Patent Publication Number: US-6342863-B2

Title: Antenna apparatus and antenna and tranceiver using the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to antenna apparatus used in an automatic driving system for automobiles and the like. More particularly, the present invention relates to an antenna apparatus using a nonradiative dielectric waveguide using a high frequency band such as the milliwave band. 
     2. Description of the Related Art 
     A known antenna apparatus is described with reference to FIG.  14 . FIG. 14 is an exploded perspective view of the known antenna apparatus. 
     Referring to FIG. 14, a known antenna apparatus  110  includes an upper conductor plate  111  and a lower conductor plate  112  made of aluminum, a dielectric strip  113  made of polytetrafluoroethylene, which is held between the upper conductor plate  111  and the lower conductor plate  112 , and a cylindrical dielectric resonator  127  disposed at a distance from an end of the dielectric strip  113 . A two-slot aperture  114  is formed on the upper conductor plate  111  at a position where the dielectric resonator  127  is disposed. 
     With this configuration, a nonradiative dielectric waveguide is formed by the upper conductor plate  111 , the lower conductor plate  112 , and the dielectric strip  113 . By adjusting the distance between the upper conductor plate  111  and the lower conductor plate  112  to half a propagating wavelength or less, only the dielectric strip  113  operates as a signal propagation area. An electromagnetic wave input from the outside is propagated through the dielectric strip  113  in a longitudinal-section magnetic (LSM) mode, which in turn is connected with the dielectric resonator  127 . The dielectric resonator  127  resonates in an HE 111  mode. The electromagnetic wave is radiated from the dielectric resonator  127  via the aperture  114  on the upper conductor plate  111 . 
     Recently, a high frequency band, such as the milliwave band, has been used for automatic driving systems for automobiles. Accordingly, there is an increasing demand for high accuracy in the antenna apparatus, such as by miniaturization of the dielectric resonator. However, the known antenna apparatus includes the dielectric strip and the dielectric resonator disposed at a predetermined separation in accordance with an operating frequency. Disposition of the dielectric resonator in order to satisfy the required characteristics is very difficult. 
     Polytetrafluoroethylene employed for the dielectric strip has a relatively large coefficient of linear expansion. Variations in temperature cause variations in the distance between the dielectric strip and the dielectric resonator, thus failing to match the operating frequency and increasing return loss. Specifically, the distance between the dielectric strip and the dielectric resonator is small in the milliwave band, so that slight variations in the distance exert a powerful influence on the characteristics of the antenna apparatus. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an antenna apparatus, and an antenna and a transceiver using the same, in which disposition of component parts including a dielectric strip is simple, and characteristics of the antenna apparatus are not susceptible to temperature variations even in a high frequency band, e.g., in the milliwave band. 
     To this end, according to an aspect of the present invention, there is provided an antenna apparatus including two substantially parallel conductors, a dielectric strip held between the two conductors, an aperture formed on one of the two conductors in the vicinity of the dielectric strip, and a matching section for matching impedance between the dielectric strip and the aperture. The matching section is continuously connected to the dielectric strip in the vicinity of the aperture. 
     Electromagnetic waves are radiated from the matching section continuously connected to the dielectric strip. There is no need to dispose a dielectric resonator at a distance from the dielectric strip, as in known antenna apparatus. In the antenna apparatus of the present invention, the dielectric strip and the matching section are integrated, eliminating detailed working to dispose the dielectric strip and the dielectric resonator at a predetermined separation. The antenna apparatus of the present invention is stable in characteristics relative to temperature variations. 
     A stub formed of a dielectric may be continuously connected to the matching section. Thus, reflection characteristics of the antenna apparatus may be improved. 
     The stub may have a length of ¼λg where λg represents a propagating wavelength. Thus, the reflection characteristics of the antenna apparatus are optimized. 
     A connecting dielectric strip having a sectional shape differing from that of the dielectric strip may be continuously connected in the vicinity of the matching section. Variations in the shape of the connecting dielectric strip permit variations in an amount of connection between the dielectric strip and the matching section, thereby adjusting the matching between the dielectric strip and the matching section. 
     The connecting dielectric strip may have a length of ¼λg relative to the propagating wavelength λg. Thus, the amount of connection and the matching between the dielectric strip and the matching section are optimized. 
     In accordance with another aspect of the present invention, there is provided an antenna including the antenna apparatus and a dielectric lens disposed in the upper part of the aperture of the antenna apparatus. 
     In accordance with another aspect of the present invention, there is provided a transceiver including the antenna and a transceiver circuit connected to the antenna. 
     Accordingly, productivity is increased, and the antenna and the transceiver with stable characteristics relative to temperature variations are obtained. 
     Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is an exploded perspective view of an antenna apparatus according to a first embodiment of the present invention; 
     FIG. 2 is a sectional view of an antenna of the present invention; 
     FIG. 3 is an exploded perspective view of the antenna apparatus of the present invention illustrating a form of another aperture; 
     FIG. 4 is an exploded perspective view of the antenna apparatus of the present invention illustrating a form of another aperture; 
     FIGS. 5A and 5B are plan views of the antenna apparatus of the present invention illustrating forms of other matching sections; 
     FIGS. 6A and 6B are plan views of the antenna apparatus of the present invention illustrating forms of other matching sections; 
     FIG. 7 is a plan view of the antenna apparatus of the present invention illustrating a form of another matching section; 
     FIG. 8 is an exploded perspective view of an antenna apparatus according to a second embodiment of the present invention; 
     FIG. 9 is a graph showing a relationship between a frequency and return loss when the length of a stub is varied; 
     FIG. 10 is an exploded perspective view of an antenna apparatus according to a third embodiment of the present invention; 
     FIGS. 11A and 11B are exploded perspective views of the antenna apparatus of the present invention illustrating forms of other connecting dielectric strips; 
     FIG. 12 is a sectional view of the antenna apparatus of the present invention illustrating a form of another nonradiative dielectric waveguide; 
     FIG. 13 is a circuit diagram of an equivalent circuit of a transceiver of the present invention; and 
     FIG. 14 is an exploded perspective view of a known antenna apparatus. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     An antenna apparatus according to a first embodiment of the present invention is described with reference to FIG.  1 . FIG. 1 is an exploded perspective view of the antenna apparatus according to this embodiment. 
     Referring to FIG. 1, an antenna apparatus  10  of this embodiment includes an upper conductor plate  11  and a lower conductor plate  12  prepared by plating aluminum or a dielectric with metal, a dielectric strip  13  made of polytetrafluoroethylene or the like, which is held between the upper conductor plate  11  and the lower conductor plate  12 , and a substantially circular matching section  20  integrated with the dielectric strip  13  and continuously connected to one end of the dielectric strip  13 . A two-slot aperture  14  is formed on the upper conductor plate  11  at a position where the matching section  20  is disposed. 
     With this configuration, a nonradiative dielectric waveguide is formed by the upper conductor plate  11 , the lower conductor plate  12 , and the dielectric strip  13 . By adjusting the distance between the upper conductor plate  11  and the lower conductor plate  12  to half a propagating wavelength or less, only the dielectric strip  13  operates as a signal propagation area. An electromagnetic wave input from the outside is propagated through the dielectric strip  13  in an LSM mode, which in turn is connected to the matching section  20 . The matching section  20  is suitably shaped in accordance with the operating frequency, thereby matching the impedance between the dielectric strip  13  and the aperture  14 . By matching the impedance between the dielectric strip  13  and the aperture  14 , the electromagnetic wave is radiated via the aperture  14  on the upper conductor plate  11 . Referring to FIG. 2, a casing  15  made of metal is formed in the vicinity of the aperture  14 , and a dielectric lens  16  is formed in the upper part of the aperture  14 , thereby constructing an antenna  30 . 
     In the antenna apparatus  10  according to this embodiment, the dielectric strip  13  and the matching section  20  are integrated. This eliminates the necessity for detailed working to adjust the distance between a dielectric strip and a dielectric resonator, as in known antenna apparatus, and increases productivity. Characteristics of the antenna apparatus  10  are stable, whereas in the known antenna apparatus, the distance between the dielectric strip and the dielectric resonator varies in accordance with temperature variations, so that the characteristics of the known antenna apparatus are variable. 
     In the present embodiment, the aperture  14  has two slots. However, other configurations are conceivable as well. Referring to FIG. 3, an antenna apparatus  10   a  is provided with a circular aperture  14   a  on an upper conductor plate  11   a  and a thin metal plate  17  having two slots between the upper conductor plate  11   a  and the matching section  20 . Referring to FIG. 4, an antenna apparatus  10   b  simply includes a circular aperture  14   b  on an upper conductor plate  11   b . In this embodiment, the shape of the matching section  20  is approximately circular. However, the matching section  20  may be of other shapes. Referring to FIGS. 5A and 5B, the shape of the matching section  20  is elliptical. Referring to FIGS. 6A and 6B, the shape of the matching section  20  is rectangular. Referring to FIG. 7, the shape of the matching section  20  is a shape with a hole in the center. Arbitrary variations of the shape of the matching section  20  permit controlling of the directivity of the antenna apparatus. 
     Referring to FIG. 8, an antenna apparatus according to a second embodiment of the present invention is described. FIG. 8 is an exploded perspective view of the antenna apparatus according to this embodiment. The same numerals as those of the first embodiment are given to the same parts as those of the first embodiment, and a detailed description is omitted. 
     In an antenna apparatus  10   c  of this embodiment, a stub  18  is formed in the opposite side of the dielectric strip  13  across the matching section  20  and is integrated with the dielectric strip  13  and the matching section  20 . By continuously connecting the stub  18  with the matching section  20 , reflection characteristics of the antenna apparatus  10   c  are improved. 
     FIG. 9 is a graph showing return loss when the length of the stub  18  is varied. Referring to FIG. 9, a solid line represents a stub length of 0λg relative to a propagation wavelength of λg, that is, when there is no stub; a chain line represents a stub length of ⅛λg; a dotted line represents a stub length of ¼λg; and a dash-dot line represents a stub length of ⅜λg. As illustrated in FIG. 9, the reflection characteristics are improved when a stub is provided compared to a configuration without a stub, and the best reflection characteristics are obtained when the length of the stub is ¼λg. 
     With reference to FIG. 10, an antenna apparatus according to a third embodiment of the present invention is described. FIG. 10 is an exploded view of the antenna apparatus according to this embodiment. The same numerals as those of the first embodiment are given to the same parts as those of the first embodiment, and a detailed description is omitted. 
     Referring to FIG. 10, an antenna apparatus  10   d  of this embodiment includes a connecting dielectric strip  19  whose width is narrower than the dielectric strip  13 . The dielectric strip  19  is continuously connected with the matching section  20 . With this configuration, an amount of connection between the dielectric strip  13  and the matching section  20  is varied, thereby adjusting the matching, compared with a configuration incorporating a direct connection between the dielectric strip  13  and the matching section  20 . Adjusting the length of the connecting dielectric strip  19  to ¼λg relative to the λg propagation wavelength optimizes the matching of the antenna apparatus  10   d.    
     Although the connecting dielectric strip  19  of this embodiment is shaped to be narrower in its width, it may be of other shapes, such as a trapezoidal shape, as shown in FIGS. 11A and 11B. 
     The embodiments described above employ a nonradiative dielectric waveguide prepared by holding a dielectric strip between an upper conductor plate and a lower conductor plate. However, other configurations are conceivable as well. Referring to FIG. 12, the nonradiative dielectric waveguide is prepared by forming a groove  25  at a position where the upper conductor plate  11  and the lower conductor plate  12  oppose each other and fitting the dielectric strip  13  in the groove  25 . With this configuration, a longitudinal-section electric (LSE) mode is not activated even when the antenna apparatus includes a bend or the like. This permits the antenna apparatus to activate only the LSM mode which is low-loss. 
     Next, a transceiver according to an embodiment of the present invention is described with reference to FIG.  13 . FIG. 13 is a circuit diagram showing an equivalent circuit of the transceiver of this embodiment. 
     Referring to FIG. 13, a transceiver  40  of this embodiment includes the antenna apparatus  10 , a circulator  41  connected to the antenna apparatus  10 , an oscillator  42  connected to one port of the circulator  41 , a mixer  43  connected to the other port of the circulator  41 , a second circulator connected between the circulator  41  and the oscillator  42 , and couplers  45  and  46 . In this embodiment, the oscillator  42  is a voltage controlled oscillator, which varies an oscillation frequency by applying a voltage to a bias terminal. The antenna apparatus  10  shown in FIG. 13 is that of the first, second, and third embodiments. The dielectric lens (not shown) is disposed in the radiating direction of the electromagnetic wave. With this configuration, the transceiver  40  propagates a signal from the oscillator  42  via the circulator  44 , the coupler  45 , and the circulator  41  into the antenna apparatus  10 , which in turn is radiated via the dielectric lens. A portion of the signal from the oscillator  42  is supplied as a local signal to the mixer  43  via the couplers  45  and  46 . A wave reflected from a target is supplied as a radio frequency (RF) signal to the mixer  43  via the antenna apparatus  10 , the circulator  41 , and the coupler  46 . The mixer  43  as a balanced mixer outputs a differential component between the RF signal and the local signal as an intermediate frequency (IF) signal. 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. Therefore, the present invention should be limited not by the specific disclosure herein, but only by the appended claims.