WO2010025778A1

WO2010025778A1 - Antenna apparatus with improved compensation network

Info

Publication number: WO2010025778A1
Application number: PCT/EP2008/061860
Authority: WO
Inventors: Sven Anders Gösta DERNERYD; Patrik Persson; Anders Stjernman; Martin Nils Johansson; Jonas FRIDÉN
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2008-09-08
Filing date: 2008-09-08
Publication date: 2010-03-11
Anticipated expiration: 2011-03-08

Abstract

An antenna apparatus (100) with first (110) and second (120) antenna elements and a first compensation network (105), said first compensation network (105) comprising a first antenna port (A1) to which said first antenna element is connected and a second antenna port (A2) to which said second antenna element is connected. The first compensation network also comprises first (P1) and second (P2) signal ports, and further comprises transmission lines (130, 140) and/or components (135) of such lengths and impedance levels that the first (P1) and second (P2) signal ports respectively are suitable for receiving and/or transmitting signals at first (f1) and second (f2) frequencies respectively with a frequency separation of a diplex distance used by the apparatus.

Description

ANTENNA APPARATUS WITH IMPROVED COMPENSATION NETWORK

TECHNICAL FIELD The present invention discloses an antenna apparatus with at least a first and a second antenna element and a first compensation network.

BACKGROUND

In modern communications equipment, such as, for example, cellular telephones or laptop computers with wireless connections, a so called compensation network is a component which may be used in order to connect a signal port in the equipment to an antenna port in the equipment.

The compensation network may compensate for, or improve the connection between signal ports and the antennas port with respect to a number of factors, such as, for example, impedance matching, mutual antenna coupling and, in the case of reception, correlation between signals, and the SINR (Signal to Interference and Noise Ratio) of received signals.

International patent application PCT/EP2006/003961 discloses an antenna system with a compensating network for counteracting coupling between antenna elements in the system.

US Patent number 5,778,308 discloses an antenna-matching network in which impedances may be adjusted.

European patent application 1 349 234 discloses a method and a system for compensation of mutual coupling between antenna elements in an antenna array system.

SUMMARY Against the background of the documents mentioned above, it is an object of the present invention to provide an antenna apparatus with an improved compensation network.

This goal is obtained by means of the present invention in that it discloses an antenna apparatus which comprises at least a first and a second antenna element as well as a first compensation network.

The first compensation network, in turn, comprises a first antenna port to which the first antenna element is connected and a second antenna port to which the second antenna element is connected. In addition, the first compensation network comprises at least a first and a second signal port, as well as transmission lines and components of such lengths and impedance levels that the first and second signal ports respectively are suitable for receiving and/or transmitting signals at first and second frequencies respectively with a frequency separation between the first and second signals which corresponds to a diplex distance used by the antenna apparatus. Such a diplex distance may, for example, be used as the duplex distance in a duplex system.

According to the invention, the first and second signal ports are suitable for receiving and/or transmitting said signals with respect to impedance matching and/or one or more of the following parameters:

• Coupling between signal ports, • Correlation between signals,

• SINR of received signals, Signal to Interference and Noise Ratio.

Thus, by means of the present invention, an antenna apparatus is obtained which can be used for input signals of different frequencies whilst still offering compensation for variations in such parameters as, for example, impedance matching, antenna mutual coupling, and, in the case of reception, correlation between signals and the SINR (Signal to Interference and Noise Ratio) of received signals.

In a particular embodiment of the invention, the antenna apparatus additionally comprises a second compensation network with transmission lines and/or components, the apparatus also comprising measuring means for measuring a first characteristic of the apparatus and means for switching between the first and second network in response to said measuring.

Accordingly, in this embodiment of the invention, it is possible to vary the compensation given by the compensation network, by which of the compensation networks that is used.

The compensation given by the compensation network can be with respect to a number of different parameters, such as, for example, one or more of the following parameters:

• Impedance matching,

• Antenna mutual coupling,

• Coupling between signal ports,

• Correlation between signals, • SINR (Signal to Interference and Noise Ratio) of received signals.

In a particular embodiment of the invention, the antenna apparatus also comprises measuring means for measuring a first characteristic of the apparatus and means to vary the compensation given by the compensation network, by varying the transmission line lengths and characteristic impedance levels, and the component values.

These and other embodiments will be described in more detail in the following description.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail in the following, with reference to the appended drawings, in which

Fig 1 shows a schematic view of a first embodiment of the invention, and Fig 2 shows a schematic view of a network of the invention, and

Fig 3 shows a schematic view of a second embodiment of the invention, and Fig 4 shows a schematic view of a third embodiment of the invention, and Fig 5 shows a schematic view of a fourth embodiment of the invention, and Fig 6 shows a schematic view of another network of the invention, and Fig 7a shows a schematic view of yet another network of the invention, and Fig 7b shows a component for use in the invention, and Fig 8 shows a possible measuring mechanism for use in the invention, and Fig 9 shows a network with an alternative topology, and Fig 10 shows another aspect of a network of the invention.

DETAILED DESCRIPTION

Fig 1 shows a schematic view of one embodiment 100 of the antenna apparatus of the invention. As shown in fig 1 , the antenna apparatus 100 comprises first and second antenna elements 110, 120, and also a compensation network 105.

As shown in fig 1 , the compensation network 105 is equipped with first and second antenna ports, shown as A1 and A2 respectively in fig 1 , as well as being equipped with first and second signal ports P1 and P2. As implied by the name, the antenna ports are used for connecting the antenna elements to the compensation network 105, and the signal ports are used for supplying signals for transmission from the apparatus 100 and/or receiving signals if the apparatus 100 is used for reception. It should thus be noted that the device 100 can be used for reception and transmission simultaneously. As shown symbolically by means of clashed lines in fig 1 , the compensation network 105 comprises a number of transmission lines 130, 140 and components 135, which connect the signal ports to the antenna ports.

According to the invention, in the embodiment 100 shown in fig 1 , the transmission lines 130, 140 and the components 135 are of such lengths (the transmission lines) and impedance levels (the transmission lines and the components) that the first P1 and second P2 signal ports are suitable for receiving and/or transmitting signals at first and second frequencies f1 , f2, respectively with a distance f 1 -f2 between the frequencies which corresponds to a diplex frequency separation used in the system, for example, as a duplex distance.

The suitability of the first P1 and second P2 signal ports lies in that they are suitable for receiving and/or transmitting said signals with respect to impedance matching and/or one or more of the following parameters:

• Coupling between signal ports,

• Correlation between signals,

• SINR of received signals, Signal to Interference and Noise Ratio.

Thus, the parameters which the compensation network is made to compensate for are impedance matching, i.e. compensating for mismatch between the signal ports and the antenna ports, and one or more of the following:

• Mutual coupling between antenna ports,

• Coupling of signals between the signal ports,

• Correlation of signals between the signal ports,

• SINR of received signals; Signal to Interference and Noise Ratio. In the embodiment 100 of fig 1 , the compensation network 105 is thus designed in advance for a certain diplex frequency separation, such as, for example, a duplex distance, i.e. a difference between transmit and receive frequencies, and a certain pair or pairs of frequencies f1 and f2. A schematic view of an example of such a compensation network 105 is shown in fig 2: the compensation network 105 of fig 2 comprises a number of transmission lines L1 , L2, L3, L4, L5, L6 and L7 as well as components C1 and C2.

The exact embodiments and the topology of the components C1 and C2 and transmission lines L1 , L2, L3, L4, L5, L6 and L7 may be varied in a large number of ways which are known to the man skilled in the field, but some examples of suitable components and transmission lines are as follows: the lines L1 , L4, L5 and L7 may be 50 ohm transmission lines, and the lines L2,

L3, and L6 may be transmission lines of other characteristic impedances and lengths, such as, for example, strip line, micro strip line, coaxial line, waveguide, whilst the components C1 and C2 may be capacitive and/or inductive components.

In an alternative embodiment 300 of the invention which is shown in fig 3, the apparatus comprises at least a second compensation network N2, shown as

105', in addition to the first compensation network N1 shown as 105. The basic design of the two compensation networks 105, 105', may or may not be the same. In addition, it should also be pointed out that an apparatus of the invention may comprise more than two compensation networks, with switches and measuring means to decide which network that is used.

In the embodiments where the antenna apparatus comprises more than one compensation network, the apparatus will also comprise measuring means 305, for measuring a first characteristic of the apparatus 300, as well as comprising means 320-323 for switching between the first 105 and the second 105' network in response to this measuring. As shown in fig 3, the measuring may be made on the "antenna side" of the compensation network, or as shown in fig. 4, on the "signal port side" of the compensation network, or a combination thereof.

Since the components of the antenna apparatus 400 of fig 4 are suitably the same as those of the apparatus 300 of fig 3, the reference numbers have, with a few exceptions, not been repeated in fig 4.

The measuring function and means will be described in more detail later in this text, but regarding the switching means 320-323, they can for example be implemented by means of so called MEMS switches, micro-electro mechanical systems, or diode switches.

In the antenna apparatus 400 of fig 4, the compensation may be made adaptive by means of switching between two (or more) compensation networks with different characteristics. In an alternative embodiment 500, which is schematically shown in fig 5, an adaptive compensation may instead be achieved by means of one and the same compensation network N5, shown as 510, which is adaptive as such.

The "adaptiveness" of the compensation network 510 is indicated in fig 5 by means of an arrow diagonally through the network 510. It should be pointed out here that the principles shown in figs 4 and 5 may also be combined, i.e. an antenna apparatus of the invention may comprise more than one adaptive compensation network, if, for example, the compensation possibilities of each network is limited and there is a need or a desire to expand the compensation range of the apparatus. In addition, an antenna apparatus of the invention may of course comprise a combination of adaptive and non- adaptive compensation networks.

Fig 6 shows a more detailed view of a possible implementation of the adaptive compensation network 510 of fig 5. In similarity to the compensation network 105 shown in fig 2, the compensation network 510 comprises transmission lines with a certain length and a certain characteristic impedance, as well as components of a certain impedance/reactance value. However, at least one component or line of the network 510 is variable. As exemplified in fig 6, such a variable component may be a variable capacitor C1 or C2, which is varied in response to measurements made by the measuring means 305, which may be similar to those used in the embodiments described previously, as shown by the use of the same reference numbers as previously.

In fig 6, the measurements which control the network 510 are made at the "antenna end" of the network. Alternatively, as shown in fig 7a, the measurements may be made at the "signal port end" of the compensation network, or a combination thereof.

The varying of the characteristics of the compensation network 510 may be achieved in a large number of ways. One such way is the variable capacitors shown in figs 6 and 7a; other such ways include one or more of the following, alone or in combination:

• Variable inductors,

• Varactor diodes,

• Phase shifters,

• Open or short-circuited transmission lines, shunt elements, which are added by means of switches, • Switches that change the lengths of one or more transmission lines,

• Sets of fixed components such as for example capacitors or inductors with different values, with switches that switch between the different components in the sets. Fig 7b shows such a set of components, in this case capacitors, with switches which switch between the different components. Naturally, in an antenna apparatus of the invention, the various embodiments shown in figs 1-7 may be combined in various ways, so that the following features are combined:

• the transmission lines of at least a first compensation network are of fixed lengths and characteristic impedance levels,

• the transmission lines of at least a first compensation network are coupled lines,

• the components of at least a first compensation network are of fixed lengths and impedance/reactance values,

• the transmission lines of at least a first compensation network are of variable lengths and/or characteristic impedance levels, with the network in question comprising measuring means such as the means 305 for measuring a first characteristic of the apparatus and means such as switches320, 321 , 322, 323 for varying the length and/or characteristic impedance level in response to the measuring,

• the components of at least a first compensation network are of variable lengths and/or impedance/reactance values, with the network in question comprising measuring means such as the means305 for measuring a first characteristic of the apparatus and means such as the switches 320, 321 , 322, 323 for varying the length and/or impedance values in response to the measuring,

• one of a plurality of compensation networks with different characteristics is selected, with the apparatus in question comprising measuring means such as the means for measuring a first characteristic of the apparatus and means such as switches for connecting the selected compensation network in response to the measuring.

In addition, although the compensation networks shown in the drawings and described above have been shown as comprising a first and a second input port, it is entirely within the scope of the present invention to use the principles described above to let a compensation network comprise additional antenna ports, and/or additional input ports, such as a third input port for a signal at a third frequency. Suitably, but not necessarily, the frequency of such a third signal would be equal to the frequency of the first and/or the second signal as used in MIMO applications. The number of antenna ports and the number of signal ports do not need to be equal.

Turning now to the nature of the measurements performed by the measuring means 305 and the corresponding decisions made, it should be pointed out that the measuring means 305 either comprise a decision making mechanism or is connected to such a mechanism, although this, for reasons of clarity has not been shown in the previous drawings. Fig 8 shows a possible measuring means 305 in more detail: as shown in fig 8, the measuring means comprises a measuring device 810, as well as a decision making means such as, for example, a microprocessor 820 and possibly a memory 830 to which the processor 820 is connected and in/from which the processor may store and/or retrieve information such as, for example, thresholds for controlling one or more compensation network.

As shown in figs 3 and 6, the input data for the measuring means 305 may be taken at the "antenna end" of the compensation networks, or at the "signal port" end of the compensation networks, as shown in figs 4, 5 and 7a. Naturally, input data from both of these ends may also be combined as input to the measuring means 305.

In the case where the measurements are made at the signal port end, the measuring means 305 attempts to maximize the received power and/or the SINR and/or the bit rate in the case of reception of signals, and in the case of transmission of signals, the purpose will be to minimize the reflections including coupling to other signal ports and thus, to maximize the transmitted power and/or the bit rate. In the case of transmission, the measuring means 305 may also use measurement data from the receiving device or devices, for example user's phones or laptop computers in a cellular system which transmit feedback signals regarding the received power level and/or other signal quality indicator measures of their received signals to the antenna apparatus.

In the case where the measurements are made at the antenna port end, as shown in figs 3 and 6, the measuring means 305 preferably measures characteristics on one or more transmission frequencies used by the apparatus, and attempts to optimize the compensation network with respect to transmit power.

Fig 9 shows a compensation network 900 with an alternative topology as compared to those shown previously, with components L2 and L10 which are open transmission lines and a component L6 which is a coupled line section.

Fig 10 shows another principle of an embodiment of the invention: any (imaginary) dividing line, D1 , which is drawn through any two-dimensional circuit model representation of the compensation network 1105 with antenna ports and signal ports on opposite sides of the dividing line will intersect more than one transmission line or a component on a transmission line if the dividing line is non-coincident to said transmission line.

The invention is not limited to the examples of embodiments described above and shown in the drawings, but may be freely varied within the scope of the appended claims. The compensation network could be connected to an antenna that is reconfigurable such that its operating frequency is changed in response to the used frequency. It should be mentioned that the measurements used by the decision making means shown in fig 8 may be either "snapshot" measurements or they may be measurements accumulated over time and then processed in order to obtain statistical data such as, for example, averages, in which case the memory 830 will be used for storing measurement data over a predetermined period of time.

Claims

1. An antenna apparatus (100, 105, 500) comprising at least a first (110) and a second (120) antenna element and a first compensation network (105), said first compensation network (105) comprising a first antenna port (A1) to which said first antenna element is connected and a second antenna port (A2) to which said second antenna element is connected, the first compensation network also comprising at least first (P 1) and second (P2) signal ports, the first compensation network further comprising transmission lines (130, 140) and/or components (135) of such lengths and impedance levels that the first (P1) and second (P2) signal ports respectively are suitable for receiving and/or transmitting signals at first (f1) and second (f2) frequencies respectively with a frequency separation between said signals which corresponds to a diplex distance used by the apparatus, the apparatus being characterized in that the first (P1) and second (P2) signal ports are suitable for receiving and/or transmitting said signals with respect to impedance matching and/or one or more of the following parameters:

• Coupling between signal ports,

• Correlation between signals, • SINR of received signals, Signal to Interference and Noise Ratio.

2. The antenna apparatus (100, 105, 300, 400, 500) of claim 1 , additionally comprising a second compensation network (105') with transmission lines and/or components, with the apparatus also comprising measuring means (305) for measuring a first characteristic of the apparatus and means for switching between the first (105) and second (105') network in response to said measuring.

3. The antenna apparatus (100, 105, 500, 300) of any of claims 1 - 2, in which the transmission lines of the first (105) and/or the second (105') compensation network are of fixed lengths and impedance levels.

4. The antenna apparatus (100, 105, 500) of any of claims 1-3, in which the components of the first (105) and/or the second (105') compensation network are of fixed lengths and impedance levels.

5. The antenna apparatus (100, 105, 300, 400, 500) of any of claims 1-4, in which the transmission lines of the first (105) and/or the second (105') compensation network are of variable lengths and/or impedance levels, with the network in question comprising measuring means (305) for measuring a first characteristic of the apparatus and means (320, 321 , 322, 323) for varying the length and/or impedance level in response to said measuring.

6. The antenna apparatus (100, 105, 300, 400, 500) of any of claims 1-5, in which the components of the first (105) and/or the second (105') compensation network are of variable lengths and/or impedance levels with the network in question comprising measuring means (305) for measuring a first characteristic of the apparatus and means (320, 321 , 322, 323) for varying the length and/or impedance level in response to said measuring.

7. The antenna apparatus (100, 105, 300, 400, 500) of any of claims 1-6, in which the first (105) and/or second (105') compensation network comprises a third signal port for a signal at a third frequency.

8. The antenna apparatus (100, 105, 300, 400, 500) of any of claims 2-7, in which the measuring means (305) is adapted to measure a signal characteristic at the signal ports and the varying means (320, 321 , 322, 323) are adapted to minimize the reflections of a transmitted signal.

9. The antenna apparatus (100, 105, 300, 400, 500) of any of claims 2-7, in which the measuring means (305) is adapted to measure a signal characteristic at the signal ports and the varying means (320, 321 , 322, 323) are adapted to maximize the power level of a received signal.

10. The antenna apparatus (100, 300, 400, 500) of any of claims 1-9, in which the diplex frequency separation corresponds to a duplex distance used by the apparatus.

11. The antenna apparatus (100, 300, 400, 500) of any of the precious claims, in which any imaginary dividing line, D1 , which is drawn through any two-dimensional circuit model representation (1105) of the compensation network with antenna ports and signal ports on opposite sides of the dividing line will intersect more than one transmission line or a component on a transmission line if the dividing line is non-coincident to said transmission line.