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 ... |
