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| Keywords: T antenna vs vertical antenna.svg T antenna b with the current in a vertical radiator a of the same height demonstrating how the horizontal wire improves its efficiency The T antenna is used at frequencies where a full quarter-wave λ/4 vertical antenna can't be built So the vertical portion of the antennas are much shorter than λ/4 These electrically short antennas have low radiation resistance and can't radiate much power The horizontal wire in the T antenna doesn't radiate radio waves but instead functions as a capacitive top-load to add capacitance to the antenna increasing the current in the top of the vertical wire <br> The red areas are graphs of the current distribution on the wires with the width perpendicular to the wire proportional to the current The current in the antennas assuming they are brought to resonance with an impedance matching network is the tail end of a sinusoidal standing wave In the vertical antenna a the current must go to zero at the top reducing the current in the upper part of the wire As can be seen in the T current flows from the top of the vertical wire into the arms of the T increasing the current in the vertical wire <br> The power output from each antenna is proportional to the square of it's effective height which is equal to the area of the red current distribution graph next to the vertical wire In a the current distribution is roughly triangular so the effective height is about L/2 In the T the current distribution is more trapezoidal approaching constant current for long horizontal wires so the effective height approaches L Therefore the radiation resistance and power output of the T antenna can be up to 4 times that of a simple vertical antenna of the same height <br> La distribution de l'intensité de couleur rouge dans une antenne verticale a et dans l'antenne T b en montrant comment le fil horizontal sert à améliorer l'efficacité du fil vertical rayonnant A la résonance le courant dans la partie de queue est une fr sinusoïde d' fr ondes stationnaires Dans l'antenne verticale le courant passe à zéro à la partie supérieure Dans le T le courant circule dans le fil horizontal augmente le courant dans la partie supérieure du fil vertical Le résistance de rayonnement et donc la puissance rayonnée est proportionnelle au carré de la superficie de la partie verticale <br />Les intensités électrique dans les deux demi-brins horizontaux sont de sens opposés donc les deux champs radioélectrique créés s'annules mutuellement seul le brin vertical participe au rayonnement de l' fr antenne radioélectrique 2012-02-23 own Chetvorno cc-zero Uploaded with UploadWizard Antenna diagrams T and inverted L antennas Wire antenna | ||||
