JP2014078772A - Circularly polarized antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circularly polarized antenna device capable of performing axial ratio adjustment without exerting influence on a result of antenna impedance adjustment.SOLUTION: A circularly polarized antenna device 100 includes a tip open type loop antenna shaped parasitic radiation element 1 of which one end is a ground point 3 and the other end is an open end 4, and a feed element 2 of which one end is arranged on the ground point 3 side and the other end is arranged on the opposite side of the ground point 3 and which includes a coupling conductor 2a formed in parallel with the parasitic radiation element 1 through a clearance. The feed element 2 also includes a feeding conductor 2b of which one end is connected to a predetermined position of the coupling conductor 2a, and a feeding point 5 located on the other end of the feeding conductor 2b.

Description

  The present invention relates to a circularly polarized antenna device suitable for GPS reception and the like, and more particularly to a circularly polarized antenna device that allows easy adjustment of antenna characteristics.

  Conventionally, a patch antenna is generally known as a circularly polarized antenna device mounted on a vehicle. Since the patch antenna is a circularly polarized antenna having directivity in the zenith direction, it is easy to use for receiving GPS (Global Positioning System) radio waves for in-vehicle use. However, the patch antenna requires an expensive dielectric material, the antenna itself needs to be covered with a radome, and the individual adjustment for obtaining the desired antenna characteristics is necessary. It was a factor that pushed it up.

  Therefore, recently, a circularly polarized antenna device has been proposed in which an antenna pattern is formed on an inexpensive insulating substrate such as a film substrate to reduce the manufacturing cost and improve the attachment to a vehicle and the antenna characteristics. .

  For example, in the circularly polarized antenna device 900 according to Patent Document 1, a parasitic radiation element 906 is disposed in a loop element 905 as shown in FIG. The parasitic radiation element 906 is capacitively coupled in the vicinity of the tip of at least one of the first element 903 extending from the hot terminal 901 that is a feeding point or the second element 904 extending from the ground terminal 902 that is a grounding point. It is arranged to do. In the illustrated example, the first element 903 is disposed so as to be capacitively coupled in the vicinity of the tip. The parasitic radiation element 906 is disposed in parallel with the loop element 905.

  The antenna impedance adjustment of the circularly polarized antenna device 900 is performed by the length A1 of the coupling portion between the parasitic radiation element 906 and the first element 903 and the separation distance B1 between the parasitic radiation element 906 and the first element 903. .

  With such a configuration, the circularly polarized antenna device 900 according to Patent Literature 1 can adjust the antenna impedance, improve the gain, and improve the bandwidth.

JP 2011-151624 A

  In the conventional circularly polarized antenna device 900, the length A1 of the coupling portion between the first element 903 and the parasitic radiation element 906 and the separation distance B1 between the first element 903 and the parasitic radiation element 906 are adjusted. The antenna impedance was adjusted by this. That is, the antenna impedance adjustment can be performed by two elements, that is, the length A1 of the coupling portion and the separation distance B1. The axial ratio can also be adjusted by adjusting the length A1 of the coupling portion and the separation distance B1. However, in this adjustment method, the antenna impedance also changes at the same time when adjusting the axial ratio, so it is very difficult to adjust the axial ratio while maintaining the antenna impedance value that has already been adjusted. It was difficult.

  The present invention has been made in view of the actual situation of the prior art, and an object of the present invention is to provide a circularly polarized antenna device capable of adjusting an axial ratio without affecting the result of antenna impedance adjustment. There is.

  In order to solve this problem, the circularly polarized antenna device according to the present invention includes a parasitic radiation element in the form of an open-ended loop antenna having one end serving as a ground point and the other end serving as an open end, and one end connected to the contact antenna. A power supply having a coupling conductor disposed on the side of the point and having the other end disposed on a side opposite to the ground point and parallel to the parasitic radiation element at a distance from each other A circularly polarized antenna device, wherein the feeding element has a feeding conductor having one end connected to a predetermined position of the coupling conductor, and feeds the other end of the feeding conductor. It has the characteristic that it is comprised so that it may have a point.

  In the thus configured circularly polarized antenna device, the antenna impedance is adjusted by adjusting the distance between the parasitic radiation element and the coupling conductor and the length of the coupling conductor. Further, the axial ratio is adjusted by providing a connection point between the coupling conductor and the feeding conductor at a predetermined position of the coupling conductor of the feeding element. Therefore, when adjusting the axial ratio, the separation distance between the parasitic radiation element and the coupling conductor and the length of the coupling conductor are not changed, so that the already adjusted antenna impedance is not affected. That is, the axial ratio adjustment can be performed without affecting the antenna impedance adjustment result.

  In the above configuration, the distance from one end of the coupling conductor to the predetermined position is different from the distance from the other end of the coupling conductor to the predetermined position.

  In the circularly polarized antenna device thus configured, the axial ratio adjustment is performed by making the distance between one end of the coupling conductor and the predetermined position different from the distance between the other end of the coupling conductor and the predetermined position. Since this is done, it is possible to easily adjust the axial ratio.

  In the above configuration, the distance between the ground point of the parasitic radiation element and the feeding point of the feeding element is a distance corresponding to the value of the antenna impedance.

  In the circularly polarized antenna device thus configured, the distance between the ground point of the parasitic radiation element and the feeding point of the feeding element is set to a distance corresponding to the value of the antenna impedance, and this distance is kept constant. Since the axial ratio adjustment is performed as it is, the axial ratio adjustment can be performed without affecting the antenna impedance.

  In the above configuration, the loop shape of the parasitic radiation element is a square shape.

  In the circularly polarized antenna device thus configured, the loop shape of the parasitic radiation element has a square shape, so that a limited space on the insulating substrate can be used effectively for antenna performance. , Antenna performance can be maximized.

  In the above configuration, the parasitic radiation element has a feature that a loop shape is a perfect circle.

  In the circularly polarized antenna device configured as described above, the proportion of the parasitic radiation elements can be reduced as compared with the case of the square shape. Therefore, electronic circuit components and the like can be arranged in the space on the substrate, and the insulating substrate can be used effectively.

  In the circularly polarized wave antenna device of the present invention, the axial ratio is adjusted by providing a connection point with the feeding conductor at a predetermined position of the coupling conductor of the feeding element. Therefore, when adjusting the axial ratio, the separation distance between the parasitic radiation element and the coupling conductor and the length of the coupling conductor are not changed, so that the already adjusted antenna impedance is not affected. That is, the axial ratio adjustment can be performed without affecting the antenna impedance adjustment result.

1 is a plan view of a circularly polarized antenna device according to a first embodiment of the present invention. It is a graph which shows the frequency characteristic of VSWR (Voltage standing wave ratio) of the circularly polarized wave antenna apparatus which concerns on 1st Embodiment. 6 is a graph showing frequency characteristics of an axial ratio of a general patch antenna, a conventional circularly polarized antenna device of a feed type, and a circularly polarized antenna device according to the first embodiment of the present invention. It is a top view of the circular polarization antenna device concerning the modification of a 1st embodiment of the present invention. It is a top view of the circularly polarized antenna device concerning a 2nd embodiment of the present invention. It is a top view of the circularly polarized wave antenna apparatus which concerns on a prior art example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view of the circularly polarized antenna device 100 according to the first embodiment, and FIG. 2 is a graph showing the frequency characteristics of the VSWR of the circularly polarized antenna device 100 according to the first embodiment. The VSWR (Voltage Standing Wave Ratio), that is, the voltage standing wave ratio, is a numerical value indicating the impedance matching state of the antenna device, and the closer to 1, the more impedance matching is indicated. FIG. 3 is a graph showing frequency characteristics of axial ratios of a general patch antenna, a conventional feed-type circularly polarized antenna device, and the circularly polarized antenna device 100 according to the first embodiment of the present invention.

[First embodiment]
As shown in FIG. 1, the parasitic radiation element 1 of the circularly polarized antenna device 100 according to the first embodiment has one end grounded at a ground point 3. A radiating conductor in the shape of a square loop having a length of L1 on one side is connected to the radiating conductor having a length of L3 extending from the grounding point 3. Further, since the other end of the parasitic radiation element 1 is an open end 4, the antenna shape of the parasitic radiation element 1 is an open-ended loop antenna shape. Note that the length of the open side of the square loop antenna shape is set to L2 shorter than the length L1 of the other side. The total length from the ground point 3 to the open end 4 of the parasitic radiation element 1, that is, the sum of the length L3 of the rising part from the ground point 3 of the parasitic radiation element 1 and each side, that is, (3 * L1 + L2 + L3) Is set to about ½ of the wavelength of the antenna operating frequency.

  The length L3 of the rising portion of the parasitic radiating element 1 from the grounding point 3 is such that the parasitic radiating element 1 is connected to the square-shaped portion of the parasitic radiating element 1 so that the parasitic radiating element 1 is not affected by the ground. The length is set so as to be separated from the point 3 to some extent.

  The feed element 2 of the circularly polarized antenna device 100 according to the first embodiment includes a coupling conductor 2a and a feed conductor 2b. One end of the coupling conductor 2 a is disposed on the ground point 3 side, and the other end is disposed on the opposite side of the ground point 3. The coupling conductor 2 a is located on the side closest to the ground point 3 of the parasitic radiation element 1. , L1 is formed in parallel with one side of the square. Further, the length is L4 shorter than the length L1 of one side of the square, and the parasitic radiation element 1 and the coupling conductor 2a are arranged with a separation distance D1 therebetween. The power supply conductor 2b has one end connected at a connection point 6 with the coupling conductor 2a and the other end serving as a power supply point 5 to which power is supplied, and has a length L5. .

  The feeding conductor 2b having a length L5 from the feeding point 5 to the connection point 6 feeds the coupling conductor 2a and also serves as an antenna radiating element so as to increase the antenna gain. It is acting on.

  The circularly polarized antenna device 100 according to the first embodiment includes a length L4 of the coupling conductor 2a formed in parallel to the parasitic radiation element 1, and a separation distance between the parasitic radiation element 1 and the coupling conductor 2a. The antenna impedance can be adjusted by adjusting D1. As described above, the adjustment of the antenna impedance, which is one of the main characteristics of the circularly polarized antenna device 100, includes the length L4 of the coupling conductor 2a and the separation distance between the parasitic radiation element 1 and the coupling conductor 2a. It can be adjusted by two factors, the length D1. In addition, the axial ratio, which is one of the other main characteristics, is also adjusted by the length L4 of the coupling conductor 2a and the distance D1 of the separation distance between the parasitic radiation element 1 and the coupling conductor 2a. it can. However, the performance of the axial ratio cannot be sufficiently obtained only by these two elements. In addition, when an attempt is made to adjust the axial ratio using these two elements, the antenna impedance that has already been adjusted will change.

  In the circularly polarized antenna device 100 according to the first embodiment of the present invention, the axial ratio is adjusted by the position of the connection point 6 between the coupling conductor 2a and the feeding conductor 2b. That is, the connection point 6 is set at a predetermined position where the length L4 of the coupling conductor 2a is divided into lengths L6 and L7 without changing the overall length. By carrying out this adjustment method, the axial ratio can be adjusted without affecting the result of the antenna impedance adjustment that has already been adjusted. Note that the predetermined position is determined by the antenna operating frequency, the shape of the parasitic radiation element 1, and the like, and therefore differs depending on the individual antenna device. Therefore, generally, a distance L6 from one end of the coupling conductor 2a to the connection point 6 at a predetermined position and a distance L7 from the other end of the coupling conductor 2a to the connection point 6 at a predetermined position are as follows. Will be different.

  The parasitic radiating element 1 has an open end, and the length of the open side is set to L2 shorter than the length L1 of the other side. By appropriately setting, the value of the axial ratio and its frequency characteristic can be improved. However, the adjustment range is narrow only by adjustment based on the length of L2, and sufficient adjustment cannot be performed. Therefore, the adjustment method for setting the connection point 6 at a predetermined position that divides the length L4 of the coupling conductor 2a described above into the lengths L6 and L7 without changing the total length thereof maximizes the axial ratio performance. This is a necessary adjustment method.

  In addition, the distance between the ground point 3 and the feeding point 5 is set to L8. This distance L8 needs to be set to a distance corresponding to the antenna impedance value of the circularly polarized antenna device 100. Accordingly, even when the length L4 of the coupling conductor 2a or the distances L6 and L7 from one end or the other end of the coupling conductor 2a to the connection point 6 is set, the distance L8 needs to be kept constant.

  FIG. 2 shows VSWR characteristics representing the frequency characteristics of the antenna impedance of the circularly polarized antenna device 100 configured as described above. The center frequency of the in-vehicle GPS signal is 1.575 GHz, and the frequency band is 3 MHz. As can be seen from FIG. 2, the value of the VSWR of the circularly polarized antenna device 100 in this band is about 1.5, which has good characteristics.

  Further, FIG. 3 shows frequency characteristics of the antenna axial ratio (Axial ratio) of the circularly polarized antenna device 100 configured as described above. The value of the axial ratio of the circularly polarized antenna device 100 at the center frequency of 1.575 GHz in the in-vehicle GPS signal band is about 1 dB or less, and has good characteristics.

  For comparison, FIG. 3 also shows an axial ratio characteristic of a general patch antenna and an axial ratio characteristic of a circularly polarized antenna of a conventional feeding method such as Japanese Patent Application Laid-Open No. 2011-151624. In the axial ratio characteristic of a general patch antenna, the antenna center frequency is shifted due to manufacturing variations. Therefore, the best value is shown at 1.580 GHz instead of 1.575 GHz actually used. And in 1.575 GHz actually used, it has deteriorated with about 5 dB. In such a case, in order to further improve the axial ratio characteristics, additional adjustment of each patch antenna is required, leading to an increase in product cost.

  In the axial ratio characteristics of the circularly polarized antenna of the conventional feeding method, the value is about 4 dB, which is good to some extent, at 1.575 GHz actually used and its surrounding frequencies. In this case, even if the antenna center frequency is slightly shifted due to manufacturing variations, the deterioration of the axial ratio characteristic is very small, and no additional adjustment for each circularly polarized antenna device is required. However, as described above, since the conventional feed-type circularly polarized antenna cannot sufficiently adjust the axial ratio, further improvement of the axial ratio cannot be expected.

  In the circularly polarized wave antenna device 100 of the present invention, since the deterioration of the axial ratio characteristic due to the variation of individual products such as a general patch antenna cannot be considered, no additional adjustment after the production of the product is required. Moreover, since the adjustment method which divides | segments the length L4 of the coupling conductor 2a mentioned above into length L6 and L7 in the predetermined position, without changing the full length, it has sufficient performance for an axial ratio characteristic. It can be adjusted until it can be held. Therefore, the axial ratio performance can be improved as compared with the circularly polarized antenna of the conventional power feeding method.

  In the circularly polarized antenna device 100 of the present invention, it is preferable that the parasitic radiation element 1 and the feeding element 2 are formed on a film-like insulating substrate (not shown).

  In such a circularly polarized antenna device 100, the parasitic radiation element 1 and the feeding element 2 are formed on a film-like insulating substrate, and therefore can be easily attached to the front or rear glass surface of the vehicle. It becomes possible. Therefore, it is suitable as the circularly polarized antenna device 100 for receiving GPS radio waves mounted on the vehicle.

  FIG. 4 is a plan view of a circularly polarized antenna device 200 which is a modification of the circularly polarized antenna device 100 according to the first embodiment, and the antenna impedance thereof is the same.

  The difference between the circularly polarized antenna device 200 shown in FIG. 4 and the circularly polarized antenna device 100 according to the first embodiment is caused, for example, by a difference in the material of the mounted insulating substrate. Since the antenna impedance needs to be adjusted by changing the material or the like of the insulating substrate to be mounted, the length of the coupling conductor 2a is changed. Here, the separation distance D1 is not changed. In the circularly polarized antenna device 200, since the antenna operating frequency is the same as that of the circularly polarized antenna device 100, the dimensions (L1, L2, L3) of the parasitic radiation element 1 are not changed. As the changed points, the length of the coupling conductor 2a is L11, the length from one end of the coupling conductor 2a to the connection point 6 is L9, and the length from the other end of the coupling conductor 2a to the connection point 6 is as follows. Is L10. The axial ratio can be adjusted by setting these lengths L9 and L10 to appropriate lengths.

  Also, as shown in FIG. 4, the distance L8 between the ground point 3 and the feeding point 5 is the same as the length of the circularly polarized antenna device 100 according to the first embodiment in order to maintain the antenna impedance. .

  FIG. 5 is a plan view of the circularly polarized antenna device 300 according to the second embodiment. The antenna impedance is the same as that of the circularly polarized antenna device 100 according to the first embodiment.

[Second Embodiment]
As shown in FIG. 5, the parasitic radiation element 11 of the circularly polarized antenna device 300 according to the second embodiment is grounded at one end, and has a diameter L12 at the tip of a conductor extending from the grounding point 13. It has a radiating conductor having a perfect loop shape. The parasitic radiating element 11 has an open-ended loop antenna shape with its tip opened, and the total length from the ground point 13 to the open end 14 of the parasitic radiating element 11 is the wavelength of the antenna operating frequency. It is set to about 1/2.

  The feeding element 12 includes a coupling conductor 12a and a feeding conductor 12b, and the coupling conductor 12a is formed in an arc shape having a length L15 along a part of a true circular radiation conductor. The parasitic radiation element 11 and the coupling conductor 12a are arranged with a separation distance D2. One end of the power supply conductor 12b is connected at a connection point 16 with the coupling conductor 12a, and the other end is a power supply point 15 to which power is supplied.

  The circularly polarized antenna device 300 according to the second embodiment includes a length L15 of the coupling conductor 12a formed along the parasitic radiation element 11, and a separation distance between the parasitic radiation element 11 and the coupling conductor 12a. The antenna impedance can be adjusted by adjusting D2. As described above, the antenna impedance can be adjusted by the length L15 of the coupling conductor 12a and the separation distance D2 between the parasitic radiation element 11 and the coupling conductor 12a according to the first embodiment. This is the same as the circularly polarized antenna device 100. The adjustment of the axial ratio is also performed depending on the position of the connection point 16 between the coupling conductor 12a and the feeding conductor 12b. That is, the connecting point 16 is set at a predetermined position for obtaining an appropriate axial ratio without changing the total length L15 of the coupling conductor 12a, that is, at a position to be divided into the lengths L13 and L14. With this adjustment method, the axial ratio can be adjusted without affecting the result of the adjustment of the antenna impedance that has already been adjusted. The predetermined position is determined by the antenna operating frequency, the shape of the parasitic radiation element 11, and the like, and therefore differs depending on the individual circularly polarized antenna device.

  The circularly polarized antenna device 300 according to the second embodiment is different from the circularly polarized antenna device 100 according to the first embodiment in that the shape of the parasitic radiation element 11 is not a square but a perfect circle. is there. Due to this difference, the proportion of the parasitic radiation element 11 can be reduced as compared with the square shape. Therefore, electronic circuit components can be arranged in a vacant space on the insulating substrate, and a limited area of the insulating substrate can be used effectively.

  As described above, the circularly polarized antenna device according to the embodiment of the present invention has been described. However, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the invention. Is possible.

  As described above, the circularly polarized antenna device 100 of the present invention includes the parasitic radiation element 1 in the form of an open-ended loop antenna with one end serving as the ground point 3 and the other end serving as the open end 4. One end of the coupling conductor is disposed on the grounding point 3 side, and the other end is disposed on the open end 4 side. The coupling conductor is formed in parallel to the parasitic radiation element 1 with a separation distance D1. A circularly polarized antenna device 100 having a feeding element 2 having 2a, the feeding element 2 having a feeding conductor 2b having one end connected to a predetermined position of the coupling conductor 2a. The other end of the conductor 2b is configured to have a feeding point 5.

  The circularly polarized wave antenna device 100 of the present invention adjusts the axial ratio by providing the connection point 6 between the coupling conductor 2a and the feeding conductor 2b at a predetermined position of the coupling conductor 2a of the feeding element 2. I did it. Therefore, when adjusting the axial ratio, the distance between the parasitic radiation element 1 and the coupling conductor 2a and the length of the coupling conductor 2a are not changed, which may affect the already adjusted antenna impedance. Absent. That is, the axial ratio adjustment can be performed without affecting the antenna impedance adjustment result.

DESCRIPTION OF SYMBOLS 1 Parasitic radiation element 2 Feeding element 2a Coupling conductor 2b Feeding conductor 3 Grounding point 4 Open end 5 Feeding point 6 Connection point 11 Parasitic radiation element 12 Feeding element 12a Coupling conductor 12b Feeding conductor 13 Grounding point 14 Open end DESCRIPTION OF SYMBOLS 15 Feeding point 16 Connection point 100 Circularly polarized wave antenna apparatus 200 Circularly polarized wave antenna apparatus 300 Circularly polarized wave antenna apparatus

Claims (5)

A parasitic radiation element in the form of an open-ended loop antenna with one end serving as a grounding point and the other end serving as an open end, one end disposed on the grounding point side, and the other end opposite to the grounding point And a feed element having a coupling conductor formed parallel to the parasitic radiation element at a distance from the parasitic radiation element, and a circularly polarized antenna device comprising:
The power feeding element has a power feeding conductor having one end connected to a predetermined position of the coupling conductor, and is configured to have a power feeding point at the other end of the power feeding conductor. Polarized antenna device.   2. The circularly polarized antenna device according to claim 1, wherein a distance between one end of the coupling conductor and the predetermined position is different from a distance between the other end of the coupling conductor and the predetermined position.   The distance between the grounding point of the parasitic radiation element and the feeding point of the feeding element is a distance corresponding to the value of the antenna impedance. Circularly polarized antenna device.   The circularly polarized antenna device according to any one of claims 1 to 3, wherein a loop shape of the parasitic radiation element is a square shape.   The circularly polarized antenna device according to any one of claims 1 to 3, wherein a loop shape of the parasitic radiation element is a perfect circle.

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