Patch antenna device

Abstract

A patch antenna device configured to receive a radio communication signal includes a circuit board, a patch antenna, and a parasitic element. The circuit board has a signal processing circuit placed thereon. The patch antenna is stacked on the circuit board and has a quadrangular radiation element. The parasitic element is disposed above the patch antenna so as to improve antenna gain characteristics of the patch antenna and configured such that the length of the upper side of the parasitic element is shorter than the width in a plan view of the radiation element of the patch antenna and that the length between the upper and lower sides of the parasitic element is longer than the length between the upper and lower sides of the radiation element of the patch antenna.

Claims

1. A patch antenna device configured to receive radio communication signals, the patch antenna device comprising: a circuit board on which a signal processing circuit is placed; a patch antenna stacked on the circuit board and having a quadrangular radiation element, the patch antenna including a first patch antenna stacked on the circuit board and configured to receive signals in a first frequency band and a second patch antenna stacked on the first patch antenna and configured to receive signals in a second frequency band; a parasitic element disposed above the second patch antenna so as to improve antenna gain characteristics of the second patch antenna and configured such that a first length of an upper side of the parasitic element is shorter than an element width in a plan view of the quadrangular radiation element of the second patch antenna and such that a second length between the upper side and a lower side of the parasitic element is longer than an element length between upper and lower sides of the quadrangular radiation element of the second patch antenna; and an integrated resin holder supporting the circuit board, the first patch antenna, and the parasitic element, the parasitic element including held portions having at least two opposing parallel sides, and the integrated resin holder including at least a pair of parasitic element locking pawls that support the two sides of the held portions of the parasitic element so as to sandwich the parasitic element from both sides such that the distance between the second patch antenna and the parasitic element is kept constant.

2. The patch antenna device according to claim 1, wherein the held portions of the parasitic element are parasitic element locking concaves that the pair of parasitic element locking pawls lock.

3. The patch antenna device according to claim 2, wherein the parasitic element locking concaves include a right-trapezoidal concave having an opening width larger than a width of each parasitic element locking pawl and having an opening bottom width smaller than the width of each parasitic element locking pawl.

4. The patch antenna device according to claim 1, further comprising an insulating spacer disposed between the patch antenna and the parasitic element so as to support the parasitic element.

5. The patch antenna device according to claim 1, wherein the parasitic element has a hexagonal shape including two opposing parallel sides and one side perpendicular to the two sides.

6. The patch antenna device according to claim 1, wherein a center of the parasitic element overlaps a center of the patch antenna in the plan view.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic perspective view for explaining a patch antenna device according to one illustrated embodiment.

(2) FIG. 2 is a schematic cross-sectional side view for explaining the patch antenna device according to the illustrated embodiment.

(3) FIG. 3 is a schematic top view for explaining the patch antenna device according to the illustrated embodiment.

(4) FIG. 4 is a schematic cross-sectional side view for explaining a configuration obtained by applying the patch antenna device according to the illustrated embodiment to a stacked patch antenna device.

(5) FIG. 5 is a schematic perspective view for explaining another stacked patch antenna device to which the patch antenna device according to the illustrated disclosure is applied.

(6) FIG. 6 is a schematic top view for explaining a parasitic element of the patch antenna device according to the illustrated embodiment.

(7) FIG. 7 is a view for explaining a change in antenna gain characteristics of a patch antenna due to a difference in the shape of the parasitic element of the patch antenna device according to the illustrated embodiment, which illustrates shape variations of the parasitic element.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(8) Preferred embodiments will be described below with reference to the accompanying drawings. FIG. 1 is a schematic perspective view for explaining a patch antenna device according to one illustrated embodiment. FIG. 2 is a schematic cross-sectional side view for explaining the patch antenna device according to the illustrated embodiment. FIG. 3 is a schematic top view for explaining the patch antenna device according to the illustrated embodiment. In FIGS. 2 and 3, the same reference numerals as those in FIG. 1 denote the same parts as those in FIG. 1. The patch antenna device according to the illustrated embodiment is configured to receive a radio communication signal. As illustrated, the patch antenna device according to the present disclosure mainly includes a circuit board 10, a patch antenna 20, and a parasitic element 30.

(9) The circuit board 10 is a member on which a signal processing circuit is placed. A circuit pattern and a ground conductor pattern are formed by etching on the circuit board 10. An amplifier circuit 14 and the like may also be placed on the circuit board 10.

(10) The patch antenna 20 is placed on the circuit board 10. The patch antenna 20 has a radiation element 22 having, e.g., a quadrangular shape. The illustrated patch antenna 20 is a ceramic patch antenna; however, the patch antenna according to the present invention is not limited to this, but may be an air-patch antenna using air as a dielectric, or may be a patch antenna using a synthetic resin as a dielectric or a patch antenna using a multilayer substrate as a dielectric. The patch antenna 20 is configured to receive signals in a frequency band for, e.g., SDARS, which is, specifically, 2.3 GHz band; however, the frequency band supported by the patch antenna 20 of the patch antenna device according to the present invention is not limited to the above frequency band and may be another frequency band. Specifically, the patch antenna 20 includes a power feed line 21 and a radiation element 22. The power feed line 21 is connected to a first power feed portion 11 of the circuit board 10. When the patch antenna 20 is a ceramic patch antenna as illustrated, a ceramic 23 is used as a dielectric. A ground conductor pattern 24 is provided on the back surface of the ceramic 23, thereby constituting a micro-strip antenna together with the radiation element 22. The patch antenna 20 is fixed onto the circuit board 10 by, e.g., a double-sided adhesive tape 25.

(11) The parasitic element 30 is used for improving antenna gain characteristics of the patch antenna 20. The parasitic element 30 is disposed above the patch antenna 20. The parasitic element 30 is, e.g., a flat plate-like body. The parasitic element 30 is, e.g., made of a conductive plate. The parasitic element 30 is disposed parallel to and opposite to the radiation surface of the radiation element 22 of the patch antenna 20. When the patch antenna device according to the present disclosure is applied to, for example, a so-called shark-fin shaped low-profile antenna device, the upward direction in FIG. 3 corresponds to a vehicle travel direction and to the tip side of the shark-fin antenna. As illustrated in FIG. 3, in the parasitic element 30 used in the patch antenna device according to the present disclosure, the length (e.g., “first length”) of the upper side of the parasitic element 30 is shorter than the width (e.g., “First Width”) in a plan view of the radiation element 22 of the patch antenna 20. Further, the length (e.g., “Second Length”) between the upper and lower sides of the parasitic element 30 is longer than the length (e.g., “Third Length”) between the upper and lower sides of the radiation element 22 of the patch antenna 20. Specifically, the parasitic element 30 of the patch antenna device according to the present disclosure is, e.g., a hexagonal plate-like body as illustrated. More specifically, the parasitic element 30 has a hexagonal shape having two opposing parallel left and right sides, a lower side perpendicular to the two sides, and an upper side shorter than the lower side and parallel to the lower side. Further, as illustrated in FIG. 3, the parasitic element 30 is disposed such that the center thereof overlaps the center of patch antenna 20 in a plan view.

(12) As illustrated in FIG. 2, the parasitic element 30 is disposed above the patch antenna 20 with an insulating spacer 50 interposed therebetween. The insulating spacer 50 is disposed between the patch antenna 20 and the parasitic element 30 so as to support the parasitic element 30.

(13) As described above, the patch antenna device according to the present disclosure has the parasitic element functioning as a wave director for the patch antenna and contributing to a size reduction and an increase in design freedom. That is, the length of the upper side of the parasitic element is shorter than the width of the patch antenna, so that the parasitic element for improving antenna gain characteristics can be disposed in a tapered area of the tip of a so-called shark-fin antenna. Further, the parasitic element having a flat plate-like shape is disposed parallel to and opposite to the radiation surface of the radiation element of the patch antenna, whereby the thickness of the entire patch antenna device can be reduced.

(14) In the above illustrated example, the patch antenna device uses one patch antenna; however, the present disclosure can be applied to a stacked patch antenna device having a stacking structure using a plurality of patch antennas. FIG. 4 is a schematic cross-sectional side view for explaining a configuration obtained by applying the patch antenna device according to the illustrated disclosure to a stacked patch antenna device. In FIG. 4, the same reference numerals as those in FIG. 1 denote the same parts as those in FIG. 1. As illustrated, in this example, as the patch antenna, a first patch antenna 20a and a second patch antenna 20b are provided.

(15) The first patch antenna 20a is stacked on the circuit board 10 and configured to receive signals in a first frequency band. The first frequency band may be a frequency band for, e.g., GNSS, which ranges from 1 GHz to 2 GHz; however, the frequency band supported by the first patch antenna 20a of the patch antenna device according to the present invention is not limited to the above frequency band and may be another frequency band. The first patch antenna 20a includes a first power feed line 21a and a first radiation element 22a. The first power feed line 21a is connected to the first power feed portion 11 of the circuit board 10. The first patch antenna 20a is fixed onto the circuit board 10 by, e.g., a double-sided adhesive tape 25a. In the illustrated example, the first patch antenna 20a is a ceramic patch antenna using a ceramic 23a as a dielectric; however, the first patch antenna 20a of the patch antenna device according to the present invention is not limited to this, but may be an air-patch antenna using air as a dielectric, a patch antenna using a synthetic resin as a dielectric, or a patch antenna using a multilayer substrate as a dielectric.

(16) The second patch antenna 20b is stacked on the first patch antenna 20a and configured to receive signals in a second frequency band. The second frequency band may be a frequency band for, e.g., SDARS, which is, specifically, 2.3 GHz band; however, the frequency band supported by the second patch antenna 20b of the patch antenna device according to the present invention is not limited to the above frequency band and may be another frequency band which is higher than the first frequency band. The second patch antenna 20b includes a second power feed line 21b and a second radiation element 22b. The second power feed line 21b is connected to a second power feed portion 12 of the circuit board 10. The second patch antenna 20b is fixed onto the first patch antenna 20a by, e.g., a double-sided adhesive tape 25b. In the illustrated example, the second patch antenna 20b is a ceramic patch antenna using a ceramic 23b as a dielectric; however, the second patch antenna 20b of the patch antenna device according to the present invention is not limited to this, but may be an air-patch antenna using air as a dielectric, a patch antenna using a synthetic resin as a dielectric, or a patch antenna using a multilayer substrate as a dielectric.

(17) The parasitic element 30 is disposed above the second patch antenna 20b and used for improving antenna gain characteristics of the second patch antenna 20b. In such a stacked patch antenna device, the length (e.g., “First Length”) of the upper side of the parasitic element 30 is shorter than the width (e.g., “Second Width”) in a plan view of the radiation element 22b of the second patch antenna 20b, and the length (e.g., “Second Length”) between the upper and lower sides of the parasitic element 30 is longer than the length (“Fourth Length”) between the upper and lower sides of the radiation element 22b of the second patch antenna 20b.

(18) In the above illustrated example, the parasitic element 30 is supported by the insulating spacer 50; however, the present invention is not limited to this. For example, as illustrated in FIG. 5, the parasitic element may be supported by an integrated resin holder. FIG. 5 is a schematic perspective view for explaining another stacked patch antenna device to which the patch antenna device according to the illustrated disclosure is applied. In FIG. 5, the same reference numerals as those in FIG. 1 denote the same parts as those in FIG. 1. In this example, the parasitic element 30 is supported by an integrated resin holder 40. The integrated resin holder 40 supports the circuit board 10, the first patch antenna 20a, and the parasitic element 30. The illustrated first patch antenna 20a is a plate-like air patch antenna; however, the patch antenna according to the present invention is not limited to this, but may be a patch antenna using, as a dielectric, a ceramic, a synthetic resin, or a multilayer substrate. The circuit board 10 has a ground conductor pattern. The ground conductor pattern constitutes a micro-strip antenna together with the first radiation element 22a. The illustrated first radiation element 22a is a quadrangular plate-like element and is disposed opposite to the circuit board 10 with a predetermined interval therefrom. In the illustrated patch antenna 20a, the power feed line 21a is formed by cutting and bending a part of the radiation surface of the quadrangular plate-like element.

(19) Details of the parasitic element 30 suitable for the patch antenna device according to the present disclosure that uses the integrated resin holder 40 will be described more specifically with reference to FIG. 6. FIG. 6 is a schematic top view for explaining the parasitic element of the patch antenna device according to the illustrated disclosure. In FIG. 6, the same reference numerals as those in FIG. 1 denote the same parts as those in FIG. 1. When the patch antenna device according to the present disclosure is applied to, for example, a so-called shark-fin shaped low-profile antenna device, the upward direction in FIG. 6 corresponds to a vehicle travel direction and to the tip side of the shark-fin antenna. The parasitic element 30 of the patch antenna device according to the present disclosure has held portions 31, 32 having at least two sides opposed to each other. For example, the parasitic element 30 has a hexagonal plate-like body as illustrated. Specifically, the held portions 31, 32 of the parasitic element 30 are formed in the opposing parallel upper and lower sides, respectively. In the example of FIG. 6, the parasitic element 30 has a hexagonal shape having two opposing left and right sides, a lower side perpendicular to the two sides, and an upper side shorter than the lower side and parallel to the lower side. By forming the held portions 31, 32 in the opposing parallel upper and lower sides, respectively, the parasitic element 30 can be supported by the integrated resin holder 40 so as to be sandwiched thereby from both sides in the horizontal direction. The held portions 31, 32 of the parasitic element 30 are configured as parasitic element locking concaves that parasitic element locking pawls 41, 42 of the integrated resin holder 40 lock. That is, the bottom sides of the parasitic element locking concaves of the held portions are the two opposing parallel sides. The presence of the parasitic element locking concaves of the held portions 31, 32 allows the position of the parasitic element 30 with respect to the second patch antenna 20b to be accurately fixed. Details of the parasitic element locking concaves of the held portions 31, 32 will be described later. In the patch antenna device according to the present disclosure, the shape of the parasitic element 30 is not limited to a hexagon and may be, for example, a trapezoid. Specifically, the trapezoid may be a quadrangle having the upper side shorter than the lower side and parallel to the lower side.

(20) Referring again to FIG. 5, the integrated resin holder 40 will be described. The integrated resin holder 40 is a member for supporting the circuit board 10 and the parasitic element 30. The integrated resin holder 40 has at least a pair of parasitic element locking pawls 41, 42. The parasitic element locking pawls 41, 42 support the two sides of the held portions 31, 32 of the parasitic element 30 so as to sandwich the parasitic element 30 from both sides in the horizontal direction such that the distance between the second patch antenna 20b and the parasitic element 30 is kept constant. The integrated resin holder 40 is made of insulating resin. The parasitic element locking pawls 41, 42 each pinch the front and back surfaces of the parasitic element 30 so as to keep the position of the parasitic element 30 in the height direction constant.

(21) As illustrated, when a plate-like air patch antenna is used as the first patch antenna 20a, the integrated resin holder 40 may further have a plate support portion 45 that is disposed between the plate-like air patch antenna and the circuit board 10 and supports the plate-like air patch antenna. That is, the integrated resin holder 40 may be configured to support also the first radiation element 22a of the plate-like air patch antenna. The use of the plate support portion 45 can prevent the first radiation element 22a of the first patch antenna 20a from being bent due to vibration or the like. Further, bosses 49 protrude from the plate support portion 45 of the integrated resin holder 40. The bosses 49 are inserted into fixing holes formed in the first patch antenna 20a for thermal welding, whereby the first patch antenna 20a is fixed to the integrated resin holder 40. Alternatively, the first patch antenna 20a may be fixed to the integrated resin holder 40 by means of screws. The integrated resin holder 40 has the plate support portion 45 as a center component and further has the parasitic element locking pawls 41, 42 and the circuit board locking pawls 46, 47 on the upper and lower sides of the plate support portion 45, respectively.

(22) The parasitic element locking pawls 41, 42 extend from the plate support portion 45 toward the parasitic element 30 to hold the parasitic element 30. The parasitic element locking pawls 41, 42 lock the held portions 31, 32 formed in the upper and lower sides of the parasitic element 30 having, e.g., a hexagonal shape as illustrated in FIG. 6 so as to pinch them. The held portions 31, 32 of the parasitic element 30 are configured as the parasitic element locking concaves that the parasitic element locking pawls 41, 42 lock. That is, the parasitic element 30 has concaves as the held portions at positions corresponding to the parasitic element locking pawls 41, 42. In the illustrated example, the parasitic element locking pawl 42, which is one of the parasitic element locking pawls that support the held portions 31, 32 having two opposing parallel sides of the parasitic element 30 so as to sandwich the parasitic element 30 from both sides in the horizontal direction, includes two side-by-side locking pawls 43, 44. Correspondingly, the held portion 32 of the parasitic element 30 includes side-by-side locking concaves 33, 34. The side-by-side locking concaves 33, 34 are locked by the side-by-side locking pawls 43, 44, respectively. The side-by-side locking concaves 33, 34 each preferably have a right-trapezoidal concave having an opening width larger than the width of each locking pawl and having an opening bottom width smaller than the width of each locking pawl. Further, the right-angled portions of the right-trapezoidal concaves of the respective side-by-side locking concaves 33, 34 are preferably positioned on a side close to each of the side-by-side locking concaves 33, 34, respectively. The oblique sides are preferably positioned on a side far from each of the side-by-side locking concaves 33, 34, respectively. More specifically, the right-angled portion of the locking concave 33 is positioned at the corner close to the locking concave 34, and the right-angled portion of the locking concave 34 is positioned at the corner close to the locking concave 33. Thus, when the parasitic element 30 is locked by the parasitic element locking pawls 41, 42 (43, 44), the parasitic element locking pawls 41, 42 (43, 44) are press-fit to the locking concaves of the held portions 31, 32 (33, 34), whereby the parasitic element 30 is fixed to the integrated resin holder 40 with the horizontal movement restricted.

(23) The following describes a change in the antenna gain characteristics of the patch antenna due to a difference in the shape of the parasitic element of the patch antenna device according to the present disclosure. FIG. 7 is a view for explaining a change in the antenna gain characteristics of the patch antenna due to a difference in the shape of the parasitic element of the patch antenna device according to the present disclosure, which illustrates shape variations of the parasitic element. Measurement was made using the configuration of the patch antenna device illustrated in FIG. 1 under the following conditions. The size of the radiation element of the patch antenna was 25 mm×25 mm. The distance between the radiation element of the patch antenna and the parasitic element was 3 mm. Parasitic elements of five different shapes illustrated in FIG. 7 were used. That is, the five different shapes were (1) hexagon (a) (lower side: 25 mm, height: 32 mm), (2) trapezoid (lower side: 30 mm, height: 32 mm), (3) triangle (lower side: 30 mm, height 32 mm), (4) square (lower side: 32 mm, height: 32 mm), and (5) hexagon (b) (lower side: 25 mm, height: 27 mm). Under the above conditions, the radiation characteristics of the patch antenna at 2330 MHz was measured. The table shown below is a horizontal plane average gain for each shape of the parasitic element. The patch antenna device according to the present invention is not limited to the above specific sizes or frequencies, and these numerical values are merely examples.

(24) TABLE-US-00001 TABLE 1 Hexagon (a) Trapezoid Triangle Hexagon (b) Square Horizontal −10.8 −11.1 −12.0 −12.2 −12.6 plane average gain (dB)

(25) From these results, it can be seen that the parasitic elements having (1) hexagonal shape (a) and (2) trapezoidal shape are high in the horizontal plane average gain and are suitable examples. Further, the horizontal plane average gain is higher in the case where the length between the upper and lower sides is long as in (1) hexagon (a) than in the case where the length between the upper and lower sides is short as in (5) hexagon (b). Further, the horizontal plane average gain becomes low in an extremely pointed shape like (3) triangle having no upper side. Thus, the parasitic element of the patch antenna device according to the present disclosure is preferably configured such that the length of the upper side is shorter than the width in a plan view of the radiation element of the patch antenna and that the length between the upper and lower sides is longer than the length between the upper and lower sides of the radiation element of the patch antenna.

(26) The patch antenna device according to the present invention is not limited to the above illustrated examples but may be variously modified without departing from the scope of the present invention.