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Abstract

An adjustable multi-band planar antenna especially applicable in mobile terminals and a radio device. The adjusting circuit (430) of the antenna is galvanically connected to a point (X) of the radiator, where the circuit can affect the places of at least two operating bands. The adjusting circuit comprises a multi-pole switch (433), by which said radiator point can be connected to one of alternative transmission lines. For example, one of two transmission lines (434, 435) is open and another shorted. A discrete capacitor (C2) can be located between the separate conductor of the transmission line and an output pole of the switch as an additive-tuning element. The adjusting circuit further comprises a LC circuit (432) between the radiator (320) and the switch. Among other things, the lengths of the transmission lines, the values of the discrete components and the distance between the antenna short-circuit point (G) and the adjusting circuit connecting point (X) are then variables from the point of view of the antenna adjusting. Such values are calculated for these variables that each of the antenna operation bands separately shifts to a desired other place when the switch state is changed. The space required for the adjusting circuit is relatively small, and a relatively high efficiency is achieved for the antenna despite of the use of a switch.

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First Claim