Multifrequency antenna for instrument with small volume

Antenna of elongated shape for an instrument of small volume, in particular a telephone-watch, capable of receiving and transmitting radiobroadcast message at at least two frequencies of high and low values, this antenna being formed, from a supply point of a first radiating element the length of which is tuned to the high frequency and at least a second radiating element, following the first, the length of this second element added to that of the first having a total length tuned to the low frequency, the first and second radiating elements being connected to each other by a resonant circuit whose resonance frequency is chosen to limit the length of the antenna to its first element when the high frequency is active and to use the total length of the antenna when the low frequency is active,

• wherein the first and second radiating elements each have a conductive strip of substantially rectangular shape and wherein the resonant circuit includes the combination of an inductor and a capacitor, said inductor being a substantially rectilinear narrow band integrally formed with at least one of said strips and connected to said strip by one of its ends,
• wherein the inductor and the capacitor are connected in series, the value of each of these components being chosen to have a resonance frequency substantially equal to the antenna's low operating frequency, and
• wherein the first and second strips rest on an insulating substrate to form a printed circuit and wherein the inductor is a narrow printed patch on said insulating substrate and connected by a first end to the first strip and by a second end to a first capacitor plate of a capacitor whose second capacitor plate is connected to the second strip, each of said first and second capacitor plates being printed on the insulating substrate, said first and second capacitor plates having the shape of a comb whose teeth interlock without touching.