ANTENNA ARRANGEMENT AND A METHOD FOR REDUCING SIZE OF A WHIP ELEMENT IN AN ANTENNA ARRANGEMENT
TECHNICAL FIELD OF THE INVENTION
The present invention relates to antenna arrangement, and specially an antenna arrangement including a microstrip antenna and a whip element. The antenna arrangement comprises a first antenna element in form of a microstrip element, a second element and a third element in from of a whip element.
DESCRIPTION OF THE RELATED ART
The wireless forms of communications have become a standard way of communication. There are many types of means for conducting a wireless communication, such as cordless telephones, lap top computers with wireless modems, satellite and cellular telephones.
The communication device, i.e. the mobile handsets rapidly become smaller and lighter and the globalization demand, multiple communication functions and standards being combined into a single unit, e.g. for communicates in multiple frequency bands.
There are a variety of different radiotelephone systems in use today. These include different analogue or digital CDMA (Code Division Multiple Access) and TDMA (Time Division Multiple Access) based systems like GSM (Global System for Mobile telecommunication), AMPS (Advanced Mobile Phone System), DAMPS(Digital Advanced Mobile Phone System), PCS (Personal Communication Services), DCS (Digital Communication System) PCN (Personal Communication Networks ), PDC 800 and 1500 and different cordless telephone systems.
Different systems operate in different frequency bands, thus requiring different antennas for maximum efficiency.
Over the past years, since the first PIFA (planar inverted-F antenna) was disclosed, there have been several types of microstrip antennas with both a feed and a ground connection. Several methods of unique feeding or loading arrangements of the antenna (or combinations of both) have been disclosed.
In order to reduce the size of a microstrip antenna, the antenna requires a load, either capacitive or inductive. An inductive load consists of slots within the antenna and a capacitive load is formed by either a dielectric material placed at certain locations or bringing the metal closer to the ground plane. Both methods of forming a capacitive load require three-dimensional structures.
To address multiple frequency bands, there are several know methods. A parasitic (or galvanic coupled) element may be placed above the antenna, where this parasitic element would have a resonance at a higher frequency band. This layered construction of the antenna requires more complex mass-production techniques than single layer microstrip antennas.
Alternatively, the antenna may consist of several elements parallel to each other. Although the antenna consists of only one layer, the parallel elements have a strong coupling, making it difficult to tune each element separately.
Furthermore, internal antennas provide the handset designer with more design freedom.
However, these antennas are performance limited. In addition, the performance of the antennas suffers when, for example, the user places their finger over the antenna (easy to do as handset size decreases). One solution is to couple the internal antenna to a whip. There are several patents covering both galvanic and capacitive connections from an internal antenna to a quarter- wavelength whip. As the phone size decreases, however, the phone is unable to accommodate a quarter-wavelength whip at low frequencies (i.e. GSM and DAMPS).
Prior art discloses several technics:
A planar inverted-F antenna is described in US 5,764,190 that is provided with a capacitive load that allows the dimensions of the antenna to be reduced from a conventional λ/4 to λ/8. GB 2 272 575 discloses a dual antenna for microwave and lower band frequencies. A microwave patch antenna 2 is directed vertically upward for communication with satellite or aircraft and a monopole, whip antenna is arranged for omnidirectional communication in the azimuth plane. In one embodiment, for microwave and VHF, the monopole antenna is constituted by the outer conductor of a coaxial feed to the patch, the VHF and microwave signals being mutually isolated by their respective skin effects inside and outside the coaxial outer conductor. In another embodiment, the monopole is an extension of a coaxial line inner conductor, the outer of which penetrates the patch antenna ground plane and patch and shorts the two together at a voltage node. The patch is fed separately by conventional coaxial feed
WO 97/49141 discloses an antenna means for a portable radio communication device, in particular a hand-portable mobile telephone, having at least one radiating element that has a meandering and cylindrical configuration. This structure is specifically advantageous in combination with an extendable and retractable whip antenna and, when having two or more meandering radiating elements, in multi-band radiating structures. The antenna device is suitable for manufacturing in large quantities, for example by a flexible printed circuit board technique.
WO9718600 discloses an antenna means for a portable radio communication device. It includes a radiating first element having a meander geometry being relatively flat and without any complete loops or turns, a radiating second element having a meander, helical, rectangular or straight geometry. The first and second elements interact to provide one or more modes of antenna operation and the first element feeds the second element in at least one operational mode. Further, an extendable and retractable feature of the second element is disclosed, as well as an antenna adapter for external connection of the inventive antenna means to an auxiliary antenna.
An antenna device for a hand-portable radio communication unit including a casing with a ground plane means cooperating with the antenna device is disclosed in WO 99/03166. The antenna device comprises first and second radiating elements being tuned to different resonant frequencies and having a common feed point. The radiating elements are disposed in a compact arrangement on a support means so as to be confined entirely in the casing. SUMMARY OF THE INVENTION
The main object of the present invention is to overcome the drawbacks of the prior art by means of a simple but yet an efficient antenna.
Another object of the present invention is to provide an antenna arrangement, which combines an internal antenna with a short whip, preferably a quarter wavelength whip, where the whip length is reduced, preferably by 50 to 60% or more.
Therefore in the initially mentioned antenna arrangement, the second and third elements are arranged between said microstrip element and a ground plane and said microstrip element is arranged with an opening to allow radiation from said second element.
In one preferred embodiment said second element is a meander, helical or straight line antenna element and said second and third elements are arranged in parallel.
Preferably, said whip connects to said second element in an extracted position, and the whip connects to said second element through galvanic, capacitive or inductive connection.
Advantageously, the second element is provided as spring for said whip.
The coupling between the first element and the second element is achieved galvanically, capacitively or inductively.
Preferably, the first element includes slits as capacitive and/or inductive loads. The antenna it is a single, double and/or multi-frequency antenna.
In an advantageous embodiment, the antenna further includes a supporting member for supporting said first antenna element. The supporting member includes a compartment for receiving said second element. In an advantageous embodiment, the second element is a helical antenna and said whip (340) is arranged coaxially in said helical antenna.
The invention involves a method for reducing size of a whip element in an antenna arrangement comprising a first antenna element in form of a microstrip element, a second element and a third element in from of a whip element. According to the method said second and third elements are arranged between said microstrip element and a ground plane and said microstrip element is arranged with an opening to allow radiation from said second element. Moreover, the second element is a meander, helical or straight line antenna element.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following, the invention will be further described in a non-limiting way with reference to the accompanying drawings in which:
Fig. 1 is a schematic perspective view of a first embodiment according to the present invention; Fig. 2 is across-section along line II-II in fig. 1 ; and
Fig. 3 is a schematic exploded view of a second embodiment according to the invention in perspective.
DETAILED DESCRIPTION OF THE EMBODIMENTS
A third method consists of making slots in the antenna at certain locations. This method, however, requires unloaded antennas.
Referring to figs. 1 and 2, the antenna 100 consists of a unique three layer antenna element, a first conductive layer 110 arranged substantially in parallel with a ground plane 120 and a third antenna layer 130. Moreover, the antenna includes a whip 140 arranged between the first and the second layers 110; 120.
The first layer 110 consists of a conducting plate connected to the supporting second layer 120 such as a printed circuit board, provided with a ground plane, which is entirely or partly covered by said conducting plate 110. The conducting plate 110 is connected to the ground plane and feeding (not shown) is provided through conductors 150 and 160, respectively. Thus, the present invention uses a probe feed which introduces extra inductance. Moreover, the invention presents only a single patch to create multiple frequencies, λloreover, the first layer 110 contains the microstrip antenna elements which may consist of loads 111-113 and multiple frequency bands. The microstrip element 110 is further provided with a hole or a slot 170 in a special location. This location depends on the geometry of the third layer 130.
The third layer is placed beneath the microstrip antenna element. This layer consists of an antenna element, which can be any of a meandering, straight line or helical element directly beneath the slot/hole 170 in the microstrip element. This third layer also includes the whip element 140. The whip is a conductive road having a first end 141 and a second end 142. The first end 141 may be provided with an insulating coating, while the second end 142 is arranged to provide contact with the third layer 130.
In retracted mode, the whip 140 makes no contact to either first 110 or third layer 130. In extended mode, the whip makes a galvanic (or capacitive) connection through its second end 142 to the top of the meandering line (in this case) on the third layer 130. The meandering line can reduce the size of the whip by up to 50%. Thus, the hole/slot 170 is required in the microstrip antenna to allow the whip and the meandering element to radiate. Without a slot/hole, the meandering element would not radiate. Obviously, the whip can be replaced by a flat meandering pattern with similar results.
The conducting plate 110, which in this example is essentially rectangular-shaped and has a pair of first (short) edges and a pair of second (long) edges, is arranged by a number of recesses or slots 111-113 constituting an inductive and a capacitive load, both loads are unique. The slots can be provided in the conducting plate in varies ways and used to vary a resonant frequency since a current has to travel a longer path. The slots are denoted: 111 and 1 13, where 111 denotes a substantially T-shaped slot having a first section substantially in parallel with one of said first edges and a second section substantially in parallel with one of said second edges. The function of slots is described in the pending Swedish application No. 9903220-3. Preferably, the second layer and the microstrip layer are coupled capacitively or inductively, or galvanically, e.g. through on a PCB.
A second preferred embodiment of an antenna 300 according to the invention is illustrated in fig. 3. The antenna 300 comprises the conductive plate 310, the ground plane 320, an antenna element 330 instead of a layer as described above, the whip 340 and a supporting member 380.
The conductive plate 310 is provided with the slot 370, which divides it into two radiator parts 311 and 312, constituting a dual band antenna. One end 313 of the plate 310 is cutout, bent and provided with projections constituting the feed and ground connections 350 and 360, respectively. In this embodiment the plate is not provided with the capacitive and inductive loads.
The ground plane 320, which is partly shown, consist preferably of a part of a printed circuit board provided with a ground plane in a communication device, such as a cellular phone.
Connection plates 321 and 322 connecting the connections 350 and 360 to feed and ground are arranged on the same board. Moreover, holes 323 for assembly of the parts inside the communication device may also be provided.
The antenna element 330 is a coil, constituting a helical antenna.
The whip antenna 340 consists of a conductive rod, preferably arranged with a coating, covering at least parts of it. On one end 341, the whip is provided with an enlargement 343 and a knob 344. The other end 342 of the whip, which is slightly widened, is arranged to contact the antenna element 330, galvanically and/or capacitively, preferably when it is extracted.
The supporting member 380, made of plastic or dielectric material, is provided to support and locate the conductive plate in a correct position parallel to the ground plane and also provide a support for the helical antenna element 330 and the whip 340. To reduce the effect of the dielectric material, the supporting member is substantially prismatic cap-shaped and arranged with a substantially cylindrical compartment 381 for receiving the helical element 330 and the whip 340 substantially coaxially to the helical element. The whip extends out of the comportment 381 through a hole 382, which is arranged at the end of a tapering section 383 provided at one end of the compartment 381. The tapering section 383 is arranged as a stop and holder in cooperation with a conical section 345 at the second end of the whip. Moreover, the diameter of the hole 383 is so arranged that it holds the whip in retracted position in cooperation with the enlargement 343. The supporting member is provided with recesses 384 and holes 345 for assembly inside the communication device.
It is also possible to use the coil 330, parts of it or an additional coil to spring-load the whip, for easily extracting the whip. In this case, however, locking and holding mechanisms must be provided. It is also possible to combine coil, meander and whips of different lengths for different applications.
The antenna arrangement according to the invention can be used in any device with a need for receiving and/or transmitting electro-magnetical waves, and because of its small size it is most suitable for use in cellular phones or the like.
The invention is not limited to the shown embodiments but can be varied in a number of ways, e.g. through combination of two or more embodiments shown, without departing from the scope of the appended claims and the arrangement and the method can be implemented in various ways depending on application, functional units, needs and requirements etc.