| Summary: | 碩士 === 國立臺北科技大學 === 電腦通訊與控制研究所 === 91 === In this thesis, a broadband microstrip antenna with a defective ground plane is proposed. With the presence of slots embedded in nonradiating edges and a normal ground plane, the antenna exhibits dual-band operation while, with the presence of a defective ground plane and a normal patch radiator, the antenna shows a bandwidth enhancement and frequency reduction of the fundamental mode. When a pair of slots embedded in the patch radiator and a defective ground plane are utilized in a microstrip antenna, the impedance bandwidth could reach almost 11% compared to that of the reference antenna, whose central frequency is 2.46GHz, with only 2.4% impedance bandwidth. This broadband technique exploiting a defective ground plane composed of 25 cross-shaped lattices has been investigated experimentally, offering a new idea for bandwidth enhancement in the design of microstrip antennas.
In the second design, a broadband loop slot antenna incorporating an asymmetric photonic bandgap structure in the feed network has been investigated and implemented since the spurious emission is a crucial issue for diverse communication systems. In order to alleviate such a severe symptom, an asymmetric photonic bandgap structure with compact dimensions has been utilized to eliminate unwanted high order modes. It not only suppresses unwanted modes successfully, but broadens the impedance bandwidth of loop slot antenna simultaneously. The impedance bandwidth of the proposed antenna could reach 1541MHz, which is about 70% with respect to the central frequency of 2200MHz.
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