Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Reexamination Certificate
1998-11-18
2002-01-15
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
C343S795000, C343S7000MS
Reexamination Certificate
active
06339406
ABSTRACT:
The present invention relates to an antenna for radiating and receiving circular polarized electromagnetic signals with microwave or mm-wave frequencies.
Such antennas are particularly interesting for communication scenarios, in which a light of the sight (LOS) propagation is to be used. The typical application can be in satellite-earth-communication, indoor LOS wireless LANS or outdoor LOS private links. The special advantage of such circular polarized antennas, besides that there is no need for an antenna orientation, is the feature of the additional physical attenuation of the reflected waves due to the polarization rotation changes, which makes the propagation channel much better and the overall system more resistant in the case of a multipath propagation. This advantage appears particularly when a LOS path is existing.
There are mainly two major application areas, where circular polarized antennas with particularly shaped antenna characteristics are required. The first application is a uniform coverage application, in which a circular polarized base or remote station antenna communicates with a mobile or stationary antenna in an indoor environment or in which a circular polarized satellite antenna communicates with earth antennas. The second application is an outdoor application, in which a circular polarized antenna located on an land mobile platform (e.g. a car or a train) communicates with a satellite.
In the first application the uniform coverage is the main problem. In an indoor application, which is e.g. shown in
FIG. 1
, the uniform coverage is required in the case, where an indoor circular polarized antenna
1
for a base station or a remote station with a LOS communication link, e.g. with an antenna
5
located on a laptop
4
or an antenna
7
located on a personal computer
6
, as shown in
FIG. 1
, is considered. If the circular polarized antenna
1
has a common radiation pattern, the signal strength Gmax at the edge of the receiving zone is attenuated much more compared to the strength Gmin in direction of a central axis A of the circular polarized antenna
1
because of the fact that the receiver at the edges receives electromagnetic waves, which have passed a larger distance, compared to those in the center of the receiving antenna, so that the physical attenuation is larger. This difference can be clearly seen in
FIG. 1
, where one has shortest distance to larger distance ratio variations between 1:4 to 1:8 leading to a physical attenuation level difference from 12 to 18 dB. In this case and if h
2
−h
1
=1,5 m, the cell diameter will be between 11.6 m and 27,3 m.
In an outdoor environment, in which a circular polarized satellite antenna is in communication with one or more earth antennas the uniform coverage problem described above is similar. The following explanations are related to the indoor environment, but are also true for the outdoor environment of the first application. A constant flux illumination of a cell, for example in
FIG. 1
a room with a ceiling
2
and floor
3
, whereby the circular polarized antenna
1
is located in the middle of the ceiling
2
, implies that the elevation pattern G(&PHgr;) of the circular polarized antenna, i.e. the base station antenna
1
in the example of
FIG. 1
, ideally compensates the free space attenuation associated with the distance d between the transmitting antenna and the receiving antenna. In order to optimize the transmitted power level, e.g. by an increase of the communication ratio or a reduction of the transmitted power for a constant communication ratio, and to minimize the necessity of a power control or to minimize the required power control range, there are two approaches. The first approach is for a case, in which the receiving antenna is a pointed antenna, whereby the antenna pattern should correspond to the ideal radiation pattern of an antenna as shown in FIG.
2
. In an ideal case, if a mobile or portable antenna terminal has a common antenna pointed directly to the circular polarized antenna (base station antenna), the elevation gain G of the ideal radiation pattern is designed by the following equation:
G=G
min×sec
2
&PHgr;=G
×[(
h
2
−h
1
)
2
+R
2
]/[(
h
2
−h
1
)
2
] for &PHgr;<&PHgr;max
G=0 for &PHgr;>&PHgr;max
The parameters are shown and explained in reference to
FIG. 1. h
1
is the vertical distance between the ceiling
2
, on which the circular polarized antenna
1
is located, and the floor
3
. h
2
is the vertical distance between the mobile antenna
5
,
7
and the floor
3
. R is the radial distance of the mobile antenna
5
,
7
from the central axis A of the circular polarized antenna
1
. d is the distance between the circular polarized antenna
1
and the corresponding mobile antenna
5
,
7
. &PHgr; is the angle between the central axis A of the circular polarized antenna
1
and the direction of the distance d.
The maximum Gmax of the radiation pattern G occurs at &PHgr;=&PHgr;max and the minimum Gmin at &PHgr;=0, i.e. the direction of the central axis A. A rough estimate of the antenna gain G can be obtained from the above formula in view of
FIGS. 1 and 2
, which represent the maximum directivity calculated for an ideal sec
2
&PHgr; pattern as a function of R, h
1
and h
2
, as is expressed in the above equation.
The second approach is that in a case, in which both communication antennas are the same, the sum of their radiation patterns should give the characteristics described in the above equation.
The problem of obtaining such an ideal radiation characteristic is partially solved in the state of the art for linear polarized antennas by utilizing only non-planar and non-printed structures, e.g. by a wave guide antenna with dielectric lenses or a monopole antenna with a shaped reflector. The first solution requires a very large dielectric body which increases the weight, size and finally the costs of the antenna. This antenna is therefore impractical for a production of a large number of antenna, especially for lower frequencies. The second solution has principle disadvantages in shadowing in the middle of the antenna pattern, in reproducibility problems as well as in a requirement for a very large reflector plane. Finally, both of these solutions do not show circular polarization and do not allow a printed planar assembly, which makes antenna solutions cheap in the production and more suitable for different applications.
Known circular polarized printed planar antennas usually utilize a microstrip technology or a strip-line with different variations of feeding effects. However, in these approaches is the main beam the same as the plane vector of the printed structure, so that a uniform cell coverage is not assured. Further, they only allow a relatively narrow band application due to the frequency selective matching and the axial ratio. One solution of achieving a circular polarization of the microstrip patches is by means of two feeding points within one patch, as in U.S. Pat. Nos. 5,216,430, and in 5,382,959. Another solution of achieving circular polarization of the microstrip patches by means of a particular shaping of the orthogonal patches by cutting the corners or by making notches are disclosed in EP 0434268B1 and in EP525726A1.
The second application for circular polarized antennas is in a case, in which circular polarized signals are transferred between a stationary satellite
8
and an circular polarized antenna
10
, which is e.g. located on the roof of a car
9
, as shown in FIG.
3
. In
FIG. 3
, a typical scenario of such an outdoor application is shown. In
FIG. 4
, an ideal pattern for an outdoor application for a communication between a satellite
8
and a circular polarized antenna
10
located on a land mobile platform (car
9
) is shown. For such an ideal antenna pattern, a tracking device for the circular polarized antenna
10
is not needed, so that regardless of the orientation of the car
9
the pattern of the circular polarized antenna
Brankovic Veselin
Nesic Aleksandar
Frommer William S.
Frommer & Lawrence & Haug LLP
Le Hoang-anh
Shallenburger Jol H.
Sony International (Europe) GmbH
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