JP2640012B2 - Planar antenna - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar antenna, and more particularly to an antenna using a microstrip element such as a microstrip line.

[Prior Art] The present applicant has previously proposed a planar antenna as shown in FIG. This is because the ground conductor 2 covers the entire back surface of the dielectric substrate 1.
And a so-called microstrip line antenna in which crank-shaped microstrip lines 31 to 38 are provided on the surface of the dielectric substrate 1. In the so-called microstrip line antenna, the planar antenna is provided above the dielectric substrate 1 in which the microstrip lines 31 to 38 are provided. The conductors 81 and 82 having a length that resonates with radio waves at the operating frequency are placed in the polyester film 7 separated by a distance corresponding to about a half wavelength of the operating frequency or an integer multiple thereof at the frequency to be transmitted or received at A large number of strip lines are arranged close to each other in the extension direction X and the Y direction orthogonal to the strip line. 6 is a conductor
A dielectric plate made of, for example, foamed resin or the like provided to maintain the above-mentioned interval between 81, 82 and the microstrip lines 31 to 38, and the conductors 81, 82 are actually, for example, thin films of polyester resin. It is formed by vapor deposition of metal or printing with conductive ink on a dielectric film having high radio wave transmittance. The conductors 81 and 82 are attached by sticking this film on the dielectric plate 6. .

In such a planar antenna, when a radio wave of a use frequency is radiated from the microstrip lines 31 to 38, it reaches the conductors 81 and 82. At this time, the conductors 81 and 82 have a length that resonates with the radio wave of the operating frequency.
A large resonance current flows through 1, 82, and the gain can be improved.

[Problems to be Solved by the Invention] However, in the above-mentioned planar antenna, the conductors 81 and 82 are rectangular and extend only in the X and Y directions. , 82 have the largest resonance, but the resonance current is smaller for an electric field in the middle direction between the X and Y directions. The radio waves radiated from the microstrip lines 31 to 38 are not only radiated from the linear portions but also considerably radiated from the truncated corners D. It is difficult to analyze the radiated electric field from the corner D, but it is considered that there is a radiated electric field in a direction different from the X and Y directions. Therefore, in the above planar antenna, the magnitude and phase of the resonance current differ from the radiation in the X and Y directions with respect to the radiation from the corner D, so that the antenna is originally circularly polarized as shown in FIG. The axial ratio of the microstrip line antenna is such that the maximum amplitude direction is oblique to the X and Y directions as shown in FIG. It is difficult to correct such an axial ratio with a crank-type microstrip line antenna, and the gain of circularly polarized waves cannot be improved.

An object of the present invention is to provide a planar antenna having improved gain by improving the axial ratio.

Means for Solving the Problems In order to achieve the above object, the present invention provides a microstrip antenna formed to radiate radio waves of a use frequency from a microstrip element provided on a substrate, From the surface of the substrate on which the microstrip element is provided, about 1 / (λ) of the wavelength λ of the working frequency.
2 or on a plane at a distance of an integral multiple thereof, at a distance of about 1 / 2λ in the first direction and about 1 / 4λ in a second direction perpendicular to the first direction. A plurality of circular elements having a diameter of about 0.3λ to 0.37λ, which are aligned and spaced apart from each other.

The number of planes on which a plurality of circular elements are provided may be one, but a plurality of such elements may be provided in the vertical direction. In this case, the interval between these planes is λ / 2 or an integral multiple thereof.

[Operation] According to the present invention, the radio wave of the use frequency radiated from the microstrip element reaches the aligned circular element. These circular elements resonate with the arriving radio waves.
Moreover, since the circular elements are regularly arranged, they resonate in the same pattern regardless of the direction in which radio waves arrive.

Embodiment FIG. 1 to FIG. 8 show a first embodiment. This embodiment also has a microstrip line antenna similar to the above-mentioned conventional one. In this microstrip antenna, as shown in FIG.
1.7, a ground conductor 2 made of aluminum is laminated on the back surface of a dielectric substrate 1 made of foamed polyethylene having a length of 20 cm and a width of 14 cm, and a micro-structure having a crank-shaped pattern as shown in FIG. The strip lines 31 to 38 are formed of, for example, copper foil. As an example, substrate 1,
The thicknesses of the ground conductor 2 and the microstrip lines 31 to 38 are 0.8 mm, 1 mm, and 0.03 mm, respectively.

As shown in FIG.
Assuming that the extension direction of 38 is X, the direction perpendicular thereto is Y, and the direction perpendicular to substrate 1 is Z, microstrip line 31
Numerals 38 through 38 alternately include relatively long portions A in the X direction and relatively short portions B in the X direction, and portions A and B are connected by a portion C in the Y direction. Each of the microstrip lines 31 to 38 is provided with four such crank-shaped parts. As an example,
The frequency used is 12 GHz, and radio waves are radiated in the W direction inclined 28 degrees from the Z direction to the X direction. In other words, in the case of the side-looking type directional characteristics, the dimensions of each part are as follows. The length of the center is 29.2 mm. The length of the center of the part B is 21.0 mm. The length of the center of the part C is 10.0 mm. It should be noted that such side-looking directional characteristics are such that, in the case of a broadside directional characteristic in which radio waves are radiated in the Z direction, when the planar antenna is mounted in the middle of the pole, the Z direction and the geostationary satellite are changed. They must be arranged to face each other, and the installation is troublesome,
If side-looking directional characteristics are used, radio waves are emitted at a predetermined angle from the Z direction, so that it is not necessary to arrange the Z direction to face a geostationary satellite, and mounting is facilitated.

As shown in FIG. 3, the microstrip line 31,
32 input conductors 311 and 321 are on conductor 11, input conductors 331 and 341 on microstrip lines 33 and 34 are on conductor 12, and input conductors 351 and 361 on microstrip lines 35 and 36 are on conductor 13.
In addition, the input conductors 371, 3 of the microstrip lines 37, 38
81 are connected to the conductors 14, respectively. And conductor
The conductors 11 and 12 are coupled to the conductor 15, the conductors 13 and 14 are coupled to the conductor 16, and the conductors 15 and 16 are coupled to the input terminal 4.
These conductors 311, 321, 331, 341, 351, 361, 371, 38
1, 11, 12, 13, 14, 15, 16 and the input terminal 4 are also formed of copper foil on the substrate 1 like the microstrip lines 31 to 38.

The output conductors 31 of the microstrip lines 31, 32
2, microstrip line between 322 and ground conductor 41
33, 34 between the output conductors 332, 342 and the ground conductor 42, between the microstrip lines 35, 36, the output conductors 352, 362 and the ground conductor 43, and microstrip lines 37, 38, the output conductors 372, 382. Terminating resistor between ground conductor 44
51, 52, 53, 54 are soldered. These conductors 312, 322, 332, 342, 352, 362, 372, 382, 41, 42,
43 and 44 are also formed of copper foil on the substrate 1 like the microstrip lines 31 to 38. Terminating resistors 51 to 54
Is set equal to the impedance of the microstrip lines 31 to 38. The ground conductor 41
44 are grounded at a high frequency by being electrostatically coupled to the ground conductor 2.

A dielectric plate, for example, a low-density styrene foam plate 6 is laminated on the surface of the substrate 1 having the microstrip lines 31 to 38, and a thin polyester film 7 is laminated on the surface of the styrene foam plate 6. . On the surface of the polyester film 7, a large number of conductive circular elements 8 are formed by, for example, aluminum evaporation, as shown in FIG. As an example, when the operating frequency of this planar antenna is 12 GHz, the thickness of the styrene foam plate is 12.5 mm to 15 mm, which is 0.5 to 0.6λ (λ is the wavelength of the operating frequency), and the diameter of the conductive circular element 8 is
7.7 mm to 9.25 mm, which is 0.30 to 0.37λ. As shown in FIG. 1, each conductive circular element 8 has a distance from the center to the center in the X direction (row direction) of about 0.5λ (13.7 m).
m) and about 0.25λ (7.6m) in the Y direction (row direction).
m), and in each row, each conductive circular element in the even-numbered row is shifted by about 0.25λ from the conductive circular element in the odd-numbered row. As shown in FIG. 3, each of the conductive circular elements 8 is arranged in the same pattern in each of the 12 element regions R, each having a long crank and a short crank.
Is located. For example, in the one element region R1 shown in the upper right of FIG. 1 and the one element region R2 shown in the upper left, conductive circular elements 8 corresponding to the positions of the respective cranks are provided. One element region R is formed over two microstrip lines connected to the same terminating resistor.

The solid line shown in FIG. 6 shows a change in gain when the diameter of the conductive circular element 8 is changed in the configuration shown in FIG. 1. When the diameter is set to 0.3 to 0.37λ, the gain is improved. Is evident. The dotted line in the figure shows the gain change when the length of the waveguide element is changed in the above-described conventional planar antenna using a rectangular waveguide element. In this embodiment, the gain is improved by only about 2.8 dB at the maximum as compared with the planar antenna without the waveguide element, whereas in this embodiment, the gain is lower than the planar antenna without the conductive circular element 8. But the gain has been improved to about 3dB, up to about 3.8dB.

The solid line shown in FIG. 7 shows a change in gain when the thickness t of the styrofoam plate 6 is changed in the configuration shown in FIG. 1. From this, the thickness t of the styrofoam plate 6 is set to about λ / 2. It is clear that the gain is improved even when the integral multiple of. Note that the dotted line in the figure shows a change in gain when the thickness t of the styrofoam 6 is changed in the above-described planar antenna using the conventional rectangular waveguide element. Although the gain is improved by setting it to an integral multiple of λ / 2, it is clear that the gain of this embodiment is higher.

In addition to the reasons described above, the gain is improved because the conductive circular elements 8 are arranged regularly as described above, so that the conductive circular elements 8 resonate in the same pattern against an electric field from any direction. This is because there is no large change in the axial ratio. In the case of this embodiment as well, the circular polarization as shown by the solid line in FIG. 8 (a) changes as shown by the solid line in FIG. 8 (b), but is radiated from the microstrip lines 31 to 38. By setting the axial ratio of the radio wave to be vertically long as shown by the dotted line in FIG. 7A, it is possible to obtain perfect circular polarization as shown by the dotted line in FIG.

In the microstrip antenna shown in FIG.
The diameter of the conductive circular element 8 is 8.5 mm, and the thickness of the dielectric plate 6 is 14 m.
Assuming m, a gain of 26 dB was obtained, and the antenna aperture efficiency as viewed from the projected area reached about 80%.

A second embodiment is shown in FIG. 9 and FIG. In this embodiment, as shown in FIG. 10, 16 microstrip lines 3a, 3a ... on a substrate 1a having a length of 50 cm and a width of 44 cm.
Are provided, and each of the microstrip lines 3a, 3a,... Comprises ten crank-shaped elements. Reference numeral 100 denotes a shield plate, which is provided so as to surround the power supply circuit of the microstrip lines 3a, 3a,..., And has a height of, for example, 7 mm. The shield plate 100 is provided to reduce radiation loss of radio waves radiated from the power supply circuit.

Also in this embodiment, the conductive circular element 8a is arranged in the same manner as in the first embodiment, but has a diameter of 8.5 mm. The height of the styrene foam plate 6a at the end on the shield plate 100 side is 13 mm, and the height h2 at the end on the terminal side is 14.5 mm. That is, it is inclined upward from the power supply circuit side toward the terminal side.

The gain when the styrofoam plate 6a is provided in this manner is shown by a dotted line b in FIG. The gain when the height of the Styrofoam plate 6a on both the terminal side and the power supply side is made uniform to 13 mm is shown by a chain line c in FIG. As is clear from the comparison between the two, when the styrene foam plate 6a is inclined as in this embodiment, the gain is improved by about 0.3 to 0.5 dB.

This is for the following reason. The height of the styrofoam plate 6a,
That is, the amount of radiation attenuation per element of each microstrip line 3a (a decrease in signal level due to radiation when one element passes from the feeding side to the terminal side) depends on the distance between the conductive circular element 8a and each microstrip line 3a. It changes greatly. The height at which the light is attenuated most, that is, the height at which the light is radiated most is 0.58λ (14.5 mm, see FIG. 7) in the present embodiment. . That is, the radiation is reduced. In the planar antenna, the condition for maximizing the gain is to have the same electric field on the surface on which the conductive circular element 8a is provided.
When using a crank-shaped microstrip line,
The power transmitted decreases as it approaches the end,
The radiated electric field is small. Therefore, the height of the styrofoam on the terminal end side is selected to be 14.5 mm, which is most efficiently radiated, and the electric field radiated from each circular waveguide element 8a is made uniform, so that the gain is improved.

FIG. 12 shows a third embodiment. In this embodiment, the conductive circular elements 8b and 8c are provided in two layers, and the lower conductive circular element 8b has a diameter of 8 mm. The side and the terminal side are 13 mm in height, and the upper conductive circular element 8c has a diameter of 7.5 m.
m, and the height of the styrofoam plate 6c on which the conductive circular element 8c is placed is 13 mm on the power supply side and 14 mm on the terminal side.
As is clear from FIG. 12, the positions of the conductive circular elements 8b and 8c correspond to each other.

The gain of this embodiment is shown by the solid line a in FIG. As is clear from this, the provision of the conductive circular elements in two layers allows a wider band than that of the second embodiment (dotted line).

In each of the above embodiments, a foamed polyethylene substrate is used for the substrates 1 and 1a, but other substrates such as a polyethylene substrate can be used. Although the microstrip line is shown as a crank shape, a microstrip line having another shape can be used, and the microstrip line is not limited to the microstrip line antenna as long as it functions as a microstrip antenna. Further, the conductive circular elements 8, 8a are provided on a thin film of polyester resin, but any other dielectric film having a good radio wave transmittance can be used. Further, the conductive circular element is provided by vapor deposition, but may be printed on the derivative film by a conductive printing ink. Further, although foamed polystyrene is used as the derivative plate, a plate having a honeycomb structure made of a low-loss material such as paper or synthetic resin may be used instead. Further, each one element region R is provided so as to straddle two microstrip lines connected to the same terminating resistor. However, as shown by a symbol R 'in FIG. It may be formed over one microstrip line.

[Effects of the Invention] As described above, according to the present invention, it is located above the microstrip element by about a half wavelength of the operating frequency or an integer multiple thereof, and upward by about a half wavelength of the operating frequency or an integer multiple thereof. Circular waveguide elements having diameters of about 0.3λ to 0.37λ of the working frequency are regularly arranged at intervals of about λ / 2 in the first direction and at intervals of about λ / 4 in the second direction. So
The gain is significantly improved over the conventional one. Further, when the circular elements are provided in a plurality of stages, a wider band can be achieved.

[Brief description of the drawings]

FIG. 1 is a partially cutaway plan view of a first embodiment of a planar antenna according to the present invention, FIG. 2 is a partially cutaway longitudinal sectional view of the first embodiment, and FIG. 3 is a view of the first embodiment. FIG. 4 is a plan view of a microstrip antenna element substrate to be used, FIG. 4 is a plan view of a film provided with a conductive circular element used in the first embodiment, and FIG. 5 is an illustration of a radiation direction of radio waves in the first embodiment. FIG. 6 is a view showing the relationship between the diameter of the conductive circular element of the first embodiment and the length and gain of the conventional waveguide element, and FIG. 7 is a view showing the first embodiment and the conventional one. FIG. 8 is a diagram showing the relationship between the height of the polystyrene foam and the gain in FIG. 8, FIG. 8 is a diagram showing the feed electric field and the radiated electric field of the first embodiment, FIG. 9 is a side view of the second embodiment, FIG. FIG. 10 is a plan view of a microstrip antenna element substrate used in the second embodiment, and FIG. 11 is a second embodiment. FIG. 12 is a side view of the third embodiment, FIG. 13 is a partially omitted cutaway plan view of the conventional planar antenna, and FIG. 14 is a conventional plane view. FIG. 4 is a diagram illustrating a feed electric field and a radiated electric field of the antenna. 1, 1a ... substrate, 31 to 38, 3a ... microstrip line, 8, 8a, 8b, 8c ... conductive circular element.

Claims (2)

(57) [Claims] 1. A microstrip antenna formed to radiate radio waves of a use frequency from a microstrip element provided on a substrate; A second plane perpendicular to the first direction at a distance of about 1 / 2λ in the first direction on a plane at a distance of about 1/2 of the wavelength λ or an integer multiple thereof. And a plurality of circular elements having a diameter of about 0.3λ to 0.37λ aligned with each other at an interval of about 1 / 4λ in the direction. 2. A microstrip antenna formed to radiate radio waves of a use frequency from a microstrip element provided on a substrate, and a microstrip antenna formed on a surface of the substrate on which the microstrip element is provided. On a plane at a plurality of positions separated by a distance of about の of the wavelength λ or an integral multiple of the wavelength λ, and separated by a distance of about λλ in the first direction and a second angle perpendicular to the first direction. And a plurality of circular elements having a diameter of about 0.3λ to 0.37λ aligned with each other at an interval of about 1 / 4λ in two directions.