Microstrip Antenna

Abstract

To provide a microstrip antenna capable of making high radiation efficiency compatible with a large attenuation amount of a filter.SOLUTION: A microstrip antenna 10 comprises: a ground conductor 11; a patch conductor 20 opposed to the ground conductor 11 and including a first portion 21, a second portion 22 and a third portion 23; an insulation layer 12 formed between the ground conductor 11 and the patch conductor 20; and a distribution constant filter 13 connected to the first portion 21 and formed from a first conductor pattern. The first portion 21 is formed so as to extend between the second portion 22 and the third portion 23. In a direction which is vertical to an extension direction of the first portion 21, the first portion 21 is shorter than the second portion 22 and the third portion 23. The distribution constant filter 13 passes a fundamental wave, which is propagated in the first portion 21 in the extension direction of the first portion 21, and attenuates an unwanted wave which is propagated in the first portion 21 in the extension direction of the first portion 21.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a microstrip antenna, particularly for use in wireless power transmission. [Background technology]

[0002] Transmitters used in wireless power transmission emit higher-power radio waves than transmitters used in wireless communications. Therefore, when a transmitter used in wireless power transmission emits radio waves with frequencies outside the frequency band used for wireless power transmission, radio wave interference becomes a particular problem. Therefore, filters that are installed in transmitters used in wireless power transmission to reduce the radiation of radio waves with frequencies outside the frequency band used for wireless power transmission and thus reduce radio wave interference are required to have better characteristics, i.e., greater attenuation.

[0003] In conventional transmitters, increasing the number of filter stages inserted between the amplifier and the antenna increases the circuit area, thereby increasing the filter attenuation. However, there are many limitations on the circuit area of ​​a transmitter.

[0004] On the other hand, since the transmitter antenna is allowed to occupy a relatively large space to achieve the required antenna gain, adding a filter function to the antenna allows for the miniaturization of the filter inserted between the amplifier and the antenna, thereby enabling more efficient use of the volume within the transmitter.

[0005] Non-Patent Document 1 discloses a circular microstrip antenna with a patch having a slit along the fundamental mode current line. In this microstrip antenna, the patch surface current distribution of higher modes that occur near the harmonic frequencies is disturbed, which suppresses the occurrence of those higher modes and lowers the resonant frequency of those higher modes, thereby suppressing harmonic radiation. In this way, a filter function is added to this microstrip antenna.

[0006] Furthermore, Patent Document 1 discloses a microstrip antenna that includes an H-shaped microstrip patch and has high radiation efficiency. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6764163 [Non-patent literature]

[0008] [Non-Patent Document 1] Shahriar et al., "Considerations on Circular Microstrip Antennas with Slits Used as Rectenna Elements," IEICE Transactions on Electronics, Information and Communication Engineers, Japan, February 2001, Vol. J84-B, No. 2, pp. 244-253 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the microstrip antenna disclosed in Non-Patent Document 1, in order to obtain a large filter attenuation, it is necessary to increase the unloaded Q of the radiating element as a resonator and realize steep resonance characteristics. However, if the dielectric substrate of the microstrip antenna is made thin in order to increase the unloaded Q, the radiation efficiency decreases.

[0010] For example, if the fundamental frequency is in the 2.45 GHz band, a return loss of 0.18 dB, or in other words, a filter attenuation of 14 dB, can be obtained at the second harmonic frequency. However, in this case, the thickness of the dielectric substrate is 0.006 λ, where λ is the wavelength of the fundamental wave, and the unloaded Q is 107, resulting in a radiation efficiency of approximately 58%.

[0011] Furthermore, the microstrip antenna disclosed in Patent Document 1 has high radiation efficiency, but does not have a very good filtering function.

[0012] An object of the present invention is to provide a microstrip antenna that can achieve both high radiation efficiency and large filter attenuation. [Means for solving the problem]

[0013] The microstrip antenna of the present invention comprises a ground conductor, a patch conductor facing the ground conductor and having a first portion, a second portion, and a third portion, a first insulating layer formed between the ground conductor and the patch conductor, and a distributed constant filter connected to the first portion and formed of a first conductor pattern, wherein the first portion is formed to extend between the second portion and the third portion, and the first portion is shorter than the second portion and the third portion in a direction perpendicular to the extension direction of the first portion, and the distributed constant filter passes a fundamental wave propagating through the first portion in the extension direction of the first portion and attenuates unwanted waves propagating through the first portion in the extension direction of the first portion. [Effects of the Invention]

[0014] According to the present invention, a microstrip antenna can be realized that can achieve both high radiation efficiency and large filter attenuation. [Brief explanation of the drawings]

[0015] [Figure 1] Fig. 1(A) is a plan view of a microstrip antenna 10 according to a first embodiment of the present invention, and Fig. 1(B) is a cross-sectional view of the microstrip antenna 10 taken along line AA. [Figure 2] FIG. 2 is a graph illustrating the frequency characteristics of the return loss of the microstrip antenna 10 and the microstrip of the first comparative example. [Figure 3] FIG. 3 is a graph illustrating the second harmonic attenuation and radiation efficiency of the microstrip antenna 10, the microstrip antenna of the first comparative example, and the microstrip antenna of the second comparative example. [Figure 4]Fig. 4(A) is a plan view of a microstrip antenna 30 according to a second embodiment of the present invention, and Fig. 4(B) is a BB cross-sectional view of the microstrip antenna 30. [Figure 5] Fig. 5(A) is a plan view of a microstrip antenna 50 according to a third embodiment of the present invention, and Fig. 5(B) is a cross-sectional view of the microstrip antenna 50 taken along line CC. [Figure 6] FIG. 6 is a plan view of the microstrip antenna 50 without the patch conductor 60 shown. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, several embodiments of the present invention will be described. Each embodiment is an example, and partial substitution or combination of the configurations shown in different embodiments is possible. In each embodiment, differences from the previous embodiments will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[0017] First Embodiment FIG. 1(A) is a plan view of a microstrip antenna 10 according to a first embodiment of the present invention. FIG. 1(B) is an AA cross-sectional view of the microstrip antenna 10. The microstrip antenna 10 includes a ground conductor 11, a patch conductor 20, an insulating layer 12, and a distributed constant filter 13. The patch conductor 20 has a first portion 21, a second portion 22, a third portion 23, and a plurality of stubs 24. The stubs 24 are an example of a "first conductor pattern" in the present invention. The insulating layer 12 is an example of a "first insulating layer" in the present invention.

[0018] The patch conductor 20 is disposed facing the ground conductor 11. As a result, the entire surface of the patch conductor 20 faces the ground conductor 11. The patch conductor 20 is fixed to the ground conductor 11 at a distance by, for example, a spacer (not shown). The insulating layer 12 is an air layer and is formed between the ground conductor 11 and the patch conductor 20. The first portion 21 of the patch conductor 20 is formed to extend in the x-axis direction between the second portion 22 of the patch conductor 20 and the third portion 23 of the patch conductor 20. In the y-axis direction perpendicular to the x-axis direction, the first portion 21 is shorter than the second portion 22 and the third portion 23. The distributed constant filter 13 is formed by a stub 24 and is connected to the first portion 21. The distributed constant filter 13 passes a fundamental wave propagating through the first portion 21 in the extension direction of the first portion 21 and attenuates predetermined harmonics propagating through the first portion 21 in the extension direction of the first portion 21. Harmonics are an example of "unwanted waves" in the present invention.

[0019] The insulating layer 12 may be formed of an insulating material instead of an air layer.

[0020] Furthermore, the distributed constant filter 13 may attenuate second-order harmonics or higher-order harmonics.

[0021] In a modified example, the distributed constant filter 13 may attenuate both the second and third harmonics, for example.

[0022] In a modified example, the distributed constant filter 13 may attenuate spurious components other than harmonics.

[0023] The patch conductor 20 has a rectangular shape, i.e., a substantially H-shaped shape, in which a notch is cut from the center of each of the opposing sides of the rectangle toward the center of the rectangle. The first portion 21 has an elongated shape and extends in the x-axis direction. The second portion 22 and the third portion 23 each have a rectangular shape, with two sides parallel to the x-axis direction and two sides parallel to the y-axis direction.

[0024] The length L1 of the first portion 21 in the x-axis direction is λg1 / 2. The length L2 of the second portion 22 in the x-axis direction is λg2 / 2. The length L3 of the third portion 23 in the x-axis direction is λg3 / 2. The length L4 of the second portion 22 and the third portion 23 in the y-axis direction is λg4 / 2 or more. Here, λg1, λg2, and λg3 are the effective wavelengths when the fundamental wave propagates through the first portion 21, the second portion 22, and the third portion 23, respectively, in the x-axis direction. λg4 is the effective wavelength when the fundamental wave propagates through the second portion 22 or the third portion 23 in the y-axis direction.

[0025] The dimensions of the first portion 21, the second portion 22, and the third portion 23 may be slightly different from the above values.

[0026] The second portion 22 and the third portion 23 have a slit 25 and a slit 26, respectively. The slit 26 is formed near the feed point 15.

[0027] The slits 25 and 26 are not essential and may not be formed.

[0028] The patch conductor 20 is fed by a feed pin 14. A feed point 15 is located, for example, on a third portion 23 of the patch conductor 20.

[0029] When power is supplied, a current flows in the patch conductor 20 in the x-axis direction. The current flowing in the first portion 21 has an opposite phase to the current flowing in the second portion 22 and the third portion 23. As a result, the first portion 21 does not contribute to the main lobe but causes side lobes. Therefore, the first portion 21 does not contribute to radiation and acts as a transmission line. The second portion 22 and the third portion 23 act as radiating elements.

[0030] In the microstrip antenna 10, the length in the y-axis direction of the central portion of the patch conductor in the x-axis direction (the portion corresponding to the first portion 21) is shorter than that of a rectangular microstrip antenna without a notch in the patch conductor. This means that the central portion has a higher characteristic impedance and is less likely to allow current to flow. This results in a lower side lobe level.

[0031] Furthermore, the microstrip antenna 10 has the second portion 22 and the third portion 23 that function as radiating elements, but does not require a power divider as is provided in an array antenna. Therefore, compared to an array antenna that has rectangular microstrip antennas as antenna elements, the microstrip antenna 10 does not suffer from the loss that occurs in a power divider and can achieve high radiation efficiency.

[0032] The stub 24 is formed so as to branch off from the first portion 21 extending in the x-axis direction. The stub 24 has an open end and a length of 1 / 4 of the effective wavelength of the harmonic. In other words, the stub 24 is a 1 / 4-wavelength open stub for the harmonic. As can be seen from this, the distributed constant filter 13 is connected in series to the first portion 21, which acts as a transmission line, and is a band-stop filter that passes the fundamental wave and blocks the harmonics. The distributed constant filter 13 is also a resonator that resonates at the frequency of the harmonic.

[0033] The distributed constant filter 13 may be a low-pass filter or a band-pass filter configured with a distributed constant line, or may be a high-pass filter configured with a distributed constant line when attenuating spurious signals at frequencies lower than the fundamental wave.

[0034] FIG. 2 is a graph illustrating the frequency characteristics of return loss of the microstrip antenna 10 and the microstrip antenna of the first comparative example. The microstrip antenna of the first comparative example is configured similarly to the microstrip antenna 10, except that it does not have the distributed constant filter 13. The graph shown in FIG. 2 is the calculation result of an electromagnetic field simulation. Furthermore, f0 shown in FIG. 2 is the frequency of the fundamental wave. As shown in FIG. 2, the microstrip antenna 10 has a smaller return loss at the second harmonic frequency 2f0 than the microstrip antenna of the first comparative example.

[0035] FIG. 3 is a graph illustrating the second-harmonic attenuation and radiation efficiency of the microstrip antenna 10, the microstrip antenna of the first comparative example, and the microstrip antenna of the second comparative example. The microstrip antenna of the second comparative example, as shown in Non-Patent Document 1, has a circular patch with a slit along the fundamental mode current line. As shown in FIG. 3, the microstrip antenna 10 has a larger second-harmonic attenuation than the microstrip antennas of the first and second comparative examples, and a higher radiation efficiency than the microstrip antenna of the second comparative example. In this way, the microstrip antenna 10 can achieve both a large second-harmonic attenuation and a high radiation efficiency.

[0036] According to the first embodiment, the distributed constant filter 13, which attenuates unwanted waves such as harmonics, is connected to the first portion 21 of the patch conductor 20, which does not contribute to radiation and functions as a transmission line. Therefore, radiation from the antenna is not affected by the distributed constant filter 13, and unwanted waves are attenuated throughout the entire patch conductor 20, which functions as a resonator. This prevents a decrease in radiation efficiency and improves the filtering function of the antenna. Therefore, a microstrip antenna can be realized that achieves both high radiation efficiency and large filter attenuation.

[0037] Second Embodiment Fig. 4(A) is a plan view of a microstrip antenna 30 according to a second embodiment of the present invention. Fig. 4(B) is a BB cross-sectional view of the microstrip antenna 30. The microstrip antenna 30 differs from the microstrip antenna 10 according to the first embodiment in the following respects. That is, the microstrip antenna 30 includes an insulating layer 32 instead of the insulating layer 12, and a patch conductor 40 instead of the patch conductor 20.

[0038] The thickness h1 of the insulating layer 32 facing the first portion 21 and the stub 24 of the patch conductor 40 is thinner than the thickness h2 of the insulating layer 32 facing the second portion 22 and the third portion 23 of the patch conductor 40. In other words, the distance between the first portion 21 and the stub 24 of the patch conductor 40 and the ground conductor 11 is shorter than the distance between the second portion 22 and the third portion 23 of the patch conductor 40 and the ground conductor 11.

[0039] The patch conductor 40 is produced by bending a conductive plate using, for example, sheet metal processing.

[0040] The thickness h1 of the insulating layer 32 is selected so as to obtain a large filter attenuation. More specifically, the thickness h1 of the insulating layer 32 should be as thin as possible while satisfying design constraints. The thickness h2 of the insulating layer 32 is selected so as to obtain a high radiation efficiency. For example, when the operating frequency is in the 5 GHz band, the appropriate thickness h1 of the insulating layer 32 is approximately 0.4 mm, and the appropriate thickness h2 of the insulating layer 32 is approximately 1.5 mm.

[0041] According to the second embodiment, the insulating layer 32 is set thin where the distributed constant filter 13 is formed. This increases the unloaded Q of the distributed constant filter 13 as a resonator. This results in the distributed constant filter 13 having steeper resonance characteristics, i.e., steeper filter characteristics. This allows for greater filter attenuation.

[0042] Furthermore, the thickness of the insulating layer 32 is set individually at the location where the second portion 22 and the third portion 23 that function as radiating elements are formed and at the location where the distributed constant filter 13 is formed, so that the radiation efficiency does not decrease.

[0043] The second embodiment is particularly effective in the frequency band where the difference in the appropriate thickness of the insulating layer 32 becomes significant, specifically, in the frequency band below 5 GHz where the difference in the appropriate thickness of the insulating layer 32 becomes approximately 1 mm or more.

[0044] Third Embodiment Fig. 5(A) is a plan view of a microstrip antenna 50 according to a third embodiment of the present invention. Fig. 5(B) is a CC cross-sectional view of the microstrip antenna 50. Fig. 6 is a plan view of the microstrip antenna 50 in which the patch conductor 60 is not shown.

[0045] The microstrip antenna 50 differs from the microstrip antenna 30 according to the second embodiment in the following respects: the microstrip antenna 50 includes a patch conductor 60 instead of the patch conductor 40, an insulating layer 52 instead of the insulating layer 32, and a distributed constant filter 53 instead of the distributed constant filter 13. Furthermore, the microstrip antenna 50 includes an insulating substrate 56 and a conductor pattern 58. The conductor pattern 58 is an example of the "second conductor pattern" of the present invention.

[0046] The patch conductor 60 has a first portion 61 instead of the first portion 21. The first portion 61 has a width that varies with position in the x-axis direction. The ground conductor 11 is formed on one surface of the insulator substrate 56. The conductor pattern 58 is formed on the other surface of the insulator substrate 56. The conductor pattern 58 extends in the x-axis direction and has a width that varies with position in the x-axis direction. The conductor pattern 58 is formed, for example, by patterning copper foil on a printed circuit board using an etching technique. The first portion 61 of the patch conductor 60 is disposed on the conductor pattern 58 and connected to the conductor pattern 58 by soldering or the like. The distributed constant filter 53 is configured as a stepped impedance low-pass filter by the first portion 61 of the patch conductor 60 and the conductor pattern 58, which are connected to each other. The distributed constant filter 53 passes the fundamental wave and attenuates high-band spurious signals.

[0047] Although the distributed constant filter 53 is configured with a microstrip line, the distributed constant filter 53 may be configured with a coplanar waveguide or other distributed constant line.

[0048] The insulating layer 52 facing the first portion 61 of the patch conductor 60 and the portion formed by the conductor pattern 58 is composed of an insulating substrate 56. The insulating layer 52 facing the second portion 22 and the third portion 23 of the patch conductor 60 is composed of the insulating substrate 56 and an air layer 57. The air layer 57 is an example of a "second insulating layer" in the present invention. The thickness h4 of the air layer 57 is equal to or greater than the thickness h3 of the insulating substrate 56.

[0049] The insulating layer 52 may have a layer made of an insulating material instead of the air layer 57.

[0050] When the frequency band used is a high frequency band such as the microwave band, the conductor pattern of the distributed constant filter becomes very fine, making it difficult to form the conductor pattern integrally with the patch conductor. According to the third embodiment, the conductor pattern 58 is formed on an insulating substrate 56. This allows the conductor pattern 58 to be formed very finely by etching. This makes it easy to manufacture the distributed constant filter 53 even when the frequency band used is a high frequency band.

[0051] Furthermore, in the area where the second portion 22 and the third portion 23 that function as radiating elements are formed, the insulating layer 52 is made up of an insulating substrate 56 and an insulating layer such as an air layer that is equal to or thicker than the insulating substrate 56. Therefore, even if the conductor pattern of the distributed constant filter 53 is formed on the insulating substrate 56, the radiation efficiency of the second portion 22 and the third portion 23 that function as radiating elements can be set high.

[0052] Therefore, even when the frequency band used is a high frequency band, a microstrip antenna having an excellent filtering function can be realized.

[0053] Furthermore, the patch conductor 60 is fixed to the conductor pattern 58 by soldering or the like, so a structure for holding the patch conductor 60, such as a spacer, is not required. [Explanation of symbols]

[0054] 10, 30, 50...microstrip antenna 11...Grounding conductor 12, 32, 52...insulating layer 13,53...Distributed constant filter 14...Power supply pin 15...Power supply point 20, 40, 60... patch conductor 21,61…Part 1 22…Second part 23...Third part 24...Stub 25,26...Slit 56...Insulating substrate 57...Air layer 58...Conductor pattern

Claims

1. a ground conductor; a patch conductor facing the ground conductor and having a first portion, a second portion, and a third portion; a first insulating layer formed between the ground conductor and the patch conductor; a distributed constant filter connected to the first portion and formed by a first conductor pattern, the first portion is configured to extend between the second portion and the third portion; the first portion is shorter than the second portion and the third portion in a direction perpendicular to the extension direction of the first portion; a length of the first portion in the extension direction of the first portion is substantially equal to λg 1 / 2, λg 1 being an effective wavelength of the fundamental wave propagating through the first portion in the extension direction of the first portion; A microstrip antenna, wherein the distributed constant filter passes the fundamental wave propagating through the first portion in the extension direction of the first portion and attenuates unwanted waves propagating through the first portion in the extension direction of the first portion.

2. 2. The microstrip antenna according to claim 1, wherein the distributed constant filter is formed of an open stub having a length equal to 1 / 4 of the effective wavelength of the unwanted wave.

3. 3. The microstrip antenna according to claim 1, wherein the distributed constant filter includes a resonator that resonates at a frequency of the unwanted waves.

4. 4. The microstrip antenna according to claim 1, wherein the first insulating layer facing the first conductor pattern is thinner than the first insulating layer facing the second portion and the third portion.

5. an insulating substrate; a second conductor pattern formed on the insulating substrate and including at least a portion of the first conductor pattern; the ground conductor is formed on one surface of the insulating substrate, and the second conductor pattern is formed on the other surface of the insulating substrate; the first portion is disposed on the second conductor pattern; 5. The microstrip antenna according to claim 1, wherein the first insulating layer facing the second portion and the third portion is composed of the insulating substrate and a second insulating layer having a thickness equal to or greater than that of the insulating substrate.

6. The microstrip antenna according to claim 5 , wherein the second insulating layer is an air layer.

7. The first portion extends in a first direction; the second portion and the third portion have a rectangular shape, and the rectangle has two sides parallel to the first direction and two sides parallel to a second direction perpendicular to the first direction; a length of the second portion in the first direction is substantially equal to λg 2 / 2, where λg 2 is an effective wavelength of the fundamental wave when the fundamental wave propagates through the second portion in the first direction; 7. The microstrip antenna according to claim 1, wherein the length of the third portion in the first direction is substantially equal to λg3 / 2, where λg3 is the effective wavelength of the fundamental wave when the fundamental wave propagates through the third portion in the first direction.

8. A microstrip antenna as described in any one of claims 1 to 7 configured for use at a single frequency.

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