Abstract:
A broadband dipole array antenna adopted for use in radio transmission includes a feed network, radiation units and a reflection plate. The antenna is held vertically in a trough of the reflection plate, which reflects the radiation signals of the antenna to enhance antenna directionality. The antenna and the reflection plate are fastened with adhesive tape or a Velcro strip in the trough to facilitate assembly of the antenna.

Description:
FIELD OF THE INVENTION 
   The invention relates to a broadband dipole array antenna adopted for use on electronic devices to perform radio transmission, and particularly a broadband dipole array antenna that is equipped with a reflection plate with a trough formed thereon. 
   BACKGROUND OF THE INVENTION 
   With continuous advances in the wireless communication industry, users can transmit information through radio transmission systems without geographical restrictions. The antenna is an important element in such radio transmission systems. Commonly used antennas include dipole antennas, helical antennas, and the like. 
   While radio transmission is relatively free from geographical restriction, when the antenna is installed on a location with geographical obstacles (such as corners of walls, ceiling, etc.), its directional gain drops, and the communication quality of signal transmission and reception suffers. To remedy this problem, a common approach is to install a reflection plate on one side of the antenna to enhance the directionality of the antenna, boost the directional gain and improve communication quality. 
   R.O. C. patent No. 558080 entitled “Dipole antenna equipped with a reflection plate” discloses a reflective dipole antenna. It has a dipole antenna and a reflection plate. The reflection plate has an opening and is spaced from one side of the dipole antenna at a selected distance. The shortest distance between the dipole antenna and the reflection plate is 1/4λ (λ is the wavelength of the frequency spectrum). The reflection plate reflects radiation signals to improve the directional gain of radiation reception and transmission of the dipole antenna. 
   While the reflection plate can reflect the radiation signals to improve directional gain, it still is not adequate when high directionality is required. Moreover, the reflection plate has to be spaced from the antenna at a selected distance (¼λ), causing difficulty in assembly. Hence how to improve the directionality of the antenna and facilitate convenience of assembly have become issues to be resolved. 
   Refer to  FIG. 1  for a conventional antenna  10  that adopts a series feed network design. Such a design is applicable only in a selected and narrow frequency spectrum (such as 4.9˜5.0 GHz, U-NII-One/Two 5.15˜5.35 GHz, U-NII-Three 5.725˜5.875 GHz). It cannot be used with radio communication that covers multiple frequency spectrums (such as 4.9˜5.875 GHz). In such a situation, two or more antennas have to be used. Hence to increase the antenna transmission bandwidth to free users from procuring additional antennas is also is an issue to be addressed. 
   SUMMARY OF THE INVENTION 
   In view of the aforesaid problems occurring with the conventional techniques, the invention provides a broadband dipole array antenna that has a dipole array antenna and a reflection plate coupled in a normal manner to reflect the antenna radiation signals in a selected direction and enhance the directionality of the antenna. It also has a feed network containing a zigzag circuit to achieve a broad bandwidth. 
   In order to achieve the foregoing object, the broadband dipole array antenna according to the invention includes a feed network, radiation units and a reflection plate. The antenna is a printed circuit antenna with a first surface and a second surface. The feed network and the radiation units are located respectively on the first surface and the second surface to increase transmission bandwidth and generate radiation signals. 
   The reflection plate has a trough to hold the antenna vertically and reflect the radiation signals generated by the radiation units in a selected direction to enhance the directionality of the antenna. 
   The antenna and the reflection plate may be fastened with adhesive tape or a Velcro strip to facilitate assembly. Another fastening approach is to form apertures on the inner walls of the trough and the antenna on corresponding locations to be coupled by fastening elements. 
   The dipole antenna array thus constructed uses the reflection plate to enhance antenna directionality and boost directional gain. Fastening of the antenna and the reflection plate is more convenient. Hence the antenna directionality and convenience of antenna assembly are greatly improved. 
   The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of the feed network of a conventional Series Feed antenna; 
       FIG. 2  is an exploded view of the antenna of the invention; 
       FIG. 3  is a perspective view of the antenna of the invention after assembly; 
       FIG. 4A  is a plain view of a first surface of the antenna base-board of the invention; 
       FIG. 4B  is a plain view of a second surface of the antenna base-board of the invention; 
       FIG. 5A˜5C  are a radiation field graphic of V-polarization according to the invention; 
       FIG. 6A˜6C  are a radiation field graphic of H-polarization according to the invention; and 
       FIG. 7  is a chart of the voltage stationary wave ratios according to the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 2 , the broadband dipole array antenna according to the invention includes an antenna  10 , a reflection plate  20 , a metal conductive wire  30 , a connector  40 , a seat  50  and a shell  60 . 
   The antenna  10  is wedged vertically in a trough formed on the reflection plate  20 . It is a printed circuit antenna made from non-metallic material (such as Rogers RO-4350B). It has a first surface  101  and a second surface  102  formed with a required circuit pattern by chemical etching. 
   The reflection plate  20  has lugs  21  and  22  extended from two ends to wedge in slots formed on the seat  50  and the shell  60  to anchor thereon. The reflection plate  20  is made of metal that has a shielding effect upon electromagnetic waves, and can therefore reflect radiation signals generated by the antenna  10  in a selected direction to boost the directional gain of the antenna. 
   The seat  50  is formed substantially in an L-shape to anchor on a bracing rack (not shown in the drawing) and house the connector  40 . The connector  40  has one end connected to a signal feeding point  11  of the antenna  10  through the metal conductive wire  30 , and another end connected to an electronic device (not shown in the drawing). 
   The shell  60  is coupled with the seat  50  to encase the antenna  10  and the reflection plate  20  to provide protection. Refer to  FIG. 3 , the shell  60  and the seat  50  form a sealed body to cover the antenna  10  and the reflection plate  20 . 
   Refer to  FIG. 4A  for the first surface of the antenna base-board. The first surface  101  has a feed network  110 , which includes a signal feeding point  11  to serve as the center, a first feeding unit  111 , a second feeding unit  112 , a third feeding unit  113 , a fourth feeding unit  114 , and a fifth feeding unit  115 , which are formed symmetrically on the left side and the right side to become the feed network  110 . Each feeding unit has a different zigzag circuit, is extended towards two sides of the antenna  10  from the signal feeding point  11  in a zigzag manner with a decreasing zigzag path, and is connected to a transmission bus  150 . The zigzag path forms the same phase from the signal feeding point  11  to each radiation unit  120  to increase transmission bandwidth. Moreover, each branch point is coupled with an impedance matching section  151  to match the required impedance of the circuit. 
   Refer to  FIG. 4B  for the second surface of the antenna base-board. The radiation units  120  are located on the second surface  102  to couple with the signals of the feed network  110  and transmit them by radiation. Each radiation unit  120  is substantially formed in a T-shape. The signals radiated in the direction of the horizontal ends of the T-shaped structure are wider than those of the vertical end, thus having a more desirable directionality. When laying in a parallel manner directionality improves. Also, each radiation unit  120  corresponds to a feeding unit, and the radiation has a different signal gain depending on the corresponding feeding unit. This arrangement boosts the directional gain of the signals. 
   The reflection plate  20  has a trough to couple with the antenna  10  vertically and converge the electromagnetic wave radiated from the antenna  10  in a selected direction to enhance the directionality of the antenna  10 . The reflection plate  20  is made of metal such as aluminum, iron or stainless steel. The depth of the trough affects the field shape direction range of the antenna  10 . When the radiation unit  120  is located in the trough, the antenna  10  has a narrower field shape direction range. When the radiation unit  120  is located outside the trough, the antenna  10  has a wider field shape direction range. 
   The reflection plate  20  and the antenna  10  may be anchored on the lateral sides of the trough with adhesive tape or a Velcro strip to make assembly easier. Another approach is to form a plurality of first apertures  20   a  on the lateral sides of the trough of the reflection plate  20  and a plurality of second apertures  20   b  on the antenna  10  that correspond to each other and are coupled by fastening elements (such as plastic rivets, nails, plastic screws, and the like) to fasten and anchor the reflection plate  20  and the antenna  10 . 
   In addition, the invention conforms to IEEE (Institute of Electrical and Electronic Engineers) 802.11a communication protocols. By fine-tuning the distance of the feed network  110  and the radiation units  120 , and the elevation of the reflection plate  20 , the invention may be used in the frequency spectrums ranging from 4.9 GHz to 5.875 GHz. 
   The dipole array antenna thus constructed can reflect and converge radiation signals to enhance the directionality of the antenna. By coupling the reflection plate and the antenna in a vertical manner, and anchoring both with adhesive tape or a Velcro strip, assembly is more convenient. Thus the antenna directionality and convenience of assembly are improved. Also, the zigzag circuit design of the feed network allows the broadband antenna to achieve an even wider transmission bandwidth. 
   Actual tests of the invention have been conducted based on frequencies 5.15 GHz, 5.50 GHz, and 5.85 GHz. The results are indicated in radiation field graphics and a voltage stationary wave ratio test chart as follows.  FIG. 5A˜5C  are the radiation field graphic of V-polarization.  FIG. 6A˜6C  are the radiation field graphic of H-polarization.  FIG. 7  is the chart of the measured voltage stationary wave ratios with frequencies in the range of 4.50 GHz ˜6.50 GHz. 
   While the preferred embodiment of the invention has been set forth for the purpose of disclosure, modifications of the disclosed embodiment of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.