Patent Publication Number: US-6661391-B2

Title: Antenna and radio device comprising the same

Description:
FIELD OF THE INVENTION 
     The present invention relates to fixed an antenna to a radio communication apparatus for mobile communications, and a radio communication apparatus using the same antenna. 
     BACKGROUND OF THE INVENTION 
     In recent years, as a demand for mobile communications has drastically increased, radio communication apparatuses have been developed in a wide variety of forms. An example of this diversity is a radio communication apparatus capable of transmitting/receiving radio waves in multi-ranged frequency bands so that a single radio communication apparatus can handle as much information as possible. Such an apparatus includes an antenna having desirable impedance characteristics over multi-ranged frequency bands. 
     A mobile phone system is a typical example of mobile communications, which is now widely used all over the world. A frequency bandwidth for the mobile phone system varies by region: Personal Digital Cellular 800 (PDC 800) in Japan uses a frequency in a range of from 810 to 960 MHz. On the other hand, in the West, a range of from 890 to 960 MHz is used for Group Special Mobile Community (GSM), a range of from 1,710 to 1,880 MHz for Personal Communication Network (PCN), and a range of from 1,850 to 1,990 MHz for Personal Communication System (PCS). Generally, for a mobile phone corresponding to each of the multi-ranged frequency bands, a helical antenna element formed of helically wound conductive wire is widely used. 
     FIG. 12 is a general sectional view of a prior-art antenna for two frequency bands—for a range of from 890 to 960 MHz of GSM and for a range of from 1,710 to 1,880 MHz of PCN. FIGS. 13 and 14 are graphs that represent frequency characteristics of voltage standing wave ratio (VSWR) showing impedance characteristics. 
     In antenna  8  shown in FIG. 12, phosphor bronze wire-made antenna element  3  contains linear portion  1  at an inside of helical portion  2 , with a top end of linear portion  1  and helical portion  2  being connected to form one piece. Feed metal fitting  6  contains, at its top, recess portion  4  to which antenna element  3  is fixed, and at its bottom, mounting screw portion  5  by which fitting  6  is screwed into a radio communication apparatus. Dielectric resin material-made radome  7  partially covers antenna element  3  and feed metal fitting  6 . Fitting  6  is attached to a housing of a mobile phone to establish electric connections with radio-frequency circuitry of the mobile phone, so that antenna  8  can work for two frequency bands mentioned above. 
     In antenna  8  having the structure above, an electrical length totally gained from linear portion  1  and helical portion  2  of antenna element  3  is adjusted to about λ/2 in a frequency band for PCN, and is adjusted to about λ/4 in a frequency band for GSM. Thus, an electrical coupling between linear portion  1  and helical portion  2  of antenna element  3  allows impedance characteristics of antenna element  3  to be optimum in each frequency band. 
     In prior art antenna  8 , the impedance characteristics of antenna element  3  are required by which VSWR is to be at most 3 in each frequency band. However, it has been difficult for this conventional structure—i.e. an antenna element that is helically wound from one end of a straightened phosphor bronze wire—to satisfy this requirement. Suppose that an electrical length of antenna element  3  is adjusted to about λ/2 in the frequency band for PCN. As shown in FIG. 13, in the frequency band for PCN—between ▾ 3  and ▾ 4 —impedance characteristics with VSWR kept below  3  can be realized with help of an electrical coupling between liner portion  1  and helical portion  2 . On the other hand, in the frequency band for GSM—between ▾ 1  and ▾ 2 —a range with VSWR maintained below 3 becomes narrower. Now, to eliminate this inconvenience, suppose that the frequency band for GSM (between ▾ 1  and ▾ 2 ) is broadened by changing a diameter or pitch of helical portion  2  and readjusting an electrical length. This adjustment is no good for the PCN band—it changes an electrical length of antenna element  3  for the frequency band for PCN and an electrical coupling between linear portion  1  and helical portion  2 , so that VSWR in the frequency band for PCN (between ▾ 3  and ▾ 4 ) will be undesirably increased to be more than 4. Thus, there has been a problem with structure of the prior art antenna in that transmitting/receiving in either one of the frequency bands has been sacrificed for transmitting/receiving in the other of the frequency bands. 
     As another drawback, deformation or variations in diameter or pitch of helical portion  2  occurring during a manufacturing process of antenna element  3  can cause variations in impedance characteristics. For these variations, it has been difficult to get desired impedance characteristics. Providing a complicated impedance-matching circuit between an antenna and radio-frequency circuitry may be a measure for suppressing degradation of impedance characteristics due to the variations. However, this is apparently an obstacle to lower prices of mobile phones. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the problems above. It is therefore an object of the present invention to provide a reliable antenna with high productivity, which is capable of: having an easy adjustment of an electrical length of an antenna element; obtaining good impedance characteristics in desired multi-ranged frequency bands by a single antenna element; and eliminating impedance matching circuitry to minimize variations in impedance characteristics. At the same time, it is another object of the present invention to realize a cost-reduced radio communication apparatus using the antenna. 
     To achieve the aforementioned objects, the antenna of the present invention includes: an antenna element portion for transmitting/receiving waves in multi-ranged frequency bands; a feed portion for establishing electrical connections between the antenna element portion and radio-frequency circuitry of a radio communication apparatus; a dielectric material core rod mechanically supporting the antenna element portion; and a dielectric material radome partially covering the antenna element portion and the feed portion. The antenna element portion comprises an approximately helical-shaped portion and an approximately meander-shaped portion that are formed concentrically with the core rod. 
     The antenna of the present invention may be variously embodied as follows. 
     1) The dielectric material forming the core rod has a relative dielectric constant different from that of the dielectric material forming the radome. 
     2) A half-round and thin belt-shaped first conductor has a diameter generally equal to that of the core rod. A plurality of first conductors are disposed in parallel from a position close to an end of the core rod in an axial direction, at predetermined spaced intervals, on a front-round surface and rear-round surface of the core rod. Rows of the conductors are placed in a staggered arrangement between the front-round surface and the rear-round surface of the rod. A short and thin belt-shaped conductive plate joins adjacent ends of the first conductors, forming an approximately helical-shaped portion. A plurality of thin belt-shaped second conductors are placed in parallel on the core rod. As in the case of the first conductor, a short and thin belt-shaped conductive plate joins adjacent ends of the second conductors, forming an approximately meander-shaped portion. The approximately meander-shaped portion is disposed close to the approximately helical-shaped portion. 
     3) The antenna element portion may be formed from a die cutting-processed thin and conductive metal-plate. 
     4) The antenna element portion may be formed from a press-processed conductive metal-wire made of alloys of copper, or other metals, provided by an electrolytic plating process. 
     5) The antenna element portion may be formed by subjecting a thin conductive plate to an etching process to form a predetermined pattern, and then press-processing the pattern. 
     6) The antenna element portion may be formed from a press-processed flexible wiring board having a predetermined pattern formed thereon. 
     7) The antenna element portion may be formed by printing conductive paste. 
     8) The antenna element portion may be formed from sintered conductive powder. 
     9) One end of the approximately helical-shaped portion is joined with one end of the approximately meander-shaped portion so that the approximately helical-shaped portion and the approximately meander-shaped portion are disposed on the rod as a cascaded structure. 
     10) A position close to a tip of the core rod may have a connecting point, at which one end of the approximately helical-shaped portion and the approximately meander-shaped portion are connected, and at which these two portions seem to be “folded over”. The approximately meander-shaped portion is placed on the rod so as to be parallel to an axis of the approximately helical-shaped portion. 
     11) A position close to a tip of the core rod may have a connecting point, at which one end of the approximately helical-shaped portion and the approximately meander-shaped portion are connected, and at which these two portions seem to be “folded over”. At least a part of each second conductor of the approximately meander-shaped portion is circularly arc-shaped, having a diameter almost equal to that of the approximately helical-shaped portion. At the same time, an arrangement of the approximately meander-shaped portion is maintained to be concentric with the approximately helical-shaped portion, but having no contact with it. 
     12) The feed portion may be formed with the antenna element portion as one piece. 
     13) A dielectric material radome, which partially covers the antenna element portion and the feed portion, may be removed. 
     According to the present invention, each electrical length and its ratio of the approximately helical-shaped portion and the approximately meander-shaped portion can be defined easily. As compared with a conventional antenna, the antenna of the present invention can easily provide desired multi-ranged frequency bands with optimal impedance characteristics. This allows the antenna to be compact and cost-reduced, having advantages of wide frequency range, high antenna gain, and high reliability. 
     The present invention covers not only a radio communication apparatus equipped with the antenna, but also a radio communication apparatus equipped with two antennas for diverse communications. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view, taken partly in cross-section, of an antenna in accordance with a first preferred embodiment of the present invention. 
     FIG. 2 is a front view of the antenna in accordance with the first preferred embodiment. 
     FIG. 3 is a cross-sectional view seen from a front of the antenna in accordance with the first preferred embodiment. 
     FIG. 4 is a cross-sectional view seen from a right hand side of the antenna in accordance with the first preferred embodiment. 
     FIG. 5 is a top view of an antenna element of the antenna in accordance with the first preferred embodiment. 
     FIG. 6 is a graph indicating frequency characteristics of voltage standing wave ratio (VSWR) for the antenna in accordance with the first preferred embodiment. 
     FIG. 7 is a cross-sectional view seen from a front of an antenna in accordance with a second preferred embodiment. 
     FIG. 8 is a cross-sectional view seen from a right hand side of the antenna in accordance with the second preferred embodiment. 
     FIG. 9 is a circuit diagram of a radio communication apparatus, equipped with the antenna of the invention, of a third preferred embodiment. 
     FIG. 10 is a circuit diagram of a radio communication apparatus, equipped with the antenna of the invention, of a fourth preferred embodiment. 
     FIG. 11 is a circuit diagram of a radio communication apparatus, equipped with antennas of the invention, of a fifth preferred embodiment. 
     FIG. 12 is a cross-sectional view indicating an essential part of a prior art antenna. 
     FIG. 13 shows a graph indicating frequency characteristics of VSWR for the prior-art antenna. 
     FIG. 14 shows another example of a graph indicating frequency characteristics of VSWR for the prior art antenna. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention are described hereinafter with reference to the accompanying drawings, FIG.  1  through FIG.  11 . 
     First Preferred Embodiment 
     FIG. 1 is a perspective view, taken partly in cross-section, of an antenna in accordance with a first preferred embodiment of the present invention. FIG. 2 shows an appearance of the antenna. FIGS. 3 and 4 show cross-sectional views seen from a front side and from a right-hand side of the antenna, respectively. Antenna element  11  shown in FIG. 1 is formed through procedures below. 
     An approximately helical-shaped portion  12 , is made by die cutting and press-processing a thin metal plate having superior conductivity, such as a copper alloy plate. Similarly, an approximately meander-shaped portion  13 , is also made by die cutting and press-processing a thin metal plate having superior conductivity, such as a copper alloy plate. Approximately helical-shaped portion  12  and approximately meander-shaped portion  13  are connected to each other at top ends, forming antenna element  11 . Both portions  12  and  13  look like being folded over at a connecting point. Feed metal fitting  14  is connected to bottom end  13 A (see FIG. 3) of approximately meander-shaped portion  13  of antenna element  11 . Fitting  14  has, on its periphery, mounting screw portion  14 A (see FIG. 2) that is to be screwed into a radio communication apparatus using the antenna. 
     In FIGS. 1 and 2, core rod  15  is made of olefin elastomer resin having a dielectric constant of about 2.2. Rod  15  holds approximately helical-shaped portion  12  and approximately meander-shaped portion  13  of antenna element  11  so as to be concentric with an axis of the rod, providing a non-contacting state between both portions. Rod  15  also maintains an intimate contact with fitting  14 . Radome  16  is made of olefin elastomer resin having a dielectric constant of about 2.5. Radome  16  shields a periphery of antenna element I 1 , with a portion adjacent to mounting screw section  14 A of fitting  14  being exposed. 
     A shape of antenna element  11  is shown in detail in FIGS. 3 and 4. Half-round and thin belt-shaped first conductor  17  has a diameter generally the same as that of the core rod  15 . A plurality of first conductors  17  are disposed in parallel, from a position close to a tip of rod  15 , in its axial direction at predetermined spaced intervals on front-round surface  17 B and rear-round surface  17 A of the core rod. Rows of conductors  17  are placed on core rod  15  so as to form a staggered arrangement between the front-round surface and the rear-round surface of the rod. Short and thin belt-shaped conductors  18 A and  18 B join adjacent ends of the first conductors, forming approximately helical-shaped portion  12 . Similarly, a plurality of thin belt-shaped second conductors  19  are placed in parallel on a round surface of core rod  15 , from a position adjacent the tip of the rod, in its axial direction at predetermined spaced intervals. As in the case of the a joint for the first conductor, short and thin belt-shaped conductors  20 A and  20 B join adjacent ends of the second conductors, forming approximately meander-shaped portion  13 . As shown in FIG.  3  and FIG. 4, one end of approximately helical-shaped portion  12  is in an open circuited state, and another end is connected with one end of approximately meander-shaped portion  13  at joint  21  adjacent to the tip of core rod  15 . Feed metal fitting  14  is connected, as shown in FIG. 3, to another end  13 A of portion  13 . 
     In FIG. 4, each of joint portions  18 A,  18 B, and  20 A,  20 B is properly located so that second conductor  19  of approximately meander-shaped portion  13  is retained between each first conductor  17 B (indicated by solid lines in FIG.  3 ), remaining in a non-contacting state. In this way, approximately helical-shaped portion  12  and approximately meander-shaped portion  13  are formed. In this case, when antenna element  11  is formed from a combination of approximately helical-shaped portion  12  and approximately meander-shaped portion  13 , joint portions  20 A and  20 B have no contact with first conductors  17 . To realize this, as shown in the top view of the antenna element of FIG. 5, diameter C is a bit smaller than diameter D of second conductor  19  shaped to be generally half-round. In addition, joint portions  20 A,  20 B are slightly spaced from joint portions  18 A,  18 B, respectively. 
     The antenna of the embodiment is thus configured. Now will be described how the antenna works. 
     The antenna shown in FIG. 1 is screwed into a predetermined position of a radio communication apparatus (not shown) by screw portion  14 A formed around feed metal fitting  14 . Radio-frequency signals corresponding to waves transmitted/received through the antenna are communicated, via the fitting  14 , between a radio-frequency circuit (not shown) of the apparatus and the antenna. An electrical length of antenna element  11  is determined, through electrical coupling, at an optimal value having good VSWR characteristics in first and second frequency bands. 
     The electrical length is defined by many factors—an inductance of approximately helical-shaped portion  12  and approximately meander-shaped portion  13 , a stray capacitance between a plurality of the first conductors, a stray capacitance between a plurality of the second conductors, a stray capacitance between a plurality of the first conductors and a plurality of the second conductors, a dielectric constant of core rod  15 , and a dielectric constant of radome  16 . The electrical length is determined to about 3λ/8 through 5λ/8, which allows the antenna to have good impedance characteristics in the first frequency band. Similarly, the electrical length is determined to about λ/2 to provide the antenna with good impedance characteristics in the second frequency band. The two settings of the electrical length allow the antenna element  11  to effectively transmit/receive waves in two frequency ranges. A reason why single antenna element  11  can handle waves in two frequency ranges will be described below. 
     Like the antenna element of the embodiment, the prior art antenna element can change a diameter or pitch of a helical portion. In the prior art, however, a portion corresponding to approximately meander-shaped portion  13  of the embodiment can be changed only in its length and thickness due to a shape of a linear conductor. On the other hand, according to the embodiment, various parameters—length, width, number, and pitch of the second conductor of approximately meander-shaped portion  13 —can be changed. As a result, each stray capacitance and inductance mentioned above can be varied with more flexibility. Therefore, it becomes possible to obtain an electrical length appropriate for two frequency bands by changing these parameters. 
     As described above, according to the embodiment, the electrical length is varied, with help of electrical coupling, by changing a pitch or the diameter of second conductor  19  so that the antenna works with optimal impedance characteristics in the second frequency band. Furthermore, changing a pitch or the diameter of first conductor  17  provides another electrical length by which the antenna works with good impedance characteristics in the first frequency band, with the impedance characteristics in the second frequency band. Thus, the electrical length can be separately determined with no interference between each frequency band and respective VSWR characteristic. As a result, desired impedance characteristics can be obtained, as shown in FIG.  6 —a graph that indicates frequency characteristics of VSWR for the antenna, in a frequency band not only for GSM ranging from 890 to 960 MHz corresponding to the first frequency band (between ▾ 1  and ▾ 2 ), but also for PCN ranging 1,710 to 1,880 MHz corresponding to the second frequency band (between ▾ 3  and ▾ 4 ). Thus, realized is an antenna having wide frequency range and high antenna gain. 
     In addition, electrical length can be effectively extended by utilizing stray capacitance between a plurality of first conductors, stray capacitance between a plurality of second conductors, stray capacitance between a plurality of first conductors and a plurality of second conductors, and dielectric constants of the core rod and the radome. An electrical length can be actually obtained by an antenna element that is mechanically shorter in length than that usually required for the electrical length. This fact contributes to realize a compact and lightweight antenna with higher reliability. 
     Furthermore, according to the embodiment, antenna element  11  is made of a thin metal plate with superior conductivity through die-cutting and press processes. Such formation minimizes non-uniformity and deformation in a pitch of first conductors  17  and second conductors  19 , thereby realizing simple assembly with low cost. 
     Good impedance characteristics in desired frequency bands may be effectively obtained by: cutting a portion of first conductors  17  or an intentionally disposed adjusting extension of the conductors, by properly defining a number of second conductors  19 , and by changing a dielectric constant of dielectric materials forming core rod  15  or radome  16 . Strength of electrical coupling between helical-shaped portion  12  and meander-shaped portion  13  can be changed by providing second conductor  19  with a predetermined slant with respect to first conductor  17  on a front half-round surface of core rod  15 . This allows impedance characteristics to be easily and widely controlled. Joint portions  18 A,  18 B,  20 A, and  20 B are not necessarily shaped the same as ones shown in FIGS.  3  and  4 —for example, V-shaped sharp joint portions can provide as good a result as structure described above. Antenna element  11  of the embodiment is made of a thin metal plate with superior conductivity through die-cutting and press processes. Other than that, the antenna element can be formed of a metal with superior conductivity through mechanical, electrochemical, or pressurized and heated forming/processing to obtain similar effects mentioned above. The antenna element could be formed of: a metal wire with superior conductivity, such as a copper alloy or a Cu, Ni-plated metal; an etching-processed conductor; a press-processed flexible wiring board; printed conductive paste or sintered conductive powder. 
     Second Preferred Embodiment 
     FIGS. 7 and 8 are cross-sectional views seen from a front and from a right hand side of an antenna, respectively, in accordance with a second preferred embodiment. In the figures, like parts are identified by the same reference numerals as in the first embodiment and a detailed explanation will be omitted. As shown in FIGS. 7 and 8, approximately helical-shaped portion  12  and approximately meander-shaped portion  13  of antenna element  11  are formed from as with the first embodiment (see FIG.  1 ), a thin metal plate with superior conductivity, including a copper alloy plate, through die-cutting and press processing. Portion  12  and portion  13  are connected to each other at joint portion  21  adjacent to a top end of core rod  24 . In this embodiment, as shown in FIG. 7, antenna element  11  is of one-piece construction with feed terminal  23  linked to bottom end  13 A of approximately meander-shaped portion  13 . Feed terminal  23  contains elastic metal-plate contact  22 , which is firmly connected to an input/output circuit pattern of a radio-frequency circuit in a radio communication apparatus when the antenna is fixed to the apparatus (see FIG.  8 ). Terminal  23 , as shown in FIG. 7, has intimate contact with core rod  24 , which is an ABS resin-made rod having a dielectric constant of about 2.3. The rod  24  includes flexible pawl  25  at a perimeter of a bottom end of the rod. Pawl  25  is used for snap fitting the antenna into the radio communication apparatus. Radome  16  shields a periphery of antenna element  11 , with a lowermost part of rod  24  and contact  22  being exposed. 
     According to this embodiment, in addition to advantages associated with the first embodiment, antenna element  11  and feed terminal  23  are formed into one piece. The integrated structure contributes to a reduced number of parts, thereby realizing a cost-reduced antenna. 
     Third Preferred Embodiment 
     FIG. 9 is a circuit diagram of a radio communication apparatus, equipped with an antenna of a third preferred embodiment. For the same construction as that described in FIG. 1 to FIG. 4, like parts are identified by the same reference numerals and a detailed explanation will be omitted. The radio communication apparatus is, as shown in FIG. 9, designated by numeral  26 . An antenna (see FIGS. 1 and 2) is fixed to insulating resin-made housing  27  of radio communication apparatus  26 . In apparatus  26 , feeder  28  connects metal fitting  14  of the antenna to switch  29 , through which fitting  14  is connected to radio-frequency circuit  30  for a first frequency band and to radio-frequency circuit  31  for a second frequency band. 
     According to this embodiment, the antenna can be easily attached to apparatus  26 . In addition, the antenna has impedance characteristics suitable for desired multi-ranged frequency bands, which does away with a need to add a complicated impedance-matching circuit to the radio-frequency circuit in apparatus  26 . This fact realizes a low-cost antenna. 
     Fourth Preferred Embodiment 
     FIG. 10 is a circuit diagram of a radio communication apparatus, equipped with an antenna, of a fourth preferred embodiment. For the same construction as that shown in FIG.  7  and FIG. 8, like parts are identified by the same reference numerals and a detailed explanation will be omitted. The antenna—the one shown in FIG. 7, with radome  16  removed—is fixed onto a circuit board (not shown) in housing  27  of radio communication apparatus  26 , as shown in FIG.  10 . In apparatus  26 , feeder  28  connects feed terminal  23  of the antenna to switch  29 , through which the antenna is connected to radio-frequency circuit  30  for a first frequency band and to radio-frequency circuit  31  for a second frequency band. 
     According to this embodiment, in addition to advantages associated with structure in the first through third embodiments, the antenna built into the radio communication apparatus can be protected from damage when apparatus  26  is accidentally dropped or given physical shock. It is possible to provide not only smaller-sized apparatus  26 , but also easy installation of the antenna to the apparatus. As a result, a manufacturing cost of apparatus  26  can be substantially reduced. 
     Fifth Preferred Embodiment 
     FIG. 11 is a circuit diagram of a radio communication apparatus, equipped with an antenna, of a fifth preferred embodiment. For the same construction as that shown in FIGS. 7,  8  and  10 , like parts are identified by the same reference numerals and a detailed explanation will be omitted. A first antenna and a second antenna—both are the same as the antenna shown in FIG. 7, with radome  16  removed—are disposed, as shown in FIG. 11, at upper and lower portions of a circuit board (not shown) in housing  27  of apparatus  26 , respectively. Feeders  28 A,  28 B connect feed terminals  23 A,  23 B of the first and the second antennas to switch  32 , respectively. The switch  32  is connected to radio-frequency circuitry  33 . A circuit following circuitry  33  compares a receiving signal power level of the first antenna with that of the second antenna, by which circuitry  33  is automatically switched by switch  32  to the antenna having the greater receiving signal power. It thus becomes possible to perform diverse communication. 
     According to this embodiment, in addition to advantages associated with the fourth preferred embodiment, multiple use of antennas with impedance characteristics equivalent to each other in a desired frequency band can eliminate variations in impedance characteristics. This provides not only diverse communication system in a radio communication apparatus with high antenna gain and reliability, but also a cost-reduced radio communication apparatus due to simple installation of the antennas to the apparatus. 
     INDUSTRIAL APPLICABILITY 
     As described above, an antenna including an antenna element formed of a combination of an approximately helical-shaped portion and an approximately meander-shaped portion can easily adjust electric length for each of these portions. It is therefore possible to obtain good impedance characteristics in desired multi-ranged frequency bands, while realizing a smaller and cheaper antenna having a wide frequency range, high antenna gain and reliability. Using such an antenna allows installation of the antenna to a radio communication apparatus to be simple. Additionally, the antenna has good impedance characteristics for desired multi-ranged frequency bands, which does away with a need to add a complicated impedance-matching circuit to a radio-frequency circuit, thereby realizing a low-cost antenna.