A multiband antenna for a portable terminal apparatus.
TECHNICAL FIELD
The present invention relates to a multiband antenna for a portable terminal apparatus, such as a cell or mobile telephone, comprising an earth plane and an electrically conductive antenna pattern disposed a distance therefrom and formed for resonance in one lower and one upper frequency range.
BACKGROUND ART
A plurality of different designs and constructions of mobile telephone antennas are previously known in the art which can operate within two or three different frequency bands. Such antennas normally occupy a volume of 5 cm3 or more. Prior art antennas must either be disposed a secure distance from an earth plane or must co-operate with such a plane.
According as the dimensions of mobile telephones are shrinking, the space in the proximity of their antenna is become more and more at a premium for placing electric components such as loudspeakers, an IR transceiver, a vibrator, volume controls etc. All such components need a base for their mounting in position but also conductors, as well as a DC return conductor to the earth of the mobile telephone. Connecting such components to the earth plane of the mobile telephone would entail that, also in RF respects, they would be connected to earth. This would harmfully affect the function of the antenna if the distance to the antenna was slight.
PROBLEM STRUCTURE
The present invention has for its object to design the multiband antenna described by way of introduction so that it may operate within two relatively broad frequency ranges which each one encompasses two frequency bands, such as GSM 850 and 900, and in addition DCS and PCS. The present invention further has for its object to design the multiband antenna described by way of introduction in such a manner that it will be extremely compact and that the surrounding space may also be utilised for other functions and/or mounting of other electric components without, to this end, disrupting the function of the antenna. Finally, the
present invention has for its object to realise a mounting base for electric components in the proximal area at the antenna.
SOLUTION
The objects forming the basis of the present invention will be attained if the multiband antenna described by way of introduction is characterised in that the earth plane has a first section which, in terms of RF, is separate and discrete from a second section of the earth plane, that the antenna pattern is disposed a distance from the first section of the earth plane and on a carrier of electrically insulating and non-magnetic material, the carrier, in terms of configuration and size, approximately coinciding with the first section of the earth plane.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings. In the accompanying Drawings:
Fig. 1 is a perspective view of a multiband antenna according to the present invention; and
Fig. 2 shows, in the flattened state, a modified embodiment of an antenna pattern according to the present invention.
DESCRIPTION OF PREFERRED EMBODIMENT
In the description which is to be given below of the subject matter of the present invention, positional and directional indications will be given. Principally, these refer to Fig. 1 so that, for example, a "front" side is a side that is turned to face towards the observer of the Figure.
The multiband antenna which will be described in greater detail hereinbelow may be manufactured with extremely small space needs, approx. 3.5 cm3. In addition, it may be considered as a broad band dual band antenna or as a four band antenna which can operate at least between the frequencies 825 and 960 MHz in a lower frequency range and at least between the frequencies 1.71 and 1.99 GHz in an upper frequency range. These frequencies
correspond to GSM 850 and 900 as well as DCS and PCS, respectively. If the antenna is considered as a broad band dual band antenna, the band width is of the order of magnitude of 15% within each one of the frequencies.
In Fig. 1, reference numeral 1 relates to an earth plane in its entirety, reference numeral12 to an antenna pattern and reference numeral 3 to an RF generator. The earth plane 1 is disposed on a circuit card for the mobile telephone, the circuit card normally being multi-ply so that it has conductive layers on both the front and the rear sides. The circuit card may thus be double-sided. The earth plane 1 is divided into a first section 4 and a second section 5. Both of the sections of the earth plane are separate and discrete from one another in electric respects by the intermediary of a slot 6 which is through-going through the electrically conductive layer of the circuit card both on the front side and on the rear side. Suitably, the rear side and front side of the circuit card are electrically connected to one another within each one of the first section 4 and the second section 5. Such an overbridging between the front and rear sides of the circuit card can, for example, be realised by through-plating.
In addition to the electric function of serving as earth plane, the circuit card 1 which forms the earth plane serves the function of a mounting or securement base for electric components, such as a loudspeaker, an IR transceiver, a vibrator, volume controls etc.
The second section 5 of the earth plane 1 constitutes earth for the mobile telephone in terms of both DC and RF. It will be apparent from the Drawing that the RF generator 3 is earthed via a conductor 7 in an earthing point 8 on the second section 5 of the earth plane 1.
The first section 4 of the earth plane 1 is only earthed in terms of DC and receives its earth potential via an inductance 9 which cuts off RF frequencies between the two sections. Preferably, the inductance 9 is connected to the sections 4 and 5 of the earth plane on the rear side of the earth plane 1, i.e. that side which is turned to face away from the antenna pattern 2. In that the first section 4 of the earth plane is separate and discrete in RF terms from the rest of the earth plane, it will appear from the antenna pattern 2 as non-existent or transparent.
The antenna pattern 2 has a high frequency portion 10 and a low frequency portion 11.
According to the present invention, the antenna pattern 2 is disposed in its entirety on a carrier 12 which, in the illustrated embodiment, is manufactured from an electrically insulating and non-magnetic material, for example a suitable plastic material. If an insulating material is selected whose dielectric constant is >1, this implies that the physical dimensions of the antenna pattern 2 may be reduced. In its major embodiment, the carrier 12 is in the geometric form of a box which may have parallelepipedic or other geometric configuration and which, in one practical embodiment, may have the approximate dimensions of 35 x l7 x 6 mm. The box has an open rear side which, thus, is turned to face towards the circuit card 1 and, more precisely its first section 4. The open side of the box coincides approximately in terms of configuration and size with the first section 4 of the earth plane 1. It will be apparent from the Drawing that the slot 6 is located but an insignificant distance beneath the lower side of the carrier.
In many situations, the intention is to have as large an earth plane-free area in RF terms as possible at the antenna pattern 2. In such cases, the slot 6 may be located considerably further down a greater distance from the lower edge of the carrier 12.
Further, the box has a front side which is closed and which may thus be described as the bottom of the box. The upper and lower sides of the box are also closed and constitute longitudinal sides, while their ends, which are also closed, are of considerably lesser height than the length of the longitudinal sides.
In alternative embodiments, the configuration of the box may be adapted to the configuration of the casing in which the antenna device is housed, so that, for example, one or more of its defining surfaces are more or less arched. The corners may also be more or less rounded. Further, the corners need not be at right angles.
The low frequency portion 11 of the antenna pattern 2 is placed on the outside of the substantially planar and closed side of the box, i.e. its front side or bottom. The high frequency portion 10 is located on an upper longitudinal side of the box and is, therefore, located on that side of the box which is turned to face away from the second section 5 of the earth plane 1. The antenna pattern 2 may be produced in its entirety by so-called MID technology (Moulded Interconnected Device), but it may also consist of a flexfilm or other electrically conductive layer disposed on the box.
In one alternative embodiment, the high frequency portion of the antenna pattern 2 may also be disposed on the outside of the bottom of the box 12.
The box-shaped carrier 12 forms, together with the first section 4 of the circuit card, a closed space which may be utilised for mounting different components in the mobile telephone, since the first section 4 of the earth plane 1 is only DC-earthed. Preferably, this closed space may be utilised as a resonance box for a loudspeaker included in the mobile telephone.
The low frequency portion 11 of the antenna pattern 2 which is disposed on the outside of the closed bottom of the box has an excitation or supply section 13, an intermediate section 14, which is the major radiator, and a top section 15 which serves the function of a capactitative end loading for the intermediate section. Both the supply or excitation section 13 and the top section 15 are in the form of electrically conductive surfaces disposed on the carrier which, in the vertical direction, cover the entire height of the carrier and which extend from the opposing short sides of the carrier a distance in on the planar front side of the carrier. The intermediate section 14 is designed as a meander on the planar front side of the carrier and is galvanically connected both to the excitation or supply section 13 and the top section 15.
The intermediate section can hereby be given an electric length that is greater than its physical length.
The high frequency portion 10 of the antenna pattern 2 is, as was mentioned above, preferably placed on the upper side of the box-shaped carrier and is in the form of an elongate, strip- shaped conductor 16 which, at its one end, has a broadened portion 17 which is galvanically connected to the upper edge line 18 of the excitation or supply section 13, and which may be of one piece manufacture therewith.
The length of the strip-shaped conductor 16 determines the resonance frequencies in both of the upper frequency bands. If needed, the strip-shaped conductor 16 may be given such a length that its outer, free end is folded over the edge line 19 and extends down a certain degree on the end surface of the box-shaped carrier 12.
The greater part of the length of the low frequency portion 11 of the antenna pattern consists of the meandering intermediate section 14, which implies that the physical space requirements
are reduced. The capacitative end loading, which the top section 15 constitutes, makes a further contribution to it being possible to make the low frequency portion 11 physically shorter than its electric length and also that a well-defined termination is obtained.
The antenna pattern 2 has an excitation or supply point 20 and an earth point 21. The earth point and the supply point lie at diagonally opposing corners of the supply section 13, which, in the illustrated embodiment, is rectangular in shape. The rectangular shape implies that there are great possibilities for optional placing of the supply point 20 and the earth point 21. The earth point 21 is connected via an inductance 22 to the second section 5 of the earth plane 1. The mutual positioning of the supply point 20 and the earth point 21 determines the excitation or supply impedance of the antenna. By suitable positioning of both of these points, the antenna may be adapted to the impedance of the mobile telephone, normally approx. 50Ω.
The intermediate section 14 of the antenna pattern is connected to the supply section 13 in the proximity of the upper edge line 18 of the supply section 13, whereby this connection point and the earth point 21 will be located at opposing end areas of this edge line.
DESCRIPTION OF ALTERNATIVE EMBODIMENTS
The modified antenna pattern according to Fig. 2 is shown in the planar, flattened state, i.e. before being bent along the bending line 24a, 24b, 25a and 25b intimated by broken lines and applied on the box-shaped carrier 12.
In the embodiment according to Fig. 2, both the low frequency portion and the high frequency portion of the antenna pattern are disposed substantially on the front side of the carrier 12.
According to Fig. 2, the antenna pattern 2 also displays, in this embodiment, a supply section 13, an intermediate or extension section 14, and a top section 15, where the intermediate section and the top section are, in terms of function, identical with the above-described counterparts, even though their geometric configuration is slightly different. As in the above- described embodiment, the resonance frequency is determined in the lower frequency bands by the total length of the three sections 13, 14 and 15.
In the embodiment according to Fig. 2, the antenna pattern has portions which extend outside the edge lines of the front surface of the carrier 12 and which are folded in on the upper, longitudinal defining surface of the carrier, both of its opposing end surfaces and its lower, longitudinal defining surface. In Fig. 2, these portions consist of the portions that are located outside the fold lines 24a, 24b, 25a and 25b.
According to Fig. 2, the supply section 13 has a groove 26 which separates an earth connection 27 from remaining parts of the supply section, which has an RF connection extending from a lower edge of the supply section 13 and parallel with the earth connection 27. The groove 26 terminates at the upper, left-hand corner of the supply section 13, for which reason the earth point 21 on the supply section 13 has the same positioning as according to Fig. 1.
In Fig. 2, the supply section 13 has a projection 29 which extends in the longitudinal direction of the meander 14 towards the top section 15. This projection entails that the high frequency resonances of the antenna pattern 2 may be realised in the supply section 13 and the projection 29. In such instance, the length of both of the broken lines 30 and 31 determines these resonance frequencies.
The supply point 20 to the supply section may be considered as being located in the intersection between the two broken lines 30 and 31.