JP2009124259A - Antenna unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna unit arranged to cancel a direct wave from a first antenna to a second antenna through a simple configuration. <P>SOLUTION: A transmission antenna 20, a reception antenna 30, and a waveguide structure 40 located between the transmission antenna 20 and the reception antenna 30 and inverting the phase of a radio wave propagating from the transmission antenna 20 to the reception antenna 30 are arranged on a substrate 10. The waveguide structure 40 is constituted of a conductor pattern 41 formed on the substrate 10, a side board 42 consisting of an array of a plurality of through-holes connecting the conductor pattern 41 and a ground conductor 11, and a ground conductor 44. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an antenna device that cancels a direct wave from a first antenna such as a transmission antenna to a second antenna such as a reception antenna.

  For example, in the distance measuring device, as shown in FIG. 5 (a), when the transmission radio wave Px emitted from the transmission antenna is reflected by the object to be measured and received by the reception antenna as the reception radio wave Pr, The distance to the object to be measured is measured by measuring the time until reception. An antenna used for such a purpose requires an isolation value that satisfies a specified value between the antennas used for transmission and reception. That is, as shown in FIG. 5B, when the radio wave Px emitted from the transmission antenna is received as the direct wave Pr ′ by the reception antenna, the distance is erroneously detected. The isolation value is a value that indicates the amount of the direct wave Pr ′ that is directly propagated from the transmitting antenna to the receiving antenna. If this value is large, it becomes an error factor particularly when detecting an object to be measured at a short distance. .

Therefore, conventionally, a radio wave absorber is provided between each antenna for transmission and reception (Patent Document 1), and the antenna directivity in the direction in which the reception antenna is positioned with respect to the transmission antenna is increased. The isolation value was improved by a technique such as reducing the above.
JP 2002-104070 A

  However, the method of arranging the electromagnetic wave absorber and the method of increasing the antenna interval require a large space and cannot be applied to a small antenna, and the method of adjusting the antenna directivity is limited in the case of a planar antenna. There was a problem.

  An object of the present invention is to provide an antenna device capable of canceling a direct wave from a first antenna to a second antenna with a simple structure.

In order to achieve the above object, the invention according to claim 1 is the first antenna, the second antenna, the first antenna, and the second antenna located between the first antenna and the second antenna. And a waveguide structure for inverting the phase of the radio wave propagating to the antenna.
According to a second aspect of the present invention, in the antenna device according to the first aspect, the first antenna and the second antenna are formed in a patch antenna structure on a substrate having a ground conductor formed on a back surface, and the substrate The waveguide structure is formed thereon, and the waveguide structure includes a conductor pattern formed on the substrate, and a plurality of through holes arranged in a row connecting the conductor pattern and the ground conductor. It consists of the side plate which consists of, and the said ground conductor, It is characterized by the above-mentioned.
The invention according to claim 3 is the antenna device according to claim 2, wherein the waveguide structure is formed on another substrate laminated on the substrate, the conductor pattern and the ground conductor. And a waveguide structure made up of a side plate made of a plurality of through holes arranged in a row and the ground conductor.

  According to the present invention, since the direct wave reaching the second antenna from the first antenna is canceled by the waveguide structure, the isolation value between the first antenna and the second antenna can be reduced with a simple structure. Can be small.

  FIG. 1 is a perspective view showing an antenna apparatus according to one embodiment of the present invention. 10 is a substrate on which the ground conductor 12 is provided on the back surface of the dielectric plate 11, 20 is a transmitting antenna (first antenna) formed with a patch antenna structure on the upper surface of the substrate 10, and 30 is a similar receiving antenna (second antenna). , 40 is a waveguide structure.

  This waveguide structure 40 connects the conductive pattern 41 formed on the substrate 20 on the same surface as the transmitting antenna 20 and the receiving antenna 30, and the conductor pattern 41 and the ground conductor 12 on the back surface of the substrate 10. The structure is surrounded by a side plate 42 formed by through-holes and a ground conductor 12 on the back surface. The through holes that form the side plates 42 are configured to be equivalent to buried metal plates by arranging a plurality of lines in a straight line or a plurality of lines at a short pitch determined in comparison with the wavelength of the used signal. The waveguide structure 40 of the present embodiment has a structure in which two waveguides each having a waveguide filled with a dielectric plate 11 are arranged in parallel between the transmission antenna 20 and the reception antenna 30. Yes.

Here, the interval between the side plates 42 is L1, the length of the parallel sides of the transmitting antenna 20 and the receiving antenna 30 of the conductive pattern 41 is L2, and the thickness of the dielectric plate 11 is L3. L1 is the waveguide width of the waveguide structure 40, L2 is the waveguide length, and L3 is the waveguide height. Then, when λ0 is the free space wavelength and λg is the in-tube wavelength of the waveguide structure 40, the value of L1 is λg = 2 × λ0 (1)
Decide to be.

FIG. 3 shows the characteristic of the change in λg / λ0 with respect to the change in L1 / λ0 of the dielectric plate 11 (relative dielectric constant = 2.2). In FIG. 3, if L1 / λ0 = 0.37, then λg / λ0 = 2.
L1 = 0.37 × λ0 (2)
Set to. As a result, the value of L1 is set so that λg = 2 × λ0 in equation (1). The value of L2 is
L2 = λ0 (3)
Set to be.

With this setting, as shown in FIG. 2, the phase of the radio wave F1 emitted from the transmitting antenna 10 and propagating through the free space is between the entrance 40A and the exit 40B of the waveguide structure 40 (= L2). If you think about it,
(Λ0) × 2π / λ0 = 2π (4)
It changes as follows.

On the other hand, the phase of the radio wave F2 propagating inside the waveguide structure 40 is
(Λ0) × 2π / λg = (λ0) × 2π / 2 × λ0 = π (5)
It changes as follows. Therefore, the phase difference between the radio wave F1 propagating through the free space at the outlet 40B of the waveguide structure 40 and the radio wave F2 propagating through the waveguide structure 40 is π (reverse phase).

  Next, by appropriately setting the waveguide height L3 of the waveguide structure 40, the amplitude of the radio wave F2 propagating through the waveguide structure 40 is changed from the entrance 40A of the waveguide structure 40. It is set to be the same as the amplitude of the radio wave F1 propagating in the free space between the exit 40B (= L2).

  Thereby, the radio wave F1 propagating through the free space between the inlet 40A and the outlet 40B of the waveguide structure 40 (= L2) and the radio wave F2 propagating through the inside of the waveguide structure 40 are cancelled. Thus, the direct wave from the transmitting antenna 20 to the receiving antenna 30 can be canceled.

  FIG. 4 is a diagram showing the isolation characteristics between the transmitting antenna 20 and the receiving antenna 30, when the waveguide structure 40 is provided compared to when the waveguide structure 40 is not provided (conventional example) ( In this embodiment, a necessary and sufficient isolation value of −80 dB is obtained at the frequency f0 of the radio wave to be transmitted.

  In the above-described embodiment, the case where the radio waves F1 and F2 are canceled at the point of the exit 40B separated by λ0 has been described. There are many combinations of 40 numerical values L1, L2, and L3. Further, since the waveguide height L3 of the waveguide structure 40 is set by the thickness of the dielectric plate 11 of the substrate 10, the radio wave passing through the waveguide structure 40 can be obtained only with a single-layer substrate. It may be difficult to match the amplitude of F2 to the amplitude of the radio wave F1 passing outside. However, in this case, a desired waveguide height L3 can be realized by adopting a laminated substrate structure in the waveguide structure 40 portion.

It is a perspective view of the antenna apparatus of one Example of this invention. It is operation | movement explanatory drawing of the antenna apparatus of the Example. FIG. 6 is a characteristic diagram of λg / λ0 with respect to L1 / λ0 in the waveguide structure. It is an isolation characteristic figure of a present Example and a prior art example. It is explanatory drawing of distance measurement using a transmitting antenna and a receiving antenna.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10: Board | substrate, 11: Dielectric board, 12: Grounding conductor 20: Transmitting antenna 30: Reception antenna 40: Waveguide structure, 41: Conductor pattern, 42: Side plate 40A: Entrance of waveguide structure, 40B: Exit of waveguide structure, F1: radio wave propagating in free space, F2: radio wave propagating in the waveguide structure

Claims (3)

  A first antenna, a second antenna, a waveguide structure positioned between the first antenna and the second antenna and inverting the phase of a radio wave propagating from the first antenna to the second antenna; An antenna device comprising: The antenna device according to claim 1,
Forming the first antenna and the second antenna in a patch antenna structure on a substrate having a ground conductor formed on the back surface, and forming the waveguide structure on the substrate;
The waveguide structure includes a conductor pattern formed on the substrate, a side plate formed of a plurality of through holes arranged in a row connecting the conductor pattern and the ground conductor, and the ground conductor. An antenna device. The antenna device according to claim 2, wherein
A conductor pattern formed on another substrate laminated on the substrate; a side plate comprising a plurality of through holes arranged in a row connecting the conductor pattern and the ground conductor; and the ground An antenna device characterized by being replaced with a waveguide structure made of a conductor.

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