The rise of satellites in Low Earth Orbit (LEO) is causing more terrestrial electromagnetic interference in the important L- and X-band frequencies which are crucial for astronomical observations. This thesis introduces reflectarray design which can serve as a basis for an interference mitigation solution for radio telescopes. In the envisioned application, When the reflectarray is placed around the circumference of an existing radio telescope, it can drive a null into the radio telescopes radiation pattern sidelobe distribution. Since the reflectarray only occupies a small potion of the rim of the paraboloidal main reflector, its presence does not significantly effect the main lobe peak gain. Since Iridium and Starlink are the target mega-constellations, the reflectarray must be dual band. To cover the operational bandwidths of these constellations, the target bandwidth in the L-band (Iridium) is 0.7%, and that in the X-band (Starlink) is 17.1%. This makes the design of the reflectarray challenging as the frequencies are widely separated and the bandwidth in the X-band is wide The work of this thesis marks a first step in this effort. It includes a reflectarray design containing a multi-layer stack consisting of: (1) a grounded substrate, (2) an X-band slot loaded unit cell geometry, (3) a dielectric superstrate, and (4) an L-band layer containing crossed dipoles. The dual band reflectarray is dual linearly polarized to maintain symmetric response. The reflectarray is designed and simulated using full-wave solvers. The results show that the reflectarray designs are capable of pattern shaping at both bands and operate across the required bandwidths. This architecture could serve as a basis for future reflectarrays capable of nulling satellite interference from mega-constellations in observatory applications in the future. / Master of Science / The signal clarity issues stemming from the increasing number of satellites in Low Earth Orbit (LEO), particularly in the vital L- and X-band frequencies essential for global communications and radio astronomy, are the motivation of this thesis. The endeavor concentrates on designing a dual-band dual-polarized reflectarray antenna which may ultimately be used to help mitigate interference in these bands in radio telescopes. The work is focused on the frequency ranges utilized by the major satellite networks Iridium and Starlink, which operate within the L-band (1616-1626.5 MHz) and X-band (10.7-12.7 GHz). Recognizing the significance of these frequencies for global communication and also to radio astronomy, the reflectarray is designed to contribute to a an interference mitigation system which would ultimately allow for coexistence between radio telescopes and communications systems satellites. Targeting bandwidth achievements of 0.7% for the L-band and 17.1% for the X-band, the focus is on nulling interference arising across these frequency bands and thereby increasing the sensitivity of the radio telescope operating amongst these mega-constellations. The thesis documents a multilayered reflectarray antenna, containing a wide-band X-band layer of slot antennas on one layer and an L-band superstrate layer containing crossed dipoles at another, both of which utilize dual linear polarization for symmetric operation. The completed reflectarray can operate simultaneously in both bands. It has been shown in the two papers cited by {ellingson2021sidelobe,budhu2024design} that reflectarrays placed along the rim of radio telescopes main reflector can be used to drive nulls in the sidelobe envelope of its radiation pattern thereby nulling incoming interference. The antenna design of this thesis suggests a possible candidate for these interference mitigation systems where both bands are targeted.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/119454 |
| Date | 14 June 2024 |
| Creators | Bora, Trisha |
| Contributors | Electrical Engineering, Budhu, Jordan, Manteghi, Majid, Ellingson, Steven W. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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