NEC-LIST: Modelling a balanced dipole with stub

Hello,

I would like to know how to model the most used broadcast dipole
(wideband).

The antenna has a simple vertical dipole connected with a shunted
transmission line stub (short circuited by one side).

In the real antenna the transmission line is made using wires as the
antenna dipole.

This is a draw of the antenna:

                        |

                        |

                        |

            _______|

            |_______X

                        |

                        |

                        |

                        |

In the ASCII draw X is the generator.

With NEC this antenna can be modelled in three different ways:

1) The dipole with the shunt short-circuited stub modelled as a
transmission line (TL card)

2) The dipole with the shunt short-circuited stub modelled as
wires (horizontal U shape)

3) The dipole with the shunt short-circuited stub modelled as
wires with, in parallel, a shorted transmission line (TL)

The radiation patterns are similar but the third case is the best for
matching the impedance (50 Ohm).

I would like to know which one is the more realistic model, specially
regarding the antenna impedance (putting the generator where there is
the X character in the draw) that, considering the three cases, is
completely different.

Thanks.

Best regards,

Massimiliano.

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