an L-band antenna can be located behind and radiate through the Ka-band antenna. A planar periodic FSS, that is reflecting at both 20 and 30 GHz while being transparent at L-band, is designed and analyzed numerically. The FSS is incorporated in a parabolic FSS reflector antenna that is investigated by full-wave analysis tools, and the antenna shows performance comparable to conventional reflector antennas within its frequency band of operation. A planar prototype FSS is manufactured and measured with particular attention to the impact on the performance of an L-band antenna radiating through the FSS. From these investigations, it is concluded that the FSS antenna concept is well suited for hybrid L- and Ka-band operation. A printed reflectarray antenna with FSS ground-plane is demonstrated. The reflectarray produces a collimated beam as a curved reflector, but its planar profile enables conventional manufacturing techniques used for printed circuit board fabrication. For this purpose, a new type of reflectarray element, the concentric dual split-loop element, is devised and investigated. This compact element facilitates phase-adjustment at 20 and 30 GHz simultaneously, which is exploited by a developed iterative design procedure. A numerical code is implemented to synthesize and analyze reflectarrays, and two prototype reflectarray antennas are fabricated - the first with a conventional solid ground-plane and the second with an FSS ground-plane. The radiation patterns of the prototype reflectarray antennas are measured at the DTU-ESA Spherical Near-Field Antenna Test Facility, as well as the L-band transparency of the FSS-backed reflectarray antenna, and the results demonstrates the high performance of this novel shared-aperture antenna.
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Larsen, Niels, Breinbjerg, Olav, Gothelf, Ulrich, Kim, Oleksiy S.