TECHNICAL FIELD

The present invention relates to a portable antenna solution to a radio unit.

BACKGROUND ART

There are many examples of portable antenna solutions. Some portable antenna solutions comprise one or several half-wave dipole antennas attached to a garment. The human body absorbs a significant amount of the radiation from a dipole antenna, since the radiation pattern from a half-wave dipole antenna is shaped like a toroid symmetrical about the axis of the dipole with maximum radiation in the plane perpendicular to the dipole, dropping off to zero on the axis of the antenna. The absorbed radiation due to the radiation pattern of the half-wave dipole antenna results in unnecessary signal losses.

In order to obtain better antenna characteristics, prior solutions suggest that external dipole antennas may be located around the shoulder region of the garment, and the radio unit may be located in a pocket of the garment.

US 2002/0089458 discloses a garment comprising a planar inverted F antenna (PIFA) of a size and shape suitable to be accommodated in the dip between a person's shoulder blades at the upper part of the back. The antenna is connected to telecommunications equipment through a coaxial feed cable attached to a support strap extending over the shoulder over of the wearer and down the front of the torso of the wearer. A drawback with this solution is that long cables are needed between the antennas and the radio unit. The long cables decrease the flexibility of the garment and the cables may break due to bumps and shocks.

There is a need to overcome some of those problems. SUMMARY OF THE INVENTION

The object of the present invention is to overcome some of the previously mentioned problems. This is achieved by a portable device comprising a protective housing and antenna. Further the antenna comprises an antenna element and a ground plane. The antenna is integrally arranged along the protective housing. The protective housing is designed as a spacing element between the antenna element and the ground plane. Further the protective housing is adapted to hold a radio unit. An advantage of an integrally arranged antenna is that no external antenna is needed. Thereby a more robust

construction is obtained. A further advantage is that the portable device can be worn in the proximity of a human body since no external antenna is needed. The protective housing holding the radio unit makes the portable device robust and protects the antenna and the radio unit from impacts and shocks. Another advantage is that long cables are avoided, since the radio unit and the antenna are comprised in the same unit. Thereby the risk of long cables getting stuck in obstacles is avoided. According to one aspect of the invention, the protective housing is adapted to hold the radio unit in a detachable manner. An advantage of holding the radio unit in a detachable manner is that it facilitates removal of the radio unit in order to replace the radio unit, charge the radio unit or clean the portable device.

According to a further aspect of the invention, a transmission line, connecting the antenna element and the radio unit, is impedance-matched to the radio unit. An advantage of the impedance matching is that it results in lower losses due to less reflection between the transmission line and the radio unit, and thus performance of the antenna is improved.

According to another aspect of the invention, the transmission line is a coaxial cable comprising a centre conductor and a surrounding screen, the centre conductor of the coaxial cable being connected to a feed point of the antenna element and the surrounding screen being connected to the ground plane. An advantage of the coaxial cable is that most of a propagated electromagnetic wave is confined to the area inside the cable. The coaxial cable can therefore be bent and twisted without any severe effects. According to a further aspect of the invention, the antenna element is connected to the ground plane. An advantage of this connection is that the impedance matching is improved, which decreases radiation losses due to reflection between the antenna and the radio unit.

According to yet a further aspect of the invention, the protective housing comprises a base plate and at least one side plate attached to the base plate, wherein the ground plane is attached to the base plate and the antenna element is arranged along the extension of at least a part of the side plate so that the side plate forms the spacing element between the ground plane and the antenna element. An advantage of such an arrangement is that it facilitates the construction of the spacing element, since the spacing element constitutes a part of the protective housing.

According to another aspect of the invention, a cover is detachably arranged on the protective housing. An advantage of such an arrangement is that the cover further protects the antenna and the radio unit from impacts and shocks and makes the portable device more robust. According to a further aspect of the invention, the antenna element is arranged on the upper edge of the at least one side plate. An advantage of such an arrangement is that the antenna element is protected from shocks from the surroundings and from being damaged when the radio unit is inserted in or removed from the portable device.

According to yet a further aspect of the invention, the antenna element is of a Planar Inverted-F antenna, PIFA, type. The PIFA type has an antenna element which is electrically connected to the ground plane via a conducting line. An advantage of the PIFA type is that it, and therefore also the portable device, can be kept small since the PIFA type is resonant at a quarter-wavelength, thus reducing the required space needed. A further advantage is that since the PIFA type comprises a ground plane, the damping properties are improved compared to a dipole antenna arranged at a corresponding position, since the PIFA type will be less affected by being positioned in the proximity of a human body.

According to another aspect of the invention, at least one grounded parasitic element is integrally arranged along the protective housing, wherein the at least one grounded parasitic element is inductively coupled to the antenna element. An advantage with the inductive coupling is that the at least one grounded parasitic element in combination with the antenna element enhances the bandwidth of the antenna.

According to a further aspect of the invention, the antenna is attached to a printed wiring board, PWB, material. An advantage is that the PWB material provides robustness and rigidity to the antenna. A further advantage is that the risk for short circuit between the antenna element and the at least one grounded parasitic element decreases, since the PWB material has good insulating properties.

According to another aspect of the invention, the protective housing is adapted to hold the radio unit in a permanent manner. An advantage of holding the radio unit in a permanent manner is that a more compact and solid construction is obtained.

Further the invention relates to a garment adapted to house the portable device and the radio unit, incorporating the above mentioned advantages.

BRIEF DESCRIPTION OF FIGURES The invention will be further described with reference to the accompanying drawings.

Figure 1 shows a perspective view of a portable device, according to an embodiment of the invention, seen from the closed side of the portable device.

Figure 2 shows a view of isolated components of the portable device, according to an embodiment of the invention. Figure 3 shows a perspective view of the portable device, according to an embodiment of the invention, seen from the open side of the portable device.

Figure 4 shows a perspective view of the portable device, according to an embodiment of the invention, seen from the open side of the portable device including the cover on top of the protective housing. DETAILED DESCRIPTION

Figure 1 shows a perspective view of a portable device 1, according to an embodiment of the invention, seen from the closed side of the portable device 1. The portable device 1 comprises a protective housing 11. Further the portable device 1 comprises an antenna, integrally arranged along the protective housing 11. The antenna comprises an antenna element 12 and a ground plane 13. The protective housing 11 comprises a spacing element between the antenna element 12 and the ground plane 13. The protective housing 11 is adapted to hold a radio unit 14. According to an embodiment of the invention, the antenna element 12 and the ground plane 13 is electrically connected via a conducting line. The integrally arranged antenna may be attached to the protective housing 11 with pins, screws or adhesive tape. Further the antenna may be fixed to the protective housing 11 by engaging means or other holding means which may be part of the protective housing 11, for instance through injection moulding of the protective housing 11 around the antenna. It is possible that the ground plane 13 is attached to the protective housing 11 by engaging means and that the antenna element 12 is attached to the protective housing 11 by pins or screws, or vice versa.

According to an embodiment of the invention, at least one grounded parasitic element 17 is integrally arranged along the protective housing 11. The at least one grounded parasitic element 17 is inductively coupled to the antenna element 12. The antenna element 12 and each of the at least one grounded parasitic elements 17 have varying lengths, corresponding to different radio frequencies. Each of the at least one grounded parasitic elements 17 is acting as a resonator, which is excited by the induced electromagnetic field from the antenna element 12 and radiates the radio waves at a frequency in dependence on properties of each of the grounded parasitic elements 17, such as the length of each of the grounded parasitic elements 17. The excitation by the induced electromagnetic field from the antenna element 12 is possible since the at least one grounded parasitic element 17 is inductively coupled to the antenna element 12. This may be accomplished by arranging at least a part of the antenna element 12 and at least a part of the at least one grounded parasitic element 17 in parallel with each other, spaced away from each other by a distance which allows each of the at least one grounded parasitic elements 17 to be excited by the induced electromagnetic field from the antenna element 12. Alternatively, the antenna element 12 may be capacitively coupled to the grounded parasitic element 17.

The integrally arranged grounded parasitic element 17 may be attached to the protective housing 11 with pins or screws. Further the grounded parasitic element 17 may be fixed to the protective housing 11 by engaging means or other holding means which may be part of the protective housing 11.

According to an embodiment of the invention, the antenna element 12 and the ground plane 13 are attached to printed wiring board, PWB, material. It is possible that the ground plane 13 is attached to PWB material but not the antenna element 12, or vice versa.

According to an embodiment of the invention, the antenna element 12 is connected with two conducting lines to the PWB material. The PWB material is attached to the ground plane 13. One of the two conducting lines is connected to the ground plane 13. The other of the two conducting lines is connected to the radio unit 14 via a transmission line 15.

Figure 2 shows a perspective view of isolated components of the portable device 1 according to an embodiment of the invention. The protective housing 11 comprises a base plate 11a and at least one side plate lib attached to the base plate 11a. The ground plane 13 is attached to the base plate 11a. The antenna element 12 is arranged along the extension of at least a part of the side plate lib so that the side plate lib forms the spacing element between the ground plane 13 and the antenna element 12. The spacing element provides space for the radio unit 14 inside the portable device 1. The spacing element has to be higher than the thickness of the radio unit 14 in order to house the radio unit 14 inside the portable device 1. A higher spacing element may lead to lower radiation losses, since the distance between the antenna element 12 and the ground plane increases.

According to an embodiment of the invention, the antenna element 12 is arranged on the upper edge of the at least one side plate lib. Alternatively, the antenna element 12 is integrated at least partly within the side plate lib.

When the antenna element 12 is electrically connected with one conducting line to the ground plane 13 and with another conducting line to the transmission line 15, the antenna element 12 is of a so-called Planar Inverted-F antenna, PIFA, type. This facilitates impedance matching to 50 Ω. The PIFA type is resonant at a quarter-wavelength. The PIFA type does not necessarily have a perfect omnidirectional pattern. Rather, the PIFA type antenna pattern is slightly irregular in different directions. According to an embodiment of the invention, the antenna element 12 is adapted to have its Voltage Standing Wave Ratio, VSWR, minimum (the best matching to 50 Ω) at a radio frequency of 340 MHz. If the antenna element 12 is implemented as a PIFA, then 340 MHz corresponds to about 15-22 cm.

According to an embodiment of the invention, the parasitic element 17 is slightly shorter or longer than the antenna element 12. According to an embodiment of the invention, the parasitic element 17 has its VSWR minimum at 360 MHz while the antenna element 12 is most efficient at 340 MHz. Superimposed, the antenna element 12 and the parasitic element 17 provide a frequency band between 340 MHz and 360 MHz, where the antenna is resonant. By using other lengths of the antenna element 12 and the at least one parasitic element 17 other frequency bands may be covered. A plurality of parasitic elements 17 may be arranged in the portable device 1, having different lengths, shorter or longer than the antenna element 12.

According to another embodiment of the invention, the antenna element 12 and the ground plane 13 are attached to the protective housing 11 by attaching means 18. In figure 2 the attaching means 18 are illustrated as screws. The attaching means 18 may also consist of pegs, bolts, pins or any other means for attaching the antenna to the protective housing 11. The antenna element 12 and the ground plane 13 may be attached to the protective housing 11 by the same or different type of attaching means 18.

According to an embodiment of the invention, a cover 16 is arranged on the protective housing 11. The protective housing 11 and the cover 16 are made of a non-metallic material, preferably plastic. The protective housing 11 and the cover 16 may comprise a plurality of holes to facilitate removal of water from the portable device 1 and to facilitate cleaning of the portable device 1.

Figure 3 shows a perspective view of the portable device 1, according to an embodiment of the invention, seen from the open side of the portable device 1. The transmission line 15 is connected to the antenna element 12 which is configured to connect to the radio unit 14. According to an embodiment of the invention, the transmission line 15 is a coaxial cable comprising a centre conductor and a surrounding screen, the centre conductor of the coaxial cable being connected to a feed point of the antenna element 12 and the

surrounding screen being connected to the ground plane 13. Alternatively, the transmission line 15 may be any type of radio frequency transmission line.

Figure 4 shows a perspective view of the portable device 1, according to an embodiment of the invention, seen from the open side of the portable device 1 including the cover 16 on top of the protective housing 11. The cover 16 is detachably arranged on the protective housing 11. According to an embodiment of the invention, the cover 16 may be attached to the protective housing 11 with the attaching means 18. Alternatively, the cover 16 has engaging means adapted to engage around an edge of the protective housing 11. According to figure 4, the portable device 1 has a rectangular shape. An advantage of that the portable device 1 has a rectangular shape is that the space required to house a radio unit 14 having a rectangular shape is minimised. A further advantage is that the rectangular shape facilitates the construction of the portable device 1, since the arrangement of the antenna element 12 and the ground plane 13 along the protective housing 11 is facilitated by flat surfaces. The portable device 1 may instead have any other shape. For instance, the portable device 1 may have only one flat side, comprising the ground plane 13, wherein the cover 16 has a rounded shape, in order to avoid unnecessary sharp edges and corners. The portable device 1 is, if housed in a garment, preferably mounted with the flat side towards the body of a wearer of the portable device 1. Alternatively, the portable device 1 may have a cylindrical shape. According to an embodiment of the invention, the protective housing 11 and the cover 16 are integrated into one piece, having an opening sufficiently large for the insertion and the removal of the radio unit 14. Preferably, the size of the protective housing 11 is just enough to house the radio unit 14. Further preferably, the protective housing 11 has engaging means for holding the radio unit 14. According to an embodiment of the invention, the protective housing 11 has a plurality of engaging means, wherein each engaging means is configured to hold a radio unit 14 of a certain type and size.

According to an embodiment of the invention, a garment is adapted to house the portable device 1 and the radio unit 14. The portable device 1 and the radio unit 14 may be housed in a pocket or attached to the garment by holding means. It should be mentioned that the portable device 1 and the radio unit 14 may be arranged inside or attached to other units, for instance attached to a belt, attached to a weapon or arranged inside or attached to a vehicle.