Patent Publication Number: US-8970428-B2

Title: Slot antenna and radar device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The application claims priority under 35 U.S.C §119 to Japanese Patent Application No. 2010-090964, which was filed on Apr. 9, 2010, the entire disclosure of which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a structure of an antenna having a two-dimensional array of slots, and a radar device that contains this antenna. 
     BACKGROUND OF THE INVENTION 
     In comparison to the existing type of antenna including a waveguide, which has a plurality of radiating slots arranged in a longitudinal direction thereof, and a radiating horn attached to the waveguide, a slot array antenna including a radiation waveguide, which has a plurality of radiating slots arranged in lateral and longitudinal directions thereof on a two-dimensional radiation plane, has been presented in recent years for the purpose of ease in manufacturing and size reduction (WO2008/018481). The slot array antenna disclosed in WO2008/018481 includes a radiation waveguide arranged with a two-dimensional slot array and a feeding waveguide arranged with a slot array and for guiding (feeding) an electromagnetic wave to the radiation waveguide from a direction orthogonal to a propagation direction of the radiation waveguide for electromagnetic wave, which are coupled with each other (see WO2008/018481). 
     The feeding waveguide coupled to the radiation waveguide disclosed in WO2008/018481 has in general, structures shown in  FIGS. 25A and 25B . That is, the structure shown in  FIG. 25A  is what a feeding waveguide  100  is simply coupled to a radiation waveguide  200  in an orthogonal direction (width direction) thereto, and the structure shown in  FIG. 25B  is what is designed to keep the dimension of a feeding waveguide  101  in the width direction of the radiation waveguide  200  the same as or smaller than the width dimension of the radiation waveguide  200  by bending the feeding waveguide  101  to be an “L” shape. 
     In the structure shown in  FIG. 25A , a section of the feeding waveguide  100  corresponding to feeding slots  100   a  are contained within the width dimension of the radiation waveguide  200 ; however, a section of the feeding waveguide  100  on a base end  100   b  side protrudes outside the width dimension of the radiation waveguide  200 , thus limiting size reduction of the slot array antenna. Further, in the structure shown in  FIG. 25B , although the structure of the feeding waveguide  101  is contained within the width dimension of the radiation waveguide  200 , feed characteristics of an electromagnetic wave from feeding slots  101   a  of the feeding waveguide  101  to the radiation waveguide  200  become ununiform, particularly in width directions, due to a discontinuous section such as a bent section  101   c  of the feeding waveguide  101 . As a result, a transmission mode pattern of the electromagnetic wave which propagates within the radiation waveguide  200  breaks down. 
     SUMMARY OF THE INVENTION 
     The present invention is made in view of the above situations, and provides a slot antenna that allows, by improving a structure of a slot antenna, a propagation of electromagnetic wave in a proper transmission mode pattern within a radiation waveguide and a size reduction, and a radar device including the item. 
     According to an aspect of the invention, a slot antenna is provided, which includes a tubular electromagnetic wave radiation part having a hollow space, a plurality of electromagnetic wave radiating slots for radiating electromagnetic waves being formed in at least a part of a side surface of the radiation part and a plurality of feeding slots for being inputted with the electromagnetic waves being arrayed in line in another part of the side surface opposing to the radiating slots, a feeding part having a hollow space, extending along the feeding slot array, and for feeding power from the outside of the radiation part to the feeding slots, and a power guiding part having a hollow space and for guiding the power to the feeding part, the power guiding part extending in a direction orthogonal to the array direction of the feeding slots and in parallel to the center axis of the radiation part, from a location of the feeding part corresponding to at least one of the feeding slots. 
     As described above, the electromagnetic wave inputted to the power guiding part extending in the direction orthogonal to the array direction of the feeding slots and in parallel to the center axis of the radiation part, from the location of the feeding part corresponding to at least one of the feeding slots, is guided to the feeding part and further inputted to the feeding slots. Then, the electromagnetic wave is guided to the radiation part through each feeding slot. Thus, by extending the power guiding part in the direction orthogonal to the array direction of the feeding slots and in parallel to the center axis of the radiation part, from the location of the feeding part corresponding to at least one of the feeding slots, a size suppressed and compact slot antenna can be manufactured. 
     A bulged portion may be formed in at least a portion of an inner wall of the feeding part opposing to the feeding slot so that the portion of the feeding part is bulged more than an inner wall of the power guiding part facing the same side as the inner wall of the feeding part. 
     The at least one of the feeding slots may be other than the slots positioned at both ends of the array. 
     A center frequency of the electromagnetic wave may be within a range from 9.38 GHz to 9.44 GHz and the bulged portion is bulged by 1 mm to 4 mm. 
     The plurality of radiating slots may be arranged two-dimensionally. 
     The feeding slot array direction may be oriented in a direction orthogonal to the center axis of the radiation part. 
     The slot antenna may further include a radome for accommodating the radiation part, the feeding part, and the power guiding part therein. 
     The radome may have a substantial cylindrical shape, and the feeding part and the power guiding part may be arranged in parallel to the center axis of the radome and in at least one of a position at the center axis and a position near the center axis of the radome. 
     The slot antenna may further include a feeding waveguide arranged in parallel to the center axis of the radiation part and for guiding the power to the power guiding part from the outside of the power guiding part. 
     The slot antenna may further include a coaxial connector having an inner conductor and an outer conductor and for feeding the power from the feeding waveguide to the power guiding part. 
     The inner conductor may protrude inside the feeding waveguide. 
     The feeding waveguide may have a rectangular shape in cross-section, and a pair of opposing sides of the feeding waveguide in the cross-section in parallel to the array direction of the radiating slots has a length shorter than the length of the other pair of sides. 
     According to another aspect of the invention, a radar device is provided, which includes a slot antenna, an electromagnetic wave generating module for generating the electromagnetic wave to be supplied to the slot antenna, a rotation module for rotating the slot antenna so that the center axis of the radiation part horizontally rotates, and a received signal processing module for receiving an echo signal of the electromagnetic wave reflected on a reflection body and detecting the reflection body. The slot antenna includes a tubular electromagnetic wave radiation part having a hollow space, a plurality of electromagnetic wave radiating slots for radiating electromagnetic waves being formed in at least a part of a side surface of the radiation part and a plurality of feeding slots for being inputted with the electromagnetic waves being arrayed in line in another part of the side surface opposing to the radiating slots, a feeding part having a hollow space, extending along the feeding slot array, and for feeding power from the outside of the radiation part to the feeding slot, and a power guiding part having a hollow space and for guiding the power to the feeding part, the power guiding part extending in a direction orthogonal to the array direction of the feeding slots and in parallel to the center axis of the radiation part from a location of the feeding part corresponding to at least one of the feeding slots. 
     Thereby, a radar device which allows a size reduction can be manufactured. 
     A bulged portion may be formed in at least a portion of an inner wall of the feeding part opposing to the feeding slot so that the portion of the feeding part is bulged more than an inner wall of the power guiding part facing the same side as the inner wall of the feeding part. 
     A center frequency of the electromagnetic wave may be within a range from 9.38 GHz to 9.44 GHz and the bulged portion is bulged by 1 mm to 4 mm. 
     The plurality of radiating slots may be arranged two-dimensionally. 
     The feeding slot array direction may be oriented in a direction orthogonal to the center axis of the radiation part. 
     The radar device may further include a radome for accommodating the radiation part, the feeding part, and the power guiding part therein. 
     The radome may have a substantial cylindrical shape, and the feeding part and the power guiding part may be arranged in parallel to the center axis of the radome and in at least one of a position at the center axis and a position near the center axis of the radome. 
     As described above, according to the present invention, a slot antenna, and a radar device of compact size can be provided, which allow an electromagnetic wave to propagate in an appropriate mode pattern within a radiation waveguide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which the like reference numerals indicate like elements and in which: 
         FIG. 1  is an exploded view illustrating a configuration of a slot antenna according to one embodiment of the present invention; 
         FIG. 2  is an external perspective view illustrating one example of a configuration of the slot antenna; 
         FIG. 3  is detailed structure views illustrating a feeding part structure and its peripherals of the slot antenna in order to illustrate coupling characteristics, in which the part (a) of  FIG. 3  is a plan view, the parts (b) and (c) are side views, and the part (d) of  FIG. 3  is a cross-sectional view I-I of (a) of  FIG. 3 , where the feeding part structure and its peripherals are accommodated in a radome; 
         FIG. 4  is an external perspective view illustrating another example of a configuration of the slot antenna; 
         FIG. 5  is detailed structure views illustrating the example of the feeding part structure and its peripherals of the slot antenna in order to illustrate coupling characteristics, in which the part (a) of  FIG. 5  is a plan view, the parts (b) and (c) of  FIG. 5  are side views, and the part (d) of  FIG. 5  is a cross-sectional view I-I of (a) of  FIG. 5 , where the feeding part and its peripherals are accommodated in the radome; 
         FIG. 6  is a view illustrating a state of waveguide propagation mode wherein: width a=17.5 mm and length b=22.9 mm (fixed), and height c=0 mm; 
         FIG. 7  is a view illustrating a state of waveguide propagation mode wherein: width a=17.5 mm and length b=22.9 mm (fixed), and height c=1 mm; 
         FIG. 8  is a view illustrating a state of waveguide propagation mode wherein: width a=17.5 mm and length b=22.9 mm (fixed), and height c=2 mm; 
         FIG. 9  is a view illustrating a state of waveguide propagation mode wherein: width a=17.5 mm and length b=22.9 mm (fixed), and height c=3 mm; 
         FIG. 10  is a view illustrating a state of waveguide propagation mode wherein: width a=17.5 mm and length b=22.9 mm (fixed), and height c=4 mm; 
         FIG. 11  is a view illustrating a state of waveguide propagation mode wherein: width a=17.5 mm and length b=22.9 mm (fixed), and height c=5 mm; 
         FIG. 12  is a view illustrating a state of waveguide propagation mode wherein: width a=17.5 mm and length b=22.9 mm (fixed), and height c=6 mm; 
         FIG. 13  is a view illustrating a state of waveguide propagation mode wherein: width a=17.5 mm and height c=3 mm (fixed), and length b=10 mm; 
         FIG. 14  is a view illustrating a state of waveguide propagation mode wherein: width a=17.5 mm and height c=3 mm (fixed), and length b=30 mm; 
         FIG. 15  is a view illustrating a state of waveguide propagation mode wherein: length b=22.9 mm and height c=3 mm (fixed), and width a=10 mm; 
         FIG. 16  is a view illustrating a state of waveguide propagation mode wherein: length b=22.9 mm and height c=3 mm (fixed), and width a=30 mm; 
         FIG. 17  is a chart illustrating return losses (ratio of reflection to an input (unit in dB)) of microwave at frequencies (9.38 GHz, 9.41 GHz, 9.44 GHz) wherein: width a=17.5 mm, length b=22.9 mm, and height c is varied from 0.5 to 9 mm; 
         FIG. 18  is a chart illustrating return losses (ratio of reflection to an input (unit in dB)) of microwave at frequencies (9.38 GHz, 9.41 GHz, 9.44 GHz) wherein: width a=17.5 mm, height c=3 mm, and length b is varied from 10 to 30 mm; 
         FIG. 19  is a chart illustrating return losses (ratio of reflection to an input (unit in dB)) of microwave at frequencies (9.38 GHz, 9.41 GHz, 9.44 GHz) wherein: length b=22.9 mm, height c=3 mm, and width a is varied from 10 to 30 mm; 
         FIG. 20  is a chart illustrating insertion losses (ratio of loss, such as a consumption by heat energy, to an input (unit in dB)) of microwave at frequencies (9.38 GHz, 9.41 GHz, 9.44 GHz) wherein: width a=17.5 mm, length b=22.9 mm, and height c is varied from 0.5 to 9 mm; 
         FIG. 21  is a chart illustrating insertion losses (ratio of loss, such as a consumption by heat energy, to an input (unit in dB)) of microwave at frequencies (9.38 GHz, 9.41 GHz, 9.44 GHz) wherein: width a=17.5 mm, height c=3 mm, and length b is varied from 10 to 30 mm; 
         FIG. 22  is a chart illustrating insertion losses (ratio of loss, such as a consumption by heat energy, to an input (unit in dB)) of microwave at frequencies (9.38 GHz, 9.41 GHz, 9.44 GHz) wherein: length b=22.9 mm, height c=3 mm, and width a is varied from 10 to 30 mm; 
         FIG. 23  is a chart illustrating a return loss of microwave at frequencies (9.38 GHz, 9.41 GHz, 9.44 GHz) wherein: width a=17.5 mm, length b=22.9 mm, and height c=3 mm; 
         FIG. 24  is a chart illustrating an insertion loss of microwave at frequencies (9.38 GHz, 9.41 GHz, 9.44 GHz) wherein: width a=17.5 mm, length b=22.9 mm, and height=3 mm; 
         FIG. 25A  is a view illustrating a configuration of a feeding waveguide with respect to a radiation waveguide according to the conventional art, and  FIG. 25B  is a view illustrating another configuration of the feeding waveguide with respect to the radiation waveguide according to the conventional art; and 
         FIG. 26  is a schematic view illustrating a block diagram of a radar device according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, one embodiment of the invention is described in detail with reference to the accompanying drawings. 
       FIG. 1  is an exploded view illustrating a configuration of a slot antenna according to this embodiment of the present invention. The slot antenna is constituted with a feeding part structure  10  and a radiation part structure  20  as shown in  FIG. 1 . The radiation part structure  20  is for radiating an electromagnetic wave, which is propagated through an internal cavity formed by components such as a radiation waveguide structure body  21 , outside toward a designated direction. The feeding part structure  10  is for guiding (feeding) a required electromagnetic wave into the radiation waveguide structure body  21 . 
     Hereinafter, structures of the feeding part structure  10  and the radiation part structure  20  are described in detail below with reference to  FIG. 1 . The feeding part structure  10  includes a feeding waveguide structure body  11  and a plate  31  which constructs a part of a side wall of the internal cavity. The feeding part structure  10  is constructed by the feeding waveguide structure body  11  and the plate  31  positioned against each other. The feeding waveguide structure body  11  and the plate  31  are made of a conductive material such as aluminum. 
     The feeding waveguide structure body  11  is a substantially rectangular parallelepiped shape and formed with a U-shaped cross-sectional groove section  12  with a necessary dimension along a longitudinal direction (direction in parallel to the arrow “A” in  FIG. 1 ) of the body  11 . Note that, the groove section  12  functions as a feeding cavity. Further, a middle plane  13  is formed on both sides of the groove section  12  in a direction orthogonal to the longitudinal direction. Each of the middle planes  13  functions as a recipient surface when the plate  31  is covered from the top as described later. 
     A recessed section  14  having a necessary width in a part along the longitudinal direction of the groove section  12  and a necessary length along a direction orthogonal to the longitudinal direction is continuously formed from the groove section  12 . The recessed section  14  has the same depth as the groove section  12  and forms a rectangular parallelepiped shaped input cavity. At an appropriate location of a bottom surface of the recessed section  14 , a hole  15  with a necessary diameter is bored through toward the bottom. As shown in  FIG. 3 , the hole  15  is inserted, for example, with a coaxial connector  41  (omitted in  FIG. 1 ) for inputting a microwave from outside into the recessed section  14 . The coaxial connector  41  is constituted with a metal probe  42  for excitation and a cylindrical insulation material  43 , such as Teflon®, on the perimeter of the metal probe  42 . Note that, the hole  15  is arranged in a position within the recessed section  14  where the microwave can match at a frequency to be used and a standing wave can be formed in the groove section  12 . Further, the base end of the coaxial connector  41  is arranged so it is exposed within a waveguide. Thereby, the microwave (an electromagnetic wave) generated by a microwave generator, such as a magnetron or a semiconductor oscillator, is directed through this waveguide to the coaxial connector  41 . 
     The waveguide is arranged to extend in parallel to the radiation waveguide structure  21 . The waveguide has a rectangular shape in cross-section, and a pair of opposing sides of the feeding part structure  10  in the cross-section in parallel to the array direction of the radiating slots has a length shorter than the length of the other pair of sides. 
     In at least a part of the groove section, a convex step  16  (bulged portion) having a predetermined shape is formed in a section corresponding to the recessed section  14 . Note that, the feeding waveguide structure body  11  can be manufactured by first machining down to the top of the step  16 , and followed by machining down the other areas except for the step  16 , that is machining the groove section  12  and the recessed section  14  down to a necessary depth. Alternatively, forming the groove section  12  first, then followed by forming the step  16  by setting a predetermined conductive material to the groove section  12  is an acceptable method. In this embodiment, the shape of the step  16  is set to be a rectangular parallelepiped shape. That is, as shown in the part (a) of  FIG. 1 , each dimension of the step is represented as: the length dimension=b, the width dimension=a (i.e., the direction orthogonal to the length), and the thickness (height) dimension=c. 
     The top portions of the feeding waveguide structure body  11  and the middle planes  13  have a required number of mounting holes  111  and  131  formed respectively. 
     In the plate  31 , an inverted L-shaped bent section  32  is formed at one end of the length directions. Further, in the plate  31 , a flat plate section  33  is formed in the length direction from the bent section  32 , and a side surface section  34  is continuously formed by bending both ends of the plate section  33  in the width direction. 
     Note that, the feeding part is constituted with the groove section  12  and the step  16  of the feeding waveguide structure body  11 , the plate  31 , and slots  351 - 354  on the plate; and the input part is constituted with the recessed section  14  and the hole  15  of the feeding waveguide structure body  11 , and the plate  31 . 
     In this embodiment, at a predetermined position on the flat plate section  33  in the length direction, a slot  35  including the four slots  351 - 354  are linearly arranged in the width direction at a required interval. The slots  351 - 354  have the same shape and are formed by, for example, a punching process at positions corresponding to the groove section  12 . In this embodiment, the slot  353  is arranged so that its position is correspondent to the step  16 . In this manner, the recessed section  14  is arranged corresponding to either one of the inner slots  352  and  353  (slot at either ends  351  and  354  excluded), and thereby, it becomes possible to adopt a structure in which an electromagnetic wave splits into the directions along which the slots are aligned, and becomes easier to attain matching of the electromagnetic wave, and becomes possible to eliminate the deterioration (disorder) of a propagation mode as much as possible during feeding. Note that the relationship between a matching state and each dimension of the step (a, b and c) is described later. 
     Further, the plate  31  is formed with mounting holes  311  on the top portion side of the bent section  32  and mounting holes  331  in the flat plate section  33 , and, therefore, it can be fastened with the feeding waveguide structure body  11  by means of fastening members such as screws. As a result, the recessed section  14  and the groove section  12  are enclosed by the flat plate section  33 , thus constructing the waveguide as the input cavity and the feeding cavity. Further, a standing wave is generated inside the feeding cavity by utilizing a bent section  211  (described later) of the radiation waveguide structure body  21 , or, for example, by arranging a short circuit component at both ends along the direction of slot arrangement. 
     Here, the behavior of an electromagnetic wave inputted by the coaxial connector  41  is described. The electromagnetic wave transmitted through the coaxial connector  41  is radiated from the recessed section  14  and proceeds to the groove section  12 . The electromagnetic wave is re-directed into both side directions of the slot arrangement in parallel to the arrow “A” in the part (a) of  FIG. 1  without its shape of mode not substantially disordered by the shapes of the groove section  12  and the step  16 , and further moves to each of the slots  351 - 354 . Then, the uniform electromagnetic waves propagate to the radiation waveguide structure body  21  side through each of the slots  351 - 354 . 
     The radiation part structure  20  is constituted with the radiation waveguide structure body  21  and the plate  31  arranged in parallel to each other via a necessary space. The radiation waveguide structure body  21  and the plate  31  have a predetermined length in the length direction (propagation direction of electromagnetic wave) indicated by the arrow “B” in the part (c) of  FIG. 1  and form a tubular cavity between them, which serves as an antenna waveguide. Note that, the radiation waveguide structure body  21  is made of a conductive material such as aluminum. Further, the radiation waveguide structure body  21  is constituted with a radiation surface(s) by forming radiating slots  22  which are arranged two-dimensionally at least on one surface simply by, for example, a punching process. The radiating slots  22  are formed with a predetermined number of slots in the width direction (the direction A which is orthogonal to the direction B to which the electromagnetic wave propagates). In this embodiment, three radiating slots are formed in the width direction where they are alternately angled in a direction opposite to each other. The radiating slots  22  are arranged with a predetermined spacing, for example half of a wave length within the cavity, toward the direction B of electromagnetic wave propagation. Thereby, an electromagnetic wave with TEn0 mode propagates inside the radiation part structure  20 , and is radiated from the respective radiating slots  22  having necessary directionality. Note that a bent section  212  with a smaller dimension from the radiation surface than the bend section  211  is continuously formed in the propagation direction B from the bent section  211  of the radiation waveguide structure body  21 . The bent section  212  is used to be attached with the flat plate  33  of the plate  31  via a predetermined space, between which an antenna internal cavity is formed. In this way, the electromagnetic wave, which is the microwave inputted from the coaxial connector  41 , is guided through the slots  351 - 354 , to the radiation waveguide structure body  21 , and propagates toward the propagation direction B within the antenna internal cavity. Then, the electromagnetic wave obtains necessary directionality by each slot and radiated to an outside direction orthogonal to the radiation surface. 
     In this embodiment, the waveguide, the feeding part structure  10 , and the radiation part structure  20  are arranged inside a radome for accommodating the feeding part structure  10  and the radiation part structure  20  and rotating in a horizontal plane. The radome has a substantially tubular shape, and the waveguide, the feeding part structure  10 , and the radiation part structure  20  are arranged in parallel to the center axis of the radome and in at least one of a position at the center axis and a position near the center axis of the radome. 
       FIG. 2  is an external perspective view illustrating one example of a configuration of the slot antenna.  FIG. 3  is detailed structure views illustrating a feeding part structure and its peripherals of the slot antenna in order to illustrate coupling characteristics, in which the part (a) of  FIG. 3  is a plan view, the parts (b) and (c) are side views, and the part (d) of  FIG. 3  is a cross-sectional view I-I of (a) of  FIG. 3 , where the feeding part structure and its peripherals are accommodated in the radome.  FIG. 4  is an external perspective view illustrating another example of a configuration of the slot antenna.  FIG. 5  is detailed structure views illustrating another example of the feeding part structure and its peripherals of the slot antenna in order to illustrate coupling characteristics, in which the part (a) of  FIG. 5  is a plan view, the parts (b) and (c) of  FIG. 5  are side views, and the part (d) of  FIG. 5  is a cross-sectional view I-I of (a) of  FIG. 5 , where the feeding part and its peripherals are accommodated in the radome. Note that in  FIGS. 2 through 5 , the structure sections also shown in  FIG. 1  have the same reference numerals and symbols, and are omitted in description. The difference of the structure illustrated in  FIGS. 4 and 5  from that in  FIGS. 2 and 3  is a structure where the feeding waveguide structure body  11  is arranged in the opposite direction with respect to the radiation waveguide structure body  21 , the plate  31 , and the feeding part structure  10 , and the coaxial connector  41  is exposed within the end side of the feeding part structure  10  compared to the  FIGS. 2 and 3 . Note that, although the structure in  FIGS. 2 and 3  is preferred for practical use in sight of size reduction, characteristically there is no substantial difference between the two structures. 
     In this embodiment, as shown in the part (d) of  FIG. 3  and the part (d) of  FIG. 5 , some of the components (e.g., the radiation waveguide structure body  21 , the plate  31 , and the feeding waveguide structure body  11 ) which have comparatively longer width among all the components in the radome are arranged to be offset from the center axis of the radome. However, those components with comparatively longer width may preferably be arranged as closer as possible to the center axis of the radome, thereby, the diameter of the radome can be reduced. 
     In  FIGS. 1 ,  3  and  5 , the factors (parameters) for achieving a high electromagnetic wave matching are set as follows; the width dimension a for the step  16 , the length dimension b for the step  16 , and the height dimension c (from the bottom of the groove section  12 ) for the step  16 . 
       FIGS. 6 through 24  are views and charts illustrating results of simulation tests for each characteristic when each parameter is suitably changed. In this embodiment, the microwave frequency used is: the center frequency is 9.41 GHz and the zone is between 9.38 GHz to 9.44 GHz. In each frequency, the dimensions a, b and c are set as; the width a=17.5 mm, the length b=22.9 mm, and the height c=3 mm. Note that the longitudinal size of the wavelength within the waveguide cross section corresponding to the frequency 9.41 GHz is 22.2 mm which is set somewhat larger for a waveguide of a feeding part so that the microwave within the range can pass through in a suitable manner. 
       FIGS. 6 through 12  are views illustrating states of a waveguide propagation mode with the width a=17.5 mm and the length b=22.9 mm remaining the same while the height c is changed from 0 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, and 6 mm. 
       FIG. 6  illustrates the case when c=0 mm, in which the shape of the first magnetic field loop, whose position corresponds to the step  16 , is significantly deteriorated toward the propagation direction of the electromagnetic wave. Further, each magnetic field component shows various intensity, and it is ununiform toward the direction B especially at the position where corresponds to the step  16 . 
       FIG. 7  illustrates the case when c=1 mm, in which the shape of the first magnetic field loop, whose position corresponds to the step  16 , is slightly deteriorated in the propagation direction of the electromagnetic wave. Therefore, similar to the case shown in  FIG. 6 , each magnetic field component shows various intensity, and it is ununiform toward the direction B especially at the position where corresponds to the step  16 . 
       FIG. 8  illustrates the case when c=2 mm, in which the shapes of the first magnetic field loops, whose position corresponds and positions are adjacent to the step  16 , are slightly deteriorated in the propagation direction of the electromagnetic wave. On the other hand, each magnetic field component shows not so much variation in intensities, and the ununiformity toward the direction B at the position where corresponds to the step  16  is significantly reduced. 
       FIG. 9  illustrates the case when c=3 mm, in which the shapes of the first magnetic field loops, whose position corresponds and positions are adjacent to the step  16 , are slightly deteriorated in the propagation direction of the electromagnetic wave. On the other hand, each magnetic field component shows not so much variation in intensity, and the ununiformity toward the direction B at the position where corresponds to the step  16  is significantly reduced. 
       FIG. 10  illustrates the case when c=4 mm, in which the shapes of the first magnetic field loops, whose position corresponds and positions not correspond to the step  16 , are slightly deteriorated in the propagation direction of the electromagnetic wave. Therefore, similar to the case shown in  FIG. 7 , each magnetic field component shows variation in intensity, and it is ununiform toward the direction B especially at the position where corresponds to the step  16 . 
       FIG. 11  illustrates the case when c=5 mm, in which the shapes of the first magnetic field loops, whose position corresponds and positions not correspond to the step  16 , are significantly deteriorated toward the propagation direction of the electromagnetic wave. Further, each magnetic field component shows various intensity, and it is ununiform toward the direction B especially at a position where corresponds to a step  16 . 
       FIG. 12  illustrates the case when c=6 mm, in which the shapes of the first magnetic field loops, whose position corresponds and positions not correspond to the step  16 , are significantly deteriorated toward the propagation direction of the electromagnetic wave. Further, each magnetic field component shows various intensity, and it is ununiform toward the direction B especially at the position where corresponds to a step  16 . 
       FIGS. 13 and 14  are views illustrating states of waveguide propagation mode with the width a=17.5 mm and the height c=3 mm remaining the same while the length b is 10 mm and 30 mm. 
       FIG. 13  illustrates the case when b=10 mm, in which the shapes of the first magnetic field loops, whose position corresponds and positions are adjacent to the step  16 , are relatively deteriorated toward the propagation direction B. Further, each magnetic field component shows various intensity, and it is ununiform toward the direction B especially at the position where corresponds to the step  16 . 
       FIG. 14  illustrates the case when b=30 mm, in which the shape of the first magnetic field loops, whose position corresponds and positions are adjacent to the step  16 , are significantly deteriorated toward the propagation direction B, and its intensity is weak. Further, the intensity of each magnetic field component toward the direction B is weaker overall. 
       FIGS. 15 and 16  are views illustrating states of waveguide propagation mode with the length b=22.9 mm and the height c=3 mm remaining the same while the width a is 10 mm and 30 mm. 
       FIG. 15  illustrates the case when a=10 mm, in which the shape of the first magnetic field loops, whose position corresponds and positions are adjacent to the step  16 , are relatively deteriorated toward the propagation direction B. Further, each magnetic field component shows various intensity, and it is ununiform toward the direction B especially at the position where corresponds to the step  16 . 
       FIG. 16  illustrates the case when a=30 mm, in which the shape of the first magnetic field loops are not particularly deteriorated toward the propagation direction B. On the other hand, each magnetic field component shows various intensity, and it is ununiform toward the direction A orthogonal to the direction B. 
       FIGS. 17 through 19  are charts illustrating return losses (ratio of reflection to an input (unit in dB)) of microwave at the frequencies (9.38 GHz, 9.41 GHz, 9.44 GHz) when the width a, the length b, and the height c are varied appropriately.  FIG. 17  illustrates the return losses of microwave at respective frequencies, where the width a=17.5 mm and the length b=22.9 mm, and the height c (horizontal axis) is varied from 0.5 mm to 9 mm. As illustrated in  FIG. 17 , the return losses of microwave at the frequencies are approximately −30 dB or below in each case when the height c is close to 3 mm. 
       FIG. 18  illustrates the return losses of microwave at respective frequencies, where the width a=17.5 mm and the height c=3 mm, and the length b (horizontal axis) is varied from 10 mm to 30 mm. As illustrated in  FIG. 18 , the return losses of microwave at the frequencies are approximately −30 dB or below in each case when the length b is close to 22.9 mm. 
       FIG. 19  illustrates the return losses of microwave at respective frequencies, where the length b=22.9 mm and the height c=3 mm, and the width a (horizontal axis) is varied from 10 mm to 30 mm. As illustrated in  FIG. 19 , the return losses of microwave at the frequencies are approximately −30 dB or below in each case when the width a is close to 17.5 mm. Note that, where the width a is other than 17.5 mm, for example, high 15 mm or near 16.5 mm, the return losses of microwave at the frequencies are approximately −30 dB or below in each case. 
       FIGS. 20 through 22  are charts illustrating insertion losses (ratio of loss, such as consumption by heat energy, to an input (unit in dB)) of microwave at the frequencies (9.38 GHz, 9.41 GHz, 9.44 GHz) when the width a, the length b, and the height c are varied appropriately.  FIG. 20  illustrates the insertion losses of microwave at respective frequencies, where the width a=17.5 mm and the length b=22.9 mm, and the height c (horizontal axis) is varied from 0.5 mm to 9 mm. As illustrated in  FIG. 20 , the insertion losses of microwave at the frequencies are extremely low at approximately −0.12 dB when the height c is 2 mm to 3 mm. 
       FIG. 21  illustrates the insertion losses of microwave at respective frequencies, where the width w=17.5 mm and the height c=3 mm, and the length b (horizontal axis) is varied from 10 mm to 30 mm. As illustrated in  FIG. 21 , the insertion losses of microwave at the frequencies are extremely low at approximately −0.12 dB when the length b is near 23 mm including 22.9 mm. 
       FIG. 22  illustrates the insertion losses of microwave at respective frequencies, where the length b=22.9 mm and the height c=3 mm, and the width a (horizontal axis) is varied from 10 mm to 30 mm. As illustrated in  FIG. 22 , the insertion losses of microwave at the frequencies are extremely low at approximately −0.12 dB when the width a is approximately 15 mm to 18 mm. 
       FIG. 23  is a chart illustrating the return loss of microwave within the frequency band (the band including 9.38 GHz, 9.41 GHz, and 9.44 GHz) where the width a=17.5 mm, the length b=22.9 mm, and the height c=3 mm. The return loss is approximately −30 dB or below when the frequency is within 9.38 GHz to 9.44 GHz. 
       FIG. 24  is a chart illustrating the insertion loss of microwave within the frequency band (the band includes 9.38 GHz, 9.41 GHz, and 9.44 GHz) where the width a=17.5 mm, the length b=22.9 mm, and the height c=3 mm. The insertion loss is extremely low at approximately −0.12 dB or below when the frequency is within 9.38 GHz to 9.44 GHz. 
     As described above, for the microwave with the center frequency of 9.41 GHz and the frequency band width of 9.38 GHz to 9.44 GHz, the best dimensions for the step  16  are the length b=22.9 mm, the width a=17.5 mm, and the height c=3 mm. 
     The slot antenna of this embodiment may be utilized in a radar device for ships, for example.  FIG. 26  is a schematic view illustrating a block diagram of the radar device of this embodiment. The radar device is equipped with a high-frequency circuit module. The high-frequency circuit module is equipped with a magnetron as a high-frequency wave generator for being driven intermittently by a driving module and outputting through oscillation a pulsating electromagnetic wave (a microwave). The high-frequency circuit unit is also equipped with a rotary joint which transmits a microwave to the aerial module side including the slot antenna, which becomes a rotation side where rotates in a horizontal plane. The slot antenna is rotated (circled) around its vertical axis by a rotation driving module such as a motor. The microwave radiation surface of the radiation waveguide part on the slot antenna is pointed toward a horizontal direction and has characteristics that give a microwave a necessary level of narrow directivity both in horizontal and vertical directions. In this configuration, a pulsating microwave is generated by a magnetron pulsed by the driving unit. The microwave travels through the rotary joint, the feeding waveguide part, the radiation waveguide part, and then is radiated toward all the horizontal directions from the radiation surface of the radiation waveguide part. 
     Note that the present invention can adopt following aspects. 
     (1) When the center frequency and the frequency band of microwave, which are to be used, are changed, the dimensions for the step  16 , the length b, the width a, and the height c are set based on a wave length in the waveguide and the frequency band correspondingly. Note that the length b of the step  16  is affected by the size of the waveguide and the frequency which are used. The length b may be shortened when the waveguide is smaller or the frequency used is higher. Further, the width a of the step  16  is affected by the size of the waveguide and the frequency which are used. The width a may be narrowed when the waveguide is smaller or the frequency used is higher. Further, the height c of the step  16  is affected by the size of the waveguide and the frequency which are used, and is determined based on the frequency used. 
     (2) In this embodiment, the coaxial connector unit  41  is used; however, the waveguide may additionally be utilized to re-direct an electromagnetic wave. 
     (3) Each of the length b, the width a, and the height c of the step  16 , which are the parameters, may be appropriately designed in order to optimize its dimensions. That is, by analyzing the changes in direction and degree of the deterioration of the mode distribution, the return losses, and the insertion losses, corresponding to an adjustment in direction and amount in each parameter, a further optimized dimension can be obtained. 
     (4) The step  16  is not limited to the rectangular parallelepiped shape; it may be a cylindrical shape. Even with the cylindrical shape, it is possible to efficiently diverge an electromagnetic wave inputted to the recessed section  14  into the both of width directions of the groove section  12 . 
     (5) In this embodiment, the slot  35  ( 351 - 354 ) of the feeding part has four slots in the width direction, and the slots  22  of the radiation waveguide structure body  21  has three slots in the width direction. However, not limited to this, it may be designed various different types of slot array corresponding to a relationship with the frequency used, and an applied mode pattern. 
     In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued. 
     Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “has,” “having,” “includes,” “including,” “contains,” “containing” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a,” “has . . . a,” “includes . . . a,” “contains . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, contains the element. The terms “a” and “an” are defined as one or more unless explicitly stated otherwise herein. The terms “substantially,” “essentially,” “approximately,” “about” or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1% and in another embodiment within 0.5%. The term “coupled” as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is “configured” in a certain way is configured in at least that way, but may also be configured in ways that are not listed.