Communications: radio wave antennas – Antennas – Antenna components
Reexamination Certificate
2002-04-18
2004-09-21
Vannucci, James (Department: 2821)
Communications: radio wave antennas
Antennas
Antenna components
C343S914000
Reexamination Certificate
active
06795039
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna system in which millimeter waves or sub-millimeter waves having a frequency exceeding 100 GHz are used to reduce the influence of sunlight collected in the vicinity of a focal point of an antenna, and relates to a method for manufacturing such an antenna system.
2. Description of the Related Art
FIG. 7
is an illustration showing the structure of a conventional antenna system. In
FIG. 7
, a reference numeral
1
denotes an antenna panel; a reference numeral
2
denotes a coating film painted in white or with a semi-gloss on the front surface of the antenna panel
1
; and a reference numeral
3
denotes an assistant reflecting mirror disposed on the focal portion of the antenna panel
1
. Incident radio waves of millimeter waves or sub-millimeter waves are focused on the assistant reflecting mirror
3
by the antenna panel
1
. On the other hand, since sunlight entering the antenna panel
1
is as short as 1 &mgr;m or less in terms of its wavelength, as compared with the millimeter waves or the sub-millimeter waves, it is irregularly reflected by the front surface of the coating film
2
painted in white or with a semi-gloss, and is not focused on the assistant reflecting mirror
3
.
However, if the frequency used in this kind of antenna system is higher, there is a problem that the radio waves of millimeter waves or sub-millimeter waves passing through inside the coating film
2
are attenuated, to thereby lower the antenna sensitivity or to degrade the observed signals to noise ratio.
In order to solve such a problem, in the related art, there is an antenna system disclosed, for example, in Japanese Patent Application Laid-Open No. 62-131611.
FIG. 8
is a schematic sectional view of a conventional antenna system disclosed in the same gazette. In
FIG. 8
, a reference numeral
1
denotes an antenna panel and a reference numeral
4
denotes fine bumps and dips formed on one surface of the antenna panel
1
. The object of this related art is to manufacture an antenna panel which has a diameter of about 50 cm and which can be used without painting.
This antenna panel
1
is manufactured as follows: very small grooves are formed on the front surface of a flat plate previously, though they may be formed later, and then the flat plate is bent and deformed to form the antenna panel
1
. In this manner, the elimination of the coating film
2
makes it possible to use the antenna panel
1
even in a high frequency. Further, the fine bumps and dips formed on the front surface of the antenna panel
1
restrain the light reflected by the antenna panel
1
from being collected on a light collecting portion, which results in preventing an assistant reflecting mirror disposed at the light collecting portion from rising in temperature.
The aforementioned gazette discloses that the fine bumps and dips on the front surface of the antenna panel
1
are formed by making scratches in the shape of straight lines or curved lines on the front surface of the antenna panel
1
, or by blasting or etching the front surface. Here, the scratches in the shape of straight lines or curved lines are mechanically made by an abrasive paper, an abrasive cloth, a grinder or the like.
FIG. 9
is a graph to show the sunlight reflecting characteristics of a polished surface of a flat plate sample which is made of aluminum (Al) and mechanically polished, and
FIG. 10
is an illustration to show a method of measuring the reflecting characteristics. As shown in
FIG. 10
, the flat plate sample is disposed just opposite to the sun and the reflecting characteristics is measured with an illuminator which is provided with a lightproof cylinder, so that the sunlight is detected only from the front, by changing the angle of the illuminator with respect to the flat plate sample is changed. The surface roughness of the #
40
polished product is 4.4 &mgr;m RMS (Root Mean Square) and as shown in
FIG. 9
, the illuminance is very high near the angle of 0 degree and the sunlight is not scattered greatly. Here, the character #
40
designates the grain size of abrasive grains and the abrasive grain size becomes smaller as the number is larger.
Theoretically, the extent to which the reflecting scattering characteristics is required is determined as follows.
FIG. 11
is a characteristic graph to show the relationship between the ratio of scattered light collected on an assistant reflecting mirror (450 mm) which is in a focal portion and the scattering angle (half width having a half of a peak value), in the case of a large-size millimeter-wave parabolic antenna system which is of the order of 10 m. In this case, energy entering a parabolic antenna is 1×10
5
W when the parabolic antenna is just opposite to the sun. When this energy is multiplied by the collecting ratio of the sunlight and the absorptivity of the assistant reflecting mirror, the temperature rises by about 100° C. if the light collecting ratio is 0.015. Such temperature rising is considered to be a limit in use, though not sufficient, if time for the parabolic antenna to be just opposite to the sun is not so long. As shown in
FIG. 11
, the scattering angle (half width) is 55 degrees when the light collecting ratio is 0.015 and thus the scattering angle needs to be larger than the above value of 55 degrees.
In the sample shown in
FIG. 9
which is mechanically polished, the scattering angle, that is, the half width having a half of the peak value is 10 degrees and the light collecting ratio at this time is 0.3, so according to a similar calculation, the temperature rises up to 2,000° C. Since this temperature exceeds the melting point of aluminum, means of polishing is not applicable to a surface processing method of the parabolic antenna which is of the order of 10 m.
On the other hand, in the sunlight reflecting characteristics of a flat plate sample which is made of aluminum and whose surface is subjected to blasting, the surface subjected to blasting has a surface roughness of about 0.4 &mgr;m RMS and shows a scattering angle larger than 55 degrees. Further, in the sunlight reflecting characteristics of a flat plate sample which is made of aluminum and whose surface is etched, the etched surface has a surface roughness of about 1.2 &mgr;m RMS and shows a large scattering angle and good scattering characteristics. However, the surface subjected to an electrolytic polishing or a chemical polishing becomes very smooth in surface irregularity and is not applicable.
As is evident from the above description, among methods described in the above gazette, a surface processing for preventing the sunlight from being collected on the assistant reflecting mirror when it is applied to a parabolic antenna of the order of 10 m is only blasting and etching.
In the antenna panel
1
of a parabolic antenna for millimeter waves and sub-millimeter waves, in the case where the diameter is about 10 m, a mirror surface accuracy is required to be a very high accuracy of 10 &mgr;m or less RMS. In many cases, in the antenna panel
1
of the parabolic antenna using a usual wavelength a little longer than the millimeter waves and the sub-millimeter waves, the mirror surface accuracy is required to be larger than 200 &mgr;m RMS. In manufacturing the antenna panel
1
like this, a thin plate is deformed and fixed to ribs (reinforcing members), which are also deformed in advance, by means of welding, adhesion, riveting or the like. However, it is difficult to achieve a mirror surface accuracy higher than this level by this manufacturing method. Therefore, the mirror surface side needs to be formed by machining, which can produce a high surface accuracy.
Further, since the antenna panel is too heavy if it is a large block, the back surface thereof needs to be machined so as to thin the panel. If the panel is only machined to reduce its thickness, it has no sufficient rigidity and thus needs to have a structure in which reinforcing ribs are fixed to the back surface thereof. In such a
Kawaguchi Noboru
Takimoto Atsushi
Ura Masashi
Yamashita Mikio
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