Circularly polarized slot antenna element and method for adjusting the circularly polarized slot antenna element

Abstract

This invention provides a circularly polarized slot antenna element and a method for adjusting the same that are less susceptible to characteristic deviations caused by variations in the precision of the implementation work. [Solution] A circularly polarized slot antenna element is provided, comprising: a dielectric substrate (11) which is rectangular in plan view, a transmission line (12) extending perpendicular to the left-right direction of the dielectric substrate (11) on one surface, a ground conductor (13) with a left conductor portion (13a) and a right conductor portion (13b) arranged along the transmission line (12) to the left and right of the transmission line (12), a left slot antenna portion (14) arranged to the left of the transmission line (12), a right slot antenna portion (15) arranged to the right of the transmission line (12), a first diagonal slot portion (16) arranged at a corner of the dielectric substrate (11) near either the left slot antenna portion (14) or the right slot antenna portion (15), and a second diagonal slot portion (17) arranged at a diagonal position of the first diagonal slot portion (16) of the dielectric substrate (11).

Description

Technical Field

[0001] The present invention relates to a circularly polarized slot antenna element used in UWB (Ultra Wide Band) or the like and a method for adjusting the circularly polarized slot antenna element.

Background Art

[0002] One of the inventors of the present invention has previously been developing small or thin planar antenna elements, and has proposed a thin single-sided radiation antenna provided with a ground conductor for radiation, a transmission line for inputting a signal to the ground conductor, and a slot having a predetermined shape on the surface of a dielectric substrate having a rectangular shape in plan view (see, for example, Patent Document 1).

[0003] Alternatively, a planar antenna element provided with a ground conductor for radiation, a transmission line, and a slot having a predetermined shape on the surface of a dielectric substrate, and further provided with a shielding conductor surface on the back surface of the dielectric substrate, and a method for adjusting that enables the design of an antenna suitable for a wide band by adjusting resonance points has been proposed (see, for example, Patent Document 2).

[0004] All of the above planar antenna elements are linearly polarized slot antenna elements. In a linearly polarized slot antenna element, radio waves of horizontal polarization or vertical polarization are transmitted or received, and adjustment of the direction of the antenna is required. On the other hand, a circularly polarized slot antenna element is known. Since the circularly polarized slot antenna element does not require adjustment of the direction of the antenna because of its lack of dependence on a specific direction, and further, since UWB itself has characteristics of low power consumption, low output, and high range resolution, its use in a wireless sensor network system or the like is expected. One of the inventors of the present invention has also been developing a circularly polarized slot antenna element (see, for example, Patent Document 3).

[0005] The circularly polarized slot antenna element described in Patent Document 3 is constructed using four antenna elements and connected using a coplanar transmission line. By supplying signals to all antenna elements in the same phase, reinforcement of electromagnetic waves occurs, generating a peak of left-hand circularly polarized radiation on the upper surface of the antenna.

[0006] Here, one antenna element is itself a circularly polarized slot antenna element, and two slot antennas are provided on a single dielectric substrate. In particular, the extension direction of one of the two slot antennas is made perpendicular to the extension direction of the other slot antenna, and the width dimensions of each slot antenna are further adjusted (see, for example, Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2008-312090 [Patent Document 2] Japanese Patent Publication No. 2009-124285 [Patent Document 3] Japanese Patent Publication No. 2016-213800 [Non-patent literature]

[0008] [Non-Patent Document 1] Koji Fujita, et al., "Development of a UWB Circularly Polarized Flexible Antenna," Proceedings of the IEICE General Conference, 2013(1), 110. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] When using the circularly polarized slot antenna element described in Non-Patent Document 1 (hereinafter referred to as the "conventional circularly polarized slot antenna element"), there was a problem in that it was often difficult to design the power supply wiring that inputs the signal to the transmission line on the dielectric substrate. In other words, with the conventional circularly polarized slot antenna element, due to the arrangement of the power supply points, it was not possible to connect the power supply wiring to the power supply point as coplanar feeding (GSG feeding), and it was necessary to do so as GS feeding, which is half of that state.

[0010] Therefore, when conventional circularly polarized slot antenna elements are implemented in communication devices, special installation work is required for the power supply wiring connected to the conventional circularly polarized slot antenna elements. This not only reduces the ease of implementation but also creates a problem where deviations in characteristics are likely to occur due to variations in the precision of the implementation work.

[0011] Therefore, the inventors conducted research to develop a circularly polarized slot antenna element that can transmit and receive circularly polarized radio waves while using the GSG feeding method used for conventional linearly polarized slot antenna elements, and thus arrived at the present invention. [Means for solving the problem]

[0012] The circularly polarized slot antenna element of the present invention comprises a transmission line extending linearly along a direction perpendicular to the left-right direction of the dielectric substrate on one surface of a dielectric substrate which is rectangular in plan view; a ground conductor connecting the end of the transmission line, with a left conductor portion and a right conductor portion arranged along the transmission line on the left and right sides of the transmission line, respectively; a left slot antenna portion located to the left of the transmission line; a right slot antenna portion located to the right of the transmission line; a first diagonal slot portion located at a corner of the dielectric substrate near either the left slot antenna portion or the right slot antenna portion; and a second diagonal slot portion located at a diagonal position of the first diagonal slot portion of the dielectric substrate.

[0013] Furthermore, the circularly polarized slot antenna element of the present invention also has the following features. (1) The left slot antenna part or the right slot antenna part close to the first diagonal slot part is arranged with an offset by the amount of the first diagonal slot part. (2) On the other surface of the dielectric substrate provided with the ground conductor and the transmission line, it has a conductive layer covering the surface.

[0014] Further, in the adjustment method of the circularly polarized slot antenna element of the present invention, in the above circularly polarized slot antenna element, the adjustment of the frequency characteristics of the axial ratio is performed by adjusting the size of the first diagonal slot part and / or the second diagonal slot part. It is characterized by that.

Advantages of the Invention

[0015] According to the present invention, by arranging the left conductor part and the right conductor part of the ground conductor on the left and right of the transmission line respectively, the connection of GSG power supply can be enabled, and the characteristics of the circularly polarized slot antenna element that often occur during mounting can be suppressed. Moreover, by arranging the first diagonal slot part and the second diagonal slot part at diagonal positions respectively, it can function as a suitable circularly polarized slot antenna element.

Brief Description of the Drawings

[0016] [Figure 1] It is an explanatory diagram of the circularly polarized slot antenna element according to the present invention. [Figure 2] It is an explanatory diagram of another embodiment of the circularly polarized slot antenna element according to the present invention. [Figure 3] It is a dimensional explanatory diagram of the circularly polarized slot antenna element according to the embodiment of the present invention. [Figure 4] It is a dimensional explanatory diagram of the circularly polarized slot antenna element for comparison. [Figure 5] It is the antenna electric field distribution of the circularly polarized slot antenna element according to the present invention. [Figure 6] It is an explanatory diagram of the simulation model. [Figure 7] It is a graph of the S11 characteristics evaluated by simulation. [Figure 8] It is a graph of the forward gain evaluated by simulation. [Figure 9] It is a graph of the front axial ratio evaluated by simulation. [Figure 10] It is a graph of the radiation pattern in the XZ direction evaluated by simulation. [Figure 11] It is a graph of the radiation pattern in the YZ direction evaluated by simulation.

Embodiments for Carrying out the Invention

[0017] As shown in FIGS. 1 and 2, the circularly polarized slot antenna elements 10, 10' of the present invention are antenna elements provided with a transmission line 12 and a ground conductor 13 on one surface of a dielectric substrate 11 having a rectangular shape in plan view.

[0018] The dielectric substrate 11 is an insulating substrate used for a printed wiring board, and a copper foil layer is provided on one surface. By patterning this copper foil layer into a predetermined shape, the transmission line 12 and the ground conductor 13 are formed. The patterning of the copper foil layer is performed by providing an etching mask having a predetermined pattern on the upper surface of the copper foil layer provided on the upper surface of the dielectric substrate 11 and etching the copper foil layer. In the present embodiment, the dielectric substrate 11 has a copper foil layer provided on one surface, but as will be described later, a copper foil layer may also be provided on the other surface.

[0019] The transmission line 12 is provided so as to linearly extend along a direction orthogonal to the left-right direction of the dielectric substrate 11 having a rectangular shape in plan view. In particular, the transmission line 12 is located at a substantially central position in the left-right direction of the dielectric substrate 11, and the end portion is used as a feeding point P. The transmission line 12 at the feeding point P is made wider than the transmission line 12 closer to the center of the dielectric substrate 11 than this feeding point P, making it easier to connect to a signal line (not shown) for inputting a desired signal.

[0020] The grounding conductor 13 is arranged on the left and right sides of the transmission line 12, with the left conductor portion 13a and the right conductor portion 13b positioned along the transmission line 12, forming a coplanar line. By making the transmission line 12 near the power supply point P a coplanar line in this way, it is easier to maintain the stability of the GSG power supply.

[0021] The ground conductor 13, which has a left conductor portion 13a and a right conductor portion 13b, is positioned to bypass the left slot antenna portion 14 and the right slot antenna portion 15 provided on the dielectric substrate 11, and connects to the end of the transmission line 12. The left slot antenna portion 14 is positioned on the left side of the transmission line 12, and the right slot antenna portion 15 is positioned on the right side of the transmission line 12, and both are positioned as far away as possible from the feed point P.

[0022] In this embodiment, the left slot antenna section 14 and the right slot antenna section 15 have the same shape, and are horizontally elongated rectangles that extend parallel to the left-right direction of the dielectric substrate 11.

[0023] In a dielectric substrate 11 provided with a left slot antenna section 14 and a right slot antenna section 15, as shown in Figure 1, a first diagonal slot section 16 is positioned at the upper right corner 11a of the dielectric substrate 11, which is close to the right slot antenna section 15, and a second diagonal slot section 17 is positioned at the lower left corner 11c of the dielectric substrate 11, which is diagonally opposite to the first diagonal slot section 16. Alternatively, as shown in Figure 2, a first diagonal slot section 16' is positioned at the upper left corner 11d of the dielectric substrate 11, which is close to the left slot antenna section 14, and a second diagonal slot section 17' is positioned at the lower right corner 11b of the dielectric substrate 11, which is diagonally opposite to the first diagonal slot section 16'.

[0024] Specifically, the first diagonal slot sections 16 and 16' are positioned at the upper right corner 11a or upper left corner 11d of the dielectric substrate 11, which is closer to either the left slot antenna section 14 or the right slot antenna section 15, and the second diagonal slot sections 17 and 17' are positioned at the lower left corner 11c or lower right corner 11b of the dielectric substrate 11, which is diagonally opposite the first diagonal slot sections 16 and 16'.

[0025] As shown in Figure 1, by positioning the first diagonal slot section 16 in the upper right corner 11a, the right slot antenna section 15 is offset by the amount of the first diagonal slot section 16, and is positioned closer to the feed point P than the left slot antenna section 14. The left slot antenna section 14 and the right slot antenna section 15 have their extension directions (longitudinal directions) parallel to each other.

[0026] Similarly, as shown in Figure 2, by positioning the first diagonal slot section 16' at the upper left corner 11d, the left slot antenna section 14 is offset by the amount of the first diagonal slot section 16', and is positioned closer to the feed point P than the right slot antenna section 15. The left slot antenna section 14 and the right slot antenna section 15 have their extension directions (longitudinal directions) parallel to each other.

[0027] In this way, by providing first diagonal slot portions 16, 16' and second diagonal slot portions 17, 17' at one diagonal position on the dielectric substrate 11, a circularly polarized slot antenna element can be created.

[0028] In this embodiment, the first diagonal slot sections 16 and 16' have a larger area than the second diagonal slot sections 17 and 17'. The first diagonal slot sections 16 and 16' and the second diagonal slot sections 17 and 17' could have the same area, or the second diagonal slot sections 17 and 17' could have a larger area than the first diagonal slot sections 16 and 16'. However, when evaluating the characteristics as a circularly polarized slot antenna element, it was found that having the first diagonal slot sections 16 and 16' have a larger area than the second diagonal slot sections 17 and 17' was more preferable.

[0029] In this embodiment, as described above, the dielectric substrate 11, which does not have a transmission line 12 and a ground conductor 13, does not have a copper foil layer on the other side (back side), thereby making the dielectric substrate 11 a bidirectional circularly polarized slot antenna element. However, by providing a conductive layer such as a copper foil layer covering the other side (back side) and making this conductive layer function as a floating metal, it is possible to make it a unidirectional circularly polarized slot antenna element. [Examples]

[0030] The following describes a circularly polarized slot antenna element constructed using a printed circuit board with a 0.036 mm thick copper foil layer on a 1.6 mm thick insulating substrate. In this embodiment, the circularly polarized slot antenna element is designed assuming a resonant frequency of 9.25 GHz. The dielectric substrate 11 has a dielectric constant ε r =4.6 and tanδ=0.01. As shown in Figure 3, the dielectric substrate 11 is rectangular with a vertical dimension of 15 mm and a horizontal dimension of 15 mm, with a square first diagonal slot portion 16 with a vertical dimension of 6 mm and a horizontal dimension of 6 mm provided in the upper right corner 11a, and a square second diagonal slot portion 17 with a vertical dimension of 5.5 mm and a horizontal dimension of 5.5 mm provided in the lower left corner 11c. The left slot antenna portion 14 and the right slot antenna portion 15 are horizontally elongated rectangles with a vertical dimension of 2.5 mm and a horizontal dimension of 7 mm, with the left slot antenna portion 14 positioned 10.2 mm from the side edge 11e of the dielectric substrate 11 on the feed point P side, and the right slot antenna portion 15 positioned 6.2 mm from the side edge 11e of the dielectric substrate 11 on the feed point P side. In the circularly polarized slot antenna element of this embodiment, a mounting area 11f for mounting a coaxial cable is provided adjacent to the feed point P.

[0031] Furthermore, as a circularly polarized slot antenna element for comparison, a circularly polarized slot antenna element described in Non-Patent Document 1 was used. This circularly polarized slot antenna element is constructed using a printed circuit board 18 having a 0.02 mm copper foil layer on a flexible insulating substrate with a thickness of 0.254 mm. The printed circuit board 18 has a dielectric constant ε r=3.5 and tanδ=0.0015. As shown in Figure 4, the printed circuit board 18 is rectangular in shape with a vertical dimension of 16 mm and a horizontal dimension of 16.3 mm. An upper left slot portion 18d with a vertical dimension of 4 mm and a horizontal dimension of 2 mm is provided at the upper left corner 11d' of the printed circuit board 18, a lower right slot portion 18b with a vertical dimension of 7.2 mm and a horizontal dimension of 6 mm is provided at the lower right corner 11b' of the printed circuit board 18, and a lower left slot portion 18c with a vertical dimension of 2 mm and a horizontal dimension of 2 mm is provided at the lower left corner 11c' of the printed circuit board 18. An expansion slot portion 18e with a vertical dimension of 0.5 mm and a horizontal dimension of 0.5 mm is provided in the lower left slot portion 18c, and a first slot antenna portion 19a with a vertical dimension of 5.8 mm and a horizontal dimension of 0.1 mm is provided extending vertically from this expansion slot portion 18e of the printed circuit board 18. A first connecting line 21a with a length of 0.4 mm extending in the left-right direction is provided at the upper end of the first slot antenna section 19a. A second connecting line 21b with a length of 1 mm extending in a direction perpendicular to the left-right direction is provided at the end of this first connecting line 21a. A second slot antenna section 19b with a vertical dimension of 1 mm and a horizontal dimension of 11.5 mm is provided on this second connecting line 21b, extending in the left-right direction. The corner portion formed by the lower left slot section 18c and the extended slot section 18e is the feed point P'.

[0032] [Antenna field distribution] Figure 5 shows the electric field distribution when signals with different phases are input to the circularly polarized slot antenna element of the present invention shown in Figure 3. The input signals are 9.25 GHz in frequency, and Figure 5 shows the cases of phase 0°, phase 90°, phase 180°, and phase 270°. As the phase changes by 90°, the point where the electric field leaks out, indicated by the circle in the figure, shifts by 90°, indicating that circular polarization is being radiated. In other words, the antenna element shown in Figure 3 is a circularly polarized slot antenna element.

[0033] [Evaluation through simulation] The circularly polarized slot antenna element shown in Figure 4 and the circularly polarized slot antenna element of the present invention shown in Figure 3 were evaluated by simulation under the following states A to E, as shown in Figure 6. A: When power is supplied directly to power supply point P', B: When power is supplied to power supply point P' via a coaxial cable, C: Power supply point P', power is supplied to P via coaxial cable, and on the left and right sides of the coaxial cable When a 20 x 20 mm ground plane (GND) is provided for the transmission line, D: Power supply point P', power is supplied to P via coaxial cable, and on the left and right sides of the coaxial cable When a 40 x 20 mm ground plane (GND) is provided for the transmission line, E: Power supply point P', power is supplied to P via coaxial cable, and on the left and right sides of the coaxial cable When a 60 x 20 mm ground plane (GND) is provided for the transmission line. In the bidirectional circularly polarized slot antenna element of this embodiment, instead of being able to provide a grounding surface on the back surface of the dielectric substrate 11, a transmission line grounding surface was provided along the coaxial cable for evaluation. In Figures 6 to 11, the upper row of the figures shows the various states of the circularly polarized slot antenna element shown in Figure 4, and the lower row of the figures shows the various states of the circularly polarized slot antenna element of the present invention shown in Figure 3.

[0034] [Evaluation of S11 characteristics] As shown in the lower part of Figure 7, the circularly polarized slot antenna element of the present invention exhibits good matching near the resonant frequency.

[0035] [Evaluation of frontal gain] In Figure 8, the solid line represents left-hand circular polarization, and the dashed line represents right-hand circular polarization. As shown in the lower part of Figure 8, the circularly polarized slot antenna element of the present invention exhibits good gain near the resonant frequency.

[0036] [Evaluation of front axis ratio] As shown in the lower part of Figure 9, the circularly polarized slot antenna element of the present invention exhibits excellent characteristics, with a level of 2 dB or less near the resonant frequency.

[0037] [Evaluation of radiation patterns in the XZ direction] With the lower left corner 11c of Figure 3 as the origin, the direction toward the lower right corner 11b as the X-axis, the direction toward the upper left corner 11d as the Y-axis, and the direction perpendicular to this XY plane as the Z-axis, the radiation pattern in the XZ direction is shown in Figure 10. As shown in the lower part of Figure 10, there are no side lobes, indicating low directivity, and it shows performance equivalent to that of a conventional circularly polarized slot antenna element.

[0038] [Evaluation of radiation patterns in the YZ direction] Figure 11 shows the radiation pattern in the YZ direction. Compared to conventional circularly polarized slot antenna elements, there is a trend towards improvement in both the back lobe and front beam.

[0039] Thus, comparative tests confirmed that the circularly polarized slot antenna element of the present invention exhibits superior characteristics compared to conventional circularly polarized slot antenna elements. In particular, it was confirmed that the circularly polarized slot antenna element of the present invention is less susceptible to the influence of the transmission line ground surface provided along the coaxial cable.

[0040] In the circularly polarized slot antenna element of the embodiment described above, the resonant frequency is designed to be 9.25 GHz. The frequency characteristics of the axial ratio can be adjusted by adjusting the size of the first diagonal slot sections 16, 16' or the second diagonal slot sections 17, 17'.

[0041] The resonant frequency may be adjusted by adjusting only the size of either the first diagonal slot section 16, 16' or the second diagonal slot section 17, 17'. Alternatively, the ratio of the size of the first diagonal slot section 16, 16' to the size of the second diagonal slot section 17, 17' may be kept constant, so that changing the size of one also changes the size of the other.

[0042] Specifically, in the case of the circularly polarized slot antenna element of this embodiment, the size of the second diagonal slot portions 17, 17' could be adjusted relatively easily by setting it to a fixed value selected from 78-90%, more preferably 82-86%, of the size of the first diagonal slot portions 16, 16'.

[0043] In particular, by making the first diagonal slot sections 16, 16' and / or the second diagonal slot sections 17, 17' square in plan view, as in the circularly polarized slot antenna element of this embodiment shown in Figure 3, the only parameter to change is the length of the first diagonal slot sections 16, 16', making adjustment easier. [Explanation of Symbols]

[0044] 10, 10' circularly polarized slot antenna element 11 Dielectric substrate 11a Upper right corner 11b,11b' Lower right corner 11c,11c' Lower left corner 11d,11d' Upper left corner 11e Side edge 11f mounting area 12 Transmission lines 13 Ground conductor 13a Left conductor section 13b Right side conductor section 14 Left slot antenna section 15 Right-side slot antenna section 16,16' First diagonal slot section 17,17' Second diagonal slot section 18 Printed Wiring Boards 18b Lower right slot section 18c Lower left slot 18d Upper left slot section 18e Expansion slot section 19a First slot antenna section 19b Second slot antenna section 21a First connecting line 21b Second connecting line P,P' power supply point

Claims

1. On one side of a dielectric substrate that is rectangular in plan view, A transmission line extending linearly along the direction perpendicular to the left-right direction of the dielectric substrate, A left conductor section and a right conductor section are arranged along the transmission line to the left and right of the transmission line, respectively, and a ground conductor is connected to the end of the transmission line, The left slot antenna section is located on the left side of the aforementioned transmission line, The right-side slot antenna section is located to the right of the aforementioned transmission line, A first diagonal slot portion is positioned at the corner of the dielectric substrate that is close to either the left slot antenna portion or the right slot antenna portion, A second diagonal slot portion is positioned diagonally to the first diagonal slot portion of the dielectric substrate. A circularly polarized slot antenna element having the following characteristics.

2. The circularly polarized slot antenna element according to claim 1, wherein the left slot antenna portion or the right slot antenna portion adjacent to the first diagonal slot portion is offset by the amount of the first diagonal slot portion.

3. The circularly polarized slot antenna element according to claim 1 or claim 2, wherein the dielectric substrate on which the ground conductor and the transmission line are provided has a conductive layer covering that surface.

4. A method for adjusting a circularly polarized slot antenna element according to claim 1 or claim 2, A method for adjusting a circularly polarized slot antenna element, wherein the frequency characteristics of the axial ratio are adjusted by adjusting the size of the first diagonal slot portion and / or the second diagonal slot portion.

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