Fractal dipole antenna

A fractal dipole antenna includes a dielectric substrate, first and second closed-loop radiating elements, each of which is formed on the dielectric substrate, and first and second fractal radiating elements, each of which is formed on the dielectric substrate and is surrounded by and connected to a respective one of the first and second closed-loop radiating elements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an antenna, more particularly to a fractal dipole antenna.

2. Description of the Related Art

In U.S. Pat. No. 7,113,141, there is disclosed a conventional fractal dipole antenna. However, the conventional fractal dipole antenna is not operable within the worldwide interoperability for microwave access (WiMAX) frequency band.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a fractal dipole antenna that is operable within the WiMAX frequency band.

According to the present invention, a fractal dipole antenna comprises a dielectric substrate, first and second closed-loop radiating elements, and first and second fractal radiating elements. The first closed-loop radiating element is formed on the dielectric substrate. The first fractal radiating element is formed on the dielectric substrate, and is surrounded by and connected to the first closed-loop radiating element. The second closed-loop radiating element is formed on the dielectric substrate and is spaced apart from the first closed-loop radiating element. The second fractal radiating element is formed on the dielectric substrate, and is surrounded by and connected to the second closed-loop radiating element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, the preferred embodiment of a fractal dipole antenna1according to this invention is shown to include a dielectric substrate2, first and second closed-loop radiating elements3,5, and first and second fractal radiating elements4,6.

The fractal dipole antenna1of this invention is operable within the worldwide interoperability for microwave access (WiMAX) frequency band, has a small physical size, and is, therefore, applicable to electronic devices (not shown), such as a PDA or a mobile phone.

The dielectric substrate2has a generally rectangular shape, opposite first and second surfaces21,22, opposite first and second edges23,24, and opposite third and fourth edges25,26. In this embodiment, the dielectric substrate2is an FR-4 substrate.

The first closed-loop radiating element3is formed on the first surface21of the dielectric substrate2, has a generally rectangular shape, and includes opposite first and second segments31,32and opposite third and fourth segments33,34. The first, second, and third segments31,32,33of the first closed-loop radiating element3are flush with the first, second, and third edges23,24,25of the dielectric substrate2, respectively. In this embodiment, each of the first and second segments31,32of the first closed-loop radiating element3has a dimension of 16 millimeters, and each of the third and fourth segments33,34of the first closed-loop radiating element3has a dimension of 15 millimeters. Such dimensions work favorably toward achieving a small physical size of the fractal dipole antenna1of this invention.

The second closed-loop radiating element5is formed on the first surface21of the dielectric substrate2, is spaced apart from the first closed-loop radiating element3, has a generally rectangular shape, and includes opposite first and second segments51,52and opposite third and fourth segments53,54. The first, second, and third segments51,52,53of the second closed-loop radiating element5are flush with the first, second, and fourth edges23,24,26of the dielectric substrate2, respectively. In this embodiment, the first and second closed-loop radiating elements3,5are symmetrical along a first symmetrical axis (I).

In an alternative embodiment, each of the first and second closed-loop radiating elements3,5has one of a square shape, a circular shape, an elliptical shape, and a triangular shape.

The first fractal radiating element4is formed on the first surface21of the dielectric substrate2, is surrounded by the first closed-loop radiating element3, and includes spaced apart first and second fractal members41,42, each of which is connected to the fourth segment34of the first closed-loop radiating element3. In this embodiment, the first and second fractal members41,42of the first fractal radiating element4are symmetrical along a second symmetrical axis (II) transverse to the first symmetrical axis (I). Preferably, with further referenceFIG. 2, each of the first and second fractal members41,42of the first fractal radiating element4has a shape of a Hilbert curve.

It is noted that an iteration ratio of self-similarity of the shape of each of the first and second fractal members41,42of the first fractal radiating element4is two.

In an alternative embodiment, each of first and second fractal members41,42of the first and second fractal radiating element4has a shape of one of a Pythagorean tree, a Cantor set, a Sierpinski gasket, a Sierpinski carpet, a Koch curve, a Ceasro curve, a Levy curve, a Peano curve, a Dragon curve, an H-fractal, and a tree fractal.

The second fractal radiating element6is formed on the first surface21of the dielectric substrate2, is surrounded by the second closed-loop radiating element5, and includes spaced apart first and second fractal members61,62, each of which is connected to the fourth segment54of the second closed-loop radiating element5. In this embodiment, the second fractal radiating element6is symmetrical to the first fractal radiating element4along the first symmetrical axis (I).

The fractal dipole antenna1further includes spaced apart first and second protrusions8,9formed on the first surface21of the dielectric substrate2and disposed between the first and second closed-loop radiating elements3,5. The first protrusion8has a T-shape, and includes a first segment81that extends from the fourth segment34of the first closed-loop radiating element3and that is disposed parallel to the first symmetrical axis (I), and a second segment82that extends transversely from the first segment81of the first protrusion8and along the second symmetrical axis (II) and that is connected to a signal source (not shown). The second protrusion9has a T-shape, and includes a first segment91that extends from the fourth segment54of the second closed-loop radiating element5and that is disposed parallel to the first symmetrical axis (I), and a second segment92that extends transversely from the first segment91of the second protrusion9and along the second symmetrical axis (II) and that is connected to an electrical ground (not shown) In this embodiment, the first and second protrusions8,9are symmetrical along the first symmetrical axis (I).

The fractal dipole antenna1further includes spaced apart first and second coupling elements71,72that are formed on the second surface22of the dielectric substrate2and that are disposed between the first and second-closed loop radiating elements3,5and between the first and second protrusions8,9. The construction as such permits the fractal dipole antenna1of this invention to achieve a wide operating bandwidth. In this embodiment, the first and second coupling elements71,72are symmetrical along the second symmetrical axis (II). Preferably, each of the first and second coupling elements71,72has a T-shape.

Experimental results, as illustrated inFIG. 3, show that, the fractal dipole antenna1of this invention indeed has a wide operating bandwidth. Moreover, as illustrated inFIG. 4, the fractal dipole antenna1of this invention has a substantially figure-of-eight radiation pattern on the E-plane and a substantially omnidirectional radiation pattern on the H-plane when operated at 3570 MHz. Further, as illustrated inFIG. 5, the fractal dipole antenna1of this invention has a high gain.