Abstract:
The invention provides a dielectric lens, wherein the dielectric lens is rotation-symmetrically shaped, and a flat end is disposed at a part of the edge the dielectric lens. By the above described structure and arrangement, it become possible to widen a half-value angle in the direction which the flat ends of the lens are disposed without reducing a gain significantly.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a dielectric lens, a dielectric lens antenna including the same, and a wireless device including the same. More specifically, the present invention relates to a dielectric lens applied for a motor-vehicle-mounted radar which uses millimeter-waves, a dielectric lens antenna including the same, and a wireless device including the same. 
     2. Description of the Related Art 
     With the recent advance of motor-vehicle-mounted radar, control of the directivity of an antenna has been a significant concern. 
     FIGS. 11A,  11 B and  11 C show a prior art dielectric lens. FIG. 11A is a plan view, FIG. 11B is a front view, and FIG. 11C is a side view. In a dielectric lens  1 , a lens  2  is substantially in a shape formed by cutting a part of a sphere. In the plan view, it is formed rotation-symmetrically, namely, in a round form, and in the front view and the side view, it is formed in a circular form. The lens  2  is made of dielectric materials such as ceramics, resin, plastic, or their composite materials. The focal direction of the dielectric lens  1  is the -z-axis direction. 
     FIGS. 12A,  12 B and  12 C show a dielectric lens antenna including the dielectric lens  1  shown in FIG. 11A,  11 B and  11 C. FIG. 12A is a plan view; FIG. 12B is a front view; and FIG. 12C is a side view. In FIG. 12, the dielectric lens antenna  5  is formed by disposing a primary radiator  7  at the focal point  6  of the dielectric lens  1 . 
     FIG. 13 shows a conceptual view (a front view) illustrating the directivity of a beam radiated from the dielectric lens  1  of the dielectric lens antenna  5  shown in FIGS. 12A,  12 B and  12 C. In FIG. 13, the same reference numerals are given to the same parts as those in FIG. 12 or the equivalent parts to those in FIG. 12; their descriptions are omitted. As shown in FIG. 13, the shape of beam  3  radiated from the dielectric lens  1  of the dielectric lens antenna  5  is a pencil-beam shape on the x-z side. In this case, the length (the height in FIG. 13) of z-axis direction of the beam  3  indicates the magnitude of a gain of the dielectric lens antenna  5 , and the width of the beam  3  indicates the magnitude of the beam width of the dielectric lens antenna  5 . 
     As seen above, the gain of the dielectric lens antenna  5  amounts to a maximum value in the z-axis direction. With respect to the z-axis direction, the angle in which a gain decreases by 3 dB from the maximum value, namely, the angle in which the gain amounts to a half is referred to a half-value angle, which indicates the directivity of the antenna. The shape of the beam  3  radiated from the dielectric lens  1  of the dielectric lens antenna  5  is the same on all the sides which include the z-axis and parallel to the z-axis, such as the x-y side, so that the line connecting points of the half-value angles forms a round form when viewed from the front of the dielectric lens antenna  5 . In addition, the half-value angle is substantially indicated by a formula: 
     
       
         A half-value angle (θ)=70λ/D 
       
     
     (λ: wavelength of the used frequency, 
     D: antenna-aperture diameter) 
     Thus, a half-value angle is inversely proportional to an antenna aperture diameter. In contrast, the wider the aperture diameter, the larger the gain. 
     A motor-vehicle-mounted radar does not necessarily require the information of a vertical direction (up-and-down directions) with respect to a traveling direction of a motor vehicle. On the contrary, in order to prevent malfunctions due to reactions with a pedestrian overpass or a viaduct, it may be better for the radar to have less information of a vertical direction. Meanwhile, the information of a horizontal direction (a traveling direction and right-and-left directions of a motor vehicle) is primarily necessary, since other motor vehicles and obstacles are targeted. This can require a wide-angle antenna, in which a beam is narrowed in the vertical direction, whereas it is widened in the horizontal direction. In this case, in order to widen the beam, namely, to widen the half-value angle, it is necessary to make the antenna-aperture diameter smaller, namely, it is necessary to reduce the diameter of the dielectric lens. However, reducing the diameter of the dielectric lens leads to decrease in gain, thereby it creates a problem in which the lens can only detect at close range when it is used in radar. In addition, reducing the diameter of the dielectric lens leads to extension of the beam not only in the horizontal direction but also in the vertical direction; it thereby leads to further decrease in the gain in the horizontal direction. 
     SUMMARY OF THE INVENTION 
     To overcome the above problems, preferred embodiments of the present invention provide a dielectric lens capable of widening a half-value angle in a specified direction without decreasing a gain significantly, a dielectric lens antenna including the same, and a wireless device including the same. 
     One preferred embodiment of the present invention provides a dielectric lens and a dielectric lens antenna including the dielectric lens, wherein the dielectric lens is rotation-symmetrically shaped, and a flat end is disposed at a part of the edge the dielectric lens. In the dielectric lens antenna, a primary radiator is disposed at the focal point of the dielectric lens. 
     By the above described structure and arrangement, it become possible to widen a half-value angle in the direction in which the flat ends of the lens are disposed without reducing a gain significantly. 
     Preferably, in the above described dielectric lens, a first flat end and a second flat end are respectively disposed at a part of the edge the dielectric lens and opposed to each other. This structure and arrangement allows the half-value angles of the dielectric lens and the dielectric lens antenna to be smaller in the vertical direction (horizontal direction) and to be greater in the horizontal direction (vertical direction). 
     In the above described dielectric lens antenna, the primary radiator and the dielectric lens may be connected by a supporting plate extending in a taper shape from the outer periphery of the primary radiator to the edge of the dielectric lens over the entire circumference; and at least inner surface of the supporting plate may be made of metal. 
     By the above described structure and arrangement, spillover losses can be reduced to thereby high efficiency is achieved. 
     Another preferred embodiment of the present invention provides a wireless device comprising the above described dielectric lens antenna. 
     Use of the dielectric lens antenna of the present invention can control extension of a beam to reduce malfunctions of a wireless device. 
     Other features and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention which refers to the accompanying drawings, wherein like reference numerals indicate like elements to avoid duplicative description. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIGS. 1A,  1 B and  1 C show one preferred embodiment of a dielectric lens according to the present invention, in which FIG. 1A is a plan view; FIG. 1B is a front view; and FIG. 1C is a side view. 
     FIGS. 2A,  2 B and  2 C show another preferred embodiment of a dielectric lens antenna according to the present invention, in which FIG. 2A is a plan view; FIG. 2B is a front view; and FIG. 2C is a side view. 
     FIGS. 3A and 3B show a conceptual view illustrating the directivity of a beam radiated from the dielectric lens of a dielectric lens antenna shown in FIGS. 2A,  2 B and  2 C, in which FIG. 3A is a front view; and FIG. 3B is a side view. 
     FIG. 4 shows a relationship between the amount of cut-away parts of the lens and gains of the dielectric lens antenna according to the present invention. 
     FIG. 5 shows a relationship between the amount of cut-away parts of the lens and half-value angles of the dielectric lens antenna according to the present invention. 
     FIG. 6 shows a plan view of the dead space in a state in which a conventional dielectric lens antenna is attached to a rectangular frame. 
     FIG. 7 shows a plan view of the dead space in a state in which the dielectric lens antenna of the present invention is attached to a rectangular frame. 
     FIGS. 8A,  8 B and  8 C show yet another preferred embodiment of the dielectric lens according to the present invention, in which FIG. 8A is a plan view; FIG. 8B is a front view; and FIG. 8C is a side view. 
     FIGS. 9A,  9 B and  9 C show yet another preferred embodiment of the dielectric lens antenna according to the present invention, in which FIG. 9A is a plan view; FIG. 9B is a front view; and FIG. 9C is a side view. 
     FIG. 10 shows a block diagram of a preferred embodiment of a wireless device according to the present invention. 
     FIGS. 11A,  11 B and  11 C show a view of a prior art dielectric lens, in which FIG. 11A is a plan view; FIG. 11B is a front view; and FIG. 11C is a side view. 
     FIGS. 12A,  12 B and  12 C show a view of a prior art dielectric lens, in which FIG. 12A is a plan view; FIG. 12B is a front view; and FIG. 12C is a side view. 
     FIG. 13 shows a conceptual view (a front view) illustrating the directivity of a beam radiated from the dielectric lens of the dielectric lens antenna shown in FIGS. 12A,  12 B and  12 C. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Regarding a dielectric lens  10  shown in FIGS. 1A,  1 B and  1 C, when compared to a prior art dielectric lens shown in FIG. 11A, the left edge of the lens  2  is linearly cut away from the rotation-symmetrical form, namely, the round form so as to make a flat first end  11 , whereas the right edge of the same is linearly cut away so as to make a flat second end  12 . The first end  11  and the second end  12  are opposed to each other. 
     In terms of the formation of the first end  11  and the second end  12 , for the sake of convenience, a description has been provided that they are formed by cutting away the edge of the lens  2 . In addition, even in the hereinafter description, the expression of cutting away the edge of the lens will be used for the convenience. However, when the lens is actually formed, the forming method is not limited to the one in which the ends are formed by cutting away the edge after forming the lens rotation-symmetrically. It may be possible to form the lens in a shape having an end from the beginning. 
     Referring to FIGS. 2A,  2 B and  2 C, the dielectric lens antenna  15  is formed by disposing a primary radiator  7  in the focal point  6  of the dielectric lens  10 . 
     FIGS. 3A,  3 B and  3 C show a conceptual view illustrating the directivity of a beam  13  radiated from the dielectric lens  10  of the dielectric lens antenna  15  shown in FIG.  2 . For comparison, the shape of the beam  3  radiated from the conventional dielectric lens antenna  5  shown in FIG. 13 is indicated by dashed lines. 
     As shown in FIG. 3A, the shape of the beam  13  radiated from the dielectric lens  10  of the dielectric lens antenna  15 , when compared to the shape of the conventional beam  3 , extends in the x-axis direction, namely, in a direction in which the first end  11  and the second end  12  are formed by cutting away the edge of the lens  2 ; thereby, a half-value angle widens. In contrast, the maximum gain becomes a little smaller than that of the conventional art, since the aperture area is reduced due to cutting-away of the edge of the lens. Meanwhile, as shown in FIG. 3B, in the y-axis direction, namely, in the direction in which the edge of the lens is not cut away, the shape of the beam  13  is substantially the same as that of the conventional one, although the maximum gain is smaller; and the half-value angle is almost the same. 
     FIGS. 4 and 5 respectively show the relationship between the amount of cut-away parts of the lens  2  and the antenna-gain, and the relationship between the amount of cut-away parts of the lens  2  and the half-value angle, respectively, in terms of the dielectric lens  10  used in the dielectric lens antenna  15  according to the present invention. In this case, the diameter of the lens  2  is 73 mm. In FIG. 5, a shows a half-value angle on the x-z side and b shows a half-value angle on the y-z side. 
     As shown in FIG. 4, the larger the amount of cut-away parts of the lens  2 , the smaller the aperture area of the dielectric lens  10 ; thereby the gain tends to be smaller, too. In addition, as shown in FIG. 5, the larger the amount of cut-away parts of the lens  2 , the exponentially wider the half-value angle a on the y-z side, namely, in the cut-away direction. The half-value angle b on the y-z side is not influenced by the amount of cut-away parts of the lens  2 . 
     In this way, in the dielectric lens  10 , it is to be understood that formation of the first end  11  and the second end  12  by cutting away mutually opposing two places of the edge of the lens  2  permits extension of a beam only in the direction in which the edge has been cut away. Furthermore, the dielectric lens antenna  15  is formed by using the dielectric lens  10  in such a manner that the x-axis direction is used as the horizontal direction and the y-axis direction is used as the vertical direction in FIGS. 2A,  2 B and  2 C. This permits formation of an antenna in which the beam does not extend in the horizontal direction, whereas it hardly extends in the vertical direction. 
     The above-described dielectric lens antenna extending a beam in the horizontal direction is effective to a radar of mono-pulse system (a radar for measuring a distance and an angle with respect to a target by emitting a one-time-pulse signal in a wide range to receive a reflected signal by two or more antennas disposed mutually having a distance therebetween). However, it is more convenient for a radar of beam-scan system (a radar for measuring an angle with respect to a target by performing an action of measuring a distance to the target from a reflected signal by emitting a signal in a narrow range, while sequentially changing the angle of the antenna in the horizontal direction) to make a beam in the horizontal direction narrower. Thus, in such a case, the vertical and horizontal directions in a plan view of the dielectric lens antenna shown in FIGS. 2A,  2 B and  2 C are inverted to use the x-axis direction vertically and the y-axis direction horizontally. This makes the beam toward the horizontal direction narrower; thereby malfunctions with respect to the angle of a target in beam-scanning can be reduced. 
     Generally, a dielectric lens is often attached to a rectangular frame. FIG. 6 shows a plan view of a prior art round dielectric lens  1 , which is attached to a rectangular frame  20 . As seen in FIG. 6, attaching the round dielectric lens  1  to the rectangular frame  20  allows a dead space  21  (a region which does not serve as the aperture face of the dielectric lens) to be produced between the frame  20  and the dielectric lens  1  when view from the front. In this case, the area of the dead space  21  with respect to the frame  20  is approximately 21.5%. 
     Meanwhile, FIG. 7 shows a plan view of the dielectric lens  10  of the present invention, which is attached to a rectangular frame  22 . As seen in FIG. 7, the dielectric lens  10  originally has a rectangle shape substantially when viewed in the plan view, since the mutually opposing two places of the edge of the lens  2  are cut away to form the first end and the second end. When the dielectric lens  10  is attached to the rectangular frame  22 , the dead space  23  between the frame  22  and the dielectric lens  10  can be formed to be smaller than the prior art dielectric lens  1  shown in FIG.  6 . For example, if the mutually opposing two places of the edge of the lens  2  are cut away at the position of ¼ of the radius, respectively, to form the first end and the second end, the frame  22  becomes a rectangle having two sides in the proportion of 3-to-4, and the area of the dead space  23  with respect to the frame  22  is approximately 10.4%, so that the area can be significantly smaller than that of the conventional art. 
     Furthermore, in a motor-vehicle-mounted radar, a dielectric lens antenna is mounted on the front of the vehicle, with the z-axis direction being oriented toward the direction in which the vehicle travels. In this case, since the dead space of the dielectric lens antenna is vertical to the traveling direction, air resistance increases and snow is likely to easily accumulate thereon. In this point, according to the dielectric lens antenna  10  of the present invention, the smaller the area of the dead space, the smaller the air resistance and the less the accumulation of snow, so that degradation of antenna characteristics can be reduced. 
     Referring to FIGS. 8A,  8 B and  8 C, in the dielectric lens  30 , a third end  31 , in which the edge of the upper side of the lens  2  is linearly cut away to be flat, is formed, in addition to the first end  11  and the second end  12  formed on the dielectric lens  10 . Whereas a fourth end  32 , in which the edge of the lower side is linearly cut away to be flat, is formed. In other words, four places of the edge of the lens  2  are cut away to form flat ends, respectively, so that the lens  2  is formed to be a shape close to a square when viewed in the plan view. 
     Such an arrangement permits the shape of a beam of the dielectric lens antenna using the dielectric lens  30  to be extended both in the horizontal direction and in the vertical direction. As a result, it is impossible to change the shape of a beam in the vertical direction and the horizontal direction as in the case of the dielectric lens antenna  15  shown in FIG.  2 . However, although it is not shown here, it is clear that the dead space with respect to the rectangular frame is greatly smaller than that in the case where the diameter of the lens  2  is simply reduced. Accordingly, this can control both the reduction of the aperture area due to the miniaturization of the dielectric lens and the gain reduction so as to make both of them relatively small. 
     In contrast, when the diameter of the lens  2  of the dielectric lens  30  is extended to be as long as a diagonal line of the frame  20  shown in FIG. 6, and then the four places of the edge are cut away so as to be contained in the frame  20 , the dead space is smaller than that of the dielectric lens  1  shown in FIG. 6, (namely, the aperture area is larger), so that a dielectric lens and a dielectric lens antenna having the same aperture diameter (namely, the same half-value angle) and yet offering a larger gain can be obtained. 
     Referring to FIGS. 9A,  9 B and  9 C, the dielectric lens antenna  40  is formed in such a manner that the primary radiator  7  and the dielectric lens  10  in the dielectric lens antenna  15  shown in FIGS. 2A,  2 B and  2 C are connected by a supporting plate  41  extending in a taper shape over the entire circumference from the outer periphery of the primary radiator  7  to the edge of the dielectric lens  10 . In this case, the inner surface of the supporting plate  41  is covered with metal coating to reflect electromagnetic waves. 
     Forming the dielectric lens antenna  40  in this way can reduce losses (spillover losses) due to electromagnetic waves leaking before reaching the dielectric lens  10  from the primary radiator  7 , which are the losses increased due to formation of flat ends by cutting away the edge of the lens  2 . Reduction of spillover losses leads to achievement of high efficiency, so that miniaturization of the aperture area of the dielectric lens, namely, miniaturization of the dielectric lens antenna can be achieved. Furthermore, retaining of the primary radiator  7  and the dielectric lens  10  by the supporting plate  41  permits the positional relationship between the primary radiator  7  and the dielectric lens  10  to be stable so as to reduce changes in the antenna characteristics with respect to vibrations or shocks, for instance, a positional deviation of the primary radiator  7  with respect to the focal point of the dielectric lens  10 . 
     Although the dielectric lens antenna  40  shown in FIGS. 9A,  9 B and  9 C adopts a supporting plate whose inner surface is coated with metal, it is possible to obtain similar advantages by sticking a metal plate onto the inner surface or by using a supporting plate whose entire part is made of metal. 
     In addition, in the above embodiments, the two or four places of the edge of the lens are cut away to form flat ends. However, it may be possible to adopt an arrangement in which one, three, five or more places of the edge are cut away to form flat ends so as to obtain similar advantages. 
     As a preferred embodiment of a wireless device according to the present invention, FIG. 10 shows a block diagram of a motor-vehicle-mounted millimeter-wave radar. In FIG. 10, a millimeter-wave radar  50  is composed of the dielectric lens antenna  15  shown in FIGS. 2A,  2 B and  2 C, an oscillator  51 , circulators  52  and  53 , a mixer  54 , couplers  55  and  56 , and a signal-processing circuit  57 . 
     In the millimeter-wave radar  50  having such an arrangement, the oscillator  51  uses Gunn diode as an oscillation device and uses varactor diode as an oscillation-frequency control device to form a voltage-controlled oscillator. Bias voltage for Gunn diode and frequency-modulation control voltage VCO-IN are input to the oscillator  51 ; and a transmission signal as the output is input to the coupler  55  through the circulator  52  so as not to return a reflection signal. The coupler  55  divides the transmission signal into two to emit one of them from the dielectric lens antenna  15  through the circulator  53  and inputs the other one as a local signal to the circulator  56 . Meanwhile, the signal received by the dielectric lens antenna  15  is input to the coupler  56  through the circulator  53 . The coupler  56  acts as a 3 dB-directional coupler to divide the local signal sent from the coupler  55  into equal parts with a phase difference of 90 degrees so as to input two mixer circuits of the mixer  54 , whereas the coupler also divides the received signal sent from the circulator  53  into equal parts with a phase difference of 90 degrees so as to input to the two mixer circuits of the mixer  54 . The mixer  54  performs balance-mixing of the two signals in which the local signal and the received signal are mixed and outputs the frequency-difference component of the local signal and the received signal as an IF signal so as to input to the signal processing circuit  57 . 
     The above millimeter-wave radar  50  can obtain distance information and relative velocity information from the IF signal with the signal-processing circuit  57 , for example, by providing a triangular wave information as the above VCO-IN signal. Accordingly, when this is mounted in a motor vehicle, the relative distance and the relative velocity with respect to other vehicles can be measured. Moreover, use of the dielectric lens antenna according to the present invention permits reduction of malfunctions by extending or narrowing a beam in a specified direction. 
     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the forgoing and other changes in form and details may be made therein without departing from the spirit of the invention.