Dual-fed coupled stripline PCB dipole antenna

[0002] 1. Field of the Invention

[0003] The present invention relates in general to wireless communication systems and components, and in particular to a printed circuit board configured dual-fed coupled stripline PCB dipole antenna.

[0004] 2. Description of the Related Art

[0005] Communication system designers are constantly seeking ways to improve the performance of system components and signal processing circuits, but without substantially increasing complexity of hardware or costs. For example, designers always want received and transmitted signals to be stronger. Almost all conventional antennas have had either only one plane (XZ-plane or YZ-plane or XY-plane) with significant polarization energy, or a complicated or excessively large structure.

[0006] A conventional sleeve antenna comprises a radiation element having an electrical length of one quarter wavelength, a sleeve having an electrical length of one quarter wavelength, and a coaxial cable for feeding electric power to the radiation element. An outer conductor of the coaxial cable is connected to the sleeve, while an inner conductor of the coaxial cable is connected to the radiation element.

[0007] A conventional inverted coaxial dipole antenna has a central conductor of a coaxial cable connected via a feeding line to a sleeve, wherein the feeding line is extended through a slot which is formed in an outer tube of the antenna.

[0008] A conventional stripline antenna is shown in FIG. 4. The antenna comprises a coupler 70, a radiation element 72 spaced apart from but adjacent the coupler 70 and serving as an antenna element, a dielectric substrate 75 on which the antenna element is disposed, a ground plane 74 under the dielectric substrate 75, a feed point 71 on the coupler 70, and a short point 73 disposed on the radiation element 72 and shorted to the ground plane 74.

[0009] Conventional antennas such as those described above have a number of disadvantages.

[0010] Conventional sleeve antennas and inverted coaxial dipole antennas involve complicated fabrication and adjustment, because the feeding coaxial cable is connected to the sleeve. This makes quality control in manufacturing difficult.

[0011] Stripline or microstrip antennas can solve the above problems associated with conventional sleeve antennas and inverted coaxial dipole antennas. However, the polarization energy of stripline or microstrip antennas is significant in only one plane (XZ-plane or YZ-plane or XY-plane), and is minimal or even faded in the other two planes. Additionally, the intensity of the utilized polarization energy changes with the orientation of the antenna. Thus optimum radiation efficiency may not be always achieved. For documentation that describes and illustrates conventional antennas, attention is directed to U.S. Pat. No. 4,069,483 and Taiwan Patent Application No. 87112281.

[0012] U.S. Pat. No. 4,833,482 discloses a circularly polarized microstrip antenna array which comprises two independent linearly polarized arrays. The first and second antenna arrays are fed with two independent signals about 90 degrees apart, and independently radiate a horizontally linearly polarized wave and a vertically linearly polarized wave respectively. Far afield, these waves become a circularly polarized wave. Each antenna array also has a plurality of stripline conductors having a plurality of radiation elements protruding outwardly therefrom in a direction of about 45 degrees from the stripline conductors. This antenna arrangement, however, is difficult to manufacture and increases production costs. Moreover, the stripline conductors disposed adjacent each other cause mutual interference, which reduces radiation efficiency. The copending application with an unknown serial number filed Mar. 5, 2001 with the title “STRIPLINE PCB DIPOLE ANTENNA” having the same inventors and the same assignee with the instant application, discloses one approach to improve the aforementioned shortcomings.

[0013] A preferred embodiment of the present invention provides two dipole antenna elements that are arranged perpendicularly to each other to form a single antenna, a PCB on which the two dipole antenna elements are disposed, and two feeding lines connected with the two dipole antenna elements respectively. This perpendicular arrangement makes use of two planes of the XZ-plane, XY-plane and YZ-plane. The antenna obtains optimum polarization energy by selecting the strongest energy plane. This achieves maximized radiation efficiency under any particular orientation of the antenna. The strongest energy plane is selected by controlled switching, by means of dual-fed signal mode.

[0014] In order to effectively minimize interference, two T-shaped dipole arms of each dipole antenna element are disposed on opposite surfaces of the PCB. Such T-shaped configurations also make the antenna more compact.

[0015] FIG. 1 is a top plan view of a dual-fed coupled stripline PCB dipole antenna in accordance with the present invention.

[0016] FIG. 2 is a perspective view of the antenna of FIG. 1.

[0017] FIG. 3 is a graph of experimental results for the antenna of FIG. 1.

[0018] FIG. 4 is a perspective view of a section of a conventional antenna.

[0019] As indicated in the above description of the related art, conventional antennas often neglect two of the three polarization energy planes. It has been found that improved performance is achieved by providing two dipole antenna elements perpendicular to each other, as detailed below.

[0020] Referring to FIGS. 1 and 2, a dipole antenna of the present invention comprises two dipole antenna elements 1, 2 which are substantially the same as each other, a generally square PCB 3, and two feeding lines 4 which comprise coaxial electric cables.

[0021] Since both dipole antenna elements 1, 2 are essentially the same, only the dipole antenna element 1 will be described in detail. The dipole antenna element 2 will be described only briefly. The dipole antenna element 1 is made from copper cladding, and comprises first and second dipole arms 11, 12. The first dipole arm 11 comprises a first head section 111, a first arm section 112, and a second arm section 113. Similarly, the second dipole arm 12 comprises a second head section 121, a third arm section 122 and a fourth arm section 123. The first and second head sections 111, 121 may be trapezoid, rectangular, triangular etc., and are aligned with each other and symmetrically opposite each other. In the preferred embodiment, the first and second head sections 111, 121 are generally trapezoid. The first and third arm sections 112, 122 respectively extend to the first and second head sections 111, 121, and serve as transmission sections of the dipole antenna element 1. The second and fourth arm sections 113, 123 are thin rectangular strips, and are perpendicular to and contact the first and third arm sections 112, 122, respectively. One of the second and fourth arm sections 113, 123 serves as a coupler shorted to the ground, and the other of the second and fourth arm sections 113, 123 serves as a radiation section of the dipole antenna element 1. First and second feed points 5, 6 are provided on the first and second head sections 111, 121, respectively.

[0022] The PCB 3 serves as a substrate, and has an upper surface 31 and a lower surface 32. Each feeding line 4 comprises an outer cylindrical conductor (not labeled), and a coaxial internal conductor (not labeled). The outer and inner conductors are connected with the first and second feed points 5, 6, respectively.

[0023] The first and second dipole arms 11, 12 are disposed on the lower surface 32 and the upper surface 31 of the PCB 3, respectively. A width of the first arm section 112 gradually increases from one end thereof to another end thereof. The first arm section 112 is wider than the third arm section 122. This configuration can broaden frequency band.

[0024] The dipole antenna element 2 is substantially the same in structure as the dipole antenna element 1. The dipole antenna elements 1, 2 are generally perpendicular to each other, and are arranged at two adjacent side portions of the PCB 3. Corresponding functional sections of the dipole antenna elements 1, 2 are perpendicular to each other, including the corresponding radiation sections. Thus the dipole elements 1, 2 independently radiate a horizontally linearly polarized wave and a vertically linearly polarized wave, respectively. Under any given orientation, the dipole antenna can measure the two polarization energy planes produced, compare the measurements, and then select the stronger of the two planes by controlling the feeding lines 4.

[0025] As is well known in the art, VSWR is one of the most important standards for measuring antenna characteristics. Prevailing industry standards require that VSWR be less than 2.0. As seen in FIG. 3, the dual-fed coupled stripline PCB dipole antenna of the present invention meets this requirement.

[0026] The VSWRs of the dipole antenna elements 1, 2 are both less than 2.0 in a frequency band ranging between 2.4 GHz and 2.5 GHz.

[0027] While an embodiment in accordance with the present invention has been shown and described, it is to be understood that the present invention is not limited to such embodiment. Numerous changes and modifications can be made to the present invention as known to persons skilled in the art, without departing from the spirit and scope of the present invention. The invention is therefore not to be limited to the details shown and described herein, but is intended to cover all such changes and modifications as are obvious to persons of ordinary skill in the art.