Dual band antenna

#The present invention relates to a dual band antenna, and more particularly, to a dual band antenna having a single radiating arm operating at dual frequency bands.

#With the current developments in communication technology, many electronic devices need to receive and transmit signals in dual frequency ranges. The electronic devices, therefore, need to have dual band antennas operating in dual frequency ranges. U.S. Pat. No. 6,166,694 discloses a dual band antenna. The conventional dual band antenna includes two radiating arms which are of different lengths and which are capable of being tuned to different frequency bands. However, each radiating arm of the conventional antenna is only resonant at one frequency band. The radiating arms occupy a relatively large space. Furthermore, if an electrical device needs a conventional antenna to operate at multiple frequency bands, the antenna has to have an additional radiating arm for each additional frequency band. These radiating arms must occupy extra printed board space and may result in complex shapes. These multiple radiating arms are also disadvantageous when a designer has to decrease the size of the antenna.

#The present invention is directed to an improved dual band antenna having a single radiating arm with a closed loop, which operates at dual frequency bands, which obviates adding extra radiating arms, which prevents occupation of extra space.

#FIG. 1 is a top view of a dual band antenna of the present invention.

#FIG. 2 is a bottom view of the dual band antenna of FIG. 1.

#FIGS. 3A and 3B respectively illustrate two other embodiments of the present invention for application in different environments.

#As shown in FIGS. 1 and 2, a dual band antenna 1 according to the present invention comprises a printed wiring board (PWB) 20, a conductive antenna trace 10 and a grounding plate 30.

#The PWB 20 is substantially rectangular and comprises opposite first and second surfaces 20a, 20b. The antenna trace 10 is disposed on the first surface 20a and comprises a single radiating arm 100 and a matching means 13 extending from the radiating arm 100. The radiating arm 100 includes a meandering segment 12 and a linking segment 11. The meandering segment 12 extends serpentineformly along the first surface 20a, forming a plurality of U-shaped bends (not labeled). The meandering segment 12 includes a free end 15 and a feed point 14 defined at opposite ends thereof. The feed point 14 is defined through the PWB 20. The linking segment 11 extends between uppermost points (not labeled) of two adjacent arms (not labeled) of a U-shaped bend, thereby sealing an opening (not labeled) of the U-shaped bend to form a closed loop (not labeled). In this preferred embodiment, the linking segment 11 is disposed at an endmost U-shaped bend 16 which includes the feed point 14 along one of its arms (not labeled). Impedance matching of the dual band antenna 1 is performed by the matching means 13. By adjusting the dimension, shape and position of the matching means 13, the impedance of the dual band antenna 1 can be changed. The grounding plate 30 is disposed on the second surface 20b of the PWB 20 and is spaced a distance from the feed point 14 along a longitudinal direction of the second surface 20b.

#A cable, which is provided to transmit signals between the antenna 1 and a signal processing circuit (not shown, since such circuits are well known in the art), comprises a conductive core wire and a conductive ground shield around the core wire. The core wire is inserted through the PWB 20 at the feed point 14, from the second surface 20b to the first surface 20a, and is soldered to the antenna trace 10 on the first surface 20a. The ground shield connects with the grounding plate 30 on the second surface.