Importance

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Abstract

An adjustable multiband antenna especially intended to mobile terminals. The antenna structure comprises a radiator (320), a feed element (330) and an adjusting circuit (350). The radiator is a conductive part of the outer cover (COV) of a radio device or conductive coating of the cover. It is fed electromagnetically by a feed element which is isolated from the radiator by a relatively thin dielectric substrate. The feed element is connected either directly or through an intermediate element (340) to the antenna port of the device and to the ground plane (310), and it is shaped so that the antenna has at least two operating bands. The adjusting circuit is connected to an adjusting point (AP) in the feed element, and the reactance between the adjusting point and ground and thus the electric size of the antenna can be changed by means of a switch (SW) in the adjusting circuit. Among other things, the component values of the adjusting circuit and the distance between the short-circuit (SP) and adjusting (AP) points in the feed element are variables from the point of view of the antenna adjustment. Displacements, which have desired directions and lengths, are obtained for at least two operation bands of the antenna independently from each other by changing the switch state. The efficiency of the antenna is better than of the corresponding known antennas, and its matching can be made good both in lower and upper operating band of the antenna.

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