Patent Publication Number: US-2022231423-A1

Title: Radar antenna

Description:
TECHNICAL FIELD 
     The present disclosure relates to an antenna, and more particularly, to a radar antenna. 
     BACKGROUND ART 
     According to the recent trend, a radar antenna is used to transmit/receive a signal for detecting an object around a vehicle. The radar antenna enables a driver to determine whether an object is present, the distance to the object, the moving direction of the object, and the moving speed of the object, and to identify and classify the object, on the basis of a scattered wave or reflected wave which is transferred after a radio wave radiated by the radar antenna has collided with the object. 
     Recently, research is being conducted on technologies for widening the detection range of the radar antenna and raising the performance of the radar antenna, in order to advance an anti-collision radar of an autonomous vehicle for the age of driverless vehicles. 
     However, the conventional radar antenna is made of metal and thus has a large weight. Furthermore, the conventional radar antenna includes a waveguide formed by stacking a plurality of plates, which makes it difficult to perform an assembly process. Moreover, eccentricity which occurs during the assembly process may degrade the reliability and performance of the radar antenna. 
     SUMMARY OF INVENTION 
     Technical Problem 
     The present disclosure is proposed to solve the above conventional problem, and an object of the present disclosure is to provide a radar antenna which can raise performance and minimize a loss, and secure productivity because the radar antenna can be reduced in size, easily assembled and manufactured at low cost. 
     Solution to Problem 
     To achieve the object, a radar antenna according to an exemplary embodiment of the present disclosure includes an antenna body; a slot radiation part and a slot reception part formed on one side of the antenna body; a transmission port and a reception port formed on the other side of the antenna body; and a plurality of waveguides formed in the antenna body, and configured to connect the slot radiation part to the transmission port, and connect the slot reception part to the reception port, wherein the slot radiation part includes a first slot radiation part configured to radiate a radio wave in a first detection range, and a second slot radiation part and a third slot radiation part configured to radiate radio waves in a second detection range having a larger width and distance than the first detection range. 
     The second and third slot radiation parts may be respectively arranged on both sides of the first slot radiation part, the first to third slot radiation parts may each include a plurality of slots, and the number of slots included in each of the second and third slot radiation parts may be larger than the number of slots included in the first slot radiation part. 
     The first slot radiation part may include a plurality of slots arranged in one row in a top-to-bottom direction, and the plurality of slots include in one row are arranged so that portions thereof do not sit on a straight line which connects the uppermost slot to the lowermost slot. The first slot radiation part may include a plurality of slots which are successively arranged at predetermined intervals in a zigzag manner in a top-to-bottom direction. 
     The second and third slot radiation parts may each include a plurality of slots arranged in a plurality of rows in top-to-bottom and side-to-side directions, and the plurality of slots included in at least one row may be arranged so that portions thereof do not sit on a straight line which connects the uppermost slot to the lowermost slot. The plurality of slots included in at least one row in each of the second and third slot radiation parts may be arranged in a zigzag manner. 
     The second and third slot radiation parts may each include a plurality of slots arranged in a plurality of rows in top-to-bottom and side-to-side directions, and the uppermost slot in the outermost row among the plurality of rows and the uppermost slot in a row inside the outermost row may be arranged to deviate from each other in a side-to-side direction. The uppermost slot in the outermost row may be disposed at a lower level than the uppermost slot in the row inside the outermost row, and the uppermost slots in the respective rows may be disposed at levels that gradually increase from the outermost row toward the row inside the outermost row. The number of slots included in the outermost row may be equal to the number of slots included in the row inside the outermost row. 
     The slot reception part may be located at the center bottom of the front side of the antenna body, the slot reception part may include a plurality of slots arranged in a plurality of rows in top-to-bottom and side-to-side directions, and the slots included in each of the rows may be arranged on a straight line. 
     The number of the reception ports may be larger than the number of the transmission ports. 
     The antenna may include a first plate and a second plate, and the plurality of waveguides may be formed by assembling the first and second plates. The waveguide may be a straight channel formed by coupling the first to third slot radiation parts, a plurality of slot grooves which are formed on the rear side of the first plate so as to communicate with the slot reception part, and a plurality of concave grooves which are formed on the front side of the second plate so as to communicate with the transmission port and the reception port, respectively. 
     In the second slot radiation part, the transmission port formed as one slot on one side of the concave groove may be connected to the second slot radiation part formed as a plurality of slots in a longitudinal direction of the slot groove along the waveguide formed by the concave groove and the slot groove. 
     The bottoms of the slot grooves corresponding to the second slot radiation part may be arranged on the same line in a horizontal direction so as to correspond to a horizontal concave groove including the transmission port. In the slot reception part, the reception port formed as one slot in the middle of the concave groove may be connected to the slot reception part formed as a plurality of slots in the longitudinal direction of the slot groove through the waveguide formed by coupling the concave groove and the slot groove. The slot groove may have an inclined wall formed at a position facing a slot formed in the concave groove and configured to guide a radio wave. 
     Advantageous Effects 
     According to the present disclosure, the slot radiation parts may be configured as two kinds of slot radiation parts to effectively detect an object at a long distance and an object at a short distance, and the air waveguide may be applied to raise the performance while minimizing a loss. 
     Furthermore, the slot radiation part may include a plurality of slots arranged in a plurality of rows, and the plurality of slots included in each of the rows may be arranged in a zigzag manner, which makes it possible to raise the gain of the antenna and acquire high directionality, while reducing the size of the antenna. 
     Furthermore, since the radar antenna having a waveguide structure for connecting slots is manufactured by coupling two plates each configured by coating a molding product with metal, the radar antenna may be easily assembled, and manufactured at low cost, which makes it possible to secure productivity. 
     Therefore, the radar antenna may be applied to a vehicle, thereby contributing to not only effectively detecting an object at a long distance and an object at a short distance, but also advancing an anti-collision radar of an autonomous vehicle. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view illustrating a front side of a radar antenna in accordance with an embodiment of the present disclosure. 
         FIG. 2  is a perspective view illustrating a rear side of the radar antenna in accordance with the embodiment of the present disclosure. 
         FIG. 3  is a perspective view illustrating the front side of the radar antenna in accordance with the embodiment of the present disclosure. 
         FIG. 4  is a cross-sectional view taken along line A-A of  FIG. 3 . 
         FIG. 5  is a cross-sectional view taken along line B-B of  FIG. 3 . 
         FIG. 6  is a cross-sectional view taken along line C-C of  FIG. 3 . 
         FIG. 7  is a diagram illustrating a front side of a first plate in accordance with the embodiment of the present disclosure. 
         FIG. 8  is a diagram illustrating a rear side of the first plate in accordance with the embodiment of the present disclosure. 
         FIG. 9  is diagram illustrating a front side of a second plate in accordance with the embodiment of the present disclosure. 
         FIG. 10  is diagram illustrating a rear side of the second plate in accordance with the embodiment of the present disclosure. 
         FIGS. 11A and 11B  are diagrams illustrating a slot radiation part on the front side of the first plate and a slot groove on the rear side of the first plate in accordance with the embodiment of the present disclosure. 
         FIG. 12  is a diagram illustrating a radome-integrated radar package to which the embodiment of the present disclosure is applied. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. 
     Referring to  FIGS. 1 to 3 , a radar antenna  10  in accordance with an embodiment of the present disclosure includes an antenna body  100 , slot radiation parts  111 ,  113  and  114 , a slot reception part  115 , transmission ports  121 ,  123  and  124 , reception ports  125  and a waveguide  130 . 
     In order to promote understandings in the embodiment of the present disclosure, the side on which the slot radiation parts  111 ,  113  and  114  and the slot reception part  115  are formed is referred to as a front side, and the side on which the transmission ports  121 ,  123  and  124  and the reception ports  125  are formed is referred to as a rear side. 
     The antenna body  100  forms the exterior of the radar antenna  10 , and is formed in a plate shape with a predetermined thickness. The slot radiation parts  111 ,  113  and  114  and the slot reception part  115  are formed on the front side of the antenna body  100 , and the transmission ports  121 ,  123  and  124  and the reception port  125  are formed on the rear side of the antenna body  100 . 
     The slot radiation parts  111 ,  113  and  114  radiate radio waves, and the slot reception part  115  receives radio waves reflected from an object after the radio waves radiated from the slot radiation parts  111 ,  113  and  114  have collided with the object. The slot radiation parts  111 ,  113  and  114  are each composed of slots for transmitting radio waves, and the slot reception part  115  is composed of slots for receiving radio waves. 
     As illustrated in  FIG. 1 , the slot radiation parts  111 ,  113  and  114  are configured as two kinds of slot radiation parts, i.e. a first slot radiation part  111  and second and third slot radiation parts  113  and  114 , and the slot reception part  115  is configured as one kind of slot reception part. 
     The first slot radiation part  111  radiates radio waves in a first detection range, and the second and third slot radiation parts  113  and  114  radiate radio waves in a second detection range having a larger width and distance than the first detection range. 
     The first detection range is a short distance equal to or less than a preset distance, and the second detection range is a long distance equal to or more than the preset distance. For example, the first detection range may be equal to or less than 100 m, and the second detection range may be equal to or more than 100 m. 
     The first slot radiation part  111  radiates Tx SSR (short range radar) radio waves at a small beam angle, and the second and third slot radiation parts  113  and  114  radiate Tx LLR (long range radar) radio waves at a relatively large beam angle. 
     The first slot radiation part  111  is located at the center top of the front side of the antenna body  100  in order to radiate radio waves at a small beam angle, and the second and third slot radiation parts  113  and  114  are respectively located on both sides of the first slot radiation part  111  in order to radiate radio waves at a relatively large beam angle. 
     The radio waves transferred from the transmission ports  121 ,  123  and  124  illustrated in  FIG. 2  to the first slot radiation part  111  illustrated in  FIG. 1  are the same as those transferred from the transmission ports  121 ,  123  and  124  illustrated in  FIG. 2  to the second and third slot radiation parts  113  and  114  illustrated in  FIG. 1 . However, since a signal is split due to the left and right directionality of the second and third slot radiation parts  113  and  114 , the radio waves radiated through the second and third slot radiation parts  113  and  114  have a larger beam angle than those radiated through the first slot radiation part  111 . 
     The second and third slot radiation part  113  and  114  and the first slot radiation part  111  are each composed of a plurality of slots. The second and third slot radiation parts  113  and  114  each have a larger number of slots than the first slot radiation part  111 . This is in order to raise the performance of the antenna by widening the detection range to a wider bandwidth. 
     The slot reception part  115  is located at the center bottom of the front side of the antenna body  100 . 
     The slot reception part  115  has a plurality of slots arranged in a plurality of rows. Desirably, the plurality of slots included in the slot reception part  115  are formed as a plurality of rows arranged in vertical and horizontal directions. 
     Referring to  FIG. 2 , the transmission ports  121 ,  123  and  124  and the reception ports  125  are formed on the rear side of the antenna body  100 . The radar antenna  10  includes a substrate  20  disposed on the rear side thereof, the substrate  20  serving to transmit a radio wave to the outside through the radar antenna  10  and process a radio wave received through the radar antenna  10 . 
     The transmission ports  121 ,  123  and  124  are connected to transmission terminals  21 ,  23  and  24  of the substrate  20 , and the reception ports  125  are connected to a reception terminal  25  of the substrate  20 . The substrate  20  is a substrate on which the transmission terminals  21 ,  23  and  24  and the reception terminal  25  are separately located (see  FIG. 12 ). 
     The number of the reception ports  125  is larger than the number of the transmission ports  121 ,  123  and  124 . In an embodiment, four reception ports  124  and three transmission ports are provided. In order to optimize the reception performance, the number of the reception ports  125  may be set to a larger value than the number of the transmission ports  121 ,  123  and  124 . 
     The transmission ports  121 ,  123  and  124  may be arranged at wide intervals to radiate radio waves in a wider range, and the reception ports  125  may be arranged at relatively narrow intervals to optimize the radio wave reception performance. 
     In an embodiment, the transmission ports  121 ,  123  and  124  include the center transmission port  121  connected to the first slot radiation part  111  and the left transmission port  123  and the right transmission port  124 , which are respectively arranged on both sides of the center transmission port  121  and connected to the second slot radiation part  113  and the third slot radiation part  114  which are located on the left and right in  FIG. 2 , respectively. The number of the reception ports  125  corresponds to the number of rows in the arrangement of the slots forming the slot reception part  115 . 
     In an embodiment, four reception ports  125  are formed to correspond to the four rows of slots included in the slot reception part  115 , respectively. 
     Referring to  FIG. 3 , the antenna body  100  includes a waveguide  130  formed by assembling a first plate  110  in which the first to third slot radiation parts  111 ,  113  and  114  and the slot reception part  115  are formed and a second plate  120  in which the transmission ports  121 ,  123  and  124  and the reception ports  125  are formed. 
     The first plate  110  and the second plate  120  are manufactured as a molding product, and coated with metal. When the waveguide  130  is formed by assembling the first and second plates  110  and  120  manufactured as molding products, the antenna assembling work is performed more easily than a method for manufacturing an antenna through a multilayer stacking method. Furthermore, since the first and second plates  110  and  120  are manufactured as molding products, the dimension accuracy of the antenna is secured to prevent an occurrence of deviation, and the product reliability is secured. 
     Furthermore, when the first and second plates  110  and  120  are manufactured as molding products, coated with metal, and then assembled to form the antenna, the productivity of the antenna may be improved much more than the multilayer stacking method. The reason to coat the first and second plates  110  and  120  with high-conductivity metal is in order to efficiently transmit and receive radio waves. The radio waves come into contact with the metal while passing through the waveguide  130 , thereby having directionality. 
     The first and second plates  110  and  120  may be made of various materials. Desirably, however, the first and second plates  110  and  120  may be made of PEI (Polyetherimide) which is one of high-performance engineering plastics. The metal with which the molding product is coated may be one or more metals selected from copper, silver and nickel. Since the PEI has excellent bonding strength with the coating metal, the metal does not peel off after the molding products are coated with the metal. 
     The first and second plates  110  and  120  may be assembled through fixing parts  150 . The fixing parts  150  may each include a bolt and nut which are fastened through fixing holes  141  and  142  formed in the first and second plates  110  and  120  (see  FIGS. 1 and 2 ). 
     The waveguide  130  is a hollow tube whose inner circumferential surface is coated with metal, and serves as a transmission line for transmitting a radio wave. The waveguide  130  includes a first waveguide  130   a , a second waveguide  130   b  and a third waveguide  130   c.    
     The waveguide  130  includes a plurality of straight channels which connect the transmission ports  121 ,  123  and  124  to the slot radiation parts  111 ,  113  and  114 , and connect the reception ports  125  and the slot reception part  115 . Specifically, the waveguide  130  serves as a straight channel for connecting one slot, corresponding to each of the transmission ports  121 ,  123  and  124  and the reception ports  125 , to a plurality of slots corresponding to each of the slot radiation parts  111 ,  113  and  114  and the slot reception part  115 . 
     That is, radio waves transmitted from the transmission terminals  21 ,  23  and  24  illustrated in  FIG. 12  to the transmission ports  121 ,  123  and  124  are transferred to the slot radiation parts  111 ,  113  and  114  through the waveguide  130 , and radio waves received through the slot reception part  115  are transferred to the reception ports  125  through the waveguide  130 . 
     Referring to  FIG. 4 , the first waveguide  130   a  is formed on the rear side of the first slot radiation part  111  formed in the first plate  110  so as to correspond to the row of the slots, and the transmission port  121  formed as one slot in the second plate  120  is connected to the first waveguide  130   a  corresponding to the row. At a bottom position of the first waveguide  130   a , facing the transmission port  121 , an inclined wall  110   a  is formed to guide a radio wave. 
     In such a radar antenna, a Tx radio wave is transferred through the transmission port  121 , formed as one slot on one side of the bottom of the first waveguide  130   a , and introduced into the first waveguide  130   a  via the inclined wall  110   a . Then, the Tx radio wave transferred along the first waveguide  130   a  is radiated to the outside through the first slot radiation part  111  which is formed through the front side of the first waveguide  130   a  and composed of the plurality of slots arranged in one row. 
     Furthermore, as illustrated in  FIG. 5 , a Tx radio wave is introduced into the second waveguide  130   b  through the transmission port  123  which is provided as one slot on one side of the bottom of the second waveguide  130   b  formed on the rear side of the first plate  110 . Then, the introduced Tx radio wave is transferred along the second waveguide  130   b , and radiated to the outside through the second slot radiation part  113  composed of a plurality of slots arranged on the front side of the second waveguide  130   b . Although not illustrated, the third slot radiation part  114  may have a symmetrical structure with the second slot radiation part  113 . 
     Referring to  FIG. 6 , an Rx radio wave in the radar antenna is introduced into the third waveguide  130   c  through the slot reception part  115  composed of a plurality of slots arranged on the front side of the third waveguide  130   c , introduced into the reception port  125  formed as one slot at the middle bottom of the third waveguide  130   c , and received through the reception port  125 . 
     The slots becoming the transmission ports  121  and  123  through which Tx radio waves are introduced into the first and second waveguides  130   a  and  130   b  are disposed on one sides of the bottoms of the first and second waveguides  130   a  and  130   b , and the slot becoming the reception port  125  through which the Rx radio wave introduced into the third waveguide  130   c  is received is disposed at the middle bottom of the third waveguide  130   c.    
     In order to raise the radiation efficiency, the radar antenna is designed to radiate the Tx radio waves, introduced into one sides of the bottoms of the first and second waveguides  130   a  and  130   b , through the first, second and third radiation parts  111 ,  113  and  114  including the plurality of slots formed on the front sides of the first and second waveguides  130   a  and  130   b , while transferred along the first and second waveguides  130   a  and  130   b . In this case, when the radio wave is radiated, the phase of the radio wave is merged with the phases of neighboring radio waves, which raises the gain of the antenna. On the contrary, in order to efficiently optimize the reception performance, the radar antenna is designed to transfer the Rx radio wave, introduced through the third waveguide  130   c , to the slot formed at the middle bottom of the third waveguide  130   c.    
     If a radio wave is not received but transmitted through the structure of  FIG. 6 , the radio wave does not move along the waveguide, but moves straight so as to be radiated. Thus, the gain of the antenna is lowered. 
     Hereafter, the first and second plates constituting the antenna body will be described in detail. 
     Referring to  FIGS. 7 and 8 , the first plate  110  is formed in a plate shape. The first plate  110  includes the first slot radiation part  111 , the second slot radiation part  113 , the third slot radiation part  114  and the slot reception part  115 . 
     The first slot radiation part  111  includes a plurality of slots arranged in one row on the same plane in a top-to-bottom direction on the drawings. Desirably, the plurality of slots included in the first slot radiation part  111  are arranged in one row on the same plane in the top-to-bottom direction. Furthermore, the plurality of slots are arranged so that portions thereof do not sit on a straight line connecting the uppermost slot  111   a  and the lowermost slot  111   b.    
     More desirably, the plurality of slots included in the first slot radiation part  111  are successively formed at predetermined intervals in the top-to-bottom direction, while arranged in a zigzag manner. 
     The reason why the slots included in the first slot radiation part  111  are arranged in one row is in order to form a small beam angle. The small beam angle is used to detect an object at a short distance. Furthermore, the reason why the slots include in the first slot radiation part  111  are arranged in a zigzag manner is in order to constantly maintain the interval between the slots and to reduce the length of the antenna more than when slots are arranged in a straight line. 
     The second slot radiation part  113  and the third slot radiation part  114  are respectively disposed on both sides of the first slot radiation part  111 , with a predetermined distance provided therebetween. The second slot radiation part  113  and the third slot radiation part  114  may be symmetrically disposed with the first slot radiation part  111  interposed therebetween. As the beam patterns of radio waves radiated from the second and third slot radiation parts  113  and  114  are merged with the beam pattern of a radio wave radiated from the first slot radiation part  111 , the directionality of the radio waves may be reduced. 
     The second and third slot radiation parts  113  and  114  each include a plurality of slots arranged in a plurality of rows in top-to-bottom and side-to-side directions. Desirably, the plurality of slots included in each of the second and third slot radiation parts  113  and  114  are formed on the same plane and arranged in a plurality of rows in the side-to-side and top-to-bottom directions. 
     For example, the plurality of slots included in at least one row of the second slot radiation part  113  are arranged so that portions thereof do not sit on a straight line connecting the uppermost slot  113   a  and the lowermost slot  113   b  in the corresponding row. 
     More desirably, the plurality of slots constituting at least one row in the second slot radiation part  113  are successively formed at predetermined intervals in the top-to-bottom direction, while arranged in a zigzag manner. 
     The reason why the plurality of slots constituting the second slot radiation part  113  are arranged in a plurality of rows is in order to optimize the number of slots for the gain of the antenna. Furthermore, the reason why the plurality of slots constituting the second slot radiation part  113  are arranged in a plurality of rows and the plurality of slots included in each of the rows are arranged in a zigzag manner is in order to acquire a high gain and high directionality. The third slot radiation part  114  has the same structure as the second slot radiation part  113 . 
     When the slots constituting the first slot radiation part  111  and the second and third slot radiation parts  113  and  114  are arranged at predetermined intervals on the same plane in the top-to-bottom and side-to-side directions, the gain of the antenna may be increased to acquire a very sensitive directional characteristic. Furthermore, when the slots constituting the first slot radiation part  111  and the second and third slot radiation parts  113  and  114  are arranged in a zigzag manner, the length of the antenna may be shortened while the gain thereof is raised. 
     For example, the slots of the second slot radiation part  113  are arranged so that the position of the uppermost slot  113   a  in the outermost row among the plurality of rows deviates from the positions of the uppermost slots  113   a ′ and  113   a ″ in rows inside the outermost row in the side-to-side direction. Desirably, in the second slot radiation part  113 , the heights of the uppermost slots  113   a ,  113   a ′ and  113   a ″ in the respective rows in the top-to-bottom direction have a relationship of ( 113   a &lt; 113   a ′&lt; 113   a ″) from the outermost row toward the rows inside the outermost row. 
     More desirably, the slots of the second slot radiation part  113  are arranged in a reverse V shape while the heights of the uppermost slots  113   a ,  113   a ′ and  113   a ″ have a relationship of ( 113   a &lt; 113   a ′&lt; 113   a ″) from the middle row toward the outermost row. Specifically, in the arrangement of the slots included in the second slot radiation part  113 , the uppermost slot  113   a ″ in the middle row has the largest height, and the uppermost slot  113   a  in the outermost row has the smallest height. This is in order to raise the gain by adjusting the positions of the slots in the respective rows in consideration of phases. 
     Since the positions of the slots in the respective rows of the second slot radiation part  113  are adjusted so that the slots deviate from one another, the phases of radio waves radiated through the slots are merged with the phases of neighboring radio waves, which increases the gain of the antenna. When the gain of the antenna is high, it indicates that the antenna can send a stronger radio wave in a specific desired direction. 
     In the second slot radiation part  113 , the slots included in the outermost row are arranged so as to deviate from the slots included in the rows inside the outermost row, but the number of the slots included in the outermost row is equal to the number of the slots included in each of the rows inside the outermost row. 
     The third slot radiation part  114  may be disposed symmetrically with the second slot radiation part  113  on the basis of the first slot radiation part  111 , and have the same structure as the second slot radiation part  113 . 
     The slot reception part  115  is disposed at the center bottom of the first plate  110 . 
     The plurality of slots included in the slot reception part  115  are arranged in a plurality of rows in the top-to-bottom and side-to-side directions. The slots included in each of the rows of the slot reception part  115  are arranged on a straight line. The number and arrangement shape of the slots included in the slot reception part  115  are set to optimize the radio wave reception performance. 
     Referring to  FIG. 8 , a plurality of slot grooves  130   a - 1 ,  130   b - 1  and  130   c - 1  are formed on the rear side of the first plate  110 . The slot grooves  130   a - 1 ,  130   b - 1  and  130   c - 1  are coupled to concave grooves  130   b - 2  and  130   c - 2  formed on the front side of the second plate  120 , thereby forming the waveguide  130 . The slot groves  130   a - 1 ,  130   b - 1  and  130   c - 1  communicate with the slots in the respective rows, which form the first to third slot radiation parts  111 ,  113  and  114  and the slot reception part  115 . Therefore, when the first plate  110  is seen from the rear side, the plurality of slots are formed in each of the slot grooves  130   a - 1 ,  130   b - 1  and  130   c - 1  in the longitudinal direction of the first plate  110 . 
     The slot grooves  130   a - 1 ,  130   b - 1  and  130   c - 1  each have a length enough to include the slots in the corresponding row, and have a concave cross-section. The edges of the slot grooves  130   a - 1 ,  130   b - 1  and  130   c - 1  are rounded or each have an inclined wall to reduce a polarization loss while the radio waves are easily transferred. 
     Although the slots included in each of the rows in the second and third slot radiation parts  113  and  114  are arranged in a zigzag manner in the top-to-bottom direction, the distance (a) between the outermost row and the row inside the outermost row is so uniform as to remove side lobes. As the side lobes are removed, the main beam pattern is formed as a strong beam pattern to raise the directionality. When the directionality is high, it indicates that the antenna can transmit a stronger radio wave in a specific direction. 
     The side lobes indicate that radio waves from the horizontal slots are radiated in directions other than the direction of the main beam. When radio waves are radiated from a slot array antenna, the largest beam pattern which was originally intended is the main beam, and the other small beam patterns are the side lobes. The main beam and the side lobes need to be properly harmonized with each other, in order to make a sharp and strong main beam pattern. 
     In order to optimize the influence of the side lobes according to a waveguide offset (deviation), the distance (b) between the lowermost slot in the outermost row of the second slot radiation part  113  and the fixing hole  141  and the distance (a) between the respective rows may be set to the optimized constant distances. 
     The bottoms of the slot grooves  130   b - 1  corresponding to the second and third slot radiation parts  113  and  114  are disposed on the same line in the horizontal direction so as to correspond to the concave grooves  130   b - 2  including the transmission ports  123  and  124 . Thus, the radio waves introduced into the transmission ports  123  and  124  may be split and transferred to the slot grooves  130   b - 1  of the respective rows through the concave groove  130   b - 2 , and radiated to the outside through the slots of the respective rows. 
     The slot reception part  115  is located at the center bottom of the first plate  110 . The slot reception part  115  includes a plurality of slots arranged in a plurality of straight line patterns. The slots included in the slot reception part  115  are arranged in a plurality of straight line patterns, in order to optimize the radio wave reception performance. The slots included in the slot reception part  115  may be arranged in a zigzag manner, if necessary. 
     Referring to  FIGS. 9 and 10 , the second plate  120  is formed in a plate shape corresponding to the first plate  110 . The second plate  120  includes the transmission parts  121 ,  123  and  124  and the reception ports  125 , which are formed therein. 
     The concave grooves  130   b - 2  extended in the side-to-side direction are formed on the front side of the second plate  120 , corresponding to the transmission ports  123  and  124  located on both sides of the center transmission port  121 . The concave groove  130   b - 2  has a length enough to include the bottoms of the slot grooves  130   b - 1  corresponding to the second slot radiation parts  113  and  114 , such that radio waves can be transmitted to the plurality of slot grooves  130   b - 1 . The transmission ports  123  and  124  are formed in the centers of the respective concave grooves  130   b - 2  such that radio waves are easily spread. The transmission ports  123  and  124  are located on one side of the slot grooves  130   b - 1 , i.e. at the bottoms thereof 
     Therefore, the radio waves introduced into the concave grooves  130   b - 2  through the transmission ports  123  and  124  are transferred in the side-to-side direction along the concave grooves  130   b - 2 , and introduced into the bottoms of the respective slot grooves  130   b - 1 . The radio waves introduced into the bottoms of the respective slot grooves  130   b - 1  are radiated to the outside through the plurality of slots formed in the slot grooves  130   b - 1 , while transferred upward along the slot grooves  130   b - 1 . 
     Since the slots of the first slot radiation part  111  are arranged in one row, no concave groove is formed on the front side of the second plate  120 , corresponding to the center transmission port  121 . 
     The concave grooves  130   c - 2  are formed on the front side of the second plate  120 , corresponding to the reception ports  125 . The number of the concave grooves  130   c - 2  corresponds to the number of the reception ports  125 , and the concave grooves  130   c - 2  are formed in the top-to-bottom direction. 
     The concave grooves  130   c - 2  are coupled to the plurality of slot grooves  130   c - 1  formed in the first plate  110 , and form the waveguide  130 . The reception ports  125  are formed in the middles of the respective concave grooves  130   b - 2 , and serve to optimize the reception performance. 
     As such, the waveguide  130  is formed by coupling the plurality of slot grooves  130   a - 1 ,  130   b - 1  and  130   c - 1 , which are formed on the rear side of the first plate  110  so as to communicate with the slot radiation parts  111 ,  113  and  114  and the slot reception part  115 , to the plurality of concave groove  130   b - 2  and  130   c - 2  which are formed on the front side of the second plate  120  so as to communicate with the transmission ports  121 ,  123  and  124  and the reception ports  125 . 
     Therefore, the radiation part for transmitting a radio wave has a structure in which one slot formed on one side of the concave groove  130   b - 2  is connected to the plurality of slots formed in the longitudinal direction in the slot groove  130   b - 1  along the second waveguide  130   b  which is a T-shaped straight channel formed by the coupling between the concave groove  130   b - 2  and the slot groove  130   b - 1 . 
     The reception part for receiving a radio wave has a structure in which one slot formed in the middle of the concave groove  130   c - 2  is connected to the plurality of slots formed in the longitudinal direction in the slot groove  130   c - 1  of the third waveguide  130   c  which is a straight channel formed by the coupling between the concave groove  130   c - 2  and the slot groove  130   c - 1 . 
     When the first and second plates  110  and  120  are assembled, the waveguide  130  formed by the coupling between the slot grooves  130   a - 1 ,  130   b - 1  and  130   c - 1  of the first plate  110  and the concave grooves  130   b - 2  and  130   c - 2  of the second plate  120  may have a hollow and semicircular cross-section. When a high-frequency radio wave having a short wavelength is transmitted through a metal tube, a loss thereof is minimized. 
     Specifically, when the first and second plates  110  and  120  are assembled, the slot grooves  130   b - 1  of the first plate  110 , corresponding to the second and third slot radiation parts  113  and  114 , are covered by the front side of the second plate  120 , and the bottoms of the slot grooves  130   b - 1  are coupled to the concave grooves  130   b - 2  of the second plate  120  so as to communicate with the concave grooves  130   b - 2 . 
     Furthermore, when the first and second plates  110  and  120  are assembled, the slot groove  130   a - 1  corresponding to the first slot radiation part  111  is covered by the front side of the second plate  120 , and only the transmission port  121  communicates with the slot groove  130   a - 1 . 
     Furthermore, when the first and second plates  110  and  120  are assembled, the slot reception part  115  is coupled to the concave groove  130   c - 2  formed to correspond to the front side of the second plate  120 , and covered by the front side of the second plate  120 . 
     Referring to  FIGS. 11A and 11B , the interval (c) between the slots of the slot radiation part  113  in the top-to-bottom direction and the interval (b) between the neighboring slots in the side-to-side direction are regular and constant. 
     The above-described radar antenna is a slot array antenna with a flat waveguide, which is suitable for a vehicle antenna, and various variables such as the sizes, number, shapes and distances of the slots may be adjusted to make various characteristics like an array antenna. 
     Furthermore, an air waveguide is applied to provide a high gain antenna which has a small loss even at a high frequency. 
     Furthermore, since the radar antenna is manufactured by plating a plastic molding product with metal, the radar antenna has a shielding effect and heat radiation effect. 
     Referring to  FIG. 12 , the radar antenna  10  may be manufactured as a radome-integrated antenna package in which the radar antenna  10  having the substrate  20  disposed on the rear side thereof is seated on a seating groove  51  of a rear radome  50 , and a front radome  40  is coupled to the top of the radar antenna  10 . 
     The front and rear radomes  40  and  50  serve to protect the radar antenna  10  from corrosion, such that the radar antenna  10  is stably operated. The front and rear radomes  40  and  50  may be made of a material which hardly scatters radio waves, such that radio wave reliably pass through the radomes, and formed through plastic injection molding. 
     The transmission ports  121 ,  123  and  124  of the radar antenna  10  may be connected to the transmission terminals  21 ,  23  and  24  of the substrate  20  so as to transmit radio waves, and the reception ports  125  may be connected to the reception terminals  25  of the substrate  20  so as to receive reflected radio waves. The substrate  20  is a substrate on which the transmission terminals  21 ,  23  and  24  and the reception terminals  25  are separately located. 
     The above-described radar antenna  10  is a slot array antenna with a flat waveguide, which is suitable for a vehicle antenna, and various variables such as the sizes, number, shapes and distances of the slots may be adjusted to make various characteristics like an array antenna. 
     The aging characteristics of the radar antenna in accordance with the present disclosure were measured. 
     The first and second plates  110  and  120  were manufactured as molding products through an injection molding process using PEI, and the molding products were coated with copper, silver and nickel, in order to measure the bonding strengths between the molding products and the respective metals. 
     The aging test was performed under the following conditions: a thermal cycle test was repeated in 100 cycles at a temperature of −50° C. to 150° C., the molding products were stored at a high temperature of 150° C. for 1,000 hours, and a temperature humidity test was performed at a temperature of 85° C. and a humidity of 85% RH for 1,000 hours. 
     The result of the aging test shows that the metal with which the molding product was coated did not peel off, in all the cases where the molding product was coated with copper, silver and nickel, respectively. 
     The test result shows that two plates formed by coating the molding products with metal can be coupled to manufacture a radar antenna having a waveguide structure which connects slots. 
     The injection molding makes it possible to manufacture a radar antenna having a waveguide with an accurate dimension. Furthermore, the injection molding may reduce the weight of the radar antenna, and secure the convenience of the assembly process and the productivity. 
     Furthermore, the sizes, intervals and shapes of the slots forming the slot radiation part and the slot reception part in the radar antenna may be precisely adjusted. As the slots are arranged in a zigzag manner, the size of the antenna may be reduced. Furthermore, the gain of the antenna may be raised through the plurality of slots arranged in a plurality of rows. 
     In particular, the radar antenna may include two kinds of slot radiation parts to effectively detect an object at a long distance and an object at a short distance, thereby contributing to advancing an anti-collision radar of an autonomous vehicle. 
     Although the preferred exemplary embodiments of the present disclosure have been described above, it is understood that the present disclosure may be modified in various forms, and those skilled in the art may practice various modified examples and changed examples without departing from the scope of the claims of the present disclosure.