APPENDIX B

Definitions of Terms Useful to ESA

Bandwidth | The frequency range over which the impedance mismatch factor does not exceed a specified value. Common values are half-power () and 88% power (). Bandwidth is often expressed as a percent; the frequency range is divided by the center frequency. |

Broadband antenna | An antenna whose bandwidth is roughly an octave or more. |

Directivity | The ratio of the peak of the radiation intensity to the radiation intensity averaged over all directions. |

Efficiency | The ratio of peak radiation intensity to the one that would be obtained if conduction and dielectric losses were absent. |

ESA | An electrically small antenna; usually taken as fitting in a sphere of diameter . |

Gain | Directivity reduced by conduction and dielectric losses, and by impedance mismatch losses. Note: The IEEE definition does not include mismatch losses; industry uses the definition given above. |

Radian sphere | A hypothetical sphere of radius ; the sphere encloses the antenna. Note: ESA usually use a radian sphere whose radius is half that above. |

Superdirective antenna ... |