JPH02270404A - Case for circular antenna - Google Patents

Abstract

PURPOSE:To prevent deterioration in the characteristic due to water drop or the like by constituting the case such that the shape of projection of the case upper face with respect to the perpendicular direction of the substantial flat part is contained in the upper disk of the circular antenna contained in the case. CONSTITUTION:An antenna case 9 is made of a material such as a resin plate and a circular antenna is contained in the inside. Then the size is set so as to have a relation of phiA>phiC, where phiA is the minor diameter of a disk 1 of the circular antenna and phiC is the major diameter of the case upper face and the case upper face is supported with the side face with a sudden slope. Thus, the case upper part, that is, the flat part shape is smaller than the disk 1 and the projection in the perpendicular direction is contained in the disk 1. That is, when the flat part of the upper face of the case is made smaller than the disk 1, even when water drop is adhered to the part, no effect is given onto the characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a case for housing a circular antenna (also called an annular patch antenna), and particularly to a case supplement whose characteristics are less likely to deteriorate due to adhesion of rain or the like.

[Prior art]

Conventional circular antennas are described, for example, in "The Institute of Electronics, Information and Communication Engineers Technical Research Report AP 87-53, pp. 21-24, Kaneda, Koso et al., 'Axisymmetric Mode Annular Patch Antenna and Its Power Feeding Method'" There is something.

FIG. 3 is a plan view and a side view of the circular antenna described above.

In FIG. 3, a metal disk 1 and a base plate 2 are connected in parallel via a plurality of short pins 3. Electric signals are supplied from the coaxial cable 5 through a power supply pin 4 provided at the center of the disk 1, and radio waves are radiated from the gap between the disk 1 and the ground plate 2.

[Problem to be solved by the invention]

In the above circular antenna, the circular plate 1 and the ground plate 2 are
Since radio waves are emitted from the gap between the disk 1 and the disk 1, the characteristics will not deteriorate even if there is a metal or dielectric material directly above the disk 1.
If there is a dielectric material, metal, etc. outside the edge of the disk 1, radio waves will be reflected, and the antenna characteristics will deteriorate.

For example, FIG. 4 is a diagram showing the return loss characteristics of the antenna when a resin plate 7 is provided on the top of the circular antenna 6 and water 'a8 equivalent to a precipitation of 100 mm/h adheres thereon.

As can be seen from FIG. 4, when water droplets adhere, the center frequency shifts and the bandwidth changes compared to when no water droplets adhere.

Therefore, in cases such as conventional antenna cases, which have a resin cover with a larger area than the circular antenna in order to house the circular antenna inside, if water droplets adhere to the top surface of the case, water droplets may also form diagonally above the edge of the circular antenna. Since areas where water droplets adhere are formed, characteristics change due to the reasons mentioned above, resulting in a problem of performance deterioration.

The present invention has been made to solve the problems of the prior art as described above, and an object of the present invention is to provide a case for a circular antenna that can prevent characteristic deterioration due to adhesion of water droplets during rainy weather.

[Means to solve the problem]

In order to achieve the above object, in the present invention, the projected shape in the vertical direction of a substantially planar portion of the upper surface of the case is the shape of the upper disk (for example, the above-mentioned disk 1) of the circular antenna housed in the case. It is configured to fit inside.

Note that the above-mentioned substantially flat portion means a flat surface to which water droplets tend to adhere, or a portion with a gentle slope that is approximately equal to the flat surface.

[Effect]

As described above, characteristic deterioration due to adhesion of water droplets occurs when there are water droplets outside the edge of the disk 1, and hardly occurs when there are water droplets only directly above the disk 1. therefore,
If the projected shape of the substantially planar portion of the upper surface of the case in the vertical direction is configured to fit within the disk 1, there will be no planar portion diagonally above the disk 1 to which water droplets may adhere. It is possible to prevent property deterioration due to adhesion of.

〔Example〕

FIG. 1 shows an embodiment of the present invention, in which (a) shows a perspective view and (b) shows a sectional view.

In FIG. 1, 9 is an antenna case made of, for example, a resin plate, and a circular antenna is housed inside. If the minor axis of the circular plate l of the circular antenna is φ^, and the major axis of the top surface of the case is φC, the dimensions are set so that φ^>φC, and the top surface of the case is supported by the steeply sloped side surfaces. .

Therefore, the shape of the upper surface of the case, that is, the plane part, is smaller than the disc 1, and its vertical projected shape is arranged to fit within the disc 1.

Next, the effect will be explained.

FIG. 5(a) shows a circular antenna (to which the present invention is applied) resonating in the TMol mode as shown in FIG. 5(b).
is the directional characteristic of In this case, radio waves are not radiated toward the upper surface of the disk 1. This is because an electric field vector 12 is generated as shown in FIG. 5(b), and radio waves are radiated from the side surface of the disk 1. Therefore, in a portion above the disk 1 that is smaller than the area of the disk 1, there may be something, such as a water droplet, that obstructs the radiation of radio waves.

It has been confirmed through an experiment in which a cloth soaked in water was placed directly on the top surface of the disk 1 that this did not affect the characteristics in any way.

Therefore, as in the present invention, the projected shape of the portion of the top surface of the antenna case to which water droplets etc. adhere is configured to fit within the disk 1, that is, the planar portion of the top surface of the case is configured to be smaller than the disk 1. Then, even if water droplets or the like adhere to that part, the characteristics will not be affected. Furthermore, the side surface of the case, which would affect radiation from the antenna if water droplets adhered thereto, has a steep slope and is shaped to prevent water droplets from adhering to it, so there is no risk of affecting the characteristics.

Next, FIG. 2 is a sectional view of another embodiment of the present invention, (
(a) shows the case of a conical or pyramidal antenna case 10, and (b) shows the case of a dome-shaped antenna case 11.

First, for the conical or pyramidal case shown in (,),
If there is no flat part on the top of the case that water droplets can adhere to, that is, if the flat part is extremely small,
In this case, since there are no places where water droplets can adhere, no deterioration of characteristics occurs.

In addition, the dome-shaped case shown in (b) has a gently sloped part on the upper surface of the case that is not completely flat, but is almost flat.
In other words, there is a portion that can be regarded as a substantially flat surface to which water droplets tend to adhere. In this case, according to the present invention, if the above-mentioned substantial plane portion is set to be smaller than the disk 1, deterioration of the characteristics can be prevented as in the case of FIG. 1.

〔Effect of the invention〕

As explained above, according to the present invention, the projected shape of the substantially planar portion of the upper surface of the case in the vertical direction is configured to fit within the upper disk of the circular antenna housed in the case. The area where water droplets etc. adhere to the case surface can be limited to the inner side above the disk 1 where they do not affect the characteristics of the antenna, thereby making it possible to prevent characteristic deterioration due to water droplets etc. This effect can be obtained.

[Brief explanation of drawings]

1 and 2 are sectional views of an embodiment of the present invention, FIG. 3 is a plan view and a side view showing the structure of a circular antenna, FIG. 4 is a diagram showing changes in characteristics due to adhesion of water droplets, and FIG.
The figure is a directional characteristic diagram of a circular antenna with TMOI mode resonance. <Explanation of symbols> 1... Disc plate 2... Base plate 3... Short pin 4... Power supply pin 5... Coaxial cable 6... Circular antenna 7... Resin plate 8... Water droplets 9 to 11...Antenna case 12...Electric field vector

Claims (1)

[Claims] An antenna case for housing a circular antenna, characterized in that the vertically projected shape of a substantially planar portion of the upper surface of the case is configured to fit within the upper disk of the circular antenna housed within the case. Case for circular antenna.