Patent Description:
Currently, an ID and a layout in a communications terminal are increasingly compact, and a global roaming requirement causes an increasing quantity of frequency bands that need to be supported by each mobile phone. Consequently, antenna commissioning and a PCB layout are very complex.

A tunable antenna is used in an existing communications terminal, and the tunable antenna selects a frequency band based on network searching. The mobile phone has many frequency bands. The tunable antenna does not need to support all the frequency bands at the same time, and only needs to tune a matching circuit based on an actual operating frequency band. For a tunable radio frequency front-end, for example, a tunable duplex and a tunable filter, one frequency band may be split into two parts for tuning. The two parts are a transmit link and a receive link respectively. Independent tuning and independent configuration of the entire links can be implemented. However, a current duplexer uses a transmit antenna and a receive antenna that are integrated together. In this case, isolation of the transmit antenna and the receive antenna needs to be considered. If dynamic tuning is performed, isolation of a common end of the transmit antenna and the receive antenna needs to be considered. Consequently, it is difficult to meet a requirement of a current product. Document <CIT> generally provides a RF front end to simultaneously transmit and receive signals for cellular telecommunications, comprising a tunable duplexer selectively connected to an antenna, configured to transmit and receive radio frequency communication signals in a group of at least two bands; and a tunable transmit filter in the duplexer, capable of being tuned to have an inductance value approximately matching at least two inductance values corresponding respectively to pass the at least two bands in the group, each of the at least two bands in the group having a positive duplex offset and each of the at least two inductance values that correspond respectively to the at least two bands in the group, having an inductance value that approximately matches the inductance values corresponding respectively to the other bands in the group. Document <CIT> generally utilizes small, narrow-band and frequency adaptable antennas to provide coverage to a wide range of wireless modes and frequency bands on a host wireless device. The antennas have narrow pass-band characteristics, require minimal space on the host device, and allow for smaller form factor. The frequency tunability further allows for a fewer number of antennas to be used. The operation of the antennas may also be adaptably relocated from unused modes to in-use modes to maximize performance. These features of the antennas result in cost and size reductions
Document <CIT> discloses a tunable radio front end comprising: a first and second tunable impedance matching networks, a transmission signal path comprising a first tunable filter in communication with the first tunable impedance matching network, and a reception signal path comprising a second tunable filter.

This application provides a tunable antenna and a communications terminal, to improve antenna isolation. In particular, there is provided a tunable antenna and a communications terminal, having the features of respective independent claims. The dependent claims relate to preferred embodiments.

According to a first aspect, this application provides a tunable antenna, as defined in claim <NUM>, suitable to be applied to a communications terminal. The tunable antenna includes a radio frequency integrated circuit, where the radio frequency integrated circuit is used to send signals in different frequency bands; and further includes a second antenna and a first antenna, where the first antenna is used to transmit a signal, the second antenna is used to receive an antenna signal, and the receive antenna and the first antenna are separately connected to the radio frequency integrated circuit. To implement adjustment, a frequency modulation branch has a plurality of frequency bands, and can implement transmission or receiving in different frequency bands. The first antenna is connected to the radio frequency integrated circuit through the first frequency modulation branch. The second antenna is connected to the radio frequency integrated circuit through a second frequency modulation branch. The first antenna corresponds to a first frequency, the second antenna corresponds to a second frequency, and the first frequency and the second frequency are respectively a transmit frequency and a receive frequency in a specified frequency band. It can be learned from the foregoing description that, when the tunable antenna is being designed, the first antenna and the second antenna are separately disposed, and the first antenna and the second antenna are respectively connected to the radio frequency integrated circuit through the frequency modulation branches. Therefore, frequency bands of the first antenna and the second antenna may be separately adjusted. In addition, isolation between the first antenna and the second antenna includes isolation between the transmit antenna and the receive antenna, and isolation between the frequency modulation branches. This improves the isolation between the second antenna and the first antenna.

When the frequency modulation branch is specifically disposed, different manners may be used for implementation. The first frequency modulation branch includes a plurality of first frequency band branches, where the plurality of first frequency band branches correspond to different frequency bands, one end of each first frequency band branch is connected to the first antenna through a first selector switch, and the other end is connected to the radio frequency integrated circuit through a second selector switch.

During specific disposition, there may be one or more first frequency modulation branches. For example, there are two first frequency modulation branches, and the two first frequency modulation branches are connected to the first antenna through one first selector switch.

To improve a communication effect of the antenna, the tunable antenna further includes a power amplifier, where one end of the power amplifier is connected to the radio frequency integrated circuit, and the other end is electrically connected to the second selector switch. A signal sent from the radio frequency integrated circuit is amplified by the power amplifier and then transmitted to the first antenna. This improves performance of the antenna.

Filters are used when the first frequency band branches are specifically set to correspond to different frequency bands. A filter is disposed on each first frequency band branch. In addition, the filters on the first frequency band branches correspond to different frequency bands.

When the switches are specifically disposed, the first selector switch and the second selector switch each are a one-pole multi-throw switch. An immovable end of the first selector switch is connected to the first antenna, and a movable end is connected to each first frequency band branch in a one-to-one correspondence. An immovable end of the second selector switch is electrically connected to the power amplifier, and a movable end is connected to each second frequency band branch in a one-to-one correspondence. Different frequency band branches are selected by using the one-pole multi-throw switch.

The second antenna is a full-band antenna, so that the second antenna can receive signals in a plurality of frequency bands.

When the second antenna is implemented, the second frequency modulation branch includes a plurality of second frequency band branches, and the plurality of second frequency band branches correspond to different frequency bands. One end of each second frequency band branch is connected to the radio frequency integrated circuit, and the other end is optionally connected to the second antenna through a third selector switch.

In addition to the frequency modulation branch, another manner may be used. For example, the first frequency modulation branch includes a tunable filter.

Similarly, a tunable filter may also be used for the second frequency modulation branch.

In addition to the first antenna and the second antenna, the tunable antenna disclosed in this application further includes a third antenna. When the third antenna is specifically disposed, the third antenna is connected to the radio frequency integrated circuit through a second frequency modulation branch. The second frequency modulation branch has a plurality of frequency bands, so that the third antenna can correspond to different frequency bands.

When a third frequency modulation branch is specifically disposed, the second frequency modulation branch includes a plurality of second frequency band branches, and the plurality of second frequency band branches correspond to different frequency bands. One end of each second frequency band branch is connected to the radio frequency integrated circuit, and the other end is optionally connected to the third antenna through a fourth selector switch. A frequency band corresponding to the third antenna is selected by using the fourth selector switch.

During specific disposition, the fourth selector switch may be a one-pole multi-throw selector switch. A movable end and an immovable end corresponding to the fourth selector switch are respectively connected to the third antenna and the second frequency band branch.

According to a second aspect, a communications terminal is provided, where the communications terminal includes the tunable antenna according to any one of the foregoing descriptions. When the tunable antenna is being designed, the first antenna and the second antenna are respectively connected to the radio frequency integrated circuit through the frequency modulation branches. Therefore, frequency bands of the first antenna and the second antenna can be separately adjusted. This improves isolation between the second antenna and the first antenna.

To facilitate understanding of a tunable antenna provided in this embodiment of this application, an application scenario of the tunable antenna is first described. The tunable antenna is applied to a communications terminal, and the communications terminal may be a common communications terminal such as a base station or a signal tower.

<FIG> shows a structure of a tunable antenna in the prior art. The antenna includes a radio frequency integrated circuit <NUM>. The radio frequency integrated circuit <NUM> is connected to a main antenna <NUM>, and the main antenna <NUM> is used as both a transmit antenna and a receive antenna. During specific connection, the radio frequency integrated circuit <NUM> is connected to a plurality of parallel duplexers <NUM> by using a power amplifier <NUM>. Different duplexers <NUM> are selected for connection by using a selector switch <NUM>. It can be seen from <FIG> that, the duplexer uses a transmit antenna and a receive antenna that are integrated together, and in this case, isolation of the transmit antenna and the receive antenna needs to be considered. If dynamic tuning is performed, isolation of a common end of the transmit antenna and the receive antenna needs to be considered. Consequently, it is difficult to meet a requirement of a current product.

As shown in <FIG>, an LTE band <NUM> is used as an example. A frequency range is from <NUM> to <NUM>. However, a transmit frequency of an antenna is from <NUM> to <NUM>, and a receive frequency of the antenna is from <NUM> to <NUM>. In the prior art, tuning needs to be performed on (<NUM>-<NUM>) MHz, that is, a bandwidth of <NUM> as shown by the dotted line a in <FIG>. Even for a solution of tuning after frequency band division, considering an LTE bandwidth of <NUM>, for example, the first channel, tuning needs to be performed on <NUM> to <NUM>, that is, a bandwidth of <NUM> as shown by a double-dotted line b in <FIG>. However, a current duplexer uses a transmit antenna and a receive antenna that are integrated together, so that isolation of the transmit antenna and the receive antenna needs to be considered. If dynamic tuning is performed, isolation of a common end of the transmit end and the receive end needs to be considered, and a bandwidth requirement needs to be met. Consequently, final tuning efficiency may not be very good, and especially, efficiency of an edge frequency may be unsatisfactory. Therefore, in this embodiment of this application, as shown in <FIG>, two separate filters <NUM> are used to replace one duplexer <NUM> in the prior art. As shown by solid lines in <FIG>, when the separate filters are used (one filter corresponds to transmitting, and the other filter <NUM> corresponds to receiving), frequencies corresponding to the two filters <NUM> are shown by two solid curves c in <FIG>, and a bandwidth corresponding to each filter <NUM> is <NUM>. In this way, separate isolation and tuning for transmitting and receiving are implemented. The following describes in detail the tunable antenna provided in this embodiment of this application with reference to the accompanying drawings.

Solutions disclosed in this application provide a tunable antenna. The tunable antenna is applied to a communications terminal. The following describes the tunable antenna provided in the embodiments of this application with reference to the accompanying drawings. First, <FIG> shows a structure of a tunable antenna according to an embodiment of this application. The tunable antenna mainly includes: a radio frequency integrated circuit <NUM>, a first antenna <NUM>, and a second antenna <NUM>. The radio frequency integrated circuit <NUM> is used to send a signal to the first antenna <NUM> and receive a signal from the second antenna <NUM>. The first antenna <NUM> corresponds to a first frequency, and the second antenna <NUM> corresponds to a second frequency. The first frequency and the second frequency are respectively a transmit frequency and a receive frequency in a specified frequency band. More specifically, the first antenna <NUM> is used to transmit a signal, the second antenna <NUM> is used to receive a signal, and both the first antenna <NUM> and the second antenna <NUM> are main antennas. The specified frequency band may be any frequency band in a band <NUM> to a band <NUM>, as shown in the following table.

The radio frequency integrated circuit <NUM> is connected to the first antenna <NUM> through a first frequency modulation branch. There may be one or two first frequency modulation branches. As shown in <FIG>, there are two first frequency modulation branches: a first frequency modulation branch 50a and a first frequency modulation branch 50b. In this case, the radio frequency integrated circuit <NUM> is connected to the first frequency modulation branch 50a and the first frequency modulation branch 50b. In addition, the first antenna <NUM> is connected to the first frequency modulation branch 50a and the first frequency modulation branch 50b by using a selector switch. The first frequency modulation branch 50a and the first frequency modulation branch 50b are both frequency modulation branches, and correspond to different modulation frequencies. Certainly, one first frequency modulation branch <NUM> may be alternatively used. <FIG> is a schematic diagram of using one first frequency modulation branch <NUM> for the first antenna <NUM> and the radio frequency integrated circuit <NUM>. A principle of using one first frequency modulation branch <NUM> is similar to a principle of using the first frequency modulation branch 50a and the first frequency modulation branch 50b. The following uses the first frequency modulation branch 50a and the first frequency modulation branch 50b as an example for description.

When the first frequency modulation branch 50a and the first frequency modulation branch 50b are used, different structures may be used for implementation. <FIG> shows specific structures of the first frequency modulation branch 50a and the first frequency modulation branch 50b. The following describes the first frequency modulation branch 50a and the first frequency modulation branch 50b with reference to <FIG>.

First, both the first frequency modulation branch 50a and the first frequency modulation branch 50b include a plurality of parallel frequency band branches. The first frequency modulation branch 50a includes a plurality of parallel first frequency band branches 51a, and the plurality of parallel first frequency band branches 51a have different frequency bands. Similarly, the first frequency modulation branch 50b includes a plurality of parallel first frequency band branches 51b. The plurality of parallel first frequency band branches 51b have different frequency bands. In addition, the frequency bands corresponding to the first frequency band branches 51a are also different from those corresponding to the first frequency band branches 51b. During specific implementation, that the first frequency band branch 51a and the first frequency band branch 51b have different frequency bands, different first frequency band branches 51a have different frequency bands, and different first frequency band branches 51b have different frequency bands is implemented by disposing different filters. As shown in <FIG>, a filter is separately disposed on each first frequency band branch 51a and each first frequency band branch 51b. Filters on different frequency band branches (the first frequency band branch 51a and the first frequency band branch 51b) correspond to different frequency bands. In this way, different frequency band branches correspond to different frequency bands.

For a quantity of first frequency band branches 51a and a quantity of first frequency band branches 51b, the quantity of first frequency band branches 51a may be different from the quantity of first frequency band branches 51b. As shown in <FIG>, there are four first frequency band branches 51a, and there are four first frequency band branches 51b. Certainly, another different quantity of branches may alternatively be used. For example, there are three first frequency band branches 51a, and there are five first frequency band branches 51b, or there are other different quantities of branches.

When the radio frequency integrated circuit <NUM> is connected to the first antenna <NUM> by using the first frequency modulation branch 50a or the first frequency modulation branch 50b, a specific disposition manner is as follows: The radio frequency integrated circuit <NUM> is connected to the first frequency modulation branch 50a by using a first power amplifier 60a. The first power amplifier 60a is connected to one of the plurality of first frequency band branches 51a through a second selector switch 52a. The other ends of the plurality of first frequency band branches 51a are connected to the first selector switch <NUM>, and are further connected to a main transmitter circuit <NUM> through the first selector switch <NUM>. In the structure shown in <FIG>, both the first selector switch <NUM> and the second selector switch 52a are one-pole multi-throw switches. A movable end of the first selector switch <NUM> is connected to the first antenna <NUM>. There are a plurality of immovable ends, and the plurality of immovable ends are connected to the first frequency band branches 51a and the first frequency band branches 51b in a one-to-one correspondence. A movable end of the second selector switch 52a is connected to the first power amplifier 60a. The second selector switch 52a has four immovable ends, and the four immovable ends are respectively connected to the four first frequency band branches 51a. When the radio frequency integrated circuit <NUM> is connected to the first antenna <NUM> through the first frequency modulation branch 50a, the first selector switch <NUM> and the second selector switch 52a select a same first frequency band branch 51a, and a signal path is as follows: the radio frequency integrated circuit <NUM> - the first power amplifier 60a - the second selector switch 52a - one first frequency band branch 51a - the first selector switch <NUM> - the first antenna <NUM>.

Still referring to <FIG>, similarly, for the first frequency modulation branch 50b, the radio frequency integrated circuit <NUM> is connected to the first frequency modulation branch 50b through a second power amplifier 60b. The second power amplifier 60b is connected to the plurality of first frequency band branches 51b through a second selector switch 52b. The other ends of the plurality of first frequency band branches 51b are connected to the first antenna <NUM> through the first selector switch <NUM>. The second selector switch 52b is also a one-pole multi-throw switch, and is specifically a one-pole four-throw switch in <FIG>. In addition, a movable end of the second selector switch 52b is connected to the second power amplifier 60b, and each of four immovable ends of the second selector switch 52b is connected to one first frequency band branch 51b. When the radio frequency integrated circuit <NUM> is connected to the first antenna <NUM> through the first frequency modulation branch 50b, the second selector switch 52b and the first selector switch <NUM> select a same first frequency band branch 51b, and a signal path is as follows: the radio frequency integrated circuit <NUM> - the second power amplifier 60b - the second selector switch 52b - one first frequency band branch 51b - the first selector switch <NUM> - the first antenna <NUM>.

<FIG> shows a case in which one first tunable frequency band branch <NUM> is used. In this case, the radio frequency integrated circuit <NUM> is connected to a power amplifier <NUM>. The power amplifier <NUM> is connected to a second selector switch <NUM>. The second selector switch <NUM> is connected to a plurality of first frequency band branches <NUM>. The other ends of the plurality of first frequency band branches <NUM> are connected to the first selector switch <NUM>. The first selector switch <NUM> is connected to the first antenna <NUM>. The first frequency modulation branch <NUM> includes a plurality of first frequency band branches <NUM>, and the plurality of parallel first frequency band branches <NUM> have different frequency bands. The first frequency band branches <NUM> are specifically implemented by disposing different filters. As shown in <FIG>, a filter is disposed on each first frequency band branch <NUM>, and filters on different first frequency band branches <NUM> correspond to different frequency bands, so that different frequency band branches correspond to different frequency bands. One end of each first frequency band branch <NUM> is connected to an immovable end of the first selector switch <NUM>, and the other end is connected to an immovable end of the second selector switch <NUM>. A movable end of the second selector switch <NUM> is connected to the power amplifier <NUM>, and a movable end of the first selector switch <NUM> is connected to the first antenna <NUM>. During use, the first selector switch <NUM> and the second selector switch <NUM> select a same frequency band branch <NUM>. A transmit signal of the radio frequency integrated circuit <NUM> is transmitted through the following path: the power amplifier <NUM> - the second selector switch <NUM> - the first frequency band branch <NUM> - the first selector switch <NUM> - the first antenna <NUM>.

In the tunable antenna shown in <FIG>, a filter used for the first frequency modulation branch 50a and a filter used for the first frequency modulation branch 50b are non-tunable filters. In this embodiment of this application, a tunable filter may be alternatively used. As shown in <FIG>, filters on both the first frequency modulation branch 50a and the first frequency modulation branch 50b are tunable filters, so that the filter can be adjusted to correspond to a corresponding frequency band. It should be understood that, when the tunable filter shown in <FIG> is used, each tunable filter corresponds to a different adjustable frequency band and a different adjustable range, so as to correspond to a different frequency band of the first antenna <NUM>.

The first power amplifier 60a and the second power amplifier 60b in <FIG> may be disposed based on a requirement. When power amplification is not required, the first power amplifier 60a and the second power amplifier 60b may not be disposed.

In addition to the structure of the first frequency modulation branch 50a and the first frequency modulation branch 50b shown in <FIG>, a structure shown in <FIG> may be alternatively used. In the structure shown in <FIG>, the first frequency modulation branch 50a is a branch with a tunable filter, and the first frequency modulation branch 50b is also a branch with a tunable filter. In this case, the first frequency modulation branch 50a and the first frequency modulation branch 50b each are a single branch. During specific connection, as shown in <FIG>, the radio frequency integrated circuit <NUM> is connected to the first frequency modulation branch 50a through the first power amplifier 60a, and is connected to the first frequency modulation branch 50b through the second power amplifier 60b. The first selector switch <NUM> is a single-pole double-throw switch. Immovable ends of the first selector switch <NUM> are in a one-to-one correspondence with the first frequency modulation branch 50a and the first frequency modulation branch 50b, and a movable end of the first selector switch <NUM> is connected to the first antenna <NUM>. The first frequency modulation branch 50a and the first frequency modulation branch 50b are selected by using the first selector switch <NUM> to connect to the radio frequency integrated circuit <NUM>. In addition, a corresponding frequency band is adjusted by adjusting the tunable filter on the first frequency modulation branch 50a and the tunable filter on the first frequency modulation branch 50b. Using the first frequency modulation branch 50a as an example, by adjusting a resonance point of the tunable filter, the first frequency modulation branch 50a may be equivalent to different first frequency band branches in <FIG>. Therefore, a structure of the entire first frequency modulation branch 50a is simplified by using one tunable filter. During specific setting, in <FIG>, the tunable filter on the first frequency modulation branch 50a is used to adjust an intermediate frequency and a high frequency of the first antenna <NUM>, and the tunable filter on the first frequency modulation branch 50b is used to adjust a low frequency of the first antenna <NUM>. Certainly, the tunable filter on the first frequency modulation branch 50a may be alternatively used to adjust a low frequency of the first antenna <NUM>, and the tunable filter on the first frequency modulation branch 50b may be alternatively used to adjust an intermediate frequency and a high frequency of the first antenna <NUM>.

As shown in <FIG>, one first frequency modulation branch <NUM> on which one tunable filter is disposed may be alternatively used to adjust a frequency band. In this case, no selector switch is required, and the entire transmitter circuit includes only the radio frequency integrated circuit <NUM>, the power amplifier <NUM> connected to the radio frequency integrated circuit, the first frequency modulation branch <NUM> connected to the power amplifier, and the first antenna <NUM> connected to the first frequency modulation branch <NUM>. During use, a transmit signal of the radio frequency integrated circuit <NUM> is transmitted through the following path: the power amplifier <NUM> - the first frequency modulation branch <NUM> - the first antenna <NUM>. During transmission, the tunable filter is adjusted to a frequency band corresponding to the transmit signal.

It can be learned from the foregoing description that the disposed first frequency modulation branch 50a and the disposed first frequency modulation branch 50b can separately control a frequency band of a main transmit antenna. Still referring to <FIG>, when the second antenna <NUM> is disposed, the tunable antenna provided in this embodiment of this application is also used to separately control a frequency band.

As shown in <FIG>, for the tunable antenna provided in this embodiment of this application, the radio frequency integrated circuit <NUM> is connected to the second antenna <NUM> by using a second frequency modulation branch <NUM>. When the second frequency modulation branch <NUM> is disposed, the second frequency modulation branch <NUM> includes a plurality of second frequency band branches <NUM>. In addition, the plurality of second frequency band branches <NUM> correspond to different frequency bands. One end of each second frequency band branch <NUM> is connected to the radio frequency integrated circuit <NUM>, and the other end is optionally connected to the second antenna <NUM> by using a third selector switch <NUM>. The third selector switch <NUM> is also a one-pole multi-throw switch. Still referring to <FIG>, the second frequency modulation branch <NUM> includes five second frequency band branches <NUM>, and different second frequency band branches <NUM> correspond to different frequency bands. During specific disposition, one filter is disposed on each second frequency band branch <NUM>, and different filters correspond to different frequency bands. The different filters are disposed to control frequency bands corresponding to different second frequency band branches <NUM>. The third selector switch <NUM> is a one-pole multi-throw switch, and corresponds to a one-pole five-throw switch in the structure shown in <FIG>. In addition, a movable end of the third selector switch <NUM> is connected to the second antenna <NUM>, and each immovable end of the third selector switch <NUM> corresponds to one second frequency band branch <NUM>. During connection, one second frequency band branch <NUM> is selected by using the third selector switch <NUM>. In this case, a signal connection is as follows: the second antenna <NUM> - the third selector switch <NUM> - the second frequency band branch <NUM> - the radio frequency integrated circuit <NUM>.

The filter on the second frequency band branch <NUM> may be a non-tunable filter shown in <FIG>, or may be a tunable filter shown in <FIG>. When the tunable filter shown in <FIG> is used, tunable filters on the second frequency band branches <NUM> have different adjustment ranges, so as to correspond to different frequency bands of the second antenna <NUM>.

Certainly, it should be understood that the second frequency modulation branch <NUM> provided in this embodiment of this application is not limited to the structure in <FIG>, and may alternatively use the structure in <FIG>. In this case, the second frequency modulation branch <NUM> is a branch with a tunable filter. A resonance point of the tunable filter is adjusted, so that the second antenna <NUM> corresponds to different frequency bands. The tunable filter connecting the third antenna <NUM> and the radio frequency integrated circuit <NUM> may be one tunable filter or two tunable filters connected in parallel. As shown in <FIG>, the two tunable filters connected in parallel are used. In this case, the third selector switch <NUM> is correspondingly disposed to select a different tunable filter to connect to the second antenna <NUM>. Certainly, when the two tunable filters are selected, the two tunable filters correspond to different adjustment frequency bands, and separately correspond to a high frequency, an intermediate frequency, and a low frequency of the second antenna <NUM>. For details, refer to descriptions of the two tunable filters corresponding to the first antenna <NUM>.

As shown in <FIG>, there may be one first frequency modulation branch <NUM> and one second frequency modulation branch <NUM>. In addition, a tunable filter is disposed on each of the first frequency modulation branch <NUM> and the second frequency modulation branch <NUM>. In this case, no selector switch is required, and the radio frequency integrated circuit <NUM> is directly connected to the first frequency modulation branch <NUM> and the second frequency modulation branch <NUM>. The first frequency modulation branch <NUM> is connected to the first antenna <NUM>. The second frequency modulation branch <NUM> is connected to the second antenna <NUM>. During use, a receive signal is received through the following path: the second antenna <NUM> - the second frequency modulation branch <NUM> - the radio frequency integrated circuit <NUM>. During signal receiving, the tunable filter is adjusted to a frequency band corresponding to a transmit signal. For example, when a signal in a frequency band of band <NUM> is being received, the tunable filter is adjusted to <NUM> to <NUM>. During signal transmission, a transmit signal of the radio frequency integrated circuit <NUM> is transmitted through the following path: the power amplifier <NUM> - the first frequency modulation branch <NUM> - the first antenna <NUM>. During transmission, the tunable filter is adjusted to a frequency band corresponding to the transmit signal. For example, when a signal corresponding to a frequency band of band <NUM> is being transmitted, the tunable filter is adjusted to <NUM> to <NUM>.

For the tunable antenna shown in <FIG> and <FIG>, there is one second antenna <NUM>, and the second antenna <NUM> is a full-band antenna. Certainly, there may be a plurality of second antennas <NUM>, for example, two second antennas <NUM>, three second antennas <NUM>, or a different quantity of second antennas <NUM>. In this case, different second antennas <NUM> correspond to different frequency bands. <FIG> shows two second antennas <NUM>, where a frequency band corresponding to one tunable filter on one second antenna <NUM> is band <NUM> + band <NUM>, and a frequency band corresponding to a tunable filter on another frequency modulation branch is band <NUM> + band <NUM>; and a frequency band corresponding to the other second antenna <NUM> is band <NUM>. It should be understood that the foregoing specific frequency band is a specific example. The second antenna <NUM> provided in this embodiment of this application may alternatively correspond to another different frequency band. For example, when three second antennas are used, the three second antennas are respectively corresponding to the high frequency band, the intermediate frequency band, and the low frequency band.

However, regardless of whether one second antenna <NUM> or a plurality of second antennas <NUM> are used, each second antenna <NUM> is connected to the radio frequency integrated circuit <NUM> by using a tunable branch. A structure of the second antenna is similar to the structure described above, and details are not described herein.

It should be understood that, in the foregoing specific embodiment, two different specific implementations are provided for the first frequency modulation branch 50a, the first frequency modulation branch 50b, and the second frequency modulation branch <NUM>. However, for the tunable antenna provided in this embodiment of this application, any known solution that can implement frequency band adjustment can be applied to the first frequency modulation branch 50a, the first frequency modulation branch 50b, and the second frequency modulation branch <NUM> provided in the embodiments of this application. The solution is not limited to the specific embodiments shown in <FIG>. For example, one first frequency modulation branch may be used and a non-tunable filter is used for the frequency modulation branch, but a tunable filter is used on a used second frequency modulation branch.

Still referring to <FIG>, in addition to the first antenna <NUM> and the second antenna <NUM> described above, the tunable antenna provided in this embodiment of this application further includes a third antenna <NUM>. The third antenna <NUM> is a diversity antenna. During specific connection, the third antenna <NUM> is connected to the radio frequency integrated circuit <NUM> through a third frequency modulation branch <NUM>. A structure of the third frequency modulation branch <NUM> is similar to that of the second frequency modulation branch <NUM>. Alternatively, a plurality of parallel third frequency band branches <NUM> may be used. In addition, one end of the third frequency band branch <NUM> is connected to the radio frequency integrated circuit <NUM>, and the other end is connected to the third antenna <NUM> by using a fourth selector switch <NUM>. As shown in <FIG>, the fourth selector switch <NUM> is a one-pole multi-throw switch, and specifically is a one-pole five-throw switch in <FIG>. In addition, a movable end is connected to the third antenna <NUM>, and immovable ends are respectively connected to five frequency band branches in a one-to-one correspondence. During connection, different third frequency band branches <NUM> are selected by using the fourth selector switch <NUM>. Certainly, the third frequency modulation branch <NUM> may alternatively use a structure with a tunable filter, and a structure of the third frequency modulation branch <NUM> is shown in <FIG>. Certainly, there may be one or two third frequency band branches <NUM>.

It can be learned from the foregoing description that, for the tunable antenna provided in the embodiments of this application, for a frequency division duplex frequency, all links of the main transmit antenna and the second antenna <NUM> are separately controlled. A link from a receive port of the radio frequency integrated circuit <NUM> to the antenna are adjustable, and all the links of the main transmit antenna and the second antenna <NUM> are separately controlled and separately tuned. Isolation between receiving and transmitting of the antennas includes: isolation between the first antenna and the first antenna and isolation between the first frequency modulation branch 50a and the first frequency modulation branch 50b. Compared with the prior art in which isolation is performed only by using a duplexer, the tunable antenna provided in the embodiments of this application increases isolation between the transmit antenna and the receive antenna. In addition, an embodiment of this application further provides a communications terminal. The communications terminal includes the tunable antenna according to any one of the foregoing embodiments. When the tunable antenna is being designed, the first antenna <NUM> and the second antenna <NUM> are respectively connected to the radio frequency integrated circuit <NUM> through the frequency modulation branches. Therefore, frequency bands of the first antenna <NUM> and the second antenna <NUM> can be separately adjusted. This improves isolation between the second antenna <NUM> and the first antenna <NUM>.

Claim 1:
A tunable antenna applicable to a communications terminal, wherein the tunable antenna comprises a radio frequency integrated circuit (<NUM>), a first frequency modulation branch (50a, 50b) separately connected to the radio frequency integrated circuit (<NUM>), a first antenna (<NUM>), a second antenna (<NUM>) and a second frequency modulation branch (<NUM>),
wherein the first antenna (<NUM>) is connected to the radio frequency integrated circuit (<NUM>) through the first frequency modulation branch (50a, 50b);
wherein the second antenna (<NUM>) is connected to the radio frequency integrated circuit (<NUM>) through the second frequency modulation branch (<NUM>);
wherein the first antenna (<NUM>) corresponds to a first frequency, the second antenna (<NUM>) corresponds to a second frequency, and the first frequency and the second frequency are respectively a transmit frequency and a receive frequency in a specified frequency band;
wherein the first frequency modulation branch (50a, 50b) comprises:
a plurality of first frequency band branches (51a, 51b), wherein the plurality of first frequency band branches (51a, 51b) correspond to different frequency bands, one end of each first frequency band branch (51a, 51b) is connected to the first antenna (<NUM>) through a first selector switch (<NUM>), and the other end is connected to the radio frequency integrated circuit (<NUM>) through a second selector switch (52a, 52b);
wherein the second frequency modulation branch (<NUM>) comprises a plurality of second frequency band branches (<NUM>), the plurality of second frequency band branches (<NUM>) correspond to different frequency bands, one end of each second frequency band branch (<NUM>) is connected to the radio frequency integrated circuit (<NUM>), and the other end is connected to the second antenna through a third selector switch (<NUM>); and
wherein the second antenna (<NUM>) is a full-band antenna configured to receive signals in a plurality of frequency bands.