Study On Low-profile Fractal Wideband Loop-dipole Composite Antenna

In "point to point" of the high speed wireless communication(e.g: high-speed data transmission). In order to set up a reliable communication link for portable equipments, planar antennas with higher directivity and gain are required. Thus, it is necessary to develop planar antennas with end-fire beams. In the thesis, with reference to the concept of complementary antenna, the design concept of fractal loop-dipole antenna is proposed firstly; then, the mechanism is verified through numerical simulation. Finally, the validity and effectiveness of fractal loop-dipole composite antenna design method is proved by experimental results and parameter Analysis. The main content of this thesis is organized as follows:(1) At first, the state of art and the analysis methods of fractal magneto-electric dipole antenna are briefly introduced. Then, the operating principles and the equivalent source model of such antennas are studied.(2) Based on the theoretical results, using different iterations of the order of Koch fractal curves, and finally developed several miniaturized low profile wideband loop-dipole composite antennas. The new antenna for point-to-point applications in compact portable or hand-held wideband and ultra-wideband wireless devices is proposed. It used the fractal antipodal loop structure working as magnetic dipoles and the printed dipole working as electric dipoles in antennas. The size is 31 mm×30 mm×1 mm, and the bandwidth is from 2.86 to 11 GHz(SWR≤2), respectively. Besides the quasi-directional radiation pattern can be achieved in the operating frequency range.(3) Finally, planar wideband loop-dipole composite antennas are analyzed and designed by using IE3 D, and the prototypes are fabricated and experimentally studied for their frequency-domain and time-domain performance. The result show that the antenna can achieve an impedance bandwidth of more than 117%, flat gain performances, quasi-directional radiation patterns and low cross-polarization level. Moreover, good pulse fidelity is also obtained.