Fractal dipole antenna

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.

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.

Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiment with reference to the accompanying drawings, of which:

FIG. 1 is a perspective view of the preferred embodiment of a fractal dipole antenna according to the present invention;

FIG. 2 is a schematic top view of a Hilbert curve;

FIG. 3 is a plot illustrating a return loss of the preferred embodiment;

FIG. 4 shows plots of radiation patterns of the preferred embodiment on the E-plane and H-plane; and

FIG. 5 is a plot illustrating a gain of the preferred embodiment.

Referring to FIG. 1 , the preferred embodiment of a fractal dipole antenna 1 according to this invention is shown to include a dielectric substrate 2 , first and second closed-loop radiating elements 3 , 5 , and first and second fractal radiating elements 4 , 6 .

The fractal dipole antenna 1 of 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 substrate 2 has a generally rectangular shape, opposite first and second surfaces 21 , 22 , opposite first and second edges 23 , 24 , and opposite third and fourth edges 25 , 26 . In this embodiment, the dielectric substrate 2 is an FR-4 substrate.

The first closed-loop radiating element 3 is formed on the first surface 21 of the dielectric substrate 2 , has a generally rectangular shape, and includes opposite first and second segments 31 , 32 and opposite third and fourth segments 33 , 34 . The first, second, and third segments 31 , 32 , 33 of the first closed-loop radiating element 3 are flush with the first, second, and third edges 23 , 24 , 25 of the dielectric substrate 2 , respectively. In this embodiment, each of the first and second segments 31 , 32 of the first closed-loop radiating element 3 has a dimension of 16 millimeters, and each of the third and fourth segments 33 , 34 of the first closed-loop radiating element 3 has a dimension of 15 millimeters. Such dimensions work favorably toward achieving a small physical size of the fractal dipole antenna 1 of this invention.

The second closed-loop radiating element 5 is formed on the first surface 21 of the dielectric substrate 2 , is spaced apart from the first closed-loop radiating element 3 , has a generally rectangular shape, and includes opposite first and second segments 51 , 52 and opposite third and fourth segments 53 , 54 . The first, second, and third segments 51 , 52 , 53 of the second closed-loop radiating element 5 are flush with the first, second, and fourth edges 23 , 24 , 26 of the dielectric substrate 2 , respectively. In this embodiment, the first and second closed-loop radiating elements 3 , 5 are symmetrical along a first symmetrical axis (I).

In an alternative embodiment, each of the first and second closed-loop radiating elements 3 , 5 has one of a square shape, a circular shape, an elliptical shape, and a triangular shape.

The first fractal radiating element 4 is formed on the first surface 21 of the dielectric substrate 2 , is surrounded by the first closed-loop radiating element 3 , and includes spaced apart first and second fractal members 41 , 42 , each of which is connected to the fourth segment 34 of the first closed-loop radiating element 3 . In this embodiment, the first and second fractal members 41 , 42 of the first fractal radiating element 4 are symmetrical along a second symmetrical axis (II) transverse to the first symmetrical axis (I). Preferably, with further reference FIG. 2 , each of the first and second fractal members 41 , 42 of the first fractal radiating element 4 has 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 members 41 , 42 of the first fractal radiating element 4 is two.

In an alternative embodiment, each of first and second fractal members 41 , 42 of the first and second fractal radiating element 4 has 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 element 6 is formed on the first surface 21 of the dielectric substrate 2 , is surrounded by the second closed-loop radiating element 5 , and includes spaced apart first and second fractal members 61 , 62 , each of which is connected to the fourth segment 54 of the second closed-loop radiating element 5 . In this embodiment, the second fractal radiating element 6 is symmetrical to the first fractal radiating element 4 along the first symmetrical axis (I).

The fractal dipole antenna 1 further includes spaced apart first and second protrusions 8 , 9 formed on the first surface 21 of the dielectric substrate 2 and disposed between the first and second closed-loop radiating elements 3 , 5 . The first protrusion 8 has a T-shape, and includes a first segment 81 that extends from the fourth segment 34 of the first closed-loop radiating element 3 and that is disposed parallel to the first symmetrical axis (I), and a second segment 82 that extends transversely from the first segment 81 of the first protrusion 8 and along the second symmetrical axis (II) and that is connected to a signal source (not shown). The second protrusion 9 has a T-shape, and includes a first segment 91 that extends from the fourth segment 54 of the second closed-loop radiating element 5 and that is disposed parallel to the first symmetrical axis (I), and a second segment 92 that extends transversely from the first segment 91 of the second protrusion 9 and along the second symmetrical axis (II) and that is connected to an electrical ground (not shown) In this embodiment, the first and second protrusions 8 , 9 are symmetrical along the first symmetrical axis (I).

The fractal dipole antenna 1 further includes spaced apart first and second coupling elements 71 , 72 that are formed on the second surface 22 of the dielectric substrate 2 and that are disposed between the first and second-closed loop radiating elements 3 , 5 and between the first and second protrusions 8 , 9 . The construction as such permits the fractal dipole antenna 1 of this invention to achieve a wide operating bandwidth. In this embodiment, the first and second coupling elements 71 , 72 are symmetrical along the second symmetrical axis (II). Preferably, each of the first and second coupling elements 71 , 72 has a T-shape.

Experimental results, as illustrated in FIG. 3 , show that, the fractal dipole antenna 1 of this invention indeed has a wide operating bandwidth. Moreover, as illustrated in FIG. 4 , the fractal dipole antenna 1 of 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 in FIG. 5 , the fractal dipole antenna 1 of this invention has a high gain.

While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this invention is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.