RU2574320C2 - Lte antenna pair for mimo/diversity operation in lte/gsm bands - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: invention relates to loop antenna systems for operation in mobile cellular networks, particularly to operation in a LTE network, for which more than one antenna is required in each mobile telephone. A multiple input-multiple output (MIMO) antenna system comprises first and second folded or compacted loop antennae (12, 12'). Each antenna has a longitudinal extent. The antennae are mounted parallel to each other on a dielectric substrate (3) having a conductive grounding layer (31, 32). The grounding layer extends between the first and second antennae which are mounted on the substrate in areas where there is no grounding layer. The first and second antennae, during use, generate first and second radiation patterns (31, 32) and cause currents (30) to flow in the grounding layer between the antennae such that the first and second radiation patterns are inclined by an angle greater than zero.

EFFECT: improved antenna diversity characteristics.

19 cl, 15 dwg

Description

Technical field

[0001] The present invention relates to a pair of loop antennas for mobile phone applications, and in particular to operation in an LTE network for which more than one antenna is required in each mobile phone.

State of the art

[0002] The Long Term Development Project (LTE) is the latest development standard for mobile communications technology. It is designed to enable wireless providers in GSM and 3G networks to switch to fourth-generation networks and equipment (4G). LTE technologies will provide consumers with accelerated execution of existing applications, as well as open opportunities for new mobile phone applications. To provide higher information transfer rates for these new applications, the LTE system adopted the technology of multiple inputs - multiple outputs (MIMO), which requires the use of two cellular radio antennas in mobile phones. In addition, LTE uses lower frequencies than the GSM range, and the antennas of mobile phones must provide appropriate performance at frequencies reduced to 698 MHz (from the frequency currently used 824 MHz). The need to use two antennas and ensure operation at a lower frequency creates serious problems for developers of antennas for mobile devices.

[0003] In order for two antennas to provide good diversity characteristics or operate successfully in a MIMO system, they must receive signals arriving at a mobile device that propagate in different ways. This means that the antennas must have different radiation patterns, different polarizations, different phase characteristics or must be sufficiently physically separated in space.

[0004] An indicator of the similarity of the two antennas is the envelope correlation coefficient p _e , which characterizes the measure of the difference in radiation patterns of the two antennas in shape, polarization and phase. For the operation of the MIMO system, a low level of correlation is very important, because when p _e = 1, the radiation patterns are the same, and the MIMO mode or gain due to diversity is impossible. However, for p _e = 0, an optimal gain for MIMO is achieved. It is important to note that the performance of the two antennas should be similar: good performance in MIMO mode cannot be achieved if one antenna has high efficiency and the second antenna has low efficiency. Both antennas should have approximately the same efficiency, however, one or more of the above characteristics should differ.

[0005] It has recently been shown that loop antennas can be used for mobile phones, and by switching or electronic tuning, they can be configured to operate in the LTE bands as well as in the GSM bands, for example, as described in Applicant application GB 0914280.3, at the same time pending in the United Kingdom Patent Office. Recent developments aimed at expanding throughput include multi-mode loop antennas, complex power and ground circuits, as well as complex design elements that provide better matching with a 50 ohm cable. Some of these developments are described in detail in the application GB 1017472.0 of the applicant, which is simultaneously considered by the Patent Office of Great Britain, the contents of which are incorporated by reference in this application.

Disclosure of invention

[0006] The present invention provides an antenna system with multiple inputs - multiple outputs (MIMO), containing the first and second folded or compact frame antennas having a length in the longitudinal direction and mounted essentially parallel to each other on a dielectric substrate having a conductive ground layer , which passes between the first and second antennas, with the first and second antennas installed on sections of the substrate on which there is no grounding layer, and the first and second antennas during their operation They simulate the first and second radiation patterns, and also provide currents flowing in the grounding layer between the antennas in order to deflect the first and second radiation patterns relative to each other by an angle greater than zero.

[0007] The first and second antennas can be mounted relative to each other similarly to a pair of Helmholtz coils, although it is not essential and not even necessary that the antennas are relative to each other at a distance of the order of the transverse size of each frame. However, in preferred embodiments, the frames of the first and second frame antennas are substantially coaxial. The greater the distance between the first and second antennas, the greater the diversity.

[0008] Each of the two above-mentioned loop antennas can be configured as described in GB 1017472.0, namely, each loop antenna can be made as a compact frame of a conductive track deposited on a dielectric substrate by bending the frame through the edge of the substrate to form the first and second plots (patches). In other embodiments, the first and second sections may be galvanically interconnected using through jumpers in the plate, resulting in a compact frame. In other embodiments, the compact frame may be formed in one plane by a meander-shaped conductive path or otherwise folded. In all embodiments, the expression “folded or compact loop antenna” refers to a loop antenna formed by a conductive track in a topologically frame configuration that covers a smaller area than the area covered by the conductive path if it were to follow a circular path. In most cases, the path covered is less than the area covered by the conductive path if it were to follow a square or rectangular path. This is because a compact or folded frame typically contains at least one returning part when the frame loop passes from one side of the substrate to the other.

[0009] In various embodiments of the invention, two frames are used that are located in a mobile phone, in a USB dongle (adapter), and in other small devices to support MIMO or diversity operation.

[0010] The first and second antennas may have the same designs and / or characteristics, or they may be different. Both frames can be mounted vertically relative to a horizontal substrate with a grounding layer and parallel to each other. In particular preferred embodiments, the antenna system is configured such that each frame can be easily mounted vertically on a USB key circuit board of a dongle.

[0011] One end of each of the first and second loop antennas is connected to a radio frequency (RF) feeder for a corresponding signal. The other end of each loop antenna can be connected directly to ground (for example, by attaching to the ground plane), however, in preferred embodiments, the other end of the loop antennas is connected to ground through at least one inductive component to adjust the effective length of the frame. In most preferred embodiments, the other end of one or each of the loop antennas is provided with a switch that selectively switches on two or more different inductive components between the other end and the ground, which makes it possible to adjust the electrical length of the frame.

[0012] Since the loop antennas are parallel to each other and are located at a small distance from each other, one would think that it would be difficult to provide a small amount of envelope correlation in such a small area as a hardware key. However, studies of currents flowing in the conductive layer of the hardware key show that the two radiation patterns can be tilted so that there is a certain angle between them. In preferred embodiments, the angle between the radiation patterns is at least 20 °, more preferably at least 35 ° and most preferably about 50 ° or at least 50 °. For an angle of about 50 °, the correlation coefficient can be of the order of 0.4, which is considered acceptable for MIMO and diversity applications.

[0013] In a typical application of such a dongle, it may be required that the “primary” antenna span the LTE and GSM bands, and the second antenna provides LTE MIMO or diversity. This means that two antennas need not have the same design or the same characteristics. Alternatively or in addition to this, they are not required to be switched or matched in the same way.

[0014] In one embodiment, both antennas may be the same, but their electrical switching circuits may be used in the same or different ways. In some embodiments, three switching positions are provided, however, configurations with two, four and other numbers of switching positions are possible. Cross-correlation measurements between the antennas showed that p _e ≤0.5 over the entire range used by the LTE protocol.

[0015] This result, together with good bandwidth and antenna efficiency, means that they satisfy the requirements of the LTE system.

Brief Description of the Drawings

[0016] Embodiments of the invention are described below with reference to the accompanying drawings, in which:

Figure 1 - the first known configuration of a USB dongle for LTE;

Figure 2 - the second configuration of the USB hardware key for LTE;

Figures 3 and 4 are an embodiment of the present invention;

5-8 illustrate the theoretical principles underlying the embodiments of the invention;

9 is an exemplary connection diagram of an embodiment of the present invention;

10 is a graph showing input matching and isolation for an embodiment of the invention individually;

11 is a graph showing input matching and isolation for an embodiment of the invention when inserted into a laptop;

12 is a graph of antenna efficiency for an embodiment of the invention separately;

13 is a graph of antenna efficiency for an embodiment of the invention when inserted into a laptop;

Fig is a graph of isotropic 3D propagation, showing the values of the correlation coefficient and the power factor for cross-polarization in different frequency ranges of an embodiment of the present invention separately;

Fig is a graph of isotropic 3D propagation, showing the values of the correlation coefficient and the power factor of cross-polarization in different frequency ranges of an embodiment of the present invention when inserted into a laptop.

DETAILED DESCRIPTION OF THE INVENTION

[0017] Figure 1 shows schematically a first embodiment of a known MIMO USB dongle 1 with a remote casing. The hardware key 1 contains a USB connector 2, a substrate 3 of the printed circuit board, a main antenna 4 and an auxiliary antenna 5 located perpendicular to the main antenna. An alternative embodiment is shown in FIG. 2, where the auxiliary antenna 5 ′ is raised above the substrate 3 of the printed circuit board and can be rotated relative to the leg 6 on which it is mounted. For clarity, only some elements of the hardware key are shown, although it should be understood that other components, such as memory circuits and processors, are located on the substrate 3 of the printed circuit board. MIMO USB dongles of this type are usually intended for use as USB modems that can be inserted into a laptop or other computer to enable data exchange using an LTE mobile network. The primary antenna 4 is for receiving and transmitting LTE, GSM and HSPA signals, and the secondary antenna 5, 5 ′ provides spatial diversity for LTE signals. However, the auxiliary antenna 5, 5 ′ has lower characteristics than the main antenna 4, and therefore the USB dongle 1 as a whole does not provide optimal characteristics when operating in MIMO mode, and the data transfer rate will be low.

[0018] Figures 3 and 5 show an embodiment of the present invention (also in schematic form). MIMO USB dongle 10 contains a USB connector 2, a substrate 3 of a printed circuit board in the form of a dielectric board such as FR4, a conductive ground layer 11, and two compact frame antennas 12, 12 ′ located parallel to each other on the long edges of the plate 3 As you can see, the frame antennas 2, 12 ′ are mounted vertically relative to the plane of the plate 3 in those places where there is no grounding layer 11. However, the grounding layer 11 passes between the antennas 12, 12 ′.

[0019] Each antenna 12, 12 ′ comprises a frame formed by a conductive track 16, 16 ′ printed or otherwise formed on a dielectric substrate 13, 13 ′. In particular, each loop antenna 12 may comprise a dielectric substrate 13 having first 14 and second 15 opposite surfaces, as well as a conductive track 16 formed on the plate 13, on which a power point 17 and a ground point 18 are provided adjacent to each other the first surface 14 of the substrate 13, and the conductive path 16 departs from the power point 17 and from the ground point 18 in opposite directions, reaches the edge of the dielectric substrate 13, and then goes to the second dielectric surface 15 of the substrate 13 and then passes along the second surface 15 along the path corresponding to the path of this track on the first surface 14, after which it is connected to the corresponding sides of the conductive circuit formed on the second surface 15, which extends into the central part of the frame formed by the conductive path 16 on the second surface 15, and the conductive circuit contains inductive and capacitive elements. Instead of a conductive circuit containing inductive and capacitive elements, the two ends of the conductive path 16 on the second surface 15 can be connected galvanically by a simple conductive load plate, or the conductive path 16 can form a continuous frame on the second surface 15. Alternatively, instead of the power point 17 and the ground point 18, the antenna 12 can have two ground points 18, and the excitation can be carried out using a separate frame or an asymmetric antenna (not shown) with direct excitation, which is connected to the antenna 12 using inductive or capacitive coupling .

[0020] As shown in FIG. 3, the dielectric substrates 13, 13 ′ have central cutouts 19, 19 ′ located at those locations where the electric field strength will be maximum during operation. This helps increase antenna efficiency.

[0021] In the area 20 of the substrate 3 of the printed circuit board and the ground plane 11 between the antennas 12, 12 ′ and the USB connector 2, other circuit components (not shown) may be located. Generally speaking, these other components of the circuit can also be located between antennas 12, 12 ′ if they do not cause too much interference to antennas 12, 12 ′.

[0022] As you can see, the construction of embodiments of the present invention, in contrast to the above-described known structures, is symmetrical about a plane of symmetry passing along the center line of the USB dongle.

[0023] Figure 5-8 illustrates the theoretical principles underlying the embodiments of the present invention. Since the loop antennas 12, 12 ′ are parallel to each other and are located at a small distance from each other, one would think that it would be difficult to ensure a small value of the envelope correlation in such a small area as the dongle 10. However, studies of currents 30 flowing in the grounding layer 11 of the hardware key 10 show that the two radiation patterns 21, 22 can be tilted so that there is a 50 ° angle between them. With this angle, a correlation coefficient of 0.4 can be obtained, which is considered acceptable for MIMO and diversity applications. In particular, it should be noted that the location of the antennas 12, 12 ′ at the diagonally opposite corners of the substrate 3 of the circuit board of the dongle 10 leads to the fact that these antennas operate in the same mode, which entails a high correlation value and loss of diversity. In order to obtain an average or low correlation value and, accordingly, acceptable diversity, it is necessary to place the antennas 12, 12 ′ on one edge or on one edge of the substrate 3 of the printed circuit board.

[0024] FIG. 8 shows the first 31 and second 32 radiation patterns generated by the antenna system, from which it is seen that they are tilted to each other at an angle of 50 °, thereby providing acceptable diversity.

[0025] In a typical application of such a dongle, the “primary” antenna 12 should cover the LTE and GSM bands, and the second antenna 12 ′ should provide LTE MIMO or diversity. This means that the two antennas 12, 12 ′ need not necessarily have the same design or characteristics, and they should not be switched or matched in the same way. In the considered embodiments, both antennas 12, 12 ′ have the same design, however, their electrical switching circuits can be used the same or differently, as shown in Fig. 9.

[0026] Figure 9 shows a substrate 3 with a grounding layer 11 and with two portions 23, 23 ′ on opposite edges, on which the grounding layer 11 is absent. Antennas 12, 12 ′ have excitation points 17, 17 ′, respectively, which are connected respectively to the inputs 24, 24 ′ of the RF signal and to the antenna matching circuits 25, 25 ′. Antennas 12, 12 ′ also have grounding points 18, 18 ′, respectively, which are connected to ground via switches 26, 26 ′, which allow switching between three different grounding connections 27, 27 ′ with different inductances. The control of the switches 26, 26 ′ is carried out along the control lines 28, 28 ′. In this embodiment, three switching positions are shown, however, configurations with two, four and other numbers of switching positions are possible. Cross-correlation measurements between antennas 2, 12 ′ showed that p _e ≤0.5 over the entire range used in the LTE protocol. This result, together with the good bandwidth and efficiency of the antennas 12, 12 ′, means that they satisfy the requirements of the LTE system.

[0027] FIG. 10 is a graph illustrating input matching and isolation in two different positions (that is, with different inductances connected between antennas and ground) in four bands, namely, in the LTE band 746-798 MHz, in the GSM band, in the WCDMA band and in the LTE band 2500 2690 MHz for an embodiment of the present invention separately.

[0028] Fig. 11 is a graph corresponding to that of Fig. 10, but with the insertion of a hardware key 10 into a laptop.

[0029] FIG. 12 is a graph of antenna efficiency for an embodiment of the present invention in four bands: 740-800 MHz, 820-960 MHz, 1710-2170 MHz, and 2500-2690 MHz.

[0028] FIG. 13 is a graph corresponding to that of FIG. 12, but with the insertion of a hardware key 10 into a laptop.

[0031] FIG. 14 is a graph of isotropic 3D propagation showing the curves of the correlation coefficient and the cross-polarization power coefficient in different frequency ranges (740-800 MHz, 820-960 MHz, and 1710-2170 MHz) for an embodiment the present invention; moreover, the cross-polarization power factor is in the range from -15 dB to +15 dB. As you can see the measured correlation coefficient p _e ≤0.5 or less in all ranges and below 0.4 in most of the frequency spectrum.

[0032] Fig. 15 is a graph corresponding to that of Fig. 12, but with the insertion of a hardware key 10 into a laptop. Although in this case the correlation coefficient is higher at lower frequencies compared with the case of a separate hardware key 10, however, it is low enough to ensure satisfactory operation in MIMO mode and using diversity in the entire frequency spectrum.

[0033] Throughout the text of the description and claims of the present application, the words “comprise” and “include,” as well as their derivatives mean “inclusion without limitation,” that is, they do not exclude the content (inclusion) of other parts, additions, components, and integers or stages. Throughout the text of the description and claims of the present application, the indication of any signs in the singular includes several such signs, unless the context otherwise indicates. In particular, if a singular form is used in the text, then it should be understood as indicating "one or more", unless the context otherwise indicates.

Signs, integers, characteristics, compounds, chemical components or groups described in connection with a particular aspect, embodiment or example of the invention should be understood as applicable to any other aspect, embodiment or example described here, unless they are incompatible. All features disclosed in this specification (including the claims, abstract and drawings), and / or all steps of any method or process disclosed in this way, can be combined in any combination, with the exception of combinations where at least some of such features and / or steps are mutually exclusive. The invention is not limited to the details of any of the above embodiments. The invention extends to any new feature or combination of features disclosed in this specification (including the claims, abstract and drawings), or to a new one or any combination of steps of any method or process disclosed in this way.

The reader’s attention is drawn to all documents submitted simultaneously or earlier than this specification in connection with this application, and which are open to public familiarization with this specification, and the contents of all such documents are hereby incorporated by reference.

Claims (19)

1. Antenna system with multiple inputs - multiple outputs (MIMO), containing the first and second folded or compact frame antennas having each longitudinal length and mounted essentially parallel to each other on a dielectric substrate having a conductive ground layer that extends between the first and a second antenna, wherein the first and second antennas are mounted on portions of the substrate on which there is no grounding layer, and the first and second antennas, when used, form the first and second directional patterns radiation and cause currents flowing in the grounding layer between the antennas, so that the first and second radiation patterns are tilted relative to each other by an angle greater than zero. 2. The antenna system according to claim 1, in which the first and second antennas are mounted on a substrate opposite each other. 3. The antenna system according to claim 1, in which the frames of the first and second frame antennas are essentially coaxial. 4. The antenna system according to claim 1, in which each of the first and second frame antennas is configured as a frame of a conductive track, which is formed on a dielectric substrate in a compact manner by bending over the edge of the substrate to form the first and second sections. 5. The antenna system according to claim 1, in which each of the first and second frame antennas is configured as a frame of a conductive track, which is formed on a dielectric substrate in a compact manner by forming the first and second sections, which are galvanically connected using through jumpers to form a compact frame . 6. The antenna system according to claim 1, in which each of the first and second loop antennas is configured as a frame of a conductive track, which is formed on a dielectric substrate in a compact manner in one plane in the form of a meander or otherwise folded. 7. The antenna system according to claim 1, in which the first and second antennas are identical to each other in design and / or characteristics. 8. The antenna system according to claim 1, in which the first and second antennas differ from each other in design and / or characteristics. 9. The antenna system according to claim 1, in which the first end of each of the first and second loop antennas is connected to the RF feeder. 10. The antenna system according to claim 1, in which the second end of each of the first and second loop antennas is connected to the "ground". 11. The antenna system according to claim 1, in which the first and second ends of each of the first and second frame antennas are connected to the ground, and the antenna system further comprises a separate field antenna for each of the first and second frame antennas. 12. The antenna system of claim 10, in which the second end of at least one of the first and second antennas is connected to the ground through an inductive component. 13. The antenna system of claim 10, in which the second end of at least one of the first and second antennas is connected to the ground using a switch that selectively includes one of at least two different inductive components between the second end and the ground " 14. The antenna system according to claim 1, in which the correlation coefficient between the first and second antennas does not exceed 0.5 for all specified frequency ranges of operation. 15. The antenna system according to claim 1, in which, in use, the first and second radiation patterns are tilted relative to each other by an angle exceeding 20 °. 16. The antenna system according to claim 1, in which, when used, the first and second radiation patterns are tilted relative to each other by an angle exceeding 35 °. 17. The antenna system according to claim 1, in which, in use, the first and second radiation patterns are tilted relative to each other by an angle of about 50 °. 18. A hardware key for connecting to a computer, the hardware key comprising an antenna system with multiple inputs, multiple outputs (MIMO), comprising first and second folded or compact loop antennas having each longitudinal length and mounted substantially parallel to each other on the dielectric a substrate having a conductive grounding layer that extends between the first and second antennas, the first and second antennas mounted on portions of the substrate on which there is no grounding layer, and the first and a second antenna, when in use, form first and second radiation patterns and cause currents flowing in the grounding layer between the antennas so that the first and second radiation patterns are inclined with respect to each other by an angle greater than zero. 19. A mobile phone comprising an antenna system with multiple inputs - multiple outputs (MIMO), containing the first and second folded or compact frame antennas having each longitudinal length and mounted essentially parallel to each other on a dielectric substrate having a conductive ground layer, which passes between the first and second antennas, and the first and second antennas are mounted on sections of the substrate on which there is no grounding layer, and the first and second antennas, when used, form -hand and a second directional radiation pattern and cause currents flowing in the grounding layer between the antennas so that the first and second radiation patterns are inclined with respect to each other by an angle greater than zero.

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