On the efficiency and gain of antennas

@inproceedings{Karlsson2006OnTE,
  title={On the efficiency and gain of antennas},
  author={Anders Karlsson},
  year={2006}
}
The fundamental limits of the gain and efficiency of an antenna are explored. The antenna is confined in a sphere and all of the currents are assumed to run in a material with a conductivity that is a function of the radial coordinate. The analysis is based on the expansion of the electromagnetic fields in terms of vector spherical harmonics. Explicit expressions for the limits of gain and efficiency are derived for different types of antennas. 

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