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Title: Modelling, design and characterisation of terahertz photoconductive antennas
Author: Khiabani, Neda
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2013
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The area of Terahertz (THz) is one of the fastest growing research fields in recent years. THz antennas based upon photoconduction techniques are the most common devices in THz systems. However, the radiated THz power from these devices and the efficiency are very low. Also, different antenna excitation and current generation process in THz antennas, as compared to microwave antennas, requires new analyses approaches. Therefore, the motivation of this thesis is to theoretically establish why the THz antenna is inefficient; from which, general methods to improve the performance of such antennas are explored and validated. These investigations are essential to gain a better understanding of THz photoconductive antenna performance. In this research a new equation for the source conductance of a THz antenna is firstly developed. This is a prerequisite for further antenna radiated power analysis. Next, a new equivalent circuit, modelling the underlying physical behaviour of the device through the use of a lumped-element network, is developed. Through this model, various factors which affect the radiated power and efficiency of the THz photoconductive antenna are examined and compared with measurement results. This model can be applied to maximize the optical-to-THz conversion efficiency. Also, temporal voltage behaviour of the antenna can be predicted more realistically. Furthermore, a computational simulation procedure, solving both optoelectronic and electromagnetic problems, is proposed and validated by measurement results. This approach facilitates prediction of THz photoconductive antenna performance before antenna fabrication. In addition, considering the requirement of high THz power and good SNR devices for various THz applications, a new top loaded THz antenna embedded on a conical horn with the trapezoidal photomixer is proposed. The generation of THz photocurrent, impedance matching and coupling of the THz wave to air (the necessary factors for power enhancement) are improved. Moreover, the new trapezoidal photomixer is examined and the measurement results show that it has better radiated THz power and SNR than the bare gap and rectangular photomixers.
Supervisor: Huang, Yi; Shen, Yaochun Sponsor: Engineering and Physical Sciences Research Council (EPSRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: TK Electrical engineering. Electronics Nuclear engineering