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Performance Analysis and Optimization of Optically Steered Arrayed Antennas with Gratings

Shabani, Mostafa | 2012

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 43076 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Akbari, Mahmood
  7. Abstract:
  8. It is well known that arrays of antennas make it possible to steer the radiation pattern without steering a physical structure. For the past few decades this has been considered for many civil and military communication systems. Recently, ultra-short pulses are considered for high resolution radars and ultra-wideband communication systems. Systems with short pulses and large antenna arrays may benefit from high resolution in both temporal and spatial domains. But the implementation of the ultra-wideband feeding circuits for such antenna arrays is a hard job even with state of the art electronics. Optical technology has been applied, successfully, to a number of radio applications such as microwave signal generation, microwave filters and antenna array beam-forming networks. Large microwave bandwidths occupy a small fraction of the optical spectrum, thus, bandwidth limitation is rarely a bottleneck in microwave-photonic implementations. Besides, low weight, small size and immunity to electromagnetic interference are among other advantages of these systems. In this thesis we provide a performance analysis for optical beam-forming networks for wideband arrays. The research methodology is dominantly based on analytical developments and numerical simulations. First we will review different structures and applicable technologies. Then we will study the selection criteria of the elements of an optical beam-former. The effects of optical beam-formers on a receiving array will be studied thoroughly. Noise and non-linear effects are discussed in chapters 3 and 4 and we will give certain suggestions for the beam-former topology. The rest of the thesis is devoted to three important issues:1- Non-linear effects of optical modulators in the front-end of a large array We will provide analytic developments for a pulse compression radar where a dual drive Mach-Zehnder modulator is placed at the receiver front end. The non-linear effects of the modulator are studied for a linearly frequency modulated pulse radar. The different bias and phase shift conditions of the modulator are derived and discussed. 2-Effects of ripple in the group delay response of dispersive time delay elements on the temporal response of pulsed arrays The ripple in group delay is inherent to many dispersive optical delay lines but is rather overlooked in the literature for beam-forming applications. We will introduce an impulse response for the beam-former and compute it through a semi-analytic approach. We measure wideband pulse array performance with the presented formulation.3- Simultaneous signal generation and beam-forming with optical elements In wideband beam-formers that wavelength tuning is used to control the bearing of the antenna array, single sideband optical modulation is hard to implement, while double sideband modulations are subject to bandwidth limitations. For certain waveforms that could be produced optically, we will provide a novel structure for simultanouse waveform generation and beam-forming. The structure can compensate for the double sideband bandwidth limitation via shaping a baseband pulse spectrum
  9. Keywords:
  10. Phased Array ; Diffraction Gratings ; Fiber Bragg Grating (FBG) ; Optical Elements ; Optical Beam Steering

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