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Metal-Only and Mechanically Reconfigurable Reflectarrays

Henderson, Kendrick
http://orcid.org/0000-0002-8361-925X
http://rave.ohiolink.edu/etdc/view?acc_num=osu1618495084156028

Abstract Details

, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Reflectarrays combine the favorable aspects of both reflectors and phased array antennas, including high aperture efficiency, high gain, low profile, low weight, and simplicity of the design. These electrical and mechanical characteristics make them an excellent candidate for satellite communication and direct broadcasting services. This dissertation makes three original contributions to the topic of reflectarrays. First, a novel circular polarized metal-only reflectarray capable of producing 360° of phase shift was designed. Second, reflectarrays with rectangular and triangular lattices are compared in terms of their ability to form a cosecant-squared beam pattern. Finally, a novel high power mechanical reconfigurable reflectarray capable of producing over 300° of phase shift was designed. Traditionally microstrip technology is used to create passive reflectarrays, with the patch antenna array printed onto a low loss dielectric substrate. As the aperture of a reflectarray can be quite large, the substrate can make the design prohibitively expensive. Additionally, the introduction of dielectric material into a harsh environment can lead to a decrease in antenna performance. To circumvent these problems, a metal-only reflectarray is a superior alternative for applications that require a fixed beam. Current metal-only designs have limited phase coverage or only work for linear polarization. In this work, a circularly-polarized multi-slot element that has 360° of phase coverage, over a 30% bandwidth spanning 18-24 GHz is presented. The fabricated reflectarray achieves a 3-dB axial ratio bandwidth of 32.5%, and a bandwidth of 10.1% for each polarization within which the gain remains within 3 dB of the peak value. Little attention is paid to an aperture’s topology in reflectarrays as most focus is on the radiating elements. Reflectarrays are traditionally designed with a rectangular lattice having 0.5λ0 by 0.5λ0 spacing as it is a standard spacing to compromises between element coupling and beam scanning. This work examines instead a triangular lattice, and compares its beamforming and gain-bandwidth performance to the traditional rectangular lattice design. The measured rectangular lattice had a lower root-mean-square-error when compared to the desired cosecant-squared beam pattern. This was due to its higher element density. The triangular lattice had an increased gain-bandwidth as inter-element coupling was lowered from increased element spacing. Reconfigurable reflectarrays are also of interest since the antenna can have a vastly simpler construction compared to an electronically scanned phased array. The reflectarray only has to perform phase compensation for the incident field from its feed horn. Modern reconfigurable reflectarrays have focused primary on using PIN and Varactor diodes for reconfiguration. The major drawback to their integration into reflectarrays is that diodes must have a bias voltage that is similar to the RF voltage that is being switched. In this work, we propose a multi-slot reconfigurable reflectarray unit cell that relies on the mechanical motion of a dielectric slab via a micromotor. This allows the antenna to withstand much higher power levels that depends on material temperature limits and the geometry of the unit cells. Using 3D printed VeroWhite Plus allows the unit cell to have 300° of phase coverage for multiple polarizations. The unit cell was tested using reconfigurable and frozen designs. The reconfigurable design was fabricated and tested using a waveguide to simulate a periodic infinite array environment. The dielectric was moved inside the unit cell via a micromotor during testing. The waveguide simulation verified the phase performance of 300° of phase shift of the unit cell. The frozen design of the unit cell was used to test the reflectarray performance. The frozen design allowed for the circumvention of the costs associated with implementing micromotors below the reflectarray’s aperture. Three dielectric slabs were fabricated that corresponded to beams at 0°, 15°, and 30° for the reflectarray. The measured boresight aperture efficiency was 16% with a gain-bandwidth of 7.45% as the gain fell down 3-dB below its peak. The maximum scanning angle of the antenna was 45° due to the propagation of surface and guided waves on the unit cell at higher incident angles. The power limit of the antenna was 80 MW per square meter.
Nima Ghalichechian (Advisor)
Chi-Chih Chen (Committee Member)
Joel Johnson (Committee Member)
Electrical Engineering; Electromagnetics; Engineering
antenna; reflectarray; reconfigurable antenna

Recommended Citations

Citations

  • Henderson, K. (n.d.). Metal-Only and Mechanically Reconfigurable Reflectarrays [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1618495084156028

    APA Style (7th edition)

  • Henderson, Kendrick. Metal-Only and Mechanically Reconfigurable Reflectarrays. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1618495084156028.

    MLA Style (8th edition)

  • Henderson, Kendrick. "Metal-Only and Mechanically Reconfigurable Reflectarrays." Doctoral dissertation, Ohio State University. Accessed APRIL 30, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=osu1618495084156028

    Chicago Manual of Style (17th edition)

osu1618495084156028
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