JP2007043546A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna device which has a wide-band/high-gain performance and is excellent in antenna producibility. <P>SOLUTION: Two spiral lines 1 are provided on a dielectric board 2, a feeding device is provided at the center of the spiral lines 1, and the tips of the spiral lines 1 are set open. A grounding conductor 3 is provided on the backside of the dielectric board 2 opposite to its front side where the spiral lines 1 are formed, larger than an area of the dielectric board 2 where the spiral lines 1 are formed, and provided with a cavity which is as deep as λ<SB>H</SB>/4. Small conductor pieces 6 are provided respectively near the tips of the spiral lines 1 at points further than the tips from the center of the antenna, the conductor thin film formed on the backside of the dielectric board are short-circuited to the conductor pieces 6 through through-holes, the conductor thin film is short-circuited to the grounding conductor 3, first resistors 9 are provided between the adjacent spiral lines 1, second resistors 10 are provided between the tips of the spiral lines 1 and the small conductor pieces 6 respectively, and a resistor pair composed of two resistors of 9 and 10 is provided at the two tips of the spiral lines 1, respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spiral antenna device, and more particularly to a small-sized spiral antenna device having broadband characteristics.

  In the fields of radar, satellite communications, and mobile communications, it is conceivable to use circularly polarized waves so that radio waves can be transmitted and received regardless of the direction of polarization. A spiral antenna is an example of an antenna that radiates circularly polarized waves over a wide band with a low attitude.

  The principle of operation of the spiral antenna can be described as a kind of traveling wave antenna. That is, by feeding power to the center of a spiral line formed by spirally winding a plurality of conductor lines, a wave travels from the feed point toward the tip of the line, and gradually radiates radio waves during that time.

  In order to radiate radio waves in one direction, a reflector composed of a reflector or a cavity is usually provided at a distance of about λ / 4 of the operating frequency on the opposite side of the radiation direction.

  In spiral antennas, residual components that do not contribute to radiation are reflected at the tip of the spiral line, and the reflected waves radiate reverse-polarization components. As a result, axial ratio characteristics that are important for circular polarization performance are affected. It will get worse. In addition, when the reflected wave reaches the feeding point, there is a problem that the matching with the feeding device is deteriorated. These problems are particularly noticeable in a low frequency band where the antenna size is small with respect to the wavelength.

Therefore, conventionally, when the wavelength of the lower limit frequency of the use frequency is λ _L , the outer dimension of the spiral line is approximately 1.5 to 2λ _L so that the antenna size is set to the wavelength of the antenna use frequency. measures such as increasing or measures such to absorb the residual component of the wave absorber provided outermost length spiral antenna is miniaturized to about 1 [lambda _L is taken of the spiral line.

  Furthermore, a method for improving the residual component absorption performance by combining a radio wave absorber and a resistor is disclosed (for example, see Patent Document 1).

JP 11-163622 A

  However, as in the prior art described above, increasing the antenna size with respect to the wavelength is against the demand for antenna miniaturization, and when considering the antenna array, the element spacing becomes wide. There arises a problem that a grating lobe occurs at the frequency band.

  On the other hand, when the radio wave absorber is provided, it is difficult to select a radio wave absorber having radio wave absorption performance over a wide band, and the manufacturability of the antenna is deteriorated from the viewpoint of the fixing method of the radio wave absorber. Furthermore, there is also a problem that the gain of the antenna is reduced by the radio wave absorber absorbing the main polarization component of the antenna.

The present invention has been made to solve the above-described problems. In a spiral antenna in which the outermost peripheral length of the spiral line is reduced to about 1λ _L , a wide band and high gain can be obtained without using a radio wave absorber. It is an object to obtain an antenna device having excellent performance and excellent antenna manufacturability.

The antenna device according to the present invention has a spiral line in which two conductor lines are spirally wound in the same direction so as not to overlap each other on a dielectric substrate, and a feeding device is provided at the center of the spiral line. The spiral line tip is open, and the upper surface of the use frequency is larger than the area where the spiral line is formed on the back side of the dielectric substrate opposite to the surface on which the spiral line is formed. In a two-wire spiral antenna having a ground conductor having a cavity with a depth of about λ _H / 4 when the wavelength of the frequency is λ _H , a conductor piece is placed at an outer position from the center of the antenna near the tip of the spiral line. Forming a conductor thin film on the back side of the dielectric substrate of the conductor piece, short-circuiting the conductor piece and the conductor thin film with a through hole, and connecting the conductor thin film to the ground conductor. A first resistor between the tip of the spiral line and the adjacent spiral line, and a second resistor between the tip of the spiral line and the conductor piece, the two resistors The body forms one pair, and the resistor pair is provided at the tip of two spiral lines.

  According to the present invention, since the antenna elements can be reduced in size, the elements can be arranged with a narrower element spacing. As a result, the frequency at which the grating lobe can be generated can be shifted to the high frequency side, and the use band of the antenna is expanded. Further, when viewed at the same frequency, the beam scanning angle range can be expanded as compared with the conventional example.

Embodiment 1 FIG.
1 to 3 are schematic views for explaining a spiral antenna device according to Embodiment 1 of the present invention.
The spiral antenna device shown in FIG. 1 has a spiral line 1 on a dielectric substrate 2 in which two conductor lines are spirally wound in the same direction so as to overlap each other. At the center of the spiral line 1, a power supply device (not shown) connected to the power supply line 4 is provided, the tip of the spiral line 1 is opened, and the opposite side of the surface of the dielectric substrate 2 forming the spiral line 1 is provided. On the back surface side, a ground conductor 3 having a cavity to be described later is provided.

  Furthermore, a conductor piece 6 is formed at a position outside the center of the antenna near the tip of the spiral line 1, and a first resistor 9 is formed between the tip of the spiral line 1 and the adjacent spiral line 1, A second resistor 10 is formed between the tip of the spiral line 1 and the conductor piece 6.

  In FIG. 1, when the surface on which the spiral line 1 is formed is defined as the xy plane, and the side toward the near side with respect to the paper is defined as the + z direction, FIG. 2 is a zx plane cross-sectional view taken along the line AB in FIG. FIG. 3 is an enlarged view of the yz plane cross-sectional view of the portion C of FIG. In FIG. 2, 5 represents a connector, in FIG. 3, 7 represents a conductor thin film, and 8 represents a through hole.

The outermost circumference length of the spiral line 1 is set to a size reduced to about 1λ _L when the wavelength of the lower limit frequency of the used frequency is λ _L.

As shown in FIG. 2, the ground conductor 3 supports the dielectric substrate 2, and the center portion thereof is larger than the area occupied by the spiral line 1, and the wavelength of the upper limit frequency of the use frequency is λ _H. Then, a cavity (hereinafter referred to as a cavity) having a depth of about λ _H / 4 is obtained. The cavity acts as a reflector, thereby radiating radio waves in a single direction (in this case + z direction). If the depth of the cavity is set to the above-mentioned dimension, the reflected wave overlaps with the direct wave in the use frequency band, so that the antenna gain is improved.

  The conductor piece 6 is provided in the vicinity of the tip of the spiral line 1, and a conductor thin film 7 is formed on the back surface side of the dielectric substrate 2 as shown in FIG. 3. The conductor piece 6 and the conductor thin film 7 are short-circuited by the through hole 8. Further, the conductor thin film 7 is short-circuited to the ground conductor 3, so that the conductor piece 6 is also short-circuited to the ground conductor 3.

  The first resistor 9 is provided between the tip of the spiral line 1 and the adjacent spiral line. The second resistor 10 is provided between the tip of the spiral line 1 and the conductor piece 6. The first resistor 9 and the second resistor 10 form a pair and are provided at the tips of the spiral lines 1 at two locations.

  Next, the effects of the present invention will be described. As described above, in the spiral antenna reduced in size with respect to the wavelength, it is necessary to suppress reflection at the tip of the spiral line 1. When considering the mode of the electric field existing at the tip of the spiral line 1, the following two modes are conceivable.

  One is a mode that stands between the tip of the spiral line 1 and the adjacent spiral line, and the other is a mode that stands between the tip of the spiral line 1 and the ground conductor 3. Therefore, it is necessary to suppress these two modes.

  Therefore, if two resistors 9 and 10 are provided as in the present invention, the mode in which the first resistor 9 stands between the tip of the spiral line 1 and the adjacent spiral line is suppressed, The mode in which the second resistor 10 stands between the tip of the spiral line 1 and the ground conductor 3 is suppressed.

How to select the resistance values of the first resistor 9 and the second resistor 10 can be determined as follows. Here, the resistance value of the first resistor 9 is expressed as R ₁ , and the resistance value of the second resistor 10 is expressed as R ₂ .

  The tip of the spiral line 1 in FIG. 1 can be equivalently modeled by a coupled microstrip line shown in FIG. In FIG. 4, 11 represents a conductor line, 12 represents a dielectric substrate, and 13 represents a ground conductor. Two conductor lines 11 are formed on the dielectric substrate 12, the width of the conductor line 11 is equal to the width of the spiral conductor 1, and the distance between the two conductor lines 11 is equal to the distance between the spiral conductors 1. And The relative permittivity and the substrate thickness of the dielectric substrate 12 are the same as those of the dielectric substrate 2. Further, the distance between the dielectric substrate 12 and the ground conductor 13 is made equal to the distance (the depth of the cavity) between the dielectric substrate 2 and the ground conductor 3 in the spiral antenna.

  The coupled microstrip line in FIG. 4 has two types of modes, an even mode in which the two conductor lines 11 are excited in the same phase and an odd mode in which the two conductor lines 11 are excited in the opposite phase. The even mode is a mode that stands between each conductor line 11 and the ground conductor 13, and this corresponds to a mode that stands between the tip of the spiral line 1 and the ground conductor 3. On the other hand, the odd mode is a mode that stands between the two conductor lines 11 and corresponds to a mode that stands between the tip of the spiral line 1 and the adjacent spiral line. The even mode and odd mode characteristic impedances are expressed as Ze and Zo, respectively.

First, if the resistance value R2 of the _second resistor 10 is selected as the characteristic impedance Ze of the even mode of the coupled microstrip line, it can be made non-reflective with respect to this mode. At this time, no matter what the resistance value R1 of the _first resistor 9 to be determined next is, the tip of the spiral line 1 and the adjacent spiral line have the same potential. Is not affected.

Subsequently, the resistance value R ₁ of the first resistor 9 is determined. In the case where a mode stands between the tip of the spiral line 1 and the adjacent spiral line, or in the odd mode of the coupled microstrip line, it can be considered that an electrical wall exists equivalently in the middle of the line. The electric wall is taken as potential reference, it can be regarded as to those at the distal end portion of the spiral line 1 in which the resistance value R ₁ half, the resistance value R ₂ of the previously determined is connected in parallel . Therefore, the resistance value R ₁ satisfying the following relational expression is selected so that the parallel connection resistance value becomes equal to the odd-mode characteristic impedance Zo of the coupled microstrip line.

Thus, it is possible to determine the resistance value R ₁ of the first resistor 9, the resistance value R ₂ of the second resistor 10. For example, if Ze = 300Ω and Zo = 50Ω, then R ₁ = 120Ω and R ₂ = 300Ω.

As an example of the effect of the present invention, FIG. 5 shows a numerical calculation example of the frequency characteristic of the axial ratio (Axial Ratio). The FDTD method (finite difference time domain method) was used for the calculation. Outermost length of the spiral line 1 is 0.64λ _L, the depth of the cavity was 0.06 _L. The dimensions and widths of the spiral line 1 were selected so that even-mode and odd-mode characteristic impedances were Ze = 300Ω and Zo = 50Ω, respectively, when modeled with a coupled microstrip line. A solid line is a result of attaching the resistor 9 and the resistor 10 according to the present invention, and a broken line is a result of a conventional example without a resistor. Both dimensions of the spiral antenna are the same. According to the present invention, it can be seen that low axial ratio characteristics can be obtained over a wide band.

  The resistor pair used in the present invention is only for suppressing reflection at the tip of the spiral line 1, and the antenna gain does not decrease as is apparent from the principle of operation of the spiral antenna.

In the above description, the relationship between the line width and the line interval of the spiral line 1 is not specifically stated, but the line width and the line interval may or may not be the same. Depending on the selected dimensions, the even-mode and odd-mode characteristic impedances when modeled with a coupled microstrip line can be obtained, so that the values of R ₁ and R ₂ can be adjusted appropriately according to the characteristic impedance values. That's fine. Further, the shape of the spiral antenna may be other than the rectangular shape as shown in FIG. 1, and may be, for example, a circular shape.

Embodiment 2. FIG.
In the first embodiment, the means for realizing the first resistor 9 and the second resistor 10 has not been clarified. However, as in the second embodiment, a spiral line using a chip resistor as the resistor is used. 1 and the conductor piece 6 may be soldered.

Many types of chip resistors are commercially available at low cost depending on the resistance value, dimensions, etc., and may be appropriately selected. In addition, when chip resistances having resistance values R ₁ and R ₂ calculated by the design method described in the first embodiment cannot be obtained, a plurality of chip resistors are connected in series or in parallel to obtain a desired value. It can be close to the resistance value. In general, since the chip resistance has a minute size with respect to the wavelength of the frequency used in the antenna, there is almost no influence on the wave characteristics even when a plurality of chip resistors are connected as described above. Moreover, there is almost no influence of the error of an attachment position.

Embodiment 3 FIG.
FIG. 6 is a schematic diagram showing a spiral antenna device according to Embodiment 3 of the present invention. The same components as those described above are denoted by the same reference numerals and description thereof is omitted. As new symbols, 14 represents a dielectric substrate with a resistive film, 15 represents a first resistive film, and 16 represents a second resistive film.

  As means for realizing the first resistor 9 and the second resistor 10 of the first embodiment, a dielectric substrate 14 with a resistance film as shown in the third embodiment may be used. Here, the first resistor film 15 corresponds to the first resistor 9 described in the first embodiment, and the second resistor film 16 is the second resistor described in the first embodiment. 10 corresponds.

  For the dielectric substrate 14 with a resistive film, a material having a resistance value of, for example, 25Ω, 50Ω, or 100Ω per unit area is commercially available. If the length of the resistance film to be formed is increased or the width is reduced, the resistance value is increased. Conversely, if the length of the resistance film is decreased or the width is increased, the resistance value is decreased. An arbitrary resistance value can be realized by adjusting the shape of the resistance film.

  Since the resistance film can be processed by an etching process in the same manner as the conductor film, an antenna with high processing accuracy and little variation in characteristics can be easily manufactured.

Embodiment 4 FIG.
In the first to third embodiments, a single spiral antenna device has been described, but a plurality of spiral antenna devices may be arranged to constitute an array antenna. If each arrayed spiral antenna element is excited with a phase difference, a phased array antenna capable of scanning a beam in an arbitrary direction can be obtained.

It is a schematic diagram which shows the spiral antenna apparatus which concerns on Embodiment 1 of this invention. It is zx plane sectional drawing in the line of AB of FIG. It is yz surface sectional drawing in the C section of FIG. FIG. 2 is a schematic diagram of a coupled microstrip line in which the tip of the spiral line 1 of FIG. 1 is equivalently modeled. It is a figure which shows the numerical calculation example of the frequency characteristic of an axial ratio (Axial Ratio) as an example of the effect by this invention. It is a schematic diagram which shows the spiral antenna apparatus which concerns on Embodiment 3 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Spiral line, 2 Dielectric substrate, 3 Ground conductor, 4 Feed line, 5 Connector, 6 Conductor piece, 7 Conductor thin film, 8 Through hole, 9 1st resistor, 10 2nd resistor, 11 Conductor line, 12 Dielectric substrate, 13 Ground conductor.

Claims (4)

On the dielectric substrate, there is a spiral line in which two conductor lines are spirally wound in the same direction so as not to overlap each other, and a power feeding device is provided at the center of the spiral line, and the tip of the spiral line is open In addition, on the back surface side of the dielectric substrate opposite to the surface on which the spiral line is formed, the wavelength of the upper limit frequency of the use frequency is λ _H in an area larger than the range in which the spiral line is formed. In a two-wire spiral antenna with a ground conductor sometimes having a cavity with a depth of about λ _H / 4,
A conductor piece is formed at a position outside the center of the antenna near the tip of the spiral line, a conductor thin film is formed on the back side of the dielectric substrate of the conductor piece, and the conductor piece and the conductor thin film are short-circuited through a through hole. The conductor thin film is short-circuited to the ground conductor, and a first resistor is provided between the spiral line tip and the adjacent spiral line, and a second resistor is provided between the spiral line tip and the conductor piece. An antenna device, comprising: a body, wherein the two resistors form a pair, and the resistor pair is provided at two distal ends of the spiral line. The antenna device according to claim 1, wherein a chip resistor is used as the resistor. The dielectric substrate with a resistance film is used as the dielectric substrate, and the spiral line and the first and second resistors are formed on the dielectric substrate with a resistance film. Antenna device. The antenna device according to any one of claims 1 to 3, wherein the antenna device is arrayed.

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