Multifrequency antenna for instrument with small volume

• US 20030030589A1
• Filed: 09/09/2002
• Published: 02/13/2003
• Est. Priority Date: 03/15/2000
• Status: Active Grant

• Current Assignee: Asulab SA (The Swatch Group AG)
• Original Assignee: Asulab SA (The Swatch Group AG)
• Inventors: Staub, Olivier, Skrivervik, Anja, Zurcher, Jean-Francois
• Granted Patent: US 6,642,895 B2
• Time in Patent Office: Days
• US Class Current: 343/718
• CPC Class Codes: G04G 21/04 using radio waves radio-controlled time-pieces G04R
• CPC Class Codes: G04R 60/00 Constructional details
• CPC Class Codes: H01Q 1/273 Adaptation for carrying or wearing by persons or animals
• CPC Class Codes: H01Q 5/321 within a radiating element or between connected radiating elements

Abstract

The antenna (1) is formed of a first strip element (3) the length (L1) of which is tuned to a high frequency (f_h) 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 (f_b). 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 (f_h). 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.

Claims

1. Antenna (1) of elongated shape for an instrument of small volume, in particular a telephone-watch, capable of receiving and transmitting radiobroadcast messages at at least two frequencies of high (f_h) and low (f_b) value, this antenna being formed, from a feed point (2), of a first radiating element (3) the length (L1) of which is tuned to the high frequency (f_h) and at least a second radiating element(4), following the first(3), the length (L2) of this second element added to that of the first having a total length (L3) tuned to the low frequency (f_b), the first and second radiating elements being connected to each other by a resonant circuit (5) whose resonance frequency (f_r) is chosen to limit the length of the antenna to its first element (3) when the high frequency (f_h) is active and to use the total length (L3) of the antenna when the low frequency (f_b) is active,

wherein the first (3) and second (4) radiating elements each have a conductive strip of substantially rectangular shape and wherein the resonant circuit (5) includes the combination of an inductor (6) and a capacitor (7, 7′

), said inductor (6) 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 (8, 8′

).

2. Antenna according to claim 1, wherein the inductor (6) and the capacitor (7, 7′

) are connected in parallel, the value of each of these components being selected so as to have a resonance frequency (f_r) substantially equal to the antenna'"'"'s high operating frequency (f_h).

3. Antenna according to claim 2, wherein the first (3) and second (4) strips are self-supporting and held in the instrument by securing means (9), wherein the inductor (6) is connected by its first end (8) to the first strip (3) and by its second end (8′

) to the second strip (4) and wherein the capacitor (7) is a discrete component having first (10) and second (10′

) terminals respectively bonded onto the first (3) and second (4) strips.

4. Antenna according to claim 2, wherein the first (3) and second (4) strips rest on an insulating substrate (11) to form a printed circuit and wherein the inductor (6) is a narrow printed path on said insulating substrate (11) and connected by its first end (8) to the first strip (3) and by its second end (8′

) to the second strip (4).

5. Antenna according to claim 4, wherein the capacitor (7, 7′

) includes a first capacitor plate (12, 12′

) printed on the insulating substrate (11) and connected to the first strip (3) and a second capacitor plate (13, 13′

) printed on the insulating substrate (11) and connected to the second strip (4), each of said first and second capacitor plates having the shape of a comb whose teeth interlock without touching.

6. Antenna according to claim 4, wherein the capacitor (7, 7′

) is a discrete component having first (14, 14′

) and second (15, 15′

) terminals respectively bonded onto the first (3) and second (4) strips.

7. Antenna according to claim 4, wherein the capacitor (7, 7′

) includes the series arrangement of first (16, 16′

) and second (17, 17′

) capacitors each including a common capacitor plate (18, 18′

) printed under the insulating substrate (11), this common capacitor plate extending partially, on the one hand, under the first strip (3) to form the first capacitor (16, 16′

) and, on the other hand, under the second strip (4) to form the second capacitor (17, 17′

), said insulating substrate (11) acting as a dielectric for each of said first and second capacitors.

8. Antenna according to claims 3 or 4, wherein the first (3) and second (4) strips are arranged at a determined distance (A) from a ground plane (19), the initial part (20) of the first strip (3) being short-circuited with this ground plane (19) and the final part (21) of the second strip (4) being left free.

9. Antenna according to claim 1, wherein the inductor (6) and the capacitor (7) are connected in series, the value of each of these components being chosen to have a resonance frequency (f_r) substantially equal to the antenna'"'"'s low operating frequency (f_b).

10. Antenna according to claim 9, wherein the first (3) and second (4) strips rest on an insulating substrate (11) to form a printed circuit and wherein the inductor (6) is a narrow printed path on said insulating substrate (11) and connected by its first end (8) to the first strip (3) and by its second end (8′

) to a first capacitor plate (12) of a capacitor (7) whose second capacitor plate (13) is connected to the second strip (4), 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.