JP6341602B2 - Broadband antenna - Google Patents

Description

  The present invention relates to a broadband antenna capable of matching in a wide band.

  In recent years, with the spread of smartphones and the like, attention has been focused on ultra-wideband (UWB) wireless systems that enable high-speed and large-capacity transmission, wireless systems that use white space in the UHF band, cognitive wireless systems, and the like. Since such a communication system is premised on using a very wide band frequency, an antenna having a wide band characteristic is required.

  In addition, in order to accommodate a broadband antenna in a portable communication device, it is important to reduce the size of the antenna itself while providing broadband characteristics. In order to realize a wide band while miniaturizing the antenna, a dielectric is disposed at the end of the ground plane that can be accommodated in the wireless communication device, a folded L-type antenna is provided on one side of the dielectric, and the other side of the dielectric is provided. An antenna device has been proposed in which a broadband monopole antenna is arranged on each surface so that a single antenna device can cover a frequency band corresponding to a plurality of wireless communication systems (see, for example, Patent Document 1). ).

JP 2011-124878 A

  However, the invention described in Patent Document 1 does not consider the downsizing of the ground plane, and the antenna device including the ground plane even if the dielectric body in which the folded L-type antenna and the broadband monopole antenna are arranged is small. As a whole, it cannot be said to be small, and it takes a large occupied space in the portable communication device, so that it cannot be said that sufficient miniaturization can be achieved.

  Accordingly, an object of the present invention is to provide a wideband antenna that can achieve matching in a necessary and sufficient wideband and can reduce the size of the entire antenna including the ground plane.

  In order to solve the above-mentioned problems, the invention according to claim 1 is a wideband antenna in which a ground conductor is provided on one surface of a dielectric substrate and at least a part of a conductive antenna element is provided on the other surface. The ground conductor has a lateral length shorter than the longitudinal length of the dielectric substrate, and the conductor upper edge of the ground conductor is positioned below the upper end of the dielectric substrate. A non-conductive region is formed between the upper end of the dielectric substrate and the upper edge of the conductor, and the antenna element is fed laterally from one end of a strip-like conductor extending in the lateral direction along the upper edge of the conductor. A monopole portion, and a vertical monopole portion extending in a vertical direction perpendicular to the conductor upper edge from the non-feed end of the horizontal monopole portion, on the feed end side of the horizontal monopole portion, By extending the dielectric substrate from the non-conductive area below the upper edge of the conductor, Then, a first horizontal monopole portion where an impedance adjustment region overlapping with the ground conductor is formed, and a second horizontal monopole without a region overlapping with the ground conductor is formed between the first horizontal monopole portion and the vertical monopole portion. Even if the pole portion is formed and the lateral length of the ground conductor is shorter than the extension length of the vertical monopole portion, the matching frequency can be set by appropriately setting the impedance adjustment region of the first horizontal monopole portion. It is characterized by being able to widen the band.

  According to a second aspect of the present invention, in the broadband antenna according to the first aspect, the vertical monopole portion of the antenna element is formed by forming a strip-like conductor on a dielectric substrate in the same manner as the horizontal monopole portion. It is characterized by that.

  The invention according to claim 3 is the broadband antenna according to claim 1, wherein the vertical monopole portion of the antenna element is a rod antenna that is electrically connected to the horizontal monopole portion.

  According to the wideband antenna according to the present invention, even if the lateral length of the ground plane conductor is shorter than the extension length of the vertical monopole portion, by appropriately setting the impedance adjustment region of the first horizontal monopole portion, The matching frequency can be widened, and it is suitable for mounting on a small apparatus such as a portable communication device.

The 1st design example in 1st Embodiment of the wideband antenna which concerns on this invention is shown, (a) is a front view which shows the antenna element arrangement | positioning surface of a wideband antenna, (b) is a right view of a wideband antenna, (c). FIG. 4 is a back view showing a ground plane conductor arrangement surface of the wideband antenna. 1 shows a comparison configuration example in which only a vertical monopole portion of the first design example in the first embodiment is an antenna element, (a) is a front view showing an antenna element arrangement surface of a comparison monopole antenna, and (b) is a front view. FIG. 4C is a right side view of the comparison monopole antenna, and FIG. 5C is a back view showing a ground plane conductor arrangement surface of the comparison monopole broadband antenna. It is a frequency characteristic figure which shows the frequency characteristic of the wideband antenna of the structure shown in FIG. 1, and the frequency characteristic of the contrast monopole antenna without a horizontal monopole part. The 2nd design example in 1st Embodiment of the wideband antenna which concerns on this invention is shown, (a) is a front view which shows the antenna element arrangement | positioning surface of a wideband antenna, (b) is a right view of a wideband antenna, (c). FIG. 4 is a back view showing a ground plane conductor arrangement surface of the wideband antenna. It is a frequency characteristic figure which shows the frequency characteristic of the wideband antenna of a 2nd design example, and the frequency characteristic of the wideband antenna of a 1st design example. It is explanatory drawing of the size change location in the antenna element and ground plane conductor in a broadband antenna. It is a frequency characteristic figure which shows the characteristic change at the time of increasing / decreasing 0.5 mm of lower edges M1B of the 1st horizontal monopole part. It is a frequency characteristic figure which shows the characteristic change at the time of increasing / decreasing 3 mm of upper edges M1U of a 1st horizontal monopole part. It is a frequency characteristic figure which shows the characteristic change at the time of increasing / decreasing 5 mm of the counter feed side edge part (right edge part) M1R of the 1st horizontal monopole part. It is a frequency characteristic figure which shows the characteristic change at the time of increasing / decreasing 0.5 mm of lower edges M2B of the 2nd horizontal monopole part. It is a frequency characteristic figure which shows the characteristic change at the time of increasing / decreasing 3 mm of upper edges M2U of the 2nd horizontal monopole part. It is a frequency characteristic figure which shows the characteristic change at the time of increasing / decreasing 5 mm of the vertical monopole connection side edge part (right side edge part) M2R of a 2nd horizontal monopole part. It is a frequency characteristic figure which shows the characteristic change at the time of increasing / decreasing 5 mm of the outer side edge (right side edge) M3R of a vertical monopole part. It is a frequency characteristic figure which shows the characteristic change at the time of changing the upper edge M3U of a vertical monopole part variously (+ 5mm, -5mm, -10mm, -20mm, -30mm, -40mm, -100mm). It is a frequency characteristic figure which shows the characteristic change at the time of increasing / decreasing 5 mm of lower edges GB of a ground conductor. It is a frequency characteristic figure which shows the characteristic change at the time of making the electric power feeding side edge (left side edge) GL of a grounding conductor increase 2.5 mm. It is a schematic perspective view of the wideband antenna of the 3rd design example which made the extension length of the vertical monopole part in the wideband antenna of the 2nd design example 208.5 mm. It is a directivity characteristic figure of 350MHz and 550MHz in the broadband antenna of the 3rd design example. It is schematic structure explanatory drawing of the wideband antenna which concerns on 2nd Embodiment which used the vertical monopole part as the rod antenna. It is explanatory drawing which shows the modification of the wideband antenna which concerns on 2nd Embodiment.

  Next, an embodiment of a broadband antenna according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a first embodiment of a broadband antenna according to the present invention, which is a first design example with dimensions (unit: mm) shown in the figure. The broadband antenna 1 is provided with an antenna element 3 serving as a monopole antenna with one surface of a dielectric substrate 2 as an antenna element disposition surface and with a ground plane conductor 4 with the other surface as a ground plane conductor disposition surface. .

  The dielectric substrate 2 is Teflon (registered trademark) (εr = 2.17, tan δ = 0.0008) having a thickness h of 0.8 mm, and the thickness t of the copper foil constituting the antenna element 3 and the ground plane conductor 4 The first design example shown in FIG. 1 is the result of designing the dielectric substrate 2, the antenna element 3, and the ground plane conductor 4 so as to be matched in the 0.2 to 0.6 GHz band.

  The ground plane conductor 4 is substantially in contact with the three sides (a pair of side edges and lower side) of the dielectric substrate 2, but the conductor upper edge portion 4a is formed so as not to be in contact with the other side (substrate upper end 2a). 4 is formed with a distance of about 240 mm from the upper end 2a of the substrate, thereby forming a non-conductive region between the upper end 2a of the dielectric substrate 2 and the upper edge 4a of the ground plane conductor 4. The In addition, signal input to and extraction from the antenna element 3 is performed from the ground conductor plate 4 side by the power feeding unit 5.

  The antenna element 3 functions as a monopole antenna. The antenna element 3 is connected to the MSL (microstrip line) part 31 connected to the power feeding part 5 and the conductor upper edge part 4a of the ground plane conductor 4 connected to the upper part of the MSL part 31. A horizontal monopole portion 32 formed in a substantially parallel lateral direction, and a vertical direction perpendicular to the conductor upper edge portion 4a from a non-feeding end (end portion not connected to the MSL portion 31) of the horizontal monopole portion 32 And a vertical monopole portion extending in the direction.

  Further, on the feeding end side of the lateral monopole portion 32, an impedance adjustment region that partially overlaps the ground conductor 4 via the dielectric substrate 2 by extending below the conductor upper edge portion 4a from the non-conductive region. Is formed, and a second horizontal monopole portion 322 that does not overlap with the ground conductor 4 is formed between the first horizontal monopole portion 321 and the vertical monopole portion 33. To do. In the first design example shown in FIG. 1, an impedance adjustment region that overlaps the upper portion of the ground conductor plate 4 by 0.662 mm is formed within the length of 155 mm of the first horizontal monopole portion 321 (FIG. 1A ) The main part is shown enlarged.

  As described above, an impedance adjustment region is provided in a part of the first horizontal monopole portion 321 of the antenna element 3 that functions as a transmission path for signals accompanying transmission and reception of radio waves, and functions as a microstrip line so that the line impedance is appropriately set. The length of the conductor side edge 4b (side length) of the ground conductor 4 is about 80 mm, and the length of the vertical monopole 33 (about 233 mm) is about 1 Even if it is shortened to about / 3, the matching frequency in the wide band antenna 1 can be widened.

  FIG. 3 shows frequency characteristics compared with the monopole antenna 101 (shown in FIG. 2) that does not include the lateral monopole portion 32 that forms the impedance adjustment region, as in the wideband antenna 1 of the present embodiment. This was determined by calculation using the moment method software IE3D of the frequency characteristic of the reflection coefficient S11. In the monopole antenna 101 composed of the monopole element 103 having the same dimensions as the vertical monopole portion 33 of the antenna element 3, the ratio band in which the matching of −10 [dB] is obtained with the reflection coefficient S11 is 0.25 to 0.28. Although it is only about 11% of [GHz], in the wideband antenna 1 of the present embodiment (first design example), the ratio band in which the matching of −10 [dB] is obtained with the reflection coefficient S11 is 0.28 to 0. It can be seen that it is useful to provide the lateral monopole portion 32 that extends to about 70% of .58 [GHz] and forms the impedance adjustment region. Moreover, since the length of the lateral monopole portion 32 in the wideband antenna 1 of the present embodiment (first design example) can be suppressed to about a quarter wavelength of the lowest matching frequency wavelength, it is suitable for downsizing of the entire antenna device. It is.

  The frequency characteristics of the broadband antenna 1 can be variously changed according to the dimensions of each part of the antenna element 3, and it is considered important to set an appropriate impedance adjustment region according to the design value of each part.

  For example, FIG. 4 shows a broadband antenna 1 ′ of a second design example that includes a dielectric substrate 2 ′ and an antenna element 3 ′ whose design dimensions are changed with respect to the broadband antenna 1 of the first design example described above. It is. However, the structure of the MSL part 31, the horizontal monopole part 32, and the vertical monopole part 33 which comprise the antenna element 3 'is the same.

  The result of calculating the frequency characteristics of the wideband antenna 1 of the second design example using HFSS (high frequency three-dimensional electromagnetic field analysis software) is shown by a solid line in FIG. Compared with the frequency characteristic (shown by a broken line in FIG. 5) of the wideband antenna 1 of the first design example described above, no remarkable matching is observed in the vicinity of 0.5 [GHz], but the reflection coefficient S11 is −10. The ratio band that can achieve the [dB] matching is about 70% of 0.25 to 0.55 [GHz].

  In the following, using the dimensions of each part of the wideband antenna 1 'as the second design example as a reference (reference design example), the reflection coefficient S11 when the dimensions of each part in the wideband antenna 1' are changed is represented by the finite element method software HFSS. The frequency characteristic which is the result of calculation using the above is shown. Note that, when using the wideband antennas 1 and 1 ', the direction such as up, down, left, and right is not related. However, in the following description, as shown in FIG. “Upside +” extending to the side, “Bottom +” extending to the opposite side, the side on which the vertical monopole portion 33 of the antenna element 3 is formed (of the dielectric substrate 2) Extending to the right side of the antenna element mounting surface is “Right +”, and extending to the opposite side (left side of the antenna element mounting surface of the dielectric substrate 2) is “Left”. We will call them “+”.

  FIG. 7 is a frequency characteristic diagram showing a characteristic change when the lower edge M1B of the first horizontal monopole portion 321 is increased or decreased by 0.5 mm. When the lower edge M1B of the first horizontal monopole part 321 is extended downward by 0.5 mm and the impedance adjustment region overlapping the ground plane conductor 4 is increased, the matching near 300 MH is deteriorated, and the lower edge of the first horizontal monopole part 321 is reduced. When M1B is retreated upward by 0.5 mm and the impedance adjustment region overlapping the ground plane conductor 4 is reduced, matching other than near 300 MHz is deteriorated. As described above, the matching of the broadband antenna 1 ′ is easily affected by the change in the impedance adjustment region due to the increase or decrease in the direction of the lower edge M1B of the first horizontal monopole portion 321, and a slight overlap state of about 0.512 mm is the broadband. It turns out that it is important to obtain the characteristics.

  FIG. 8 is a frequency characteristic diagram showing a characteristic change when the upper edge M1U of the first horizontal monopole portion 321 is increased or decreased by 3 mm. It can be seen that even if the lower edge M1U of the first horizontal monopole portion 321 is extended upward by about 3 mm or retracted downward, the alignment change is small. In addition, when the lower edge M1U of the first horizontal monopole part 321 is retracted downward by 3 mm and the first horizontal monopole part 321 is narrowed, the matching near 350 MHz is slightly improved, but the matching near 250 MHz is deteriorated. It becomes a narrow band.

  FIG. 9 is a frequency characteristic diagram showing a characteristic change when the right end M1R of the first horizontal monopole part 321 is increased or decreased by 5 mm. If the right end M1R of the first horizontal monopole part 321 is extended to the right by 5 mm, the matching near 550 MHz is improved, but the matching near 350 MHz is deteriorated and the band becomes narrow. Further, when the right end M1R of the first horizontal monopole part 321 is retracted to the left by 5 mm, the matching in the vicinity of 350 MHz is improved, but the matching in the vicinity of 260 MHz and 550 MHz is deteriorated, resulting in a narrow band.

  FIG. 10 is a frequency characteristic diagram showing a characteristic change when the lower edge M2B of the second horizontal monopole portion 322 is increased or decreased by 0.5 mm. Even if the lower edge M2B of the second horizontal monopole portion 322 is extended downward by about 0.5 mm or retracted upward, the influence on the matching characteristics is small, and the lower edge M1B of the first horizontal monopole portion 321 is changed. There is no dramatic change like the case. When the lower edge M2B of the second horizontal monopole portion 322 is extended downward by 0.5 mm, the alignment around 400 MHz is slightly deteriorated, and when the lower edge M2B of the second horizontal monopole portion is retracted upward by 0.5 mm, it is 270 MHz. The matching in the vicinity is slightly degraded.

  FIG. 11 is a frequency characteristic diagram showing a characteristic change when the upper edge M2U of the second horizontal monopole portion 322 is increased or decreased by 3 mm. When the upper edge M2U of the second horizontal monopole portion 322 is extended upward by 3 mm, matching near 300 MHz is improved, but matching near 400 MHz is deteriorated. Conversely, when the upper edge M2U of the second horizontal monopole portion 322 is retracted downward by 3 mm, matching near 300 MHz is deteriorated.

  FIG. 12 is a frequency characteristic diagram showing a characteristic change when the right end M2R of the second horizontal monopole part 322 is increased or decreased by 5 mm. Even if the right end M2R of the second horizontal monopole portion 322 is extended to the right by about 5 mm or moved backward to the left, there is no significant change in the matching characteristics. If the right end M2R of the second horizontal monopole portion 322 is extended to the right by 5 mm, the matching near 500 MHz is improved, but the matching near 350 MHz is deteriorated, and the right end M2R of the second horizontal monopole portion 322 is reduced. When retracted to the left by 5 mm, matching near 500 MHz is improved, but matching near 350 MHz is improved.

  FIG. 13 is a frequency characteristic diagram showing a characteristic change when the right end edge M3R of the vertical monopole portion 33 is increased or decreased by 5 mm. If the right edge M3R of the vertical monopole portion 33 is extended to the right by 5 mm, the matching near 350 MHz is improved, but the matching near 500 MHz is deteriorated. Further, when the right edge M3R of the vertical monopole portion 33 is retracted to the left by 5 mm, the matching in the vicinity of 350 MHz is deteriorated.

  FIG. 14 shows a frequency characteristic indicating a characteristic change when the upper edge M3U of the vertical monopole portion 33 is changed variously (+5 mm, −5 mm, −10 mm, −20 mm, −30 mm, −40 mm, −100 mm). FIG. As the upper edge M3U of the vertical monopole portion 33 is retracted downward and the extension length of the vertical monopole portion 33 is shortened, there is a tendency that both the lowest frequency and the highest frequency that can be matched become higher. Moreover, even if the upper edge M3U of the vertical monopole portion 33 is retracted downward by about 30 mm, the broadband characteristics can be substantially maintained. In particular, when the upper edge M3U of the vertical monopole portion 33 is retracted 20 mm downward, resonance is observed at 350 MHz and 550 MHz, the overall matching characteristics are good, and the extension length of the vertical monopole portion 33 is 208.mm. 5 mm is effective in reducing the size of the entire antenna. On the other hand, if the upper edge M3U of the vertical monopole portion 33 is retracted 40 mm or 100 mm downward and the extension length of the vertical monopole portion 33 is made too short, the broadband characteristics cannot be maintained.

  FIG. 15 is a frequency characteristic diagram showing a characteristic change when the lower edge GB of the ground conductor 4 is increased or decreased downward by 5 mm. If the lower edge GB of the ground conductor 4 is extended 5 mm downward to increase the lateral length of the ground plane conductor 4, the alignment is improved, but conversely, the lower edge GB of the ground conductor 4 is retracted upward 5 mm to It can be seen that the alignment is degraded when the lateral length is shortened.

  FIG. 16 is a frequency characteristic diagram showing a characteristic change when the left edge GL of the ground conductor 4 is increased to the left by 2.5 mm. Even if the left edge GL of the ground plane conductor 4 is extended to the left by 2.5 mm, there is no significant change in matching, but the matching in the vicinity of 350 MHz is slightly improved.

  As described above, from the change in the matching characteristics when the dimensions of each part are changed on the basis of the design dimension of the wideband antenna 1 ′ as the second design example, in particular, the lower edge M1B of the first horizontal monopole part 321 is changed. It is important to appropriately set the dimension (impedance adjustment region overlapping the ground plane conductor 4), and the upper edge M3U of the vertical monopole portion 33 is retracted downward so that the extension length of the vertical monopole portion 33 is increased. It was found that even if it was shortened to some extent, the broadband property could be maintained.

  FIG. 17 is a schematic perspective view of the wideband antenna 1 ″ of the third design example in which the extension length of the vertical monopole portion 33 in the wideband antenna 1 ′ of the second design example is 208.5 mm. FIG. 18 shows the directivity characteristics of 350 MHz and 550 MHz in the wideband antenna 1 ″ of the three design examples. As can be seen from this directivity, horizontal polarization and vertical polarization are mixed, which can be understood as radiation from the horizontal monopole portion 32 and the vertical monopole portion 33 of the antenna element 3. Further, the change in directivity depending on the frequency is small, and a nearly omnidirectional vertical polarization in the horizontal plane or a nearly omnidirectional horizontal polarization in the vertical plane of φ = 90 ° can be realized.

  In the broadband antennas 1, 1 ′, 1 ″ of the first embodiment described above, all of the antenna elements 3 (MSL part 31, horizontal monopole part 32, vertical monopole part 33) are arranged on the dielectric substrate 2. Although the antenna element 3 is formed on the surface, a part of the antenna element 3 may not be provided on the dielectric substrate 2.

  In the broadband antenna 11 of the second embodiment shown in FIG. 19, the ground plane conductor 14 is provided on one surface of the dielectric substrate 12, and the MSL portion 131 of the antenna element 13 and the first and second horizontal monopole portions are provided on the other surface. The structure of providing 1321 and 1322 and connecting the power feeding unit 15 to the MSL unit 131 is the same as that of the broadband antenna 1, 1 ′, 1 ″ of the first embodiment, but, for example, via the detachable connector unit 16 The rod antenna 133 that is electrically connected to the second horizontal monopole portion 1321 is a vertical monopole portion.

  In the broadband antenna 11 according to the second embodiment, the non-conductive region for forming the vertical monopole portion is not necessary, and the ground plane conductor 14 and the first and second horizontal monopole portions 1321 and 1322 of the antenna element 13 are provided. Therefore, the dielectric substrate 12 having a necessary and sufficient area is sufficient. Therefore, if only the rod antenna 133 is taken out of the apparatus housing and the dielectric substrate 12 and the like are housed inside the apparatus housing, the area occupied by the broadband antenna 11 in the apparatus housing becomes very small. It is also effective for downsizing the entire device casing.

  FIG. 20 shows a broadband antenna 11 ′ which is a modification of the broadband antenna 11 according to the second embodiment described above, and has a structure in which a dielectric substrate 12 and the like are housed in an exterior case 17. The broadband antenna 11 ′ is used, for example, by removing the detachable rod antenna 22 via the connector portion 21 of the apparatus housing 20 and attaching it to the connector portion 21.

  Specifically, a connection terminal (not shown) that can be attached to and detached from the connector portion 21 of the apparatus housing 20 is provided below the broadband antenna 11 ′ (for example, directly below the connector portion 16), and the MSL in the antenna element 13 ′. Since the portion 131 ′ is extended to the connection terminal, when the broadband antenna 11 ′ is connected to the connector portion 21 of the device housing 20, it is connected to the feeding line and the ground line of the terminal device, and the broadband antenna 11. 'Functions as an external antenna capable of realizing a wide band. In addition, you may make it utilize as the rod antenna 133 of antenna element 13 'by connecting the rod antenna 22 removed from the apparatus housing | casing 20 to the connector part 16 of broadband antenna 11'.

  The broadband antenna according to the present invention has been described based on some embodiments. However, the present invention is not limited to only these embodiments, and the configuration described in the claims is not changed. All possible wideband antennas are included as a scope of rights.

1 Broadband antenna (first embodiment)
2 Dielectric substrate 2a Upper end of substrate 3 Antenna element 31 MSL part 32 Horizontal monopole part 321 First horizontal monopole part 322 Second horizontal monopole part 33 Vertical monopole part 4 Ground plane conductor 4a Conductor upper edge part 4b Conductor side edge part 5 Feeding points

Claims (3)

A broadband antenna having a ground conductor on one surface of a dielectric substrate and at least a part of a conductive antenna element on the other surface,
The ground conductor has a lateral length shorter than the longitudinal length of the dielectric substrate, and the conductor upper edge of the ground conductor is positioned below the upper end of the dielectric substrate, so that the dielectric substrate Forming a non-conductive region between the top edge and the top edge of the conductor;
The antenna element includes a lateral monopole portion fed from one end of a strip-like conductor extending in a lateral direction along the conductor upper edge portion, and a non-feeding end of the transverse monopole portion to the conductor upper edge portion. A vertical monopole portion extending in the orthogonal vertical direction,
A first horizontal monopole portion where an impedance adjustment region is formed on the feeding end side of the horizontal monopole portion so as to extend below the upper edge portion of the conductor from the non-conductive region and overlap with the ground conductor via the dielectric substrate. Forming a second horizontal monopole portion that does not overlap with the ground conductor between the first horizontal monopole portion and the vertical monopole portion,
Even if the lateral length of the ground conductor is shorter than the extension length of the vertical monopole portion, the matching frequency can be broadened by appropriately setting the impedance adjustment region of the first horizontal monopole portion. A broadband antenna characterized by that.   The wide band antenna according to claim 1, wherein the vertical monopole portion of the antenna element is formed by forming a strip-like conductor on a dielectric substrate in the same manner as the horizontal monopole portion.   The broadband antenna according to claim 1, wherein the vertical monopole portion of the antenna element is a rod antenna that is electrically connected to the horizontal monopole portion.

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