### Abstract

Theoretically, the minimum radiation quality factor Q of an isolated resonance can be achieved in a spherical electrically small antenna by combining TM1m and TE1m spherical modes, provided that the stored energy in the antenna spherical volume is totally suppressed. Using closed-form expressions for the stored energies obtained through the vector spherical wave theory, it is shown that a magnetic-coated metal core reduces the internal stored energy of both TM1m and TE1m modes simultaneously, so that a self-resonant antenna with the Q approaching the fundamental minimum is created. Numerical results for a multiarm spherical helix antenna confirm the theoretical predictions. For example, a 4-arm spherical helix antenna with a magnetic-coated perfectly electrically conducting core (ka=0.254) exhibits the Q of 0.66 times the Chu lower bound, or 1.25 times the minimum Q.

Original language | English |
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Journal | I E E E Transactions on Antennas and Propagation |

Volume | 60 |

Issue number | 8 |

Pages (from-to) | 3551-3558 |

ISSN | 0018-926X |

DOIs | |

Publication status | Published - 2012 |

### Keywords

- Chu lower bound
- Circular polarization
- Electric dipole
- Electrically small antennas
- Fundamental limitations
- Magnetic dipole
- Quality factor

## Cite this

Kim, O. S. (2012). Minimum Q Electrically Small Antennas.

*I E E E Transactions on Antennas and Propagation*,*60*(8), 3551-3558. https://doi.org/10.1109/TAP.2012.2201096