AWR eBooks

C C H H A A P P T T E E R R I I – – S S I I N N G G L L E E E E L L E E M M E E N N T T M M I I C C R R O O S S T T R R I I P P A A N N T T E E N N N N A A ANTENNA CHARACTERIZATION Antennas are characterized and described by classification and descriptive parameters. In addition to microstrip or printed antennas, other classes of antennas are: wire, e.g. dipole or loop; aperture, e.g. horns; reflector, e.g. parabolic; and lenses. The microstrip antenna may be considered a wire antenna due to the associated property of current on the radiating element; however, microstrip antennas are commonly granted the distinction of a separate antenna classification. The most notable antenna parameters and definitions are summarized within Table 1. TABLE 1: ANTENNA PARAMETERS AND DEFINITION 2 PARAMETER DEFINITION Radiation Pattern A mathematical function or graphical representation of the radiation properties of an antenna as a function of geometric, typically spherical, coordinates. Radiation Pattern Beamwidth The angular separation between two identical points on opposite sides of the radiation pattern maximum – generally, the value definition is the half-power point. Sidelobe Level The portion of the radiation pattern bounded by relatively weak radiation intensity Directivity – D The ratio of the radiation intensity in a given direction to the radiation intensity averaged over all directions – maximum radiation is the implied direction; a measure of the ability of the antenna to focus radiated power in a given direction Gain – G The ratio of the radiation intensity in a given direction to the radiation intensity of an isotropic antenna with the same input power – unlike directivity, gain also accounts for antenna efficiency Efficiency – A numerical term which accounts for losses of the antenna from the input terminals and all elements of the antenna structure Effective Area – A e The ratio of the available power at the terminals of an antenna to the power flux density from a plane wave incident normal to the antenna. Aperture Efficiency The ratio of the effective area, A e , of an antenna to the physical area, A ph , of the antenna – mathematically: Polarization Indicates the time varying direction of the electric field vector – vertical, horizontal and circular polarization are typical Input Impedance The ratio of voltage to current at the input terminals of the antenna 2 Balanis, C. A., Antenna Theory, 3 rd Ed., John Wiley and Sons, Hoboken, NJ, 2005, chapter 2. h ph e A G A G × × = × = h l p l p 2 2 4 4 and Microstrip Antenna Design 2 www.cadence.com/go/awr

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