| This thesis has mainly concentrated on the study and design of three planar microstrip antennas. They are annular slot antenna array,circular slot antenna and sinuous antenna ,respectively. All of them have bi-directional radiation characteristic, and their main radiation directions are perpendicular to the antenna planes. In addition, the quantity of the radiant energy from both sides of the antenna planes is roughly equal.In order to expand the application areas of the above-mentioned three antennas, this thesis has added reflected cavities to one side of the antenna planes to get unidirectional radiation characteristics of these antennas. As a result, they can be used in the systems that need unidirectional radiating antennas.For the annular slot antenna array, this thesis has added a reflected cavity to one side of the antenna directly, in accordance with the narrow-band characteristic of the antenna. From this way, the annular slot antenna array has gained unidirectional radiation characteristic.For the circular slot antenna, the bandwidth of the antenna in this thesis has been designed from 3GHz to 9GHz , so, this antenna is an UWB antenna. For UWB antennas, if we only add reflected cavities to one side of the antenna planes to achieve unidirectional radiation characteristic, the bandwidths of the antennas will be sharply deteriorated, because of the introduction of the reflected resonant length from the cavities. In order to maintain the ultra bandwidth of the circular slot antenna, this thesis has added triangle tuning chips and cross tuning chips into the cavity to get the goal. For the sinuous antenna, the bandwidth of the antenna in this thesis has been designed from 4GHz to 14GHz , so, this antenna is also an UWB antenna. For the purpose of good unidirectional radiation characteristic and satisfactory bandwidth, this thesis has divided the reflected cavity into several parts, and filled each part with absorbing material to absorb the energy of corresponding frequency. |
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