JPS6358401B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a horn antenna device used in microwave Doppler radar, etc., and more specifically, the beam width (radiated electric field) can be increased by simply adding a simple attachment without changing the horn antenna itself. The object of the present invention is to provide an angular width that is 1/√2 of the maximum radiation direction) that can be set arbitrarily wide.

Microwave Doppler radar emits microwaves from a horn antenna into the detection range and uses the reflected waves to detect the presence or absence of people or objects. Its applications include anti-theft and automatic door activation. . By the way, when this is used, for example, to start an automatic door, the detection range is different from the direction parallel to the door for a draw door where two doors open at the same time on the left and right and a single door where only one door opens. It will be twice as different. As the detection range varies depending on the surrounding conditions at the installation location, a horn antenna with an appropriate beam width has been selected and incorporated into the Doppler radar. The beam width of the horn antenna is determined by its shape. Therefore,
Although the antennas are used for the same purpose, it is necessary to manufacture horn antennas with various beam widths depending on the surrounding conditions, which is complicated and causes high costs.

In view of the above-mentioned problems, the present invention has been made to improve the above-mentioned problem so that a horn antenna of one shape can be used with different beam widths.

In other words, this invention allows the beam width to be changed without substantially deteriorating the impedance or other characteristics of the horn antenna by partially shielding the aperture of the horn antenna with something that does not reflect microwaves, such as a radio wave absorber. This is what we discovered and applied.

For example, in a horn antenna 1 as shown in FIG. 1 and FIG.
are arranged in parallel, and when these are gradually brought closer from both sides, the opening interval d, the H plane direction, and the E
The relationship with the beam width in the plane direction is shown in FIG. In other words, the beam width when the aperture 1a is not covered by the flat radio wave absorbers 2, 2 is E.
θ _EO in the plane direction and θ _HO in the H plane direction, but as shown in Figure 1, the flat radio wave absorbers 2, 2 are
When the opening interval d in the H-plane direction is narrowed by sliding along the surface direction, the beam width in the E-plane direction does not change, but the beam width in the H-plane direction gradually increases. Therefore, by covering a portion of the aperture 1a of the horn antenna 1 with radio wave absorbers 2, 2 by an appropriate area and changing the aperture area (aperture spacing), a single horn antenna can have various beam widths. It can be given and used for different purposes.

In addition, although the above description is about the case where only the opening interval d of the openings in the H-plane direction is changed, the interval in the E-plane direction can also be reduced by using the radio wave absorber in the same way as in the H-plane direction. The beam width change in this case is also the same as in the case of the H-plane direction shown in FIG. Further, each of the H-plane direction and the E-plane direction may be changed at the same time, making it possible to set the beam width in all directions. Note that since the radio wave absorbers 2, 2 are used to cover the opening 1a, the radio wave absorbers 2, 2 are used to cover the opening 1a.
Most of the microwaves incident on 2 are absorbed, and only a small amount is reflected even though the opening 1a is closed. Therefore, the impedance of the horn antenna 1 is not deteriorated. Further, as the material of the radio wave absorber 2, for example, ferrite or foamed polystyrene containing carbon particles can be used.

Next, an example will be shown in which this radio wave absorber is attached to a horn antenna to form a horn antenna device.

In FIGS. 4 and 5, 3 is a microwave element such as a microwave oscillator or a Doppler sensor, 1 is a horn antenna, and 4 is a case. 5 is a radome that seals the horn antenna 1 inside the case;
It is made of a material that allows radio waves to pass through without causing any interference such as attenuation, such as plastic such as vinyl chloride, paper, or cloth. 2,2 is radome 5
It is a flat radio wave absorber attached to the inside of the In this configuration, the horn antenna 1 is connected to the case 4
The radome 5 to which the radio wave absorbers 2, 2 are attached is fixed by being sandwiched between the edge 4a of the case opening and the edge 1b of the horn antenna opening. ing. For example, when narrowing the distance only in the H-plane direction or the E-plane direction, the radome 5 to which the radio wave absorbers 2, 2 are attached is the sixth
As shown in the figure, when narrowing both the H plane and the E plane, it is manufactured as shown in Fig. 7. That is, for a Doppler radar having a specific horn antenna, several types of radomes 5 with radio wave absorbers 2 pasted thereon as shown in FIG. 6 or 7 are manufactured with different opening intervals d. and,
When installing a Doppler radar, a radome 5 with a radio wave absorber that provides a beam width suitable for the conditions of the installation site is selected and combined with the horn antenna 1 of the Doppler radar. In this way, one type of horn antenna can be used in common for various detection ranges. For example, when used to start an automatic door, a draw door that opens two doors simultaneously on the left and right,
In the case of a single-swing door in which only one door opens, the detection range is twice as different in the direction parallel to the door, but is the same in the direction perpendicular to the door. In order to accommodate this, it is sufficient to prepare radomes 5 having radio wave absorbers 2 that differ only in the opening interval d in the direction of one side (E-plane or H-plane).

Further, in this embodiment, the radio wave absorbers 2, 2 were attached to the radome 5 so as to have different opening intervals d, but a mechanism (not shown) for moving the radio wave absorber 2 by an adjustment knob was provided. Therefore, the opening interval d may be changed.

As explained above, the present invention provides a horn antenna and a material that does not significantly deteriorate the impedance of the horn antenna, such as a radio wave absorber, that covers the opening of the horn antenna from the edge side so as to obtain a predetermined opening interval. Since the horn antenna device is provided, the beam width thereof can be appropriately made wider than that of the horn antenna alone. In other words, by preparing several types of simple attachments (radomes with radio wave absorbers, etc.) and selectively assembling one of them, different beam widths can be given to one type of horn antenna. Can be done. When used in a Doppler radar, there is no need to prepare many types of horn antennas with different beam widths corresponding to the detection range of each installation location, which makes it possible to reduce costs.

[Brief explanation of the drawing]

Figure 1 is a front view of the aperture of a horn antenna explaining an example of the arrangement of the radio wave absorber of this invention, Figure 2 is its side view, and Figure 3 is the aperture interval and beam width when the radio wave absorber is moved. 4 is a partially sectional plan view of an embodiment of this invention, FIG. 5 is a side view thereof, and FIGS. 6 and 7 are diagrams showing different radomes to which radio wave absorbers are attached. It is a perspective view showing an example. 1... Horn antenna, 1a... Opening, 2...
...Radio wave absorber.

Claims (1)

[Claims] 1. A horn antenna, and a material that does not significantly deteriorate the impedance of the horn antenna, such as a radio wave absorber, which covers the opening of the horn antenna from the edge side so as to obtain a predetermined opening interval. A horn antenna device characterized by comprising: