Patent Publication Number: US-6222490-B1

Title: Fishbone-shaped patch antenna

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to antenna and more particularly to a fishbone-shaped patch antenna employed in radio communication base station for transmitting signals to mobile terminal and receiving signals from mobile terminal with increased half-power beamwidth in the horizontal plane. 
     2. Related Art 
     Mobile phones have become popular in recent years. More people use it as a necessary communication means in daily life. In use, mobile phone has a similar function as wired telephone. That is, mobile phone can effect a two-way communication. Further, each mobile phone has a unique number. Each mobile phone user can make a call to a called party by transmitting encoded signals via base station. 
     It is understood that most base stations effect a cellular communication principle. That is a high power transmitter for covering all areas is replaced by employing a plurality of low power transmitters in many sectors called cells. As such, many cells are employed to ensure a sufficient communication quality and desired transmitting and receiving ranges. In view of this, transmission power of base station and horizontal and vertical angle ranges of antenna are important factors. It is desired that a cost-effective design may be effected by employing a small number of antennas to obtain a wider transmission and receiving ranges. 
     A prior art rectangular patch antenna  10  is shown in FIG. 1 comprising a slot coupled microstrip patch antenna  20  made of low loss dielectric plate having a microstrip  21  in rear and a gap or slot  22  in front being connected to signal source (not shown) through a conductor  40 ; a reflector  30  made of metal plate being non-electrically connected to the rear of slot coupled microstrip patch antenna  20  so as to cause rearward radiated electromagnetic waves to reflect forward; and a resonant member  11  in front of and being non-electrically connected to slot coupled microstrip patch antenna  20  so as to increase directivity, operation band width, an d power of electromagnetic waves. 
     Signals transmitted by above antenna have a half-power beamwidth with average value of 60°-70° in the center or a maximum value of 80° in the horizontal plane. As such, it is impossible to obtain a wider transmission and receiving ranges by such conventional rectangrular antenna. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a fishbone-shaped patch antenna employed in radio communication base station serving, as signal transmitting/receiving terminal between base station and a plurality of mobile terminals, thereby increasing half-power beamwidth in the horizontal plane. 
     The advantages of the present invention are realized by providine a fishbone-shaped patch antenna comprising a slot coupled microstrip patch antenna, a reflector, and a fishbone-shaped resonant member in front of and being non-electrically connected to the slot coupled microstrip patch antenna for increasing half-power beamwidth of electromagnetic waves wherein fishbone-shaped resonant member has a planar elongated shape with a plurality of teeth formed on either of the longer edges. This fishbone-shaped resonant member can increase transmission angle as compared with conventional rectangular resonant member in the base station for obtaining a wider range of transmitting/receiving signals. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, arc given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become fully understood from the detailed description given hereinbelow illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 is a perspective view of a conventional rectangular antenna; 
     FIG. 2 is a perspective view of a first preferred embodiment of fishbone-shaped patch antenna according to the invention; 
     FIGS. 3A-3C are diagrams showing directivities measured in various operating frequencies by the conventional rectangular antenna; and 
     FIGS. 4A-4C are diagrams showing directivities measured in various operating frequencies by the fishbone-shaped patch antenna of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Generally speaking, based on applications, a number of parameters are considered in designing a desired patch antenna. These parameters comprises operating frequency, half-power beamwidth in the transmission vertical plane and horizontal plane, voltage standing wave ratio, and antenna gain. An optimal patch antenna is obtained by modifying these parameters. In view of the conventional rectangular antenna shown in FIG. 1, it is found that a reduced width of resonant member  11  has the effect of increasing half-power beamwidth in the horizontal plane. But it is not possible to arbitrarily increase the width of resonant member  11  when considering the factors such as operation bandwidth, return loss, and antenna gain. As such, there is a limit in reducing the width of resonant member  11  for increasing half-power beamwidth in the horizontal plane. 
     Referring to FIG. 2, there is shown a fishbone-shaped patch antenna  10   a  constructed in accordance with the invention comprising a slot coupled microstrip patch antenna  20   a  being in the shape of plate having a microstrip  21   a  in rear, a slot  22   a  in front being connected to signal source (not shown) through a conductor  40   a ; a reflector  30   a  made of metal plate (e.g., aluminium plate. steel plate, or plastic plate with metal film (e.g., copper film) coated) being non-electrically connected to the rear of slot coupled microstrip patch antenna  20   a  so as to cause rearward radiated electromagnetic waves to reflect forward; and a fishbone-shaped resonant member  12  having a planar elongated shape as compared to the rectangular shape of conventional one. Fishbone-shaped resonant member  12  has a plurality of teeth formed on either of the longer sides. Fishbone-shaped resonant member  12  is made of aluminium (Al) or copper (Cu) with good conductivity. 
     As shown, fishbone-shaped edges parallel to vertical resonant axis of resonant member  12  has the effect of increasing half-power beamwidth by the amount of 5-10. It is important to note that such toothed portion is related to operational frequency in respect of the size of tooth. Further, frequency changes as the tooth density changes. As such, there is no fixed size for toothed portion. Moreover, the distribution of current of resonant member  12  has a concentration in the vicinity of the vertical axis when antenna is operating in the resonant frequency. As such, a significant increase of half-power beamwidth in horizontal plane is obtained when leak current concentrates on the resonant axis. That is the reason why the fishbone-shaped resonant member  12  of the invention has more teeth in the center portion, i.e., in the vicinity of vertical resonant axis of fishbone-shaped resonant member  12 . 
     In addition, there are three types of antennas being formed by combining slot coupled microstrip patch antenna  20   a  and reflector  30   a  as detailed below. 
     1. Microstrip antenna. It serves as front open circuit of microstrip  21   a . One side of dielectric substrate of microstrip  21   a  is formed by conductor, while a plurality of feed lines are formed on the other side. Such conductor operates as an unlimited conductor when the width of conductor beneath substrate is larger than that of feed line. Further, a virtual impedance is generated in the microstrip section between the open circuit and the slot for matching with the antenna impedance. 
     2. Slot antenna. Slot  22   a  is located on resonant member  12 . Slot  22   a  has an appropriate length. As such, slot  22   a  can also serve as antenna. An electric field is generated when a high frequency current is applied to the narrow region of slot  22   a  which in turn causes a resonance. As such, slot  22   a  can transfer energy to fishbone-shaped resonant member  12  located above in order to generate a coupling effect. This coupling effect may generate a resonance between resonant member  12  and ground. This resonance phenomenon is employed by the slot-couple stacked microstrip antenna  20   a  of the invention. 
     3. Antenna with reflector  30   a . The simplest technique to decrease rearward radiation and cause rearward radiated electromagnetic waves to reflect forward is to mount reflector  30   a  in the rear of antenna. A larger antenna gain or better directivity is obtained if the size of reflector  30   a  is much larger than that of wavelength. It is also found that a certain amount of electromagnetic waves may rearward radiate in reflector  30   a  with limited size. This has an adverse effect to antenna gain. 
     Signals my be transmitted through fishbone-shaped resonant member  12  after combining above three types of antennas. Moreover, a wider half-power beamwidth in the horizontal plane may be obtained by adjusting the shape of toothed portion and the geometry along the symmetrical edges of resonant axis of fishbone-shaped resonant member  12 . 
     Referring to FIGS. 3A-3C, there is shown directivities measured in various operating frequencies by the conventional rectangular antenna wherein bandwidth is 68° and gain is 11.7 dBi at −3 dB operated in 1,850 MHz in FIG. 3A, bandwidth is 67° and gain is 11.5 dBi at −3 dB operated in 1,920 MHz in FIG.  3 B. and bandwidth is 70° and gain is 11.2 dBi at −3 dB operated in 1,990 Mhz in FIG.  3 C. 
     FIGS. 4A-4C illustrate directivities measured in various operating frequencies by the fishbone-shaped patch antenna of the invention wherein bandwidth is 83.9° and gain is 10.2 dBi at −3 dB operated in 1,850 MHz in FIG. 4A, bandwidth is 85.2° and gain is 10 dBi at −3 dB operated in 1,920 MHz in FIG. 4B, and bandwidth is 87.5° and gain is 10.1 dBi at −3 dB operated in 1,990 MHz in FIG.  4 C. 
     In comparison of data obtained by conventional antenna and fishbone-shaped patch antenna of the invention, it is found that bandwidth of the invention is increased about 15° to 18° in respective operational frequency. 
     This invention provides a fishbone-shaped patch antenna employed in base station for increasing, half-power beamwidth in the horizontal plane, obtaining a wider signal transmitting and receiving angles. Preferably, this invention is implemented as antenna for mobile communication. Most preferably, this invention can be implemented in any of radio communication systems. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.