CHAPTER 3: ANTENNAS - MIT OpenCourseWare

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97CHAPTER 3: ANTENNAS ANTENNAS couple propagating electromagnetic waves to and from circuits and devices, typically using wires (treated in Section ) or apertures (treated in Section ). In practice complicated solutions of Maxwell s equations for given boundary conditions are usually not required for system design and analysis because the antenna properties have already been specified by the manufacturer, and must only be understood. Section characterizes these general transmitting and receiving properties of ANTENNAS , which are derived in subsequent BASIC ANTENNA PROPERTIES Most ANTENNAS reversibly link radiation fields to currents flowing in wires at frequencies ranging from sub-audio through the far-infrared region. Aperture ANTENNAS that link radiation fields to materials can operate in microwave, infrared, visible, ultraviolet, X-ray, gamma ray, and even higher energy regimes.

The flux density Wm 2 incident on various targets when one-megawatt radar pulses are transmitted can be calculated using: P2 T 2 PWm G , 4R TIx S (3.1.4) Radar pulses directed toward the moon, Jupiter, and the star Antares at distances R 3u108, 1012, and 3u1016meters yield fluxes of 10 5, 10 12, and 10 21 watts/meter2, respectively.

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