Communications: radio wave antennas – Antennas – Antenna with parasitic reflector
Reexamination Certificate
1999-06-30
2001-01-09
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Antenna with parasitic reflector
C343S761000
Reexamination Certificate
active
06172650
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an antenna system, and more particularly to a slimmer or shorter antenna system for receiving microwave band signals, such as satellite broadcasting signals.
2. Description of the Related Art
FIG. 1
shows the construction of a conventional antenna system as known, for example, from Japanese Patent Laid-Open Publication No. Sho61-157105 (JPA Sho61-157105). The antenna system is for use in receiving satellite broadcasting signals and the like, and comprised of a main reflector
12
and a primary radiator
14
which are connected by a supporting arm
26
. The main reflector
12
is formed by a belt-type parabolic cylinder which is parabolic horizontally and straight vertically, and has a straight focal line in the vertical direction. The primary radiator
14
formed by a micro-strip line is arranged on the focal line of the parabolic cylinder of the main reflector
12
. As shown in
FIGS. 2 and 3
, according to this antenna system, radio waves transmitted from an artificial satellite are reflected by the main reflector
12
, and the reflected radio waves are received by the primary radiator
14
arranged on the focal line, whereby the received electric signals are processed by a high frequency circuit
24
directly connected to the primary radiator
14
. The antenna system is set, as shown in
FIGS. 1 and 3
, such that the parabolic cylinder of the main reflector
12
stands vertically in order to prevent snow accretion when installed outside.
When an antenna system as outlined above is applied to a satellite communication apparatus for moving vehicles, it is desirable that the antenna system assume a low profile in order to preserve appearance, reduce crime risk, and reduce wind resistance when traveling. In this regard, the antenna system shown in
FIG. 1
, is inconvenient in that the larger the elevation angle of the artificial satellite, the more difficult it is to slim the antenna system. More specifically, the antenna system is constructed such that the directivity thereof in the plane at an elevation angle is directed to the artificial satellite by relatively changing the difference between the height of the main reflector
12
and the height of the primary radiator
14
. Therefore, the supporting arm
26
is extended as the elevation angle of the artificial satellite is larger, which inevitably increases the entire height of the antenna system (the total height of the height of the main reflector
12
plus the height of the supporting arm
26
).
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an antenna system which is slimmer or reduced in height.
It is another object of the invention to provide an antenna system for use, e.g. as tracking antenna system etc. which is simple in construction, inexpensive, and low-profile, without degradation o f its performance.
To attain the above objects, an aspect of the invention provides an antenna system with the advantages described below.
First, an antenna system according to the present invention comprises a ground plate having an upper surface, a feed probe located on the ground plate so as to protrude from the upper surface of the ground plate, a sub-reflector standing on the upper surface of the ground plate in the vicinity of the feed probe, and a main reflector having a mirror surface which has a predetermined focal point or a predetermined focal line, and standing on the upper surface of the ground plate such that the mirror surface of the main reflector and the mirror surface of the sub-reflector face to each other across the feed probe, the focal point or the focal line being determined so as to correspond to a location of the feed probe.
In this construction, component elements arranged on the ground plate are each designed to assume a suitable size or a suitable length and to be arranged at a suitable location on the ground plate. Therefore, the feed probe and the sub-reflector cooperatively function to efficiently radiate radio waves only to the main reflector, or the main reflector functions to radiate radio waves directly to the feed probe or by way of the sub-reflector. As a result of matching of impedance obtained in a wide frequency band, a highly efficient antenna system is realized. In addition, by virtue of an effect of mirror image caused by the ground plate, the height of the antenna can be reduced to one half of a conventional antenna. In the ground plate of the present invention, only at least its surface in an area sufficient for manifesting the effect of mirror image should be constituted by a conductive material. For example, the ground plate itself may be composed of a plastic material such as polycarbonate, and a thin conductive layer may be formed on its relevant surface.
Another antenna system according to the present invention comprises a plane ground plate having an upper surface, a lower surface, and a hole, a feed probe inserted into the ground plate from the lower surface through the hole so as to protrude from the upper surface of the ground plate in a fashion being out of contact with the ground plate, a sub-reflector standing on the upper surface of the ground plate in the vicinity of the feed probe protruding from the upper surface of the ground plate, and a main reflector having a mirror surface which has a predetermined focal point or a predetermined focal line, and standing on the upper surface such that the mirror surface of the main reflector and the mirror surface of the sub-reflector face to each other across the feed probe, the focal point or the focal line being determined so as to correspond to a location of the feed probe.
According to another aspect of the invention, the ground plate can be turned around the feed probe being a rotational axis in a fashion being out of contact with the feed probe. Further, by turning the ground plate in a fashion being out of contact with the feed probe, the antenna block can be directed in a direction that receives radio waves or a direction that radiates radio waves with respect to an azimuth.
Because the feed probe does not contact with the ground plate, when, for example, the ground plate is turned with the feed probe being the rotational axis in the azimuth direction, it is unnecessary that a distribution line which feeds electric power to the feed probe be turned. This, in turn, dispenses with component elements, such as a rotary joint for allowing the distribution line to perform rotary motion, leading to contribution to reduction of manufacturing cost of the antenna system. Further, it is not necessary to mount a high frequency circuit on the ground plate, and therefore a mechanism for driving the ground plate for rotation can be simplified and downsized. Still further, the directivity in the elevation angle of the antenna block is set by determining an installing angle &thgr; of the main reflector to a desired value, and hence a separate mechanism for adjusting the elevation angle can be eliminated, which is advantageous in slimming of the antenna system.
According to another aspect of the invention, at least a periphery area around said hole in said upper surface is conductive, and an inner surface area of said hole extending from said upper surface to said lower surface by a length equal to approximately ¼ a wavelength is conductive.
Further, in the above antenna system according to the invention, the hole formed in the ground plate may have a periphery thereof provided with a circular conductor member extending from the upper surface to the lower surface by a length equal to approximately ¼ a wavelength, the circular conductor member having a hollow portion formed therein, the feed probe being inserted into the hollow portion. By providing the conductive inner surface at the hole area or the circular conductor member, even if the feed probe and the ground plate are kept from contact with each other, radio waves can be prevented from leaking to the lower surface of the ground plate, to thereby improve the efficie
Nishikawa Kunitoshi
Ogawa Masaru
Sato Kazuo
Kabushiki Kaisha Toyota Chuo Kenkyusho
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tran Chuc D
Wong Don
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