Abstract: The antenna (1) is formed of a first strip element (3) the length (L1) of which is tuned to a high frequency (fh) and at least a second strip (4), following the first (4), of length (L2). The sum of the lengths L1 and L2 results in an antenna whose length L3 is tuned to a low frequency (fb). A resonant circuit (5) including an inductor (6), connected in parallel to a capacitor (7) is located between the first and second strips (3, 4). The values of these components are chosen so that the resonant circuit resonates at the high frequency (fh). When the high frequency is active, the length of the antenna is reduced to that (L1) of the first strip. When the low frequency is active, the length of the antenna extends to the sum (L3) of the lengths of the first and second strips. The inductor (6) is a substantially rectilinear band integrally formed with at least one (3) of said strips and connected to said strip by one (8) of its ends.

Abstract: The present invention concerns a structure forming an antenna (10) intended for a portable unit of small volume, such as a timepiece, and including a radiating element (20) of substantially rectangular shape arranged at a determined distance from a ground plane and short-circuited with this ground plane by one (20b) of its ends (20a, 20b), the opposite end (20a) of said radiating element (20) being left free. According to the present invention, said structure (10) includes a case (11) forming an integral part of said ground plane and including at least a cover (12), a bottom (14), and a lateral wall (13b) facing which is arranged said radiating element (20), said case (11) forming a shielded housing able to accommodate all or part of an electronic circuit and/or other components of the portable unit. The present invention also concerns a timepiece incorporating the aforementioned antenna structure.