| Summary: | 博士 === 國立彰化師範大學 === 電機工程學系 === 103 === In this thesis, three designs for frequency, polarization, and pattern reconfigurable antennas are respectively proposed, and their possible applications are presented. First, a solar powered frequency sensors based on a rectenna composed of a frequency reconfigurable microstrip antenna and a rectifying circuit. The operating frequency of the antenna can be tuned in the range between 2 and 2.8 GHz, and, in this frequency range, the rectifier can effectively perform the conversion from RF to DC. By the measured results of the rectenna, the average conversion efficiency within the operating bandwidth of 33 % is 72.9 % over a resistive load of 1 kΩ at a power density of about 0.8 mW/cm2. A frequency sensor is successfully implemented by integrating the frequency reconfigurable rectenna with a pre-programmed microprocessor powered by solar cells.
The second design is a polarization reconfigurable antenna that can be applied into near field measurement systems. The polarization of the antenna can be switched between two orthogonal linear polarizations, and for each polarization mode, the antenna has wide operating bandwidth and low cross polarization. The reconfigurable antenna is used as a probe in a home-made cylindrical near field measurement system, and several antennas are tested with the near field system. The obtained radiation patterns have good agreements with the simulated data and the results acquired from far-field measurement systems. For one antenna under test, the required measurement time of the near field system using the polarization reconfigurable antenna as a probe is 36 % shorter than the case using a traditional open waveguide as a probe.
The final design is a beam-switched array. The array has eight radiating elements arranged in one dimension. Each element is excited with a 3-digit phase shifter with wideband operation. Seven beams directed to various angles are generated from the array. A detecting system for moving objects is developed based on the phased array, and a prototype is successfully completed. The experimental results for the array element and phase shifter are shown, respectively. The design and performance of the detecting system are also exhibited.
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