摘要: There are many communication and radar applications requiring antennas with high directionality and narrow beam width. Typically, the width and directivity of the radiation pattern of a single radiating antenna element is insuffic... 展开 There are many communication and radar applications requiring antennas with high directionality and narrow beam width. Typically, the width and directivity of the radiation pattern of a single radiating antenna element is insufficient for these applications. One method of improving these limitations is to increase the element aperture. A typical approach is to place the radiating element at the focal point of a large parabolic dish. However, for many mobile platform applications this is not a practical approach. With a narrow radiation pattern the antenna aperture must be steered to direct the signal in the desired direction.. For a large dish antenna it may be difficult to position the aperture quickly enough due to inertia effects of the massive antenna. A better method to increase the antenna aperture without the adverse consequences of a large dish structure is to use an antenna array, which is an assembly of radiating elements in a given geometrical pattern. The beam pattern of an array antenna can be adjusted by any of five parameters: the geometrical configuration of the array, the displacement between the elements, the excitation amplitude, the excitation phase, and the radiation pattern of the individual elements. As will be shown, by adjusting the phase of the signal delivered to each element it is possible to control the steering angle of the beam without physically repositioning the antenna aperture. Such an antenna is called a phased array antenna. (PAA) because a phased array antenna does not need to be physically repositioned, its reaction time can be several orders of magnitude faster than a large dish antenna. This allows PAA systems to be multifunctional, meaning they can perform many different tasks simultaneously. 收起