Patent Application
20140085160
The invention concerns in general the technical field of radio antennas. Especially the invention concerns multi-band antenna and matching circuits for the antenna for use e.g. in a mobile communication terminal.
Current wireless communication systems utilize several different radio communication standards and operate at many different frequency bands. In this fractured service environment, mobile terminals operating in multiple systems and frequency bands offer a better service coverage than single band and single-system terminals. One example of a multi-band communication terminal is a mobile terminal operating for example at four GSM bands, namely GSM850 (824-894 MHz), GSM900 (880-960 MHz), GSM1800 (1710-1880 MHz), GSM1900 (1850-1990 MHz) and further at three WCDMA bands, namely WCDMA I (1920-2170 MHz), WCDMA II (1850-1990 MHz) and WCDMA V (824-894 MHz).
In order to enable the utilization of multiple frequency bands by a mobile terminal the reception and transmission of the radio signals need to be arranged. An essential element for an operation in multiple frequency bands is an antenna and necessary circuits, such as matching circuits, thereto residing in the mobile terminal. More specifically, a compact multi-band antenna configuration with good performance is needed to realize the communication of mobile terminals with multiple bands. Currently, one approach is that mobile terminals comprise multiple antennas which are dedicated for different frequency bands, e.g. lower and higher frequencies. At the same time as the space for the antennas in the mobile terminal is becoming very limited there is a need to fit more and more antennas inside the terminal, for example to implement mobile antenna diversity.
For example, a prior art multi-band antenna module may include a substrate, first and second coupling elements i.e. antenna elements, and first and second resonant matching circuits. The first coupling element is mounted to the substrate and particularly adapted to couple a first frequency band to a ground plane through a first port. The second coupling element is also mounted to the substrate, and is adapted to couple a second frequency band to a ground plane through a second port. The ground plane may be the same, but is not itself a part of the antenna module. The first resonant matching circuit is coupled to the first port and is disposed on the substrate and has a plurality of components by means of which it is possible to implement a band-pass filter within the first frequency band and to present high impedance at least in the second frequency band. Similarly, the second resonant matching circuit is coupled to the second port and is also disposed on the substrate. The second series matching circuit has a plurality of components that implement a band-pass filter within the second frequency band and to present high impedance at least in the first frequency band.
The outmost challenge is that as the number of required operating frequency bands is increasing, it is very challenging to cover all the required bandwidths with the prior art antenna solutions. The drawback of the prior art antenna solutions according to one approach is that there is a need for a separate antenna element i.e. a coupling element for each of the frequency band. Alternatively, according to another prior art solution one antenna element, typically self-resonant antenna element, can be applied for lower and higher frequencies but in that case the antenna element needs to be big enough in size in order to realize resonances in multiple frequency bands simultaneously. Both of the prior art approaches result a fundamental challenge especially in the area of mobile terminals, because the volume reserved for antennas in the mobile terminal is limited. Furthermore, the prior art implementations force one to isolate the coupling elements from each other so that a coupling between the antenna branches can be prevented. Thus, it can be said that one challenge with the prior art antenna solutions is that antennas, with each encompassing separate frequency bands, causes waste of antenna volume, as the available antenna volume cannot be entirely utilized at any given frequency. Due to the physical limitations of electrically small antennas, it is beneficial to be able to utilize the entire antenna volume especially at the lower frequencies of operation. This way the reachable frequency bandwidth is maximal.
An objective of the invention is to present a multi-band antenna and antenna module for wireless communication. Another objective of the invention is that the multi-band antenna and the antenna module are arranged with a single antenna element.
The objects of the invention are reached by antennas and antenna modules as defined by the respective independent claims.
According to a first aspect, a multi-band antenna is provided, which comprises a ground plane, a single antenna element, a frequency multiplexing circuit, at least two feeding strips coupled between the frequency multiplexing circuit and the single antenna element and at least one feeding point arranged between the ground plane and the frequency multiplexing circuit. The multi-band antenna may further comprise at least one matching circuit, the at least one matching circuit is arranged to be coupled between the frequency multiplexing circuit and at least one feeding strip. Alternatively or in addition, the multi-band antenna may further comprise at least one matching circuit embedded in the frequency multiplexing circuit, the matching circuit providing impedance matching of at least one feeding strip of the at least two feeding strips for a predetermined frequency band. Furthermore, the multi-band antenna may further comprise two matching circuits embedded in the frequency multiplexing circuit, each of the matching circuits providing impedance matching of each of the feeding strips for at least two predetermined frequency bands. The multiplexing circuit as mentioned may be at least one of the following: diplexer, RF switch, isolation implementation. The single antenna element as mentioned may be at least one of the following: Capacitive Coupling Element, Planar inverted-F antenna, Inverted-F antenna, Planar inverted-L antenna, inverted-L antenna, loop antenna, monopole antenna.
Furthermore, the at least one feeding strip may be configured to be located, with respect to the single antenna element and the ground plane, so that a resonant wavemode of the radiating structure formed by the single antenna element and the ground plane at a given frequency is excited and wherein the at least one other feeding strip may be configured to be located, with respect to the single antenna element and the ground plane, so that that resonant wavemode of the radiating structure or non-orthogonal wavemodes with respect to the resonant wavemode at frequencies close to the resonant wavemode frequency are not excited by the at least one other feeding strips.
According to an second aspect, another multi-band antenna is provided, which comprises a ground plane, a single antenna element, a frequency multiplexing circuit and at least two feeding strips wherein dedicated feeding points are arranged for each of the at least two feeding strips, and each of the at least two feeding strips are coupled between the dedicated feeding point arranged for the feeding strip and the single antenna element. Alternatively or in addition, the multi-band antenna may further comprise at least one matching circuit, the at least one matching circuit arranged to be coupled between one dedicated feeding point and a corresponding feeding strip. The at least one matching circuit may be configured to be embedded in the frequency multiplexing circuit. The single antenna element may be at least one of the following: Capacitive Coupling Element, Planar inverted-F antenna, Inverted-F antenna, Planar inverted-L antenna, inverted-L antenna, loop antenna, monopole antenna.
According to a third aspect, a multi-band antenna module is provided, which comprises a substrate, a single antenna element mounted to the substrate, a frequency multiplexing circuit disposed on the substrate, at least two feeding strips disposed on the substrate and coupled between the frequency multiplexing circuit and the single antenna element and at least one signal port arranged to the substrate, providing an interface for at least external ground plane and a signal source, in order to provide signal to and from the antenna element through the frequency multiplexing circuit and the at least two feeding strips. The multi-band antenna module may further comprise at least one matching circuit disposed on the substrate, the at least one matching circuit is arranged to be coupled between the frequency multiplexing circuit and at least one feeding strip. Furthermore, the multi-band antenna module may also comprise at least one matching circuit embedded in the frequency multiplexing circuit and disposed on the substrate, the matching circuit providing impedance matching of at least one feeding strip of the at least two feeding strips for a predetermined frequency band. Further, the multi-band antenna module may comprise two matching circuits embedded in the frequency multiplexing circuit and disposed on the substrate, each of the matching circuits providing impedance matching of each of the feeding strips for at least two predetermined frequency bands. The multiplexing circuit disposed on the substrate may be at least one of the following: diplexer, RF switch, isolation implementation. The single antenna element mounted to the substrate may be at least one of the following: Capacitive Coupling Element, Planar inverted-F antenna, Inverted-F antenna, Planar inverted-L antenna, inverted-L antenna, loop antenna, monopole antenna.
Furthermore, the at least one feeding strip may be configured to be disposed on the substrate, with respect to the single antenna element, so that a resonant wavemode of the radiating structure formed at least partly by the single antenna element at a given frequency is excited and wherein the at least one other feeding strip may be configured to be disposed on the substrate, with respect to the single antenna element, so that that resonant wavemode of the radiating structure or non-orthogonal wavemodes with respect to the resonant wavemode at frequencies close to the resonant wavemode frequency are not excited by the at least one other feeding strips.
According to a fourth aspect, a multi-band antenna module is provided, which comprises a substrate, a single antenna element mounted to the substrate, a frequency multiplexing circuit disposed on the substrate and at least two feeding strips disposed on the substrate wherein dedicated signal ports, providing an interface to an external ground plane and at least one signal source, are arranged to the substrate for each of the at least two feeding strips, and each of the at least two feeding strips are coupled between the dedicated signal port arranged for the feeding strip and the single antenna element. The multi-band antenna module may further comprise at least one matching circuit disposed on the substrate, the at least one matching circuit arranged to be coupled between one dedicated signal port and a corresponding feeding strip. Further, the at least one matching circuit may be configured to be embedded in the frequency multiplexing circuit. The single antenna element mounted to the substrate may be at least one of the following: Capacitive Coupling Element, Planar inverted-F antenna, Inverted-F antenna, Planar inverted-L antenna, inverted-L antenna, loop antenna, monopole antenna.
The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb “to comprise” is used in this patent application as an open limitation that does not exclude the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
a and 1b illustrate antenna structures according to the invention,
a and 2b illustrate antenna structures according to first implementation of the invention,
a and 3b illustrate antenna structures according to second implementation of the invention,
a and 4b illustrate simulation results of the antenna structures according to the invention, and
The multi-band antenna according to the invention may be applied in the field of telecommunications. More specifically, mobile terminals, laptop computers, tablet computers among other similar devices configured to be wirelessly coupled to a telecommunication network may utilize the invention. The invention is not limited to any specific telecommunication technology as such. The antenna may be configured to implement e.g. WLAN, Wi-Fi, GSM, WCDMA, LTE and LTE-Advanced technologies when it comes to respective frequency bands of the wireless technologies. The mentioned wireless technologies are only examples and the invention as such is applicable to any future standards within the limitations originating from the invention.
Generally speaking the invention is based on an idea in which at least two feeding strips are arranged for one antenna element so that the antenna element can be fed through the at least two feeding strips. The at least two feeding strips are related to separate signal paths for at least two different frequency bands and the locations of the feeding strips with respect to the antenna element and the ground plane are selected to optimize the antenna operation bandwidths. The feeding of the antenna is arranged so that at least one feeding point is implemented between the at least two feeding strips and a ground plane of the antenna structure. A feeding point is physically a small gap (port) between RF ground and an excited part of the structure, across which an incident RF voltage is applied.
An antenna structure with one feeding point is illustrated in
The antenna structure may also comprise more than one feeding points. For example, it is possible to arrange one dedicated feeding point for each of the feeding strips, as depicted in
In order to achieve a full performance of the antenna structure impedances of multiple signal paths implemented at least partly by means of the multiple feeding strips and the antenna element may be matched with impedance matching networks, as described above. The impedance matching may be embedded to the frequency multiplexing with a careful design. In some cases it may be possible that at least some of the antenna branches do not need a matching. In a physical sense the multiplexing circuit, and the matching circuits if that is the case, may be implemented so that the multiplexing circuit is arranged between the feeding strips and the feeding point in the one feeding point solution. The feeding point, in turn, is between the frequency multiplexing circuit and the ground plane i.e. PCB. If the antenna implementation is such that each of the feeding strips comprise an own feeding point, the physical implementation may be such that the matching circuit is arranged between the feeding point and the feeding strip. The arrangement can be implemented in each of the antenna branches i.e. between each feeding point and the corresponding feeding strip if matching is needed. Moreover, according to the invention antenna impedance bandwidth performance can be at least partly adapted to, according to the requirements, by selecting the locations of the at least two feeding strips with respect to the antenna element and the ground plane optimally. Additionally, the shape of the at least two antenna strips may be selected optimally with respect to the desired impedance bandwidth performance.
a illustrates an implementation according to the invention in which a single feeding point is arranged in the antenna structure. Only two antenna branches are illustrated in
b illustrates the implementation of single feeding point case as a simplified electrical drawing. The combination of the antenna element 107 and the ground plane 200, i.e. the radiating structure of the antenna, is illustrated as a load 201. The feeding of the load is arranged through two signal paths each of which comprising a matching circuit 103A, 103B and a feeding strip 105A, 105B. The single feeding point is illustrated in
In the single feeding point arrangement, as depicted e.g. in
In
There is a frequency separation between the first frequency band and the second frequency band i.e. in the implementation as illustrated in
In the second matching circuit 103B, as illustrated in
Correspondingly, circuit 103B is dominantly capacitive to compensate for the inherently inductive impedance of the antenna element, i.e. CCE, at the second frequency band. Capacitors 222 and 223 together with the coil 225 form a high pass type frequency response. The additional capacitor 224 is used to adjust the CCE impedance at the second frequency band.
In order to achieve the frequency separation, and thus the frequency multiplexing, between the antenna branches by means of the matching circuits 103A and 103B the design shall advantageously follow the principles in which a lowpass frequency response of matching circuit is implemented for the first frequency band, a high-pass response of the matching circuit is arranged for the second frequency band and both branches are co-designed (i.e. suitable matching circuit topologies and component values are to be selected which result in good frequency isolation between the branches). Thus, the matching circuit 103A should be invisible to the high frequency signal fed to the antenna structure and matching circuit 103B should be invisible to the lower frequency signal fed from port 109. In order to realize this in practice, the matching circuits 103A and 103B have to be designed together to form one type of diplexer circuit in order to achieve the desired frequency multiplexing in the antenna. The term “invisible” shall be in this context understood so that from the port 101 point of view it seems that there does not exist circuit 103B at all in a signal sense, or at least the possible effect caused by the circuit 103B is not harmful for impedance matching seen from port 101, at the first frequency band. Similarly, from the port 101 point of view, it seems that there does not exist circuit 103A at all in a signal sense, or at least the possible effect caused by the circuit 103A is not harmful for impedance matching seen from port 101, at the second frequency band.
An embodiment of the antenna structure according to the invention is depicted in
b illustrates examples of the matching circuits for the first feeding strip 105A and the second feeding strip 105B. The combination of the antenna element 107 and the ground plane 200 are illustrated as a load 201 in
b and 3b illustrate examples of the matching circuits 103A, 103B on an electrical component level. However, the implementations as shown are only examples and the implementation may be selected case-by-case basis. In the example circuits, the diplexing, i.e. the frequency multiplexing, function is embedded in the matching circuits. Thus, it can be said that the frequency multiplexing may be implemented with an equivalent isolation mechanism as long as these can be configured to separate the frequencies of the signal paths associated with each feeding strip and/or match the impedance of the signal paths for the needs.
The shapes of the feeding strips 105A and 105B can be selected for enabling the desired impedance bandwidth performance. In the embodiments as depicted in
a and 4b present a simulated impedance matching of prototype antennas corresponding to
Also in the simulation of the antenna structure of
Above it is mainly described implementations in which the antenna element 107 is capacitive coupling element CCE. The CCE is typically not matched well to the feeding and as a result a matching circuit is almost always needed. However, in some cases it may be achieved that CCE is matched well enough to some frequencies and in that case it may be possible that a matching circuit is not a necessity in all antenna branches. The frequency multiplexing of signals via the multiple branches is, however, needed in the one feeding point arrangement and thus, for example, a diplexer is to be implemented. As described above one or more matching circuits for one or more of the feeding strips may be implemented within the multiplexing circuit. If the antenna element is a so called self-resonant antenna element, such as PIFA, the matching is possible, at least partly, to arrange with antenna geometry. A multiplexer is also needed with self-resonant antenna element since without the multiplexer the antenna geometry unlikely provides enough isolation between the signal paths especially at wide frequency bands.
Generally speaking any traditional antenna element can also be applied within the inventive idea. For example, a microstrip patch and any of its derivatives, such as planar inverted-F antenna (PIFA), inverted-F antenna (IFA), planar inverted-L antenna (PILA) or inverted-L antenna (ILA) as well as loop antenna or monopole antenna, can be used.
The multi-band antenna as described herein may be implemented as a module structure, which can be mounted to any device as such. In such a case, the necessary interfaces are arranged for bringing the signals to be transmitted to the antenna module from the transceiver element of the device. More specifically, such an antenna module would comprise the antenna element, the at least two feeding strips and the frequency multiplexing circuit with necessary matching circuits. The antenna module is implemented on a substrate by means of which the antenna structure can be isolated from the environment. An external ground plane as well as at least one signal source for the antenna module is provided through one of the mentioned interface, e.g. through at least one signal port, so that the common RF ground in the device into which the antenna module is installed can be utilized and the signal can be fed to and received from the antenna structure. The number of the mentioned signal ports may depend on the selected implementation of the invention as described. In case of one single signal port, i.e. the feeding point, the structure of the antenna module differs slightly of the case of more than one signal ports, i.e. feeding points. The other features and embodiments of the invention as described in the context of the antenna element are directly applicable in the case of antenna module.
Typical area of utilization such an antenna module is mobile terminals, which are configured to operate in multiple frequencies. In such area of implementation a transceiver module is coupled to the antenna module through the mentioned interfaces i.e. signal ports. Additionally, for example the PCB defining the RF ground plane within the mobile terminal may be utilized in the antenna module as described.
Some advantageous embodiments according to the invention were described above. The invention is not limited to the embodiments described. The inventive idea can be applied in numerous ways within the scope defined by the claims attached hereto.
