GB2570905A - Slot mode antennas - Google Patents

Abstract

An antenna assembly 10 or a wristwatch using such an assembly, comprises at least one circuit board 12 arranged at a distance D from a conductive body 11 to define a slot between them and where the length of the slot is defined between two connection points 14, 15 where the conductive body 11 is connected to a ground plane of the at least one circuit board 12 and where a slot antenna feed 13 is suitable for coupling an electromagnetic signal between the slot antenna and the circuit board 12. The conductive body 11 may be a bezel with a ring, elliptical, rectangular, square or some other polygon shape. The bezel 11 and the circuit board 12 may be in parallel planes and a portion of the periphery of the circuit board 12 may include a grounded conductive layer. A conductive rim structure may be attached to the at least one circuit board 12 to define part of the slot antenna. Multiple connection points may be used to form multiple slot antennas which can operate at different frequencies. The antenna assembly 10 may be used for satellite communications and global positioning systems (GPS).

Description

SLOT MODE ANTENNAS

COPYRIGHT [00011 A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.

TECHNOLOGICAL FIELD [00021 The present disclosure relates generally to an antenna apparatus for use in electronic devices such as wireless or portable radio devices, and more particularly in apparatuses using slot antennas.

BACKGROUND OF THE INVENTION [0003] Antennas are commonly found in most modern radio devices, such as mobile computers, portable navigation devices, mobile phones, smartphones, personal digital assistants (PDAs), wristwatches or other personal communication devices (PCD). Typically, these antennas comprise a planar radiating element with a ground plane that is generally parallel to the planar radiating element. The planar radiating element and the ground plane are typically connected to one another via a short-circuit conductor in order to achieve the desired impedance matching for the antenna. The structure is configured so that it functions as a resonator at the desired operating frequency. Typically, these internal antennas are located on a printed circuit board (PCB) of the radio device inside a plastic enclosure that permits propagation of radio frequency waves to and from the antenna(s).

[0004] More recently, it has been desirable for these radio devices to include a metal body or an external metallic surface. A metal body or an external metallic surface may be used for any number of reasons including, for example, providing aesthetic benefits such as producing a pleasing look and feel for the underlying radio device. However, the use of a metallic enclosure creates new challenges for radio frequency (RF) antenna implementations. Typical prior art antenna solutions, such as coupled antennas having radiator elements with a conductive ring-like structure, are not performing well in all cases e.g. due to inherent directivity in their radiation pattern. The fact that the metal housing and/or external metallic surface of the radio device acts as an RF shield which degrades antenna performance, particularly when the antenna is required to operate in several frequency bands, favors slot type antennas. Slot antennas are omnidirectional microwave antennas with linear polarization, and are used typically at frequencies between 300 MHz and 24 GHz.

[0005] Waveguide slot antennas usually have one or several longitudinal slots in the broad face of a standard rectangular waveguide, parallel to the length of the guide. A longitudinal slot cut into the wall of a waveguide interrupts the transverse current flowing in the wall, forcing the current to travel around the slot, which induces an electric field in the slot. The position of the slot in the waveguide determines the current flow. As the current in the walls of the guide are proportional to the difference in electric field between any two points, the position determines the impedance presented to the transmission line and the amount of energy coupled to the slot and radiated from the slot.

[0006] To make a slot antenna in a circular waveguide, such as one used in a watch-like GPS device or a wristop computer, an important design criteria is to locate the point of maximum electric field, which depends on the location of the slot along the periphery of the circular waveguide. In order to fix the alignment of the electric field in a circular waveguide, it must also be kept from rotating when encountering a discontinuity, such as a slot. The slot size, shape and the cavity behind are among the design variables that may be used to tune the performance.

[0007] In prior art solutions, antenna slots have been specially manufactured or created by dedicated parts and formations on the bezel and housing of wristwatch-like devices. In US 7271774 is disclosed an example of an integral slot antenna formed in a conductive material portion of an outer housing of a wrist-wearable device.

[0008] Accordingly, there is a salient need for an antenna solution for use with a wearable or wrist worn radio device having an external metallic surface such as a bezel and a casing/body made of non-conductive material.

SUMMARY OF THE INVENTION [00091 The inventors of the present disclosure have made the surprising observation that a slot antenna can be created by a bezel made of a conductive material, such as a metal, and the periphery of a circuit board itself. This offers significant advantages, as the position of the antenna structure, including but not limited to the slot and feed point, can be used to optimize the radiation pattern and therefore the reception of GNSS (Global Navigation Satellite System) signals for dedicated uses and sports, e.g. for running, walking or cycling. GNSS systems include, but are not limited to, GPS, Glonass, Galileo and Beidou navigation systems.

[00101 According to one aspect of the invention, an assembly for an antenna operating in a slot mode is provided, wherein the assembly comprises at least one circuit board of an electronic device, a conductive body arranged at a distance from said at least one circuit board and defining a slot between them, at least one feed element for coupling an electromagnetic signal between said conductive body and said circuit board, and wherein a length of the slot is defined by two connecting points at which said conductive body is connected to a ground plane of said at least one circuit board.

[0011] According to some embodiments of the invention, the circuit board is arranged in a plane parallel to and at least partly aligned with said conductive body, and has at least along a part of its periphery a conductive layer at said ground plane.

[0012] According to some embodiments of the invention, the assembly comprises an element having a connection point that connects said conductive body to a ground plane of said circuit board, said connection point being located at a first end of said slot forming said slot mode antenna. Correspondingly, the assembly may comprise the same or a different element, that has a connection point that connects said conductive body to a ground plane of said circuit board, said connection point being located at a second end of said slot forming said slot mode antenna. The element for said first and second connection points may be different, and be located at the first and second ends of said slot to thereby define the slot.

[0013] According to some embodiments of the invention, the conductive body is a bezel being a part of the housing encompassing a wristwatch-like device. The conductive body or bezel may have the shape of a ring, an ellipse, a rectangle, a square, or any other polygon.

[0014] According to some embodiments of the invention, the first and second connection points and at least one feed element in said wristwatch-like device is positioned approximately between 3 and 9 o’clock, preferably between 5 and 9 o’clock along the periphery of the device.

[0015] According to some embodiments of the invention, the assembly may comprise more than two connecting points. The circuit board and said conductive body may be arranged to define multiple slots between them. Each slot may then being defined between two connecting points and each slot may have a feed element between said connecting points, for example.

[0016] According to some embodiments of the invention, an effective width and/or length of the slot may further and at least partially be defined by conductive rim structures facing said conductive body and attached to at least one of said circuit boards along the length of said board.

[0017] According to some embodiments of the invention, at least one slot in the assembly is adapted for the reception of a GNSS (Global Navigation Satellite System) signal. The GNSS signal may be a GPS, Glonass, Galileo and/or a Beidou signal, for example.

[0018] According to a second aspect of the invention, an electronic wristwatch-like device is provided, that comprise a housing, at least one circuit board inside said housing, a conductive bezel arranged at a distance from said circuit board as part of said housing and defining a slot between them, wherein the slot comprises an antenna operating in a slot mode having a feed element for coupling an electromagnetic signal between said bezel and said circuit board, and at least two connecting points that connects said conductive bezel to a ground plane of said at least one circuit board.

[00191 The inventive antenna assembly and wristwatch device is characterized by what is set forth in the appended claims. Further features of the present disclosure, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS [00201 The features, objectives and advantages of the present disclosure will become more apparent from the detailed description set forth below, when taken in conjunction with the drawings, wherein:

[00211 FIG. 1 is presenting an assembly for an antenna operating in a slot mode in accordance with at least some embodiments of the present invention;

[00221 FIG. 2 is presenting an assembly for an antenna operating in a slot mode in accordance with at least some further embodiments of the present invention;

[0023] FIG. 3 is presenting a circular PCB mode in accordance with at least some embodiments of the present invention;

[0024] FIG. 4 shows an electronic wristwatch-like device mode in accordance with at least some embodiments of the present invention.

[0025] FIG. 5 shows an assembly for an antenna operating in a slot mode in accordance with still some further embodiments of the present invention;

[0026] FIG. 6 shows an assembly for an antenna operating in a slot mode in accordance with a variant of FIG. 5 as a further embodiment of the present invention;

[0027] FIG. 7 shows the accuracy of a prior art GPS antenna;

[0028] FIG. 8 shows the corresponding accuracy of an inventive slot mode GPS antenna;

[0029] FIGs. 9A and 9B show the RHCP radiation patterns of a prior art and an inventive antenna.

DETAILED DESCRIPTION OF EMBODIMENTS [0030] In FIG. 1 is shown an inventive assembly 10 for an antenna operating in a slot mode. The exemplary assembly comprises a circuit board (PCB) 12 for a device, such as sports watch or smart watch, and a body, such as a ring- formed bezel 11, made of a conductive material and arranged on top of and in parallel to the PCB 12. The gap having a distance D between them defines a slot that enables the assembly 10 to act as an antenna in a slot mode. The periphery of the PCB 12 is at least partly aligned with the outer shape of the bezel 11, and has at least along a part of the periphery is a metallic layer (see Fig. 3, item 33) connected to the ground level of the PCB 12.

[00311 Obviously, the bezel may take the shape of a ring, an ellipse, a square, a rectangle, or any other polygon, for example. The shape of the PCB need then to be designed accordingly.

[00321 The exemplary assembly in FIG. 1 further comprises a feed element or pin 13 for coupling an electromagnetic signal between the slot mode antenna and the PCB 12. In the embodiment shown in Fig. 1, the feed element 13 is coupled between the bezel 11 and the PCB 12. The element 13 may be implemented in a variety of ways, as a pin or pogo stick, simply as a jumper connection, or as a stud on the PCB making contact with the slot mode antenna structure at the edge of the PCB, possibly with a via conducting the signal further in a multilayer PCB, for example. Any of this variety of solutions may be used in any embodiment of the present invention, as required by design, manufacturing and signal gain considerations.

[0033] Pins 14 and 15 are connection points for grounding the conductive body 11 to a ground level on the circuit board. The distance between the connection points 14 and 15 defines the length of the slot. The pins may be a simple jumper wire, or a spring loaded contact (pogo) pin, for example. The feed pins are preferably attached to the outer edge of the PCB, bezel or other structure to which is intended to make an electrical connection with, to facilitate easy tuning. Also other attachment points than the edges are possible, but may require more tuning of other related components.

[0034] According to some embodiments, pins 14 and 15 are to be considered as the physical representation of the connection points that connect the conductive body 11 to a ground plane of the PCB 12. The pins may in some embodiments be integral parts of an insulating element (not shown) that is located between the PCB and the conductive body, as a support or otherwise. In some embodiments however, the elements containing the pins may be separate and located at the first and second ends of said slot to thereby define the slot antenna.

[00351 The assembly may in some embodiments have floating or insulated support pins (not shown) or an insulating ring that maintain the gap between the bezel 11 and PCB 12. Alternatively, or in addition, the pin 15 may be connected to ground via a frequency selective circuit (e.g. a low-pass filter) or an electronic switch 16. Thereby the same feed pin may be configured to feed the same slot assembly with two different slot lengths, a shorter between pins 14 and 15 and a longer between pin 14 and 17. Such an arrangement would make the antenna slot selectable or switchable and thus suitable for two different frequencies, as the electrical length of the slot seen by the feed point 13 is determined by pin (counterclockwise) to pin 15 on one hand or by pin 14 to pin 17 on the other hand.

[0036] Turning now to FIG. 2, a similar assembly 20 is shown as in FIG. 1, but provided with two sections of the bezel 21 coupled separately to the PCB 22, thus providing two antennas operating in the slot mode. The length of a first slot mode antenna is defined by the section (counterclockwise) between the connection points or pins 24a - 24c of the bezel 21, and the length of a second slot mode antenna is defined by the section between pins 24c 24b, correspondingly. Thus, a first slot mode antenna has grounding pins 24a and 24c. The feed element or pin 23a is located between the grounding pins, as shown.

[0037] A second slot mode antenna has a grounding pin 24b and a feed pin 23 b located close to its second grounding pin 24c, as shown.

[0038] With different lengths of the bezel sections assigned to different antennas, they become tunable to different operating frequencies, and the electronic device they are connected to will thus be able to operate as a multi-band device.

[0039] A ground plane on a printed circuit board (PCB) is a large area or layer of copper foil connected to the circuit's ground point, usually one terminal of the power supply. It serves as the return path for current from many different components. A ground plane is often made as large as possible, covering most of the area of the PCB which is not occupied by circuit traces.

[00401 A large area of copper also conducts the large return currents from many components without significant voltage drops, ensuring that the ground connection of all the components are at the same reference potential. In digital and radio frequency PCBs, a reason for using large ground planes is to reduce electrical noise and interference through ground loops and to prevent crosstalk between adjacent circuit traces. In Fig 3 is shown, for illustrative purposes, a typical circular PCB 30, with a microcontroller or -processor 31 and some copper wiring 32. According to an exemplary embodiment of the invention, the ground plane may be arranged as a copper brim 33 around the periphery of a circle-shaped PCB 30. This ensures the operation of an inventive slot-mode antenna as shown in FIGs. 1 and 2.

[0041] The processor 31 may comprise, for example, a single- or multi-core processor wherein a single-core processor comprises one processing core and a multi-core processor comprises more than one processing core. A processing core may comprise, for example, a Cortex-A8 processing core manufactured by ARM Holdings or a Steamroller processing core produced by Advanced Micro Devices Corporation. The processor 31 may comprise at least one Qualcomm Snapdragon and/or Intel Atom processor. Processor 31 may comprise at least one application-specific integrated circuit, ASIC. Processor 31 may comprise at least one field-programmable gate array, FPGA. Processor 31 may be means for performing method steps in the PCB 30.

[0042] In FIG. 4 is schematically shown an electronic wristwatch-like device 40 from above. A metallic bezel 41 encompasses the housing. Normally, during running and worn on the wrist, the device has a slot antenna running along the edge of the device, that is positioned mainly on a semi-circle sector having an arc length S between 3 and 9 o’clock. The radiation pattern of the antenna is then pointing upwards towards the sky, i.e. a satellite constellation.

[0043] The angular width (here used as a synonym to a central angle from the midpoint of a circle) of the slot antenna depends on the diameter of the device and on the materials used, where parameters such as the permittivity of dielectric materials affect the result. The angular width may be larger or narrower than the suggested 180°, resulting in Fig. 4 in the arc length S between 3 and 9 o’clock. S may be written as S= — nR , where S is the arc length, a is the central angle (in degrees) of a circle sector having the arc length S, and R is the radius of the same circle, here a circle- shaped slot antenna. The smaller the diameter of the device, the larger the angular width a should be in order to yield a specific arc length S.

[00441 In FIG. 4 is also indicated a narrower sector S’, of some 120° between 5 and 9 o’clock, approximately. The inventors have found, in contrary to prior art solutions where feed pins are usually placed in the center of the slot antenna, that the polarization characteristics of the inventive antenna assembly is working optimally, for devices carried on the wrist and when walking and/or running, if the feed pin (see FIGs. 1 and 2) between the PCB and the bezel is located in a sector which is at a distance no further than a quarter to a third of the total slot antenna length, counted from the start of the antenna. The starting point is here at the 9 o’clock position. With the positioning of the feed pin, an optimal impedance match for the antenna at the GPS resonant frequency is sought. Less tuning of other components may then be necessary in order to achieve optimum reception of the GPS or other satellite systems signals.

[0045] Generally, the feed pin or a feed connection point can be on either the bezel side of the slot or on the PCB edge side of the slot. However, the preferred placement of the feed pin is often on the bezel, in order to achieve optimal antenna radiation. PCB placement may be favored by its mechanical simplicity and can be chosen if good enough antenna performance is achievable.

[0046] The RHCP (Right Hand Circular Polarization) component of the radiation pattern seem then to have a desired dominant peak that is pointing upwards, when the device is carried on the wrist (usually the left wrist). The achievable optimum radiation pattern is partly dependent on the device, i.e. the size of the device and the impedance of the slot antenna, and partly on the incoming signal direction and polarization. The latter requires that the slot antenna and its radiation field should be facing at least partly upwards in the mainly used GNSS reception use position.

[00471 It is, according to some embodiments of the invention the effective width and/or length of the slot may be at least partially altered by conductive rim structures deposited on or attached to the ground plane of the circuit board and facing said conductive body. Such rim structures may comprise sheet metal parts etc. One example is shown in FIG. 5, with an assembly 50 that consists of a bezel ring 51, a first semi-circular PCB board 52 and a copper brim 54 arranged around the periphery of the PCB 52 as a ground plane, and a second semicircular PCB board 53 arranged beneath the first PCB board 52. Attached to the second (lowermost) PCB board 53 is a sheet metal rim 55, which width (i.e. its height in relation to PCB 52) and length may be chosen to make it form part of a GPS slot antenna, together with the PCB 52 and the bezel 51. Slot defining members 56 and 57, which may serve as grounding pins defining the ends of the slot antenna, are shown between the sheet metal rim 55 and the bezel 51. A pin- like feed element 58 is also shown. The feed elements may take a multitude of shapes and be implemented in a variety of ways, as discussed above.

[0048] FIG. 6 is a similar assembly to the one in FIG. 5, with parts 60 - 68 corresponding to parts 50 - 58 in FIG. 5. In FIG. 6, however, the metal sheet rim 65 is formed as an extension of a second lowermost PCB board 63. The rim extensions 65 may be connected to the copper brim 64 of the PCB 62 and/or to a copper brim (not shown) of the PCB 63. Again, the width (i.e. the height in relation to PCB 62) and length of the rim 65 may be chosen to make it form part of a GPS slot antenna, together with the PCB 62 and the bezel 61.

[0049] In FIGs 7 and 8 is shown the improved accuracy of the inventive slot mode antenna compared with antennas of prior art. In Fig. 7, a terrain round-trip route A-B-C was run by a person while the run was tracked by wristwatch-like GPS device having a prior art coupled radiator GPS antenna such as is known form e.g. US2017/0179581. A typical deviation at DI between the different legs of the trip can be seen at many places along the route. In Fig. 8, where a device with similar performance, but using an inventive slot mode antenna, the deviation D2 is much smaller along the legs of the route A-B-C.

[0050] In FIGs. 9A and 9B are shown the corresponding RHCP (Right Hand Circular Polarization) radiation patterns in 2 dimensions (2D). A typical wristwatch-like GPS device 91 is carried on the wrist 90 of the left hand shown in a circular cross-section in both FIGs.

9A and 9B. A typical prior art antenna radiation pattern 92, using a conventional bezel antenna with radiating elements, for example, is shown in FIG 9A. The peak 92a of the radiation pattern 92 is pointed in a lateral direction, and is less optimal in receiving an incoming satellite signal in the use position shown. The peak 93 a of the radiation pattern 93 is pointing upwards, and is thus having a strong radiation field in the 0 degree direction when the device is in its most often used position.

[00511 It may be noted from FIGs. 9A and 9B that the slot antenna on FIG. 9B performs well also in a situation where the person wears the watch on the inside of the wrist. In this case the watch is turned upside down compared to FIG. 9B, but the slot antenna radiation pattern (shown here in the 180 degree direction) then pointing in the 0 degree direction will still be wider than the corresponding 0 degree direction pattern of the prior art bezel antenna in FIG. 9A.

[0052] It will be recognized that while certain aspects of the present disclosure are described in terms of a specific sequence of steps of a method, these descriptions are only illustrative of the broader methods of the disclosure, and may be modified as required by the particular application. Certain steps may be rendered unnecessary or optional under certain circumstances. Additionally, certain steps or functionality may be added to the disclosed embodiments, or the order of performance of two or more steps permuted. All such variations are considered to be encompassed within the disclosure disclosed and claimed herein.

[0053] While the above detailed description has shown, described, and pointed out novel features of the antenna apparatus as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the fundamental principles of the antenna apparatus. The foregoing description is of the best mode presently contemplated of carrying out the present disclosure. This description is in no way meant to be limiting, but rather should be taken as illustrative of the general principles of the present disclosure. The scope of the present disclosure should be determined with reference to the claims.

Claims (24)

1. An assembly for an antenna operating in a slot mode, wherein the assembly comprises at least one circuit board of an electronic device, a conductive body arranged at a distance from said at least one circuit board and defining a slot between them, which length of the slot is defined between two connection points at which said conductive body is connected to a ground plane of said at least one circuit board, and wherein between said connection points is located at least one feed element for coupling an electromagnetic signal between said slot mode antenna and said circuit board.

2. An assembly according to claim 1, wherein said circuit board is arranged in a plane parallel to and at least partly aligned with said conductive body, and has at least along a part of its periphery a conductive layer at said ground plane.

3. An assembly according to claim 1 or 2, comprising an element having a connection point that connects said conductive body to a ground plane of said circuit board, said connection point being located at a first end of said slot forming said slot mode antenna.

4. An assembly according to any of claims 1 - 3, comprising an element having a connection point that connects said conductive body to a ground plane of said circuit board, said connection point being located at a second end of said slot forming said slot mode antenna.

5. An assembly according to any of claims 1 - 4, wherein said conductive body is a bezel being a part of the housing encompassing a wristwatch-like device.

6. An assembly according to any of claims 1 - 5, wherein said element for said first and second connection points are separate and located at the first and second ends of said slot to thereby define the slot antenna.

7. An assembly according to claims 5 or 6, wherein said first and second connection points and at least one feed element in said wristwatch-like device is positioned approximately between 3 and 9 o’clock, preferably between 5 and 9 o’clock along the periphery of the device.

8. An assembly according to any of claims 1 - 7, wherein said conductive body has the shape of a ring, an ellipse, a rectangle, a square, or any other polygon.

9. An assembly according to any of claims 1 - 8, comprising more than two connecting points.

10. An assembly according to claim 9, wherein said circuit board and said conductive body are arranged to define multiple slots between them, each slot being defined between two connecting points and each slot having at least one feed element between said connecting points.

11. An assembly according to any of claims 1-10, wherein the effective width and/or length of the slot may further and at least partially be defined by a conductive rim structure attached to at least one circuit board along the length of said board and facing said conductive body.

12. An assembly according to any of claims 1-11, wherein at least one slot in the assembly is adapted for the reception of a GNSS (Global Navigation Satellite System) signal.

13. An assembly according to claim 12, wherein said GNSS signal is selected from GPS, Glonass, Galileo and/or Beidou signals.

14. An electronic wristwatch-like device comprising a housing, at least one circuit board inside said housing, a conductive bezel arranged at a distance from said circuit board as part of said housing and defining a slot between them, wherein the slot comprises an antenna operating in a slot mode having at least two connecting points that defines the length of the slot and at which said bezel is connected to a ground plane of said at least one circuit board, and wherein between said connection points is located at least one feed element for coupling an electromagnetic signal between said slot mode antenna and said circuit board.

15. A device according to claim 14, wherein said circuit board is arranged in a plane parallel to and at least partly aligned with said conductive bezel, and has at least along a part of its periphery a conductive layer at said ground plane.

16 A device according to claim 14 or 15, comprising an element having a connection point that connects said conductive body to a ground plane of said circuit board, said connection point being located at a first end of said slot forming said slot mode antenna.

17. A device according to any of claims 14 - 16, comprising an element having a connection point that connects said conductive body to a ground plane of said circuit board, said connection point being located at a second end of said slot forming said slot mode antenna.

18. A device according to any of claims 14 - 17, wherein said element for said first and second connection points are separate and located at the first and second ends of said slot to thereby define the slot antenna.

18. A device according to any of claims 13-16, wherein said first and second connection points and said at least one feed element are positioned approximately between 3 and 9 o’clock, preferably between 5 and 9 o’clock along the periphery of the device.

19. A device according to any of claims 14 - 18, wherein said conductive bezel has the shape of a ring, an ellipse, a rectangle, a square, or any other polygon.

20. A device according to any of claims 14 - 19, wherein said slot mode antenna comprises more than two connecting points.

21. A device according to any of claims 14 - 20, wherein said circuit board and said conductive bezel are arranged to define multiple slots between them, each slot being defined between two connecting points and each slot having at least one feed element between said connecting points.

22. A device according to any of claims 14 - 22, wherein the effective width and/or length of the slot may further and at least partially be defined by a conductive rim structure attached to at least one circuit board along the length of said board and facing said conductive body.

23. A device according to any of claims 13 - 21, wherein at least one slot in the device is adapted for the reception of a GNSS (Global Navigation Satellite System) signal.

24. A device according to claim 22, wherein said GNSS signal is selected from GPS, Glonass, Galileo and/or Beidou signals.