Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2000-06-07
2001-06-26
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000, C455S090300
Reexamination Certificate
active
06252554
ABSTRACT:
The invention relates to dual mode antennas particularly suitable for mobile stations. A dual mode antenna means that it has two electrical operating states and the transition between the states is performed by changing the mechanical structure of the antenna.
Of dual mode antennas there are previously known the helix/whip antenna combinations, where the whip section is either within the mobile station or extended outside it. The last mentioned position is used when required, in order to improve the quality of the connection. The helix is stationary on the frame of the mobile station, whereby the whip extends through the helix, or is located at the end of the whip, whereby both sections are movable. A disadvantage in antennas of this type is that the helix section always remains outside the mobile station where it forms an inconvenient projection.
From the prior art is further known, i.a. from the publication WO98/56066, a dual mode plane antenna according to FIG.
1
. It contains a ground plane
11
and a radiating plane
12
raised slightly above the ground plane. The radiating plane can be moved along the grooves in a dielectric body. A peace of the grooved dielectric boy
18
is drawn in
FIG. 1
so that it can be seen at one edge of the plane
12
. When the plane is retracted the structure operates as an antenna of the planar inverted F-antenna (PIFA) type. Then the feeding is via the line
13
to a point
14
of the plane
12
. A short circuit between the plane
12
and the ground plane
11
is made at another position
15
. When the plane
12
is extracted, in the position shown in
FIG. 1
by a dotted line, the structure operates as a monopole antenna. Then the feeding is via the line
13
and the transmission line
16
to the plane
12
at a point
17
. This arrangement also comprises a short circuit of the transmission line
16
when the plane
12
is retracted, and an impedance matching when the plane
12
is extracted. These arrangements are not visible in FIG.
1
.
A disadvantage of the above described structure is the unreliability of the galvanic connection in such positions where the other part is movable. The connection can be degraded due mechanical wear of the grooves in the dielectric body, or due to a deformation of the radiating plane as a result of the use.
The object of the invention is to reduce the mentioned disadvantages relating to prior art. The antenna structure according to the invention is characterised by what is expressed in the independent claim. Some advantageous embodiments of the invention are presented in the dependent claims.
The basic idea of the invention is as follows: The antenna structure comprises an antenna of the PIFA type, which is located within the covers of the mobile station, and whip element which can be moved in relation to the PIFA. The PIFA can be a single frequency or a dual frequency antenna. When the whip element is in the lower position it has no substantial coupling to the parts of the PIFA. When the whip element is in the upper position or extracted, then its lower end forms a galvanic or capacitive coupling with the radiating element of the PIFA. If the PIFA is a single band antenna the extracted whip element substantially changes the resonant frequency of the PIFA, so that the whip element will be the radiating element at the operating band. If the PIFA is a dual-band antenna the whip element may change one of the resonant frequencies of the PIFA, preferably the lower resonant frequency, so that only the extracted whip operates as the radiating element at the lower operating band. At the higher operating band the conductive plane of the PIFA functions as the radiating element. Alternatively the extracted whip element only improves the operation of the antenna at the lower operating band without changing the resonant frequency of the PIFA. The feeding of the whip element is arranged via the PIFA, without any additional components.
An advantage of the invention is that a mobile station provided with an antenna of the invention has no inconvenient projecting parts when the mobile station is not used for communication. However, the properties of a projecting whip element can be utilised when required. The bandwidth and the gain of the PIFA depend strongly on the distance between the planes of the PIFA. The characteristics of particularly small-sized PIFA are not necessarily sufficient in all situations. As known, a whip antenna provides a good electrical performance. By combining a PIFA and a whip antenna the best properties of both antennas can be utilised.
A further advantage of the invention is that the structure according to the invention is reliable as there are a minimum of moving parts, and even a frequent moving of the whip element corresponding to normal use does not cause any substantial changes in the electrical properties. An advantage of the invention is further that the manufacturing costs of the structure are relatively low because it is simple and suited for series production. An advantage of the invention is further that the whip element generally causes a lower specific absorption rate value (SAR) than a corresponding PIFA. Further, an advantage of the invention is that the shorting of the gap in the radiating pattern of the PIFA, which realises the change of the resonance frequency, makes the antenna less sensitive to the effects of the user's hand than a conventional PIFA or a PIFA which is not shorted by the whip.
REFERENCES:
patent: 5327151 (1994-07-01), Egashira
patent: 5945952 (1999-08-01), Davidson
patent: 6031496 (2000-02-01), Kuittinen et al.
patent: WO 97/49141 (1997-12-01), None
patent: WO 98/65066 (1998-12-01), None
patent: WO 99/031 (1999-01-01), None
Abstract ofElectronics and Communications in Japan, Part 1, vol. 80, No. 8, sivuilla 39-49, Aug. 1997.
Abstract ofTransactions of the Institute of Electronics, Information and Communication Engineers B-2, vol. J81B-2, No. 10 Sivut 897-905, Oct. 1998.
Abstract ofNational Technical Report, vol. 42, No. 1, sivuilla 143-148, Feb. 1996.
Isohätälä Anne
Mikkola Jyrki
Tarvas Suvi
Clinger James
Darby & Darby
Le Hoang-anh
LK-Products OY
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