Planar antenna device

Communications: radio wave antennas – Antennas – Microstrip

Reexamination Certificate

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Details

C343S789000

Reexamination Certificate

active

06731243

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-292298, filed Sep. 26, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an on-vehicle planar antenna device for receiving satellite broadcasting.
Conventionally, there has been no technique but decreasing an antenna element size when a planar antenna device is used for obtaining high electromagnetic field radiation characteristics within the range of a wide elevation angle.
FIG. 1
illustrates a structure of a general air patch antenna device.
FIG. 1
shows a ground plane
11
, an antenna element
12
mounted on the ground plane
11
separated by a spacer
13
, and a feed point
14
to the antenna element
12
.
A microstrip antenna device stationed in the air (&egr;r=1) has a high relative antenna device gain. On the other hand, however, the half-power angle generally becomes approximately 60° to 80° depending on antenna device shapes. Consequently, a gain remarkably decreases toward a low elevation angle.
To decrease the antenna element size for widening such a narrow elevation angle range, a dielectric must be used.
FIG. 2
illustrates an example structure of a dielectric patch antenna device using the dielectric.
FIG. 2
shows a ground plane
21
, a dielectric plate
22
mounted on the ground plane
21
, an antenna element
23
provided on the dielectric plate
22
, and a feed point
24
to the antenna element
23
.
The size of the antenna element
23
is decreased by using the dielectric plate
22
. It becomes possible to obtain high electromagnetic field radiation characteristics within a wide elevation angle range.
However, the antenna element size is decreased for the dielectric patch antenna device in FIG.
2
. Compared to the air patch antenna device in
FIG. 1
, the antenna device gain greatly decreases. In addition, a loss due to the dielectric plate
22
further decreases the antenna device gain. As a result, the dielectric patch antenna device in
FIG. 2
does not provide so high a radiation level toward a low elevation angle.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a planar antenna device which satisfies both of electromagnetic field radiation characteristics over a wide elevation angle range including a low elevation angle direction and a high antenna device gain.
A planar antenna device according to the present invention comprises: a ground plane; a planar antenna element having a principal plane mounted above the ground plane; and a cavity, having an opening partially exposing the antenna element, placed on the ground plane in order to cover the entire antenna element contactlessly.
Preferred manners for the above-mentioned planar antenna device are as follows.
(1) A feed point for supplying power supply to the antenna element is further provided.
(2) An area of the opening is smaller than a size of the antenna element.
(3) The opening is placed substantially parallel to a principal plane of the antenna element.
(4) The antenna element is an air patch antenna element mounted above the ground plane separated by a spacer.
Another planar antenna device according to the present invention comprises a ground plane; a planar antenna element having a principal plane mounted above the ground plane; and a planar conductor placed substantially parallel to a principal plane of the antenna element and having an opening at substantially a center thereof.
According to the present invention, it is possible to provide excellent electromagnetic field radiation characteristics over a wide elevation angle range including a low elevation angle direction and a high antenna device gain only by adding a cavity to a conventional air patch antenna device without decreasing the antenna element size, thereby maintaining sufficiently high antenna device gain.
Further, the present invention eliminates the need to use a dielectric for obtaining a gain toward a low elevation angle. It is possible to maintain a high antenna device gain without decreasing an antenna device gain due to a dielectric loss.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.


REFERENCES:
patent: 4131894 (1978-12-01), Schiavone
patent: 4197545 (1980-04-01), Favaloro et al.
patent: 4242685 (1980-12-01), Sanford
patent: 5608263 (1997-03-01), Drayton et al.
patent: 6049309 (2000-04-01), Timoshin et al.
patent: 0 996 192 (2000-04-01), None
patent: 2054275 (1981-02-01), None
patent: 05129823 (1993-05-01), None
patent: 1995-3960 (1994-12-01), None
patent: 2000-11121 (2000-02-01), None
Notification for Filing Opinion for Korean App. No. 10-2000-0081709 (Korean, with English translation).
N. Karmakar & M. Singh, Investigations into a Circular Patch Antenna in a Cylindrical Cavity Enclosure, pp. 446-450, Proc. Singapore ICCS '94.
S.T. Jellett & M.E. Bialkowski, The Design of a Shielded, Dual Patch Antenna Array Element for Mobile Satellite Communications, pp. 140-143, Int'l Symp. Antenna and Propagation Soc'y 1993.
European Search Report for EP 00 31 1294, mailed Jan. 13, 2003.

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