Planar Antenna

Abstract

To inhibit distortion of characteristics of an axial ratio of a coplanar power supply type planar antenna with a notch compared to a case of an ideal circular polarized wave.SOLUTION: A radiation element 11 is a conductor pattern formed on a substrate surface 10a and has power feeding notches 111, 112 which are notches extending from edge parts of the pattern to power feeding points P1, P2. Power feeding lines 12, 13 are conductor patterns formed on the substrate surface 10a and extend through the power feeding notches 111, 112 to the power feeding points P1, P2. The radiation element 11 has non-power feeding notches 113, 114 which are notches provided at positions which are point symmetrical to the power feeding notches 111, 112 with respect to a center point of the radiation element 11, and having the same form as the power feeding notches 111, 112.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a planar antenna used to read information from an RF tag. [Background technology]

[0002] There is a known RFID system that realizes a desired function by reading the identification information stored in an RF tag with an RF tag reader. In an RFID system, when the orientation of the RF tag to be read relative to the antenna of the RF tag reader is not fixed, a circularly polarized antenna is used. Also, to make the antenna thin, a microstrip antenna with a coplanar power supply is used.

[0003] As an example of this type of antenna, Patent Document 1 describes a notched planar antenna in which a notch, which is a cut from the periphery of a patch-shaped pattern that serves as a radiating element to a power feed point, is formed, and a power feed line is connected to the power feed point through the notch.

[0004] That is, the input impedance of the patch pattern is highest at the edge of the pattern and decreases toward the center, so by adjusting the depth of the notch, the input impedance of the antenna can be matched to the impedance of the feed line. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-286484 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, a notched planar antenna using the coplanar feeding method has an axial ratio that is distorted from a perfect circle due to the influence of the notch, resulting in a problem in that the detection distance varies greatly depending on the orientation of the RF tag.

[0007] The present disclosure provides a technique for suppressing distortion of the axial ratio characteristics of a notched planar antenna using a coplanar feeding method compared to the case of an ideal circular polarization. [Means for solving the problem]

[0008] One aspect of the present disclosure is a planar antenna comprising a dielectric substrate, a radiating element, and a feed line. The dielectric substrate has conductor patterns formed on both sides. The radiating element is a conductor pattern formed on a first surface of the dielectric substrate, and has a feed notch which is a cut from an edge of the pattern to a feed point. The feed line is a conductor pattern formed on the first surface, and passes through the feed notch to reach the feed point. The radiating element has a non-feed notch which is a cut that is provided at a position point-symmetrical to the feed notch with respect to the center point of the radiating element and has the same shape as the feed notch.

[0009] With this configuration, the shape of the radiating element becomes more symmetrical, thereby improving the axial ratio, which is one of the performance characteristics of circularly polarized waves. As a result, linearly polarized radio waves can be received with uniform characteristics regardless of the direction of the polarization plane.

[0010] In one embodiment of the present disclosure, the device may further include a back ground, which is a conductor pattern formed on the second surface of the dielectric substrate. In one aspect of the present disclosure, the second surface of the dielectric substrate may include an exposed portion including at least a portion facing the radiating element and from which the back surface ground is removed, and may further include a conductive cover portion having a plate-like portion that covers the exposed portion and faces the portion facing the exposed portion across a low dielectric constant layer having a lower dielectric constant than the dielectric substrate, and fixed to the dielectric substrate so as to have the same potential as the back surface ground.

[0011] With this configuration, the pattern size of the radiating element can be increased, improving the gain, and the thickness of the dielectric substrate can be reduced, and the pattern configuration other than the radiating element can be made smaller.

[0012] In one aspect of the present disclosure, the exposed portion may be formed in a shape similar to that of the radiating element. With this configuration, it is possible to further improve the symmetry of not only the radiating element pattern but also the portion that forms the microstrip antenna together with the radiating element.

[0013] In one aspect of the present disclosure, the radiating element may be disposed at a position offset from the center of the dielectric substrate, and the cover portion may be disposed at a position offset toward the center of the dielectric substrate while covering the exposed portion.

[0014] According to this configuration, the symmetry of the structure formed with the cover portion can be improved regardless of the arrangement of the radiating element. In one aspect of the present disclosure, the device may further include a spacer that maintains a gap between the dielectric substrate and the cover portion.

[0015] With this configuration, it is possible to prevent the distance between the dielectric substrate and the cover portion from deviating from the design value due to warping of the dielectric substrate or the cover portion, and thus to prevent the resonant frequency of the antenna from deviating.

[0016] In one aspect of the disclosure, the spacer may be disposed at the center of the radiating element. According to this configuration, the gap between the dielectric substrate and the cover can be maintained with a minimum of configuration. Also, the resonant frequency of the antenna can be adjusted by appropriately selecting the length, diameter, material, etc. of the spacer.

[0017] In one embodiment of the present disclosure, the spacer is an insulator and may be provided in one or more portions. According to such a configuration, the resonant frequency of the antenna can be adjusted by appropriately selecting the positions and number of spacers, the length and diameter of the spacers, etc.

[0018] In one aspect of the present disclosure, the spacer may be configured to be secured at least at one end by a screw fastener. With this configuration, the spacer can be easily fixed. In particular, when the spacer is configured to be fixed by screws at both ends, the resonant frequency of the antenna can be adjusted by appropriately replacing the spacer with one having a different length, diameter, material, etc., or by adding or reducing the number of spacers.

[0019] In one aspect of the present disclosure, the device may further include a coil spring inserted between the spacer and the portion to which the spacer is screwed. With this configuration, by adjusting the strength of the screws, it is possible to finely adjust the distance between the dielectric substrate and the cover, and therefore the resonant frequency of the antenna.

[0020] In one embodiment of the present disclosure, the radiating element may have a shape that operates as a two-point feeding circularly polarized antenna. A feeding notch and a non-feeding notch may be provided for each of the two feeding points of the radiating element.

[0021] In one aspect of the present disclosure, the conductor pattern of the radiating element, including the feed line routed to the feed notch, may have a shape that is symmetrical with respect to a diagonal line of the radiating element. One aspect of the present disclosure may further include a combining / dividing circuit that combines or divides feed signals for two feed points with a phase difference of 90°. The combining / dividing circuit may be provided at a corner of a rectangular dielectric substrate. The combining / dividing circuit may be provided on either the first surface or the second surface of the dielectric substrate.

[0022] With this configuration, the space around the radiating element on the dielectric substrate can be effectively utilized. In one aspect of the disclosure, the radiating element may be shaped to act as a single-point fed circularly polarized antenna.

[0023] In one aspect of the present disclosure, it may be used as an antenna to read information from an RF tag. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a plan view of a planar antenna according to a first embodiment. [Diagram 2] 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 2 is a rear view of the planar antenna of the first embodiment. [Figure 4] 4 is a graph showing the results of calculating, by simulation, frequency characteristics of antenna gain of the planar antenna of the first embodiment. [Diagram 5] 4 is a graph showing the results of calculating, by simulation, frequency characteristics of the axial ratio of the planar antenna of the first embodiment. [Figure 6] 11 is a graph showing the results of calculating, by simulation, frequency characteristics of antenna gain by changing the amount of lateral protrusion of the rear ground that protrudes into the cover case. [Figure 7] 11 is a graph showing the results of simulating frequency characteristics of an axial ratio by changing the amount of lateral protrusion of a rear ground that protrudes into a cover case. [Figure 8] 11 is a graph showing the results of calculating, by simulation, frequency characteristics of antenna gain by changing the amount of vertical protrusion of the rear ground that protrudes into the cover case. [Figure 9] 11 is a graph showing the results of simulating frequency characteristics of an axial ratio by changing the amount of vertical protrusion of a rear ground that protrudes into a cover case. [Figure 10] FIG. 11 is a plan view of a planar antenna according to a second embodiment. [Figure 11] FIG. 11 is a rear view of the planar antenna of the second embodiment. [Figure 12] 10 is a graph showing the results of calculating, by simulation, frequency characteristics of antenna gain of the planar antenna according to the second embodiment. [Figure 13] 13 is a graph showing the results of calculating, by simulation, frequency characteristics of the axial ratio of the planar antenna according to the second embodiment. [Figure 14] FIG. 11 is a plan view of a planar antenna according to a third embodiment. [Figure 15]13 is a graph showing the results of calculating, by simulation, frequency characteristics of antenna gain of the planar antenna according to the third embodiment. [Figure 16] 13 is a graph showing the results of simulating frequency characteristics of the axial ratio of the planar antenna according to the third embodiment. [Figure 17] FIG. 13 is a plan view of a planar antenna according to a fourth embodiment. [Figure 18] FIG. 13 is a plan view of a planar antenna according to a fifth embodiment. [Figure 19] This is a modified example of the shape of the radiating element in the case of one-point feeding. [Figure 20] This is a modified example of the shape of the radiating element in the case of one-point feeding. [Figure 21] 1 is an explanatory diagram showing the shape of a radiating element having a notch for adjusting a frequency; [Figure 22] 1A and 1B are perspective views showing a reading box to which a planar antenna is applied, with its lid closed and with its lid open. [Figure 23] FIG. 13 is a plan view of a planar antenna according to a sixth embodiment. [Figure 24] 24 is a cross-sectional view taken along line XXIV-XXIV in FIG. 23. [Diagram 25] FIG. 4 is an exploded view showing how the spacer is attached. [Figure 26] FIG. 13 is an exploded view showing another method of attaching the spacer. [Figure 27] 13 is a graph showing the results of simulating the frequency characteristics of a planar antenna provided with one spacer (conductor) by changing the diameter of the spacer. [Figure 28] 13 is a graph showing the results of simulating the frequency characteristics of a planar antenna provided with one spacer (insulator) by changing the diameter of the spacer. [Figure 29] 11 is an explanatory diagram showing an example of the arrangement of spacers when a plurality of spacers are used. FIG. [Diagram 30] 13 is a graph showing the results of simulating the frequency characteristics of a planar antenna provided with a plurality of spacers (insulators) by changing the diameter of the spacers. [Diagram 31] 13 is a graph showing the results of simulating the frequency characteristics of a planar antenna provided with a plurality of spacers (conductors) by changing the diameter of the spacers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. [1. First embodiment] [1-1. Configuration] The planar antenna 1 of this embodiment is attached to a reading box 100 shown in Fig. 22, for example, and is used to read identification information from an RF tag attached to a product or the like stored in the reading box 100. Here, the planar antenna 1 is attached to at least one of the sides A and B, the back C, and the bottom D of the reading box 100. The planar antenna 1 is connected to a device that uses the planar antenna 1 via a coaxial cable. The reading box 100 may have a shielded structure.

[0026] The reading box 100 can be used, for example, for reading and managing valuables, medicines, controlled items, etc. The reading box can also be used, for example, in cases where it is necessary to read or write RF tags while suppressing radio wave interference with the surroundings. Note that the use of the planar antenna 1 is not limited to application to the reading box 100.

[0027] The planar antenna 1 includes a substrate (hereinafter, referred to as a dielectric substrate) 10 made of a dielectric material, and a cover case 20, as shown in FIGS. The dielectric substrate 10 is an insulating substrate used to form a general printed circuit board, such as a glass epoxy substrate or a composite substrate, and has conductive layers laminated on both sides of the substrate. The substrate surface of the dielectric substrate 10 has a substantially square shape.

[0028] A conductor pattern that functions as a coplanar and two-point feeding circularly polarized antenna is formed by etching or the like on a substrate surface 10a, which is a first surface of the dielectric substrate 10. The conductor pattern functions as a coplanar and two-point feeding circularly polarized antenna.

[0029] A metallic cover case 20 is attached to the substrate back surface 10b, which is the second surface, of the dielectric substrate 10. A conductor pattern (hereinafter, back surface ground) 16 is formed over the entire substrate back surface 10b except for the attachment portion of the cover case 20. The cover case 20 is connected to the back surface ground 16 so as to have the same potential as the back surface ground 16.

[0030] A radiating element 11, feed lines 12 and 13, a combining / dividing circuit 14, and a connecting portion 15 are formed on the substrate surface 10a. The connection portion 15 is formed at one of the four corners of the dielectric substrate 10 (the lower right corner in FIG. 1). The connection portion 15 includes a front ground 151 for connecting an outer conductor of a coaxial cable, a signal terminal 152 for connecting a central conductor of the coaxial cable, and a termination terminal 153 for terminating the combining / dividing circuit 14. Although not shown, the termination terminal 153 is connected to the front ground 151 via a termination resistor.

[0031] The radiating element 11 is a so-called patch antenna configured by a conductor pattern having an outline of a substantially square shape. The radiating element 11 is disposed at a position close to a corner (the upper left corner in FIG. 1) diagonally opposite the corner where the connection portion 15 is formed on the substrate surface 10a. Hereinafter, of the periphery of the radiating element 11, the side located on the upper side in FIG. 1 is referred to as the first side, the side located on the left side as the second side, the side located on the lower side as the third side, and the side located on the right side as the fourth side.

[0032] The radiating element 11 has two feed points P1 and P2. The first feed point P1 is provided on a line connecting the center of the radiating element 11 and the midpoint of a first side of the radiating element 11. The second feed point P2 is provided on a line connecting the center of the radiating element 11 and the midpoint of a second side perpendicular to the first side. Specifically, the positions of the feed points P1 and P2 are set at positions where the input impedance at the feed points P1 and P2 matches the impedance determined by the pattern width of the feed lines 12 and 13.

[0033] In the radiating element 11, feed notches 111 and 112, which are slit-shaped cutouts, are formed in a portion from the midpoint of the first side to feed point P1 and a portion from the center of the second side to second feed point P2. In addition, a non-feed notch 113 having a similar shape to feed notch 111 is formed in a position point-symmetrical to feed notch 111 with respect to the center of the radiating element 11. Similarly, a non-feed notch 114 having a similar shape to feed notch 112 is formed in a position point-symmetrical to feed notch 112 with respect to the center of the radiating element 11.

[0034] In other words, the pattern shape of radiating element 11 alone has a shape that is line-symmetric with respect to the diagonal line of radiating element 11 and the line connecting the midpoints of two opposing sides of radiating element 11 , and is point-symmetric with respect to the center of radiating element 11 .

[0035] One end of the feed line 12 is connected to a feed point P1 through a feed notch 111, and the other end is connected to the combining / dividing circuit 14. One end of the feed line 13 is connected to a feed point P2 through a feed notch 112, and the other end is connected to the combining / dividing circuit 14.

[0036] That is, the pattern shape including radiating element 11 and feed lines 12, 13 wired to feed notches 111, 112 has a shape that is line symmetrical with respect to a diagonal line extending from the upper left corner to the lower right corner of radiating element 11 in FIG.

[0037] The feed lines 12 and 13 are each formed of a microstrip line whose pattern width changes stepwise, and function as an impedance converter. The pattern width of the feed lines 12 and 13 at the combining / dividing circuit 14 side end is set so as to match the impedance of the combining / dividing circuit 14 (for example, 50 Ω). The pattern width of the feed lines 12 and 13 at the radiating element 11 side end and the depth of the feeding notches 111 and 112 are set so as to match the impedance of the radiating element 11 side end of the feed lines 12 and 13 with the impedance of the feeding points P1 and P2 (for example, several hundred Ω). For this reason, the feed lines 12 and 13 have the widest pattern width at the combining / dividing circuit 14 side end, and the pattern width becomes narrower as they approach the radiating element 11 side end.

[0038] The combining / dividing circuit 14 is configured using a hybrid ring. The combining / dividing circuit 14 is disposed between the radiating element 11 and the connection portion 15. This type of hybrid ring is usually formed in a rectangular shape, but in this embodiment, it has a shape modified into an L-shape in order to effectively utilize the substrate surface around the radiating element 11.

[0039] The combining / distributing circuit 14 has four terminals T1 to T4. Terminal T1 is connected to signal terminal 152 of connection unit 15. Terminal T2 is connected to power feed line 12. Terminal T3 is connected to power feed line 13. Terminal T4 is connected to termination terminal 153 of connection unit 15. The combining / distributing circuit 14 outputs a signal input from terminal T1 from terminals T2 and T3 with a phase difference of 90°, combines the signals input from terminals T2 and T3 by adding a phase difference of 90°, and outputs the combined signal from terminal T1.

[0040] An exposed portion 17 is provided on the back surface 10b of the dielectric substrate 10, where the pattern of the back surface ground 16 is removed, in a portion facing the portion where the radiating element 11 is formed. The exposed portion 17 may be wider than the radiating element 11. The feed lines 12 and 13 (excluding the portions that are wired to the exposed portion 17 for connection to the feed points P1 and P2) and the combining / dividing circuit 14 are provided in the non-exposed portion where the back surface ground 16 is formed.

[0041] The cover case 20 includes a peripheral wall portion 21 and a bottom wall portion 22. The peripheral wall portion 21 is a frame-shaped portion erected around the exposed portion 17. The bottom wall portion 22 is a plate-shaped portion formed so as to close one opening of the frame-shaped portion formed by the peripheral wall portion 21. The bottom wall portion 22 is formed in a shape similar to the outer shape of the radiating element 11, that is, in a substantially square shape. In the cover case 20, the exposed portion 17 and the bottom wall portion 22 face each other via an air layer corresponding to the height of the peripheral wall portion 21, and at least a part of the peripheral wall portion 21 is fixed to the back surface ground 16 so that the cover case 20 and the back surface ground 16 have a conductive potential. In addition, in FIG. 1 and FIG. 3, the thick dashed line indicated by the reference numeral 20 indicates the position where the peripheral wall portion 21 of the cover case 20 abuts against the back surface 10b of the substrate.

[0042] The cover case 20 is disposed so as to cover at least the entire exposed portion 17. In this embodiment, the two sides of the peripheral wall portion 21 located outside the side where the power-feeding notches 111, 112 are formed in the radiating element 11 are located at the boundary between the back ground 16 and the exposed portion 17. In addition, the two sides of the peripheral wall portion 21 located outside the side where the non-power-feeding notches 113, 114 are formed in the radiating element 11 are located outside the boundary between the back ground 16 and the exposed portion 17. The outside refers to the substrate end side as viewed from the center of the dielectric substrate 10. In other words, the cover case 20 is disposed at a position biased toward the center of the dielectric substrate 10 from the radiating element 11 and the exposed portion 17.

[0043] The cover case 20 and the back ground 16 form a microstrip antenna together with the radiating element 11. Since the cover case 20 faces the radiating element 11 with the dielectric substrate 10 and an air layer between them, the dielectric constant of the dielectric portion forming the microstrip antenna is smaller than the dielectric constant of the dielectric substrate 10 itself.

[0044] This suppresses the wavelength shortening rate in the portion where the radiating element 11 is formed, compared to other portions of the dielectric substrate 10. As a result, the pattern of the radiating element 11 can be made larger than in the case where the exposed portion 17 and the cover case 20 are not provided, and the gain of the radiating element 11 can be increased.

[0045] [1-2. Measurement] The characteristics of the planar antenna 1 were calculated by simulation and the results are now described. Fig. 4 shows frequency characteristics of gain of the planar antenna 1 (hereinafter, the embodiment) together with calculation results for a comparative example that does not have the non-feed notches 113, 114. Fig. 5 shows frequency characteristics of the axial ratio of the embodiment together with calculation results for a comparative example that does not have the non-feed notches 113, 114.

[0046] As shown in Figures 4 and 5, in the embodiment, the gain at around 920 to 930 MHz is improved by about 2 dB compared to the comparative example. It can also be seen that in the embodiment, the axial ratio is significantly improved over a wide frequency range compared to the comparative example. Note that the closer the axial ratio value is to zero, the closer the directivity is to a perfect circle.

[0047] Figures 6 and 8 show the frequency characteristics of the gain of the planar antenna 1, and Figures 7 and 9 show the frequency characteristics of the axial ratio of the planar antenna 1. However, Figures 6 and 7 show the results of measurements when the amount of protrusion in the lateral direction (hereinafter referred to as the width) of the back surface ground 16 is changed to 0, 1, 2, 3, and 4 mm. Figures 8 and 9 show the results of measurements when the amount of protrusion in the vertical direction (hereinafter referred to as the width) of the back surface ground 16 is changed to 0, 1, 2, 3, and 4 mm.

[0048] Here, when the positions of the radiating element 11 and the back ground 16 are in the relationship shown in FIG. 3, the positions of the four sides (hereinafter, inner sides) of the back ground 16 surrounding the exposed portion 17 are set to a protrusion amount of 0 [mm]. At the inner side of the back ground 16 facing the side on which the non-power-feeding notch 114 of the radiating element 11 is formed, the protrusion amount of the back ground 16 protruding from the position of 0 [mm] of the inner side toward the center of the radiating element 11 is the horizontal width. At the inner side of the back ground 16 facing the side on which the non-power-feeding notch 113 of the radiating element 11 is formed, the protrusion amount of the back ground 16 protruding from the position of 0 [mm] of the inner side toward the center of the radiating element 11 is the vertical width. In other words, the larger the horizontal width and vertical width, the greater the loss of symmetry in the shape of the exposed portion 17, and therefore in the shape of the microstrip antenna.

[0049] As shown in Figures 6 and 8, in both the horizontal and vertical widths, the greater the protrusion amount, i.e., the more the symmetry of the shape as a macrostrip antenna is lost, the lower the gain and the lower the frequency at which maximum gain is obtained.

[0050] As shown in Figures 7 and 9, in both the horizontal and vertical widths, the larger the protrusion, i.e., the more the symmetry of the shape as a microstrip antenna is lost, the larger the axial ratio value becomes, and the greater the distortion from ideal circular polarization becomes. However, the frequency at which the minimum axial ratio is obtained shifts higher as the protrusion in the horizontal width increases, and shifts lower as the protrusion in the vertical width increases.

[0051] [1-3. Effects] According to the present embodiment described above in detail, the following effects are achieved. (1a) In the planar antenna 1, the non-power-feeding notches 113 and 114 are provided to give the radiating element 11 a line-symmetric and point-symmetric shape, which makes it possible to suppress distortion of the axial ratio characteristics compared to an ideal circularly polarized wave. As a result, the planar antenna 1 can read information from an RF tag with a certain degree of accuracy, regardless of the orientation of the RF tag.

[0052] (1b) In the planar antenna 1, an exposed portion 17 is formed in a portion of the substrate back surface 10b facing the radiating element 11, and a cover case 20 is attached to the exposed portion. This allows the pattern of the radiating element 11 to be made larger than other portions of the dielectric substrate 10, and the gain of the radiating element 11 can be improved while suppressing an increase in the size of the dielectric substrate 10.

[0053] [2. Second embodiment] [2-1. Differences from the first embodiment] The second embodiment has a basic configuration similar to that of the first embodiment, and therefore differences will be described below. Note that the same reference numerals as those in the first embodiment indicate the same configuration, and the preceding description will be referred to.

[0054] In the first embodiment described above, the cover case 20 is formed larger than the exposed portion 17, and a portion from which the back surface ground 16 protrudes exists inside the cover case 20. In contrast, the planar antenna 1a of the present embodiment is different in that the cover case 20a is formed to be substantially the same size as the exposed portion 17, as shown in Figs.

[0055] As a result, in the planar antenna 1a, not only the shapes of the radiating element 11 and exposed portion 17, but also the shape of the cover case 20a are point-symmetric with respect to the center of the radiating element 11, and are line-symmetric with respect to the diagonal of the radiating element 11 and the line passing through the midpoints of the two opposing sides.

[0056] That is, the structure inside cover case 20a, including radiating element 11 and feed lines 12, 13 wired to feed notches 111, 112, has a shape that is line-symmetrical with respect to a diagonal line passing through cover case 20a from the upper left corner to the lower right corner in FIG.

[0057] However, the arrangement of the cover case 20a with respect to the dielectric substrate 10 is different from that of the first embodiment, and is biased toward one corner of the dielectric substrate 10 to the same extent as the radiating element 11 and the exposed portion 17.

[0058] [2-2. Measurement] The characteristics of the planar antenna 1a were calculated by simulation and the results are now described. 12 shows the frequency characteristics of the gain of the planar antenna 1a (hereinafter, Example 2) together with the calculation results for the planar antenna 1 of the first embodiment (hereinafter, Example 1). FIG. 13 shows the frequency characteristics of the axial ratio of Example 2 together with the calculation results for Example 1.

[0059] As shown in FIGS. 12 and 13, in comparison with Example 1, Example 2 has substantially the same frequency characteristic for gain, and the frequency characteristic for the axial ratio is somewhat degraded, but within a range that does not pose a problem in practical use.

[0060] [2-3. Effects] According to the second embodiment described above in detail, in addition to the effects (1a) and (1b) of the first embodiment described above, the following effects are achieved.

[0061] (2a) In the planar antenna 1a, the cover case 20a is smaller in size than the cover case 20 of the first embodiment, so that the weight of the planar antenna 1a can be reduced. [3. Third embodiment] [3-1. Differences from the second embodiment] The third embodiment has a basic configuration similar to that of the second embodiment, and therefore differences will be described below. Note that the same reference numerals as those in the second embodiment indicate the same configurations, and the preceding description will be referred to.

[0062] In the second embodiment described above, the radiating element 11, exposed portion 17, and cover case 20a are provided at a position closer to the upper left corner than the center of the dielectric substrate 10. In contrast, in the planar antenna 1b of this embodiment, the radiating element 11, exposed portion 17, and cover case 20a are provided at the center of the dielectric substrate 10, as shown in FIG.

[0063] [3-2. Measurement] The characteristics of the planar antenna 1b were calculated by simulation and the results are now described. 15 shows the frequency characteristics of the gain of the planar antenna 1b (hereinafter, Example 3) together with the calculation results for the planar antenna 1a of the second embodiment (hereinafter, Example 2). FIG. 16 shows the frequency characteristics of the axial ratio of Example 3 together with the calculation results for Example 2.

[0064] 15 and 16, in Example 3, the gain is increased and the axial ratio is decreased compared to Example 2. That is, both the gain and the axial ratio are improved. [3-3. Effects] According to the third embodiment described above in detail, in addition to the effects (1a) and (1b) of the first embodiment and the effect (2a) of the second embodiment, the following effect is achieved.

[0065] (3a) In the planar antenna 1b, the structure including the dielectric substrate 10, the radiating element 11, the exposed portion 17, and the cover case 20a has a more symmetrical shape, which can further improve the frequency characteristics of the gain and the axial ratio.

[0066] [4. Fourth embodiment] [4-1. Differences from the first embodiment] The fourth embodiment has a basic configuration similar to that of the first embodiment, and therefore differences will be described below. Note that the same reference numerals as those in the first embodiment indicate the same configuration, and the preceding description will be referred to.

[0067] In the above-described first embodiment, the outer shape of the radiating element 11 is approximately square, but in the planar antenna 1c of this embodiment, the outer shape of the radiating element 11c is formed to be approximately circular, as shown in Fig. 17. The feeding points P1, P2 are arranged on two perpendicular straight lines passing through the center of the radiating element 11c, and the feeding notches 111, 112 and the non-feeding notches 113, 114 are also formed along these straight lines.

[0068] [4-2. Effects] According to the planar antenna 1c of this embodiment described above in detail, the following effects are achieved similarly to the planar antenna 1 of the first embodiment.

[0069] In FIG. 17, the cover case 20 is in the same position and has the same size as in the first embodiment, but it may be in the same position and have the same size as the cover case 20a shown in the second or third embodiment.

[0070] [5. Fifth Embodiment] [5-1. Differences from the first embodiment] The fifth embodiment has a basic configuration similar to that of the first embodiment, and therefore differences will be described below. Note that the same reference numerals as those in the first embodiment indicate the same configuration, and the preceding description will be referred to.

[0071] In the above-described first embodiment, the case of two-point power supply has been described, but in this embodiment, the case of one-point power supply will be described. As shown in FIG. 18, a planar antenna 1d has a substrate surface 30a of a dielectric substrate 30, on which a radiating element 31 and a feed line 32 are formed by a conductor pattern.

[0072] Radiating element 31 has a substantially square shape, and triangular cutouts 313 are provided at two diagonal corners. The radiating element 31 is provided with one feed point P, one feed notch 311 and one non-feed notch 312.

[0073] The feeder line 32 is configured similarly to the feeder line 12 and functions as an impedance converter. Planar antenna 1d thus configured has a known structure for a notched circularly polarized antenna of a coplanar feeding system and a single feeding point system, except that non-feeding notch 312 is provided.

[0074] The rear ground 10 and exposed portion 17 on the rear surface of the dielectric substrate 30, and the cover cases 20 and 20a are similar to those in any of the first to third embodiments, and therefore will not be described.

[0075] [5-2. Effects] According to the present embodiment described above in detail, the following effects are achieved. (4a) According to the planar antenna 1d, the non-power-feed notch 312 makes the shape of the radiating element 31 more symmetrical than when the non-power-feed notch 312 is not present, and therefore distortion of the axial ratio characteristics can be suppressed compared to the case of an ideal circular polarization.

[0076] In this embodiment, the non-feed notch 312 is provided only at a position that is point-symmetric to the feed notch 311 with respect to the center of the radiating element 31. However, it is also possible to form four notches at the same positions as in the first embodiment, and have a structure in which one of the four notches is a feed notch and the other three are non-feed notches, thereby achieving single-point feeding.

[0077] [6. Sixth Embodiment] [6-1. Differences from the first embodiment] The sixth embodiment has a basic configuration similar to that of the first embodiment, and therefore differences will be described below. Note that the same reference numerals as those in the first embodiment indicate the same configurations, and the preceding description will be referred to.

[0078] A planar antenna 1g of this embodiment differs from the first embodiment in that it further includes a spacer 40 for maintaining the gap between the dielectric substrate 10 and the case portion 20, as shown in FIGS.

[0079] The spacer 40 is a cylindrical conductor having a screw hole 40a penetrating through the center. However, the screw hole 40a does not necessarily have to penetrate through the spacer 40 as long as it is formed at both ends of the spacer 40. The outer shape of the spacer 40 may be cylindrical or polygonal.

[0080] The spacer 40 is placed at the center of the pattern of the radiating element 11, and is fixed by screws 41, 42 as shown in Fig. 25. Therefore, holes 10c, 20c are formed in the dielectric substrate 10 and the case part 20, respectively, for inserting the screws 41, 42 that are screwed into the screw holes 40a of the spacer 40. The screws 41, 42 are conductors. The position of the spacer 40 does not need to be strictly at the center of the pattern of the radiating element 11, and may be shifted as long as it is in the vicinity of the center.

[0081] The spacer 40 has a length that maintains the distance between the dielectric substrate 10 and the case 20 at a design value. A plurality of types of spacers 40 whose lengths are slightly different from the design value may be prepared. The shorter the spacer 40, that is, the smaller the distance between the pattern of the radiating element 11 and the case 20, the higher the resonant frequency of the planar antenna 1g shifts to a higher frequency. The resonant frequency can be fine-tuned by adjusting the tightness of the screws 41 and 42 that secure the spacer 40, without changing the length of the spacer 40.

[0082] A plurality of spacers 40 with different diameters may be prepared. The center frequency of the planar antenna 1g can be adjusted by changing the length and diameter of the spacer 40. As shown in FIG. 27, the resonant frequency of the planar antenna 1g shifts to a higher frequency as the diameter of the spacer 40 increases. Simulations were performed without the spacer 40 and with the diameters of the spacer 40 being 5 mm, 7.5 mm, 10 mm, and 12.5 mm.

[0083] [6-2. Effects] According to the sixth embodiment described above in detail, in addition to the effects (1a) and (1b) of the first embodiment described above, the following effects are achieved.

[0084] (6a) According to the planar antenna 1g, by providing the spacer 40, the distance between the dielectric substrate 10 and the case part 20 can be maintained at the design value. As a result, it is possible to suppress deviation of the resonant frequency of the planar antenna 1g caused by deviation of the distance between them from the design value due to warping of the dielectric substrate 10 or the case part 20.

[0085] (6b) According to the planar antenna 1g, the resonant frequency of the planar antenna 1g can be adjusted by preparing and appropriately replacing the spacers 40 with different lengths, diameters, materials, etc.

[0086] [6-3. Modifications] In the planar antenna 1g, both ends of the spacer 40 are in direct contact with the dielectric substrate 10 and the case portion 20, respectively, and are screwed in place. However, as shown in FIG. 26, coil springs 43, 44 may be interposed between both ends of the spacer 40 and the dielectric substrate 10 and the case portion 20, respectively.

[0087] In this case, by adjusting the screwing strength, the distance between the dielectric substrate 10 and the case part 20, and therefore the resonant frequency of the planar antenna 1g, can be finely adjusted. Although the coil springs 43 and 44 are inserted into both ends of the spacer 40 in FIG. 26, they may be inserted into only one of the ends.

[0088] The spacer 40 may be fixed by a method other than screwing, such as adhesion or soldering. Both ends of the spacer 40 do not need to be fixed by the same method, and for example, one end may be fixed by a screw and the other end by a method other than screwing. The spacer 40 may be formed integrally with either the dielectric substrate 10 or the case portion 20.

[0089] 7. Other embodiments Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various aspects can be adopted without departing from the gist of the present disclosure.

[0090] (7a) In the above embodiment, the outer shape of the radiating elements 11, 11c, and 31 is shown to be a square or a circle, but the present disclosure is not limited thereto, and the outer shape of the radiating elements may be, for example, a regular polygon. In the case of a regular polygon, the number of vertices is preferably 4n, where n is a positive integer.

[0091] (7b) In the above fifth embodiment, as a circularly polarized antenna of a single-point feeding system, the outer shape of the radiating element 31 is substantially square, and the notches 313 are formed at the corners located at both ends of one diagonal line. However, the present disclosure is not limited to this. For example, as in the planar antennas 1e and 1f shown in Figs. 19 and 20, the outer shape of the radiating elements 31e and 31f may be substantially circular. In this case, the radiating elements 31e and 31f may have an angle of 45° with respect to the notch formation line, and may be provided with the notch 313e or the protrusion 313f at both ends of a line passing through the center of the radiating elements 31e and 31f. The notch formation line is a line that passes through the center of the radiating elements 31e and 31f along the formation direction of the feeding notch 311 and the non-feeding notch.

[0092] Here, Fig. 18 and Fig. 19 show a circularly polarized antenna that transmits and receives one of right-handed and left-handed circularly polarized waves. On the other hand, when configuring as a circularly polarized antenna that transmits and receives the other polarized wave, the notch 313, 313e may be formed at a position rotated 90° from the position shown in Fig. 18 and Fig. 19 as viewed from the center of the radiating element 31, 31e. Similarly, in the case of Fig. 20, when transmitting and receiving a circularly polarized wave different from the circularly polarized wave transmitted and received by the illustrated circularly polarized antenna, the protrusion 313f may be formed at a position rotated 90° from the position shown in Fig. 20 as viewed from the center of the radiating element 31f.

[0093] (7c) Radiating element 11 may have cutouts 115-118 at the four corners of the pattern as shown in Fig. 21. Cutouts 115-118 are formed by cutting out isosceles right triangles of the same size at each vertex of the square pattern shape of radiating element 11. The center frequency of radio waves transmitted and received by radiating element 11 can be finely adjusted by adjusting the size of cutouts 115-118.

[0094] (7d) The planar antennas 1, 1a, 1b, and 1c may be provided with a signal attenuator between the signal terminal 152 of the connection portion 15 and the terminal T1 of the combining / distributing circuit 14 to adjust the radiation level of the antenna. For example, a π-type ATT or the like may be used as the signal attenuator. The signal attenuator may be provided on either the front surface 10a or the back surface 10b of the substrate.

[0095] (7e) The cover cases 20 and 20a are made of a conductive material such as a thin iron plate, but when the planar antennas 1, 1a to 1f are arranged in an exposed state, a protective layer may be provided on the surface of the cover cases 20 and 20a to prevent scratches and rust. For example, silk printing or painting may be used as the protective layer.

[0096] (7f) In the above embodiment, the back ground 16 is formed on the back surface 10b of the dielectric substrate 10, but the back ground 16 does not necessarily have to be formed on the dielectric substrate 10. For example, instead of providing the back surface ground 16, a conductive plate serving as a ground may be attached to the back surface 10b of the substrate using a spacer made of a dielectric material or the like so as to be disposed opposite the back surface 10b of the substrate. In this case, a coaxial cable serving as a feed line is wired by penetrating the conductive plate. Then, the core of the coaxial cable is electrically connected to the feed point P of the radiating element 11 from the back surface 10b of the substrate, and the braided part of the coaxial cable is electrically connected to the conductive plate. A planar antenna having such a structure can also obtain the same effects as those of the above-mentioned embodiments.

[0097] (7g) In the sixth embodiment, the spacer 40 and the screws 41, 42 are made of conductors, but the spacer 40 and the screws 41, 42 may be made of an insulator such as resin. When the spacer 40 and the screws 41, 42 are made of insulators, the spacer 40 may be provided in multiple locations, not just one location. 28, when the spacer 40 and the screws 41 and 42 are made of insulating material, the resonant frequency of the planar antenna 1g is approximately the same until the diameter of the spacer 40 reaches about 10 mm (here, λ / 30), and when the diameter exceeds 10 mm, the resonant frequency shifts significantly to a lower range. λ is the wavelength corresponding to the resonant frequency of the planar antenna 1g.

[0098] 30 and 31 show the results of simulations of a planar antenna 1h shown in FIG. 29, in which a spacer 40 (in FIG. 29, the position where the screw 41 is shown) is provided at four locations around the center of the radiating element 11. When the spacer 40 and the screws 41, 42 are insulators, the larger the diameter of the spacer 40, the lower the resonant frequency of the planar antenna 1h shifts to. When the spacer 40 and the screws 41, 42 are conductors, the antenna gain is significantly reduced compared to the case where the spacer 40 is not provided, regardless of the diameter of the spacer 40, as shown in FIG. 31. Therefore, when the spacer 40 and the screws 41, 42 are insulators, a plurality of spacers 40 may be provided, but when the spacer 40 and the screws 41, 42 are conductors, it is preferable to use one spacer 40. [Explanation of symbols]

[0099] 1, 1a to 1h... Planar antenna, 10, 30... Dielectric substrate, 10a, 30a... Substrate surface, 10b... Substrate back surface, 11, 11c, 31, 31e, 31f... Radiating element, 12, 13, 32... Power feed line, 14... Combiner / divider circuit, 15... Connection portion, 16... Back surface ground, 17... Exposed portion, 20, 20a... Cover case, 21... Peripheral wall portion, 22... Bottom wall portion, 40...spacer, 41, 42...screws, 43, 44...coil spring, 111, 112, 311...power supply notch, 113, 114, 312...non-power supply notch, 151...front ground, 152...signal terminal, 153...termination terminal, 115 to 118, 313, 313e...notch, 313f...protrusion, P1, P2, P...power supply point, T1 to T4...terminal.

Claims

1. A dielectric substrate on both sides of which a conductor pattern is formed; a radiating element having a conductor pattern formed on a first surface of the dielectric substrate, the radiating element having a feeding notch that is a cut from an edge of the pattern to a feeding point; a power supply line that is a conductor pattern formed on the first surface and that passes through the power supply notch to reach the power supply point; Equipped with The radiating element is provided with a non-feeding notch which is provided at a position point-symmetrical to the feeding notch with respect to the center point of the radiating element and is a cut having the same shape as the feeding notch. Flat antenna.

2. 2. A planar antenna as claimed in claim 1, The dielectric substrate further includes a back ground, which is a conductor pattern formed on the second surface of the dielectric substrate. Flat antenna.

3. 3. A planar antenna according to claim 2, the second surface of the dielectric substrate includes at least a portion facing the radiating element, and an exposed portion is formed by removing the back surface ground; a cover portion having a plate-like portion that covers the exposed portion and is arranged to face a portion that faces the exposed portion across a low-dielectric layer having a lower dielectric constant than the dielectric substrate, the cover portion being fixed to the dielectric substrate so as to have the same potential as the back surface ground; Flat antenna.

4. 4. A planar antenna according to claim 3, The exposed portion is formed in a shape similar to that of the radiating element. Flat antenna.

5. The planar antenna according to claim 3 or 4, the radiating element is disposed at a position offset from the center of the dielectric substrate; The cover portion covers the exposed portion and is disposed at a position biased toward the center of the dielectric substrate. Flat antenna.

6. A planar antenna according to any one of claims 3 to 5, The dielectric substrate is provided with a spacer for maintaining a distance between the dielectric substrate and the cover. Flat antenna.

7. 7. A planar antenna according to claim 6, The spacer is disposed at the center of the radiating element. Flat antenna.

8. 7. A planar antenna according to claim 6, The spacer is an insulator and is arranged in one or more. Flat antenna.

9. A planar antenna according to any one of claims 6 to 8, The spacer is configured so that at least one end is fixed by a screw. Flat antenna.

10. 10. A planar antenna as claimed in claim 9, The spacer further includes a coil spring inserted between the spacer and a portion where the spacer is screwed. Flat antenna.

11. A planar antenna according to any one of claims 1 to 10, The radiating element has a shape that operates as a two-point feeding type circularly polarized antenna, The feeding notch and the non-feeding notch are provided for each of the two feeding points of the radiating element. Flat antenna.

12. 12. A planar antenna as claimed in claim 11, The conductor pattern of the radiating element, including the power feed line wired to the power feed notch, has a shape that is line-symmetrical with respect to a diagonal line of the radiating element. Flat antenna.

13. A planar antenna according to claim 11 or 12, Further comprising a combining / dividing circuit for combining or dividing the power supply signals for the two power supply points with a phase difference of 90°; The combining and dividing circuit is provided at a corner of the rectangular dielectric substrate. Flat antenna.

14. A planar antenna according to any one of claims 1 to 10, The radiating element is shaped to operate as a single-point-fed circularly polarized antenna. Flat antenna.

15. A planar antenna according to any one of claims 1 to 14, Used as an antenna to read information from RF tags Flat antenna.

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