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Design of Optimum Antennas for Wideband THz Pulses Generation Using Photoconductivity

Rahmati, Ehsan | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46517 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Ahmadi-Boroujeni, Mahdi
  7. Abstract:
  8. One of the most common devices for terahertz (THz) wave generation and detection is a Terahertz photoconductive antenna. Impedance matching between the antenna and the photoconductive material is a primary factor to obtain high optical-THz conversion efficiency. Because of the time dependant conductivity of the photoconductive material, impedance mismatching is an obstacle for generating high power THz pulses. Moreover, the range of laser power (when using Ti:Sapphire) from the excitation source varies from a few tens of milliwatts to a few watts while the radiated THz power as compared to this laser pump power is very low (in the order of a few μW); this means a low power conversion efficiency. In this thesis, we present an optimized bowtie antenna to be used in pulsed THz photoconductive sources. Then, revised versions of these antennas are proposed. Characteristics of the proposed antennas have been examined from several aspects including radiation efficiency, directivity, impedance matching and total efficiency. In order to decrease the effective permittivity of substrate and prohibit the excitation of surface waves, air holes are cut through the substrate which result in increasing directivity, total radiation and improvement of bandwidth over 0.6-1.6 THz. Moreover, bowtie and log-spiral antennas are placed on the top of a substrate lens and obtained results from numerical study are compared over 0.3-2 THz. It is shown that by placing the antennas on the dielectric substrate lens, almost all problems associated with surface waves have been overcome and a wider bandwidth can be achieved
  9. Keywords:
  10. Lens ; Photoconductive Antenna ; Terahertz Technology ; Wideband Terahertz Pulses Generation ; Bowtie Antenna ; Hexagonal Bowtie Antenna ; Log-Spiral Antenna

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