6 - Antennas and Radiation: II Antenna Elements and Arrays

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Antenna Elements and Arrays There are infinite possible antenna geometries that can be designed to achieve a variety of performance features. Among these diverse configurations, one may identify a few basic antenna elements that are often used for general-purpose wireless applications. This chapter analyzes the radiation/reception mechanism in selected basic antenna geometries: (1) dipole antenna, (2) monopole antenna, (3) wire-loop antenna, (4) slot antenna, and (5) microstrip antenna. Selected other types of antennas in use are also introduced. An antenna array is made of a number of individual antenna elements each located at a different position in space, with independent excitation to each input. Such an array may provide many practical advantages over a single antenna element. By properly designing for the individual locations and input excitations, one can achieve radiation characteristics that might not be normally feasible using a single antenna. If one can also control the input excitations to the individual elements in the real-time, the radiation characteristics of the array, such as the pointing direction or radiation pattern, can be changed in a dynamic manner. This allows significant flexibility for adjusting to a dynamically changing situation. This chapter analyzes the basic theory of a general antenna array and derives results for specific situations of a one-dimensional array and a two-dimensional array.