Antenna for wireless communications devices

The invention relates to an internal antenna (1) for a wireless handportable communication device (2), comprising: an antenna plate (3) fuinctioning as an radiator, a feed element (5) to feed the radiator (3), and attachment elements (10, 12) to attach the antenna (1) to a wireless communications device (2), which comprises an electrically conductive earth plane (4). The attachment elements (10, 12) comprise a cover structure (12) for bracing the antenna plate (3) on the wireless communications device (2). The antenna (1) further comprises a support frame (10) or spacers (21) for keeping the antenna plate (3) at a distance from the earth plane (4).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an internal antenna for a wireless 
handportable communications device and to a mobile handportable containing 
an internal antenna. 
2. Description of the Prior Art 
Antennas known to be used in mobile stations for the transmission and 
reception of radio-frequency signals include the monopole antenna and the 
helix antenna. In order to guarantee correct electrical operation these 
antennas have to be located in free space outside the case of the mobile 
station. The radio-frequency signals between the radio part of the mobile 
station and the antenna are usually transmitted by means of conductors and 
connectors. 
The monopole antenna is in principle a straight conductor above and 
substantially perpendicular to a conductive plane and its length depends 
among other things on the frequency range of the radio-frequency signal 
used. GSNI mobile communications networks, for example, use the 900-MHz 
frequency range, in which case the corresponding wavelengths in the air 
are in the range of 30 cm, approximately. Then the length of the antenna 
wire, which typically is about .lambda./2 for a monopole antenna, should 
be about 15 cm. In practical implementations the length of the antenna 
conductor can be shortened to some extent by using a so-called lengthening 
coil in the matching elements of the antenna. A known prior-art 
implementation of the monopole antenna in a mobile station is -such that 
the antenna conductor is placed inside a flexible or rigid and protective 
tubular piece of insulating material which is further attached to the 
mobile station by means of a connector. This connector also provides an 
electrical coupling between the antenna and the radio part of the mobile 
station. However, such an antenna is long in comparison to the mobile 
station itself and, placed outside the mobile station, susceptible to 
being damaged, for example by an impact upon dropping. 
Another prior-art implementation of the monopole antenna is a pull-out 
structure such that the antenna conductor or the like placed inside the 
body of a mobile station can be pulled out from the mobile station e.g. 
for the duration of a call. When pulled out to maximum extension the 
antenna conductor is locked and at the same time electrically coupled to 
the radio part of the mobile station. After the call the antenna conductor 
is usually pushed back inside the case of the mobile station. However, 
when the antenna conductor is fully inside the case of the mobile station 
the signal amplification is not as good as it would otherwise be, which 
especially in a weak signal field may cause the connection between the 
mobile communications system and the mobile station to be cut off. Then 
the antenna has to be pulled out from the case of the mobile station if 
the mobile station is to be logged on in the mobile communications system, 
e.g. to receive incoming calls. 
However, such a movable antenna comprises parts that become mechanically 
worn, so in the course of time there may arise a need to replace at least 
part of the antenna elements. Likewise, careless handling of the mobile 
station may damage the antenna conductor especially when being pulled out 
or pushed in. The wear and tear of parts and incorrect handling of the 
antenna may also cause, in addition to the need to replace parts, 
deterioration of the reliability of the mobile station. 
Helix antenna is a conductor wound into a right-hand or left-hand coil 
placed above a conductive plane. The helix structure provides a shorter 
antenna than the monopole structure when the operating frequency range is 
the same. A known prior-art implementation of the helix antenna in mobile 
stations is such that the antenna conductor is placed inside a protective 
cylindrical or conical piece of insulating material which is further 
attached to the mobile station by means of a connector. This connector 
also provides an electrical coupling between the antenna and the radio 
part of the mobile station. Also this structure, being placed outside the 
mobile station, is susceptible to damage caused e.g. by dropping the 
mobile station, as well as to other external impacts. 
Since an external antenna in a mobile station is susceptible to damage, the 
antenna itself and the attachment of the antenna to the mobile station 
have to be made durable and strong, which may impede the attempt to 
achieve the optimum electrical characteristics for the mobile station and, 
above all, increase the price of the antenna. As regards to the assembly 
work of the mobile station, an external antenna structure means more work 
stages and, therefore, increases the cost of the assembly work. The 
antenna also has to be suitable for mass production, which means that the 
connections between the parts of the mobile station and the different 
parts of the antenna have to be suitable for automatic assembly. 
Particularly with small hand-held phones the external antenna may be 
situated near the user's head when he is using the phone, which affects 
the electrical operation of the antenna. Likewise, part of the electrical 
energy radiated by the antenna may be coupled to the user's head. To 
reduce that coupled power the external antenna has to be placed in such a 
manner that it is as far away as possible from the user's head when the 
mobile station is in the operating position. This also results in some 
limitations to the design of the mobile station. 
An antenna known to avoid some of the disadvantages of the external antenna 
is the air-insulated planar inverted F antenna (abbr. PIFA). 
The PIFA antenna comprises a thin parallelogram-shaped antenna plate made 
of a conductive material such as metal or a plate coated with a conductive 
material. The lengths of the sides of the PIFA antenna depend on the 
operating frequency range of the antenna. When the operating frequency 
range is about 880 to 960 MHz, suitable dimensions of the PIFA plate are 
about 50 mm for the long sides and 25 mm for the short sides. The 
dimensions of the antenna plate are proportional to the wavelength of the 
operating frequency range. The usable frequency band can also be made 
wider with a PIFA antenna than with a helix antenna. Then it is also 
easier to manufacture the PIFA antenna such that the manufacturing 
tolerances are sufficient to guarantee the desired electrical operation. 
In the PIFA, the antenna plate is placed substantially parallel to and at a 
distance from the structure serving as the earth plane. The earth plane 
may be e.g. an at least partly conductive protective body inside the 
mobile station. One short side of the antenna plate is short-circuited to 
the earth plane by means of a conductor, and a radio-frequency signal is 
fed to the antenna plate via an electric circuit having a capacitance and 
inductance connected in series. The capacitance and inductance constitute 
a series-resonant circuit the resonating frequency of which is dimensioned 
according to the operating frequency range of the mobile station, which is 
about 880 to 960 MHz, for example. The signal feed point on the antenna 
plate may be located at the short side of the plate, near the short 
circuit. The capacitance in the series-resonant circuit is located e.g. in 
the radio part of the mobile station and the inductance is coupled between 
the antenna plate and the radio part. 
The frequency band of the antenna also depends on the distance between the 
earth plane and the different elements of the antenna plate, so that if 
the antenna plate is moved, the frequency band of the antenna is shifted 
aside from the desired frequency range. In order to prevent this, the 
antenna plate has to be securely attached to a base. In the assembly phase 
of the mobile station the antenna plate has to be attached precisely at 
the correct distance from the earth plane. The attachment shall prevent 
the antenna plate from moving with respect to the earth plane both along 
the plane of the antenna plate and along the direction perpendicular to 
that plane. 
SUMMARY OF THE INVENTION 
An object of this invention is to eliminate aforementioned disadvantages of 
prior-art antenna structures in mobile stations and to provide an antenna 
for a mobile station, which antenna is, as regards the manufacture of the 
different parts of the antenna, as simple as possible and, as regards the 
assembly of the mobile station, as easily assembled and as reliable as 
possible. The antenna advantageously comprises a PIFA antenna. The antenna 
according to the invention is characterized by an internal antenna for a 
handportable communication device having attachment means such as a cover 
structure and a support frame or spacers for bracing a narrow antenna 
plate therebetween, spaced at a fixed distance from the earth plane. The 
mobile station according to the invention is characterized by the 
incorporation of an internal antenna of the aforementioned type. 
The antenna in question has considerable advantages. Using this antenna, 
the antenna can be placed inside the outer case of the mobile station so 
that the antenna is well protected inside the case and faults caused by 
dropping the mobile station and breaking the external antenna can be 
avoided. Thanks to the PIFA antenna, the weight of the mobile station can 
be reduced. The PIFA antenna is also simple so that, as regards to the 
antenna, automatic manufacture and assembly can be applied in the 
manufacture and production of the mobile station. Furthermore, a fact that 
adds to the reliability of the mobile station is that there is no need in 
the PIFA antenna for parts which during operation move with respect to 
each other, and thus wear out. The electrical coupling of the PIFA antenna 
to an internal printed circuit board can also be realised without big and 
strong connectors. 
The antenna of the invention makes it possible to reduce the number of work 
stages in the assembly and at the same time enables accurate positioning 
of the antenna with respect to the earth plane, which is essential for the 
operation of the mobile station. The structure of the antenna also 
prevents the antenna plate from being supported by other parts of the 
antenna, so that external impacts such as bumps, changes of position and 
movements of the mobile station do not alter the dimensioning of the 
antenna as far as electrical operation is concerned. As regards to the 
assembly of the mobile station, the antenna according to the invention is 
reliable and easy to install, thereby being suitable for mass production. 
The small size of the antenna and its adaptability to varying shapes of 
mobile stations enable easy lay-out design. The antenna can be positioned 
such that during operation it is located at the rear side of the mobile 
station with respect to the user, which means that compared to an external 
antenna, considerably less power is coupled to the user's head. At the 
same time, the adverse effect of the head during operation on the 
electrical characteristics of the antenna is reduced. 
The invention is described in more detail with reference to the drawings, 
in which

DETAILED DESCRIPTION 
FIG. 1 shows a preferred embodiment of the antenna 1 according to the 
invention in connection with a wireless communications device such as a 
mobile station 2. The antenna 1 comprises an antenna plate 3 functioning 
as a planar radiator. The mobile station 2 comprises an earth plane 4 
advantageously consisting of an electromagnetic compatibility (EMC) shield 
of the mobile station the task of which is to prevent interference signals 
possibly generated by the mobile station 2 from spreading into the 
environment and, on the other hand, interference signals coming from the 
environment from affecting the operation of the mobile station 2. The 
radio-frequency signal feed is arranged by means of a feed element 5 
coupled between the antenna plate 3 and the radio part 7 (FIG. 3). The 
antenna plate 3 is short-circuited to the earth plane 4 through an 
earthing element 6 so that electrically the antenna 1 is a 
quarter-wavelength antenna. The feed element 5 is advantageously an 
inductance and the earthing element 6 is a conductor electrically 
connected to both the antenna plate 3 and earth plane 4 when the antenna 
plate is installed in its place. 
FIG. 2a shows in more detail an antenna plate panel 8 for the antenna 1 
shown in FIG. 1, and FIG. 2b shows an antenna plate 3 made from the 
antenna plate panel 8. The antenna plate panel 8 is preferably a flexible, 
thin metal plate or an electrically conductive plate, such as a plate 
coated with a conductive material. The antenna plate 3 functioning as an 
radiator is planar and advantageously shaped like a parallelogram or 
polygon. In order to position the antenna plate 3 accurately to a support 
frame 10 guide holes 9 have been punched or drilled on the antenna plate 
which are small as compared to the dimensions of the antenna plate 3. In 
this preferred embodiment illustrated by FIG. 2a the antenna 1 also 
comprises a feed element 5 made from the same panel and preferably at the 
same time as the antenna plate 3 by means of punching or other suitable 
work method, and an earthing element 6. The feed element 5 is realised 
using a stepped metal strip in which the lengths of the steps and the 
width of the strip at each step depend on the desired electrical 
operation. Operation of the feed element 5 in connection with the 
operation of the antenna 1 corresponds to an inductance and the magnitude 
of the inductance depends on the dimensions and operating frequency range 
of the feed element 5. The structural length of the earthing element 6 and 
feed element 5 at least equals the distance of their point of attachment 
in the antenna plate 3 from the corresponding point of attachment in the 
radio part 7 of the mobile station, depicted in FIG. 1 by a signal 
conductor interface 15 and earth conductor interface 16 formed in the 
conductive layer of the printed circuit board 14A. 
The distance of the antenna plate 3 from the earth plane 4 can be different 
at different parts of the antenna plate 3. The antenna plate may be 
curved, for example, as shown in the drawing. The curvature corresponds to 
the shape of the cover structure 12 so that the cover structure 12 
supports the antenna plate 3 evenly. Obviously, the nearer the antenna 
plate 3 and the earth plane 4 are to each other, the greater the 
capacitance between them. This decreases the resonating frequency of the 
antenna 1 to a certain extent, which has to be taken into account when 
dimensioning the antenna plate 3 for the desired operating frequency 
range. 
In this embodiment the antenna plate 3 also comprises spring elements 11 
made from the antenna plate panel 8 by means of punching and bending, for 
example, and attached by one side to said antenna plate. The purpose of 
the spring elements 11 is to brace the antenna plate against the surface 
of the inner side of the antenna cover structure 12 so as to accurately 
press the flexible antenna plate 3 to the support frame 10 in order to 
make sure that the distance of the antenna plate 3 from the earth plane 4 
is correct. 
It is obvious that the shape of the antenna plate 3 may be different from 
the shape of a parallelogram and from planar form so that its positioning 
in the apparatus has more alternatives. Similarly, the number and 
positioning of the spring elements 11 depend on the structure of the 
support frame 10, among other things. And, as far as electrical operation 
is concerned, the earthing element 6 can be replaced by a separate metal 
earthing conductor and the feed element 5 by a separate metal feed 
conductor which, wound into a coil, corresponds in its electrical 
operation to an inductor. An radiator can also be produced by using as an 
antenna plate 3 a molded or cast plastic sheet coated with an electrically 
conductive material or formed by mixing an electrically conductive 
substance in a plastic raw material, for example. 
The antenna 1 according to the invention can also be realised without an 
earting element 6, but then the radiator necessarily increases in size. 
An advantageous implementation of the antenna support frame 10 shown in 
FIG. 2c comprises a planar outer frame 10a made e.g. of plastic by means 
of casting, and, connected to it, a support structure 10b, 10c. The 
support frame 10 is made of a material which is an electrical insulator. 
The thickness of the support frame 10 may vary in different places. The 
shape of the outermost edge of the continuous outer frame 10a in the 
support frame 10 advantageously follows the shape of the antenna plate 3 
supported by it. 
The support frame 10 comprises guide pins 13 attached to its outer frame 
10a or its support structure 10b, 10c such that said pins are 
substantially perpendicular to the plane of the support frame 10. The 
guide pins 13 are placed on the support frame such that in the assembly of 
the antenna 1 the guide pins 13 meet the guide holes 9 at the 
corresponding locations in the antenna plate 3 and fasten it to the 
support frame 10 along the main plane of the antenna plate 3. The support 
frame's outer frame 10a or its support structure 10b, 10c comprises 
preferably flexible locking elements 14 located in the support frame 
preferably at positions corresponding to the outer edges of the antenna 
plate 3, advantageously in such a manner that the edge of the antenna 
plate 3 is braced by them. The purpose of the locking elements 14 is to 
lock the support frame 10 to the antenna cover structure 12. This is 
achieved e.g. by arranging in each locking element 14 a tooth or another 
clawlike part which in the operating position meets its counterpart (not 
shown), such as a groove, in the cover structure 12. The flexible 
structure of the locking elements 14 facilitates that the clawlike part is 
pushed aside and returns when the support frame 10 is installed in the 
cover structure 12. This has e.g. the advantage that the antenna plate 3 
is quickly installed and yet the antenna plate 3 can be accurately 
positioned with respect to the support frame 10 and, thus, with respect to 
the earth plane 4. The cover structure 12 preferably comprises flexible 
counterparts 22 which are pushed against the surface of the antenna plate 
3 when the antenna plate 3 is installed. 
The support frame in FIG. 2c also includes for the feed element 5 and 
earthing element 6 a support base 17 against which the feed element 5 and 
earthing element 6 formed from the antenna plate panel 8 are placed when 
the antenna plate 3 is installed. 
The antenna 1 described above is attached to a mobile station 2 
advantageously by attaching the cover structure 12 with the aforementioned 
structural parts of the antenna 1 e.g. by means of screws or using some 
other known method of attachment to the case 23 or printed circuit board 
14A of the mobile station. FIG. 2d presents a simplified cross section of 
the antenna 1 according to a first embodiment of the invention in the 
operating position, ie. installed in a mobile station 2. 
By way of example, dimensions are provided for the antenna 1 of FIG. 1 to 
be used in a mobile station 2 of the GSM mobile communications system. The 
frequency range is about 880 to 960 MHz, which corresponds to wavelengths 
of about 34 to 31 cm. The size of the antenna plate 3 is about 5.times.2.5 
cm and the distance from the earth plane about 2 mm at a first edge and 
somewhat greater at a second edge. The length of the earthing conductor 6 
is about 11.5 mm and it is connected to a comer of the antenna plate 3. 
The feed element 5 is connected at about 4 mm from the connection point of 
the earthing conductor 6, at a distance of about 2 mm from the edge of the 
antenna plate. 
The earthing conductor 6 can also be realised such that it is coupled 
directly to the earth plane 4, in which case about 2 mm is a sufficient 
length for the earthing conductor in the dimensioning example above. The 
contact between the earthing conductor 6 and earth plane 4 can be realised 
by means of compression, for example. A further method of implementation 
is that a capacitive plate 24, ie. an electrically conductive plate 
electrically insulated from the earth plane 4, is placed on top of the 
earth plane 4. Then the capacitive plate 24 and earth plane 4 form a 
capacitance so that high-frequency signals are short-circuited between the 
capacitive plate 24 and earth plane 4. This arrangement is illustrated in 
a simplified manner in the cross section of FIG. 5. 
FIG. 3 shows an example of a feed circuit for the antenna 1 according to 
the invention, comprising a radio part 7 of a mobile station, said radio 
part comprising, among other things, a transmitter/receiver TX/RX and an 
matching capacitance C. The matching capacitance C and the inductance used 
as an antenna feed element 5 constitute a series-resonant circuit 
preferably tuned to the operating frequency range of the antenna 1, thus 
increasing the bandwidth of the antenna 1. 
FIG. 4 shows an exploded view of the antenna 1 according to a second 
preferred embodiment of the invention. This differs from the embodiment 
depicted in FIG. 1 e.g. in that the feed element 5 and earthing element 6 
are implemented in a separate feed module 18 which can be attached by 
means of soldering, for instance, to the signal conductor interface 15 and 
earthing conductor interface 16 on the printed circuit board 14 in the 
mobile station. An advantageously opposite surface of the feed module 18 
has contacts 19, 20 which connect the feed element 5 and earthing element 
6 to the antenna plate 3 in the operating position. This embodiment does 
not include a support frame 10 proper, but the antenna plate has 
intermediate supports 21 by means of which the distance of the antenna 
plate 3 from the earth plane 4 is kept right. In this embodiment, 
installation is carried out directly to the mobile station 2, first 
attaching the feed module 18, then placing the antenna plate 3 at the 
right spot above the earth plane 4. On top of the antenna plate 3 it is 
placed a cover structure 12 which has preferably flexible protrusions 22 
by means of which the antenna plate 3 is pressed against the earth plane 4 
of the mobile station. Then the antenna plate 3 is held securely in its 
place in spite of possible impacts and other external forces directed to 
the mobile station 2. 
It is obvious that the positioning and number of guide pins 13 and locking 
elements 14 in the support frame may vary according to the application in 
question. The locking elements may also be located in the support frame in 
such a manner that they penetrate the antenna plate through holes in it. 
The locking and guiding functions can also be combined e.g. by forming in 
the guide pins 13 a claw or the like which serves as a locking element 14. 
The locking of the support frame 10 to the cover structure 12 can also be 
arranged using other attaching elements, such as screws or adhesives. 
The antenna cover structure 12 shown in the drawing is advantageously a 
parallelogram-shaped piece made by casting from a plastic material and 
having a convex outer surface. The concave inner surface of the cover 
structure 12 has recesses (not shown) made by drilling or in conjunction 
with the casting. The recesses are located in the cover structure 12 at 
locations corresponding to those of the support frame's guide pins 13 when 
the antenna is fully assembled. The function of the recesses is to align 
the support frame 10 with respect to the cover structure 12. The concave 
inner surface of the cover structure 12 also includes locking grooves made 
by drilling or in conjunction with the casting which are located at 
locations corresponding to those of the support frame's locking elements 
14 so that the support frame 10 can be locked to the cover structure 12. 
It is obvious that the shape of the cover structure's 12 edge and the 
convexity of the outer side may vary greatly according to the components 
in the immediate vicinity of which the antenna 1 is attached in the mobile 
station 2. Likewise, the cover structure 12 may comprise one or more holes 
for the attachment of the antenna 1 to the mobile station 2 by means of 
screws. The cover structure 12 may also have, attached to the collar or 
edge part, one or more locking elements 14 the purpose of which is to 
attach to edge locking grooves located at the corresponding locations in 
the mobile station 2. The attachment of the cover structure 12 secures the 
correct distance of the antenna plate 3 from the antenna earth plane 4. 
The simple structure of the antenna 1 is a considerable advantage in the 
assembly work. The antenna plate is aligned with the frame structure by 
means of guide pins 13 and antenna plate guide holes 9, and the antenna 
plate 3 is formed according to the shape of the support frame 10. The 
support frame 10 with the antenna plate 3 is aligned with the inner 
surface of the cover structure 12 by means of guide pins 13 and recesses 
in the cover structure. The locking elements 14 in the support frame 10 
are locked into edge locking grooves in the cover structure 12. Spring 
elements 11 on the antenna plate 3 are pressed against the inner side of 
the cover structure 12 and thus push the antenna plate 3 accurately 
against the support frame 10. The compressive effect can be enhanced by 
placing on the inner surface of the cover structure 12 counterparts 22 
made of a flexible material. 
The structure of the antenna 1 according to the invention was above 
described in conjunction with a mobile station 2, but it is also 
applicable to other wireless communications devices that use 
radio-frequency signals in their communications. Such devices include 
radio telephones and cordless telephones, for example. 
The present invention is not limited to the embodiments described above but 
the invention can be applied within the spirit and scope defined by the 
claims set forth below.