Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
1999-07-08
2001-05-08
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S770000
Reexamination Certificate
active
06229484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dual polarized flat antenna device including multi-layered flat antennas such as triplate antennas, and more particularly to such a device wherein transmission and reception efficiency are improved. The present invention is suitably applied to an antenna device used for a mobile unit or the like.
2. Description of the Related Art
FIGS. 1 and 2
show the structure of an antenna device disclosed in “Characteristics of Dual Polarized Flat Antenna” (Katsuya Tsukamoto, et al., Transactions of Institute of Electronics and Communication Engineers of Japan, B-II, Vol. J79-B-II, No. 8, pp. 476-484, August, 1996). According to that publication, an antenna
1
is formed by two triplate antennas
2
and
3
stacked in an orthogonal direction. The lower antenna
2
receives a horizontal polarization while the upper antenna
3
receives a vertical polarization.
The antenna
1
includes stacked layers of a lower ground plate
4
, a horizontal polarization feeding circuit plate (board)
5
, a middle ground plate
6
(radiation circuit plate for a horizontal polarization), a vertical polarization feeding circuit plate
7
, and an upper ground plate
8
(radiation circuit plate). The respective layers are isolated by a dielectric layer with a low dielectric constant interposed therebetween. The feeding circuit plates (boards)
5
and
7
have feeding probes
5
a
and
7
a,
and feeder lines
5
b
and
7
b,
respectively. The horizontal feeding probe
5
a
and the vertical feeding probe
7
a
are provided orthogonal to each other.
The middle ground plate
6
includes twin coupling slots
6
a
serving as radiation elements for each antenna element. As shown in
FIGS. 2A and 2C
, the longer side of the slot
6
a
is orthogonal to the horizontal feeding probe
5
a
in order to gain electromagnetic coupling of the horizontal feeding probe
5
a
in the lower antenna.
On the other hand, as shown in
FIGS. 2A and 2B
, the feeding probe
7
a
of the upper antenna
3
is parallel to the longer side of the slot
6
a,
and a metal portion is disposed on the bottom side of the feeding probe
7
a.
As the middle plate
6
functions as a ground plate, the electromagnetic coupling at the upper antenna
3
can be ignored.
The upper ground plate
8
includes a plurality of radiation windows
8
a
disposed corresponding to the antenna array. The radiation windows
8
a
are square aperture elements for receiving a vertical polarization and for transmitting a horizontal polarization to the lower antenna
2
.
The middle and upper ground plates
6
and
8
serving as radiation circuit plates are formed from metal or printed plates. The middle ground plate
6
functions as a radiation circuit for the lower antenna
2
and as a ground plate for the upper antenna
3
, thereby contributing to a reduction in the number of layers required.
However, as discussed in more detail below, further improvement in efficiency is desired for the above-described dual polarized flat antenna device. Especially when the antenna is mounted on a mobile unit, reduction in height is strongly desired, while maximum performance is required in a wide range of locations. Therefore, a need exists for a high efficiency antenna that can meet such demands.
In a conventional antenna, phases at the twin coupling slots
6
a
(slot pair) of each antenna element are not matched on principle, leading to the possibility of introduction of error in the reception direction. Although the phases at the slot pair can be matched if spacing between slots exceeds one wavelength, it is impractical to implement such a spacing on the antenna array. Consequently, an individual antenna element has a disadvantageously low antenna efficiency. The antenna shown in
FIGS. 1 and 2
overcomes effects of the phase mismatch by cancellation between the multitude of antenna elements. However, when an antenna consisting of a small number of elements, such as an antenna for a moving vehicle, is desired, the above cancellation effects may not be expected. Therefore, improvement in performance of a single element is desired in order to achieve a high antenna efficiency even in such an application as described above.
In addition, a conventional antenna device has a further disadvantage of polarization angle loss when mounted on a mobile unit, such as a motor vehicle. Considering CS broadcast as an example, a horizontal polarization is inclined with respect to the horizon due to the difference in latitude between a transmitting station (satellite) and a receiving station (vehicle), and the same occurs with the vertical polarization. This inclination is the polarization angle. Although there is no need to consider the polarization angle for conventional BS broadcast, in CS broadcast noise is increased due to effects of the polarization angle. If the receiving station is fixed, the direction of the antenna can be set in the beginning so as to avoid the polarization angle loss because the polarization angle remains unchanged. However, mobile units require other techniques for reducing the polarization angle loss because the polarization angle changes with the location.
A conventional antenna device has still another disadvantage because parallel plate mode radiation, electromagnetic waves that propagate between ground plates without contributing to radiation, make it difficult to reduce the height of the antenna as desired. While it is well known to efficiently utilize parallel plate mode waves by arranging antenna elements with an appropriate spacing so that the waves are radiated from other antenna elements. However, in order to reduce antenna height, the number of elements arranged in the height direction must be reduced. Thus, it is desirable to provide an antenna that allows reduction in the number of elements in the height direction while maintaining efficient use of the parallel plate mode.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a dual polarized flat antenna device with a high efficiency. While the present invention solves the above-described problems of the antenna for mobile units, its application is not limited to use in such mobile units.
(1) The present invention relates to a dual polarized flat antenna device including at least one antenna element formed by stacking flat antennas for polarizations in different directions. To achieve the above object, the flat antenna is provided with a patch type feeding probe having patch edges at the opposing ends in the polarization direction. A coupling slot for coupling a lower flat antenna with an upper antenna is disposed over said patch edges at the opposing ends of the feeding probe in the lower antenna.
According to the present invention, electromagnetic waves propagate through the coupling slot, to be received by the patch edges at the opposing ends of the probe. This process is reversed for transmission, as is possible also with all processes described below. In-phase magnetic current is generated in the patch edges at the opposing ends, to thereby match the radiation waves in phase at the opposing edges, i.e. opposing slots. As a result, efficiency of a single antenna element can be improved.
(2) In one aspect of the present invention, the feeding probe of the flat antenna is disposed to face the direction corresponding to a representative value of polarization angles in a traveling area of a mobile unit. According to the present invention, polarization angle loss can be reduced as a whole by directing the probe in accordance with the representative value of polarization angles.
Preferably, the coupling slot for coupling the lower flat antenna with the upper antenna may be disposed to be inclined corresponding to the angle at which the feeding probe is disposed. Such disposition can avoid generation of a cross polarization component resulting from deviation in direction of the probe and the coupling slot.
It may also be preferable for a plurality of antenna elements to be arranged such that they form an el
Alemu Ephrem
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Toyota Jidosha & Kabushiki Kaisha
Wong Don
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