Reconfigurable antenna system

The invention relates to a reconfigurable antenna system (1), which comprises a plurality of antenna units (10) and does not employ phase shifters. Each antenna unit (10) is by itself a reconfigurable antenna having at least an active radiating element which is coupled to one or more passive radiating elements. Each antenna unit is provided with one or more variable loads (12) that can be electrically connected/disconnected to each other and with said antenna unit (10), to selectively configure the radiating properties of the system. A bias network (70) is adopted to bias the variable loads (12) and a control unit (80) allows controlling the operation of said bias network (70). Each active radiating element is fed by at least a feeding line (501) that provides it with a suitable polarization. Hence, the system can advantageously resort to multiple polarizations, each of them being provided by a same source. Preferably, each active radiating element receive its feeding signal from the source/s by means of power dividers (60) and/or switches. Preferably, each antenna unit is covered by at least a radiating structure, comprising a plurality of passive radiating elements, which does not affect the reconfigurability of the antenna unit itself and increases the overall antenna gain. The antenna system is then characterized by remarkable beam-steering capabilities and high gain, avoiding the losses and complexities related to phase shifters and overcoming the typically small antenna gain values of current reconfigurable antenna systems.

The present invention relates to the technical field of the reconfigurable antenna systems.

As is known, most traditional antenna systems comprise one or more antennas, which radiate electromagnetic waves according to a fixed radiation pattern and polarization.

Adaptive antenna systems are known, which are capable of varying their radiation diagram, according to the needs.

These antenna systems typically comprise phased array antenna systems, switching antenna systems and reconfigurable antenna systems.

A phased array antenna system generally consists of a matrix of active antenna elements that are fed with a controllable phase, so that it can radiate electromagnetic waves according to a radiation pattern and a polarization that may be suitably controlled.

A phased array antenna system adopts multiple antenna elements to enhance the gain and multiple phase shifters to properly steer the overall radiation beam.

A phased array antenna system is generally quite effective in steering the radiation lobes with high directivity.

Unfortunately, industrial production costs are sometimes prohibitive for certain applications and the radiation efficiency is generally low due the relatively high losses of the phase shifters.

A switching antenna system typically employs multiple high gain antennas pointing towards different directions and a network of switches that allow selecting the highest gain antenna pointing towards a certain direction.

Even if it is very effective in achieving high antenna gain values, a switching antenna system has some important drawbacks.

The antenna form factor is generally very large and it is therefore sometimes not acceptable for certain applications.

Further, industrial production costs are often quite relevant.

A reconfigurable antenna system generally comprises antennas showing a different pattern and polarization, depending on the adopted current distribution on the radiating element of each antenna unit.

Adaptive antenna systems have received strong attention in the last years thanks to their capability of dynamically changing their radiation properties in response to the behavior of the wireless channel.

It is acknowledged that reconfigurable antenna systems offer some advantages with respect to other adaptive antenna systems, since they employ single active elements.

Generally, they have a smaller size and allow achieving higher radiation efficiency.

A relevant drawback of current reconfigurable antenna systems consists in that they can reconfigure their radiation pattern and/or polarization with a relatively small antenna gain values.

Therefore, in the market it is still felt the need for reconfigurable antenna systems that show relatively high beam-steering capabilities, high antenna gain values, small form factor and low industrial costs.

In order to respond to this need, the present invention provides a reconfigurable antenna system, according to the following claims.

With reference to the mentioned figures, the present invention relates to a reconfigurable antenna system1.

The antenna system1comprises a plurality of antenna units10that may be arranged according to different topologies, e.g. in parallel or according to a star configuration.

Each antenna unit10comprises at least an active radiating element11that is capable of radiating electromagnetic waves W.

For the purposes of the present invention, a radiating element is defined as an “active radiating element” in case such a radiating element is fed by one or more feeding lines that provide it with a suitable feeding signal.

The active radiating element11is advantageously fed by at least a feeding line501that provides the feeding signal51(typically a current signal).

Each antenna unit10is electrically connectable with one or more variable loads12.

The loads12may be circuit elements having variable impedance. They may be circuit elements having a variable or fixed impedance that are electrically connected/disconnected each other and with the corresponding antenna unit10, for example shorted to ground or left open, according to the needs.

According to possible embodiments of the present invention, the variable loads12may comprise one or more meta-material (CRLH) cells.

According to further embodiments, the variable loads12may comprise variable capacitors (varactors) that are arranged to vary the overall reactance of the corresponding antenna unit10, according to the needs.

Said variable capacitors may be advantageously coupled to a passive network of lumped elements, such as SMD capacitors and inductors and/or microstrip inductors and interdigital capacitors.

Thanks to the variable loads12, each antenna unit10is capable of varying the direction and/or polarization of the emitted electromagnetic radiation W.

Each antenna unit10is thus a reconfigurable antenna by itself.

The antenna system1can thus advantageously be formed by an array or matrix of antenna units10.

According to the invention, the reconfigurable antenna system1comprises a same single source50(preferably a RF source) for providing all the active radiating elements of the antenna units10with the feeding signals51.

The source50may be any device suitable to provide the feeding signals51to the active radiating elements11, so as to cause the radiation of electromagnetic waves W with a given polarization by said active radiating elements.

As it will be more apparent from some embodiments described in the following, different sources50, which operate independently one from another, may be employed in case feeding signals, which cause the active radiating elements to radiate electromagnetic waves W with different polarizations, are provided.

However, the active radiating elements11of the antenna system1are always fed by a same common source50for each given polarization of the electromagnetic waves W to be radiated. The feeding signals51may have carrying frequencies between 300 MHz and 30 GHz. Preferably the feeding signals51have radio-frequency (RF) carrying frequencies Advantageously, the feeding signals51are not phased one another. In this way, no phase shifters are required with a consequent simplification of the overall circuital structure of the antenna system1.

Further, since the antenna units10are electrically connected to a same source50for at least a given polarization of the electromagnetic waves W to be radiated, the antenna system1differs from solutions, where each active radiating element is typically connected to a separate branch of a transmitter/receiver.

Preferably, the antenna system1comprises one or more power dividers60(e.g. suitable circuit arrangements or switches) that receive a single feeding signal500from the source50and provide the feeding signals51.

The antenna system1comprises at least a bias network70(typically a DC network) for biasing the variable loads12.

The bias network70provides the variable loads12with biasing signals700, so as to obtain a certain current distribution along each antenna unit10.

This allows properly configuring the radiation lobes of each antenna unit10. The radiated electromagnetic waves W can thus be easily directed along desired directions.

According to some embodiments of the invention, the antenna system1comprises a same single bias network70for biasing the variable loads12of two or more antenna units10, (advantageously of each antenna unit10).

In this case, the bias network70is shared between the antenna units10. The same biasing signals700are thus applied simultaneously to the antenna units10. These latter can therefore be easily configured to direct the electromagnetic radiation W towards a same direction, so as to increase the overall gain along said direction.

In this way, an increased overall radiation beam is generated thanks to the superposition of the beams generated by each antenna unit10(FIG. 6).

According to this solution, the bias network70may be remarkably simplified, thereby being of relatively easy and cheap implementation.

According to other embodiments of the invention, the antenna system1comprises a plurality of bias networks70, each of which is arranged to bias the variable loads12of a corresponding antenna unit10.

In this case, each bias network70works independently from the others and it allows the corresponding antenna unit10to radiate electromagnetic waves W towards a different direction, if needed.

By independently controlling the radiation properties of each antenna unit10, it is possible to compensate possible radiation imbalances caused by phase lags or delays that may be introduced by the power dividers60.

Preferably, the antenna system1comprises a control unit80(e.g. a digital processing device) that provides control signals81for controlling the operation of the bias network70and, possibly, of the power dividers60.

According to some embodiments of the present invention, one or more antenna units10(preferably each antenna unit10) comprise one or more first passive radiating elements16.

For the purposes of the present invention, a radiating element is defined as a “passive radiating element” in case such a radiating element is not fed by any feeding line connected to a source50.

The first passive radiating elements16are positioned in the proximity of the active element11, so as to be electromagnetically coupled with this latter, when said active radiating element11radiates electromagnetic waves.

In order to ensure a good electromagnetic coupling, the maximum distance between the radiating elements11and16must be lower than the carrying wavelength λ.

The passive radiating elements16are thus excited by the proximity coupling with the active radiating element11and are therefore capable of radiating electromagnetic waves W.

The number of the passive radiating elements16may vary according to the needs. Basically, the larger is the number of passive radiating elements, the wider is the angle that can be scanned by each antenna unit10.

In the embodiments shown inFIGS. 2-3, 7each antenna unit10comprises a single active radiating element11that is sided by two passive radiating elements16.

Of course, other arrangements are possible, according to the needs.

Preferably, the variable loads12of each antenna unit10are electrically connectable to the passive radiating elements16.

Thanks to the bias network70, the variable loads12can vary their impedance and/or be electrically connected/disconnected each other and with each of the passive radiating elements16.

The bias signals700provided by the bias network70thus allow varying the current distribution both in the active and passive radiating elements11,16, thereby allowing properly configuring the radiation pattern of the antenna unit10.

According to other embodiments of the present invention, one or more antenna units10comprise a plurality of feeding lines501A,501B for feeding the active radiating element11with a plurality of feeding signals51A,51B, so that said active radiating element radiates electromagnetic waves W having a plurality of predefined polarizations.

In an embodiment (FIGS. 3, 8), one or more antenna units10(preferably each antenna unit10) comprise a first feeding line501A and a second feeding line501B for feeding the active radiating element11.

The first feeding line501A feeds the active radiating element11with a first feeding signal51A, so that the active radiating element11radiates electromagnetic waves W having a first predefined polarization.

On the other hand, the second feeding line501B feeds the active radiating element11with a second feeding signal51B, so that the active radiating element11radiates electromagnetic waves W having a second predefined polarization.

The feeding line501A and501B may receive the feeding signals51A,51B from two independent sources50or from a same single source50that can be switched between the mentioned feeding lines.

Each antenna unit10can thus be provided with independent feeding lines501A,501B to cause the active radiating element11to radiate electromagnetic waves W with different polarizations, e.g. a horizontal and a vertical polarization.

Since the polarizations are different, the radiated electromagnetic waves W do not mutually interfere.

Preferably, the antenna system1is advantageously provided with a first feeding tree501A that is coupled to a first source providing the first feeding signals51A and with a second feeding tree501B that is coupled to a second source providing the second feeding signals51B.

It has to be evidenced that, also in this embodiment, the antenna units10are always fed by a same source for at least a given polarization of the electromagnetic waves W to be radiated, in accordance to the invention.

Thanks to this solution, the antenna system1works as two independent reconfigurable antenna systems transmitting with different polarizations.

Of course, according to other embodiments, the antenna units10may comprise a larger number (more than two) of feeding lines that may be fed by a corresponding number of sources50or by a single source50switching between said feeding lines.

Also in this case, it is evidenced that a same single common source50is arranged to provide feeding signals to cause the radiating elements to radiate electromagnetic waves W with at least a given polarization.

Preferably, the antenna system1comprises advantageously one or more first and second variable loads12A,12B.

As the variable loads12, the loads12A,12B may be circuit elements having variable impedance. They may be circuit elements having a variable or fixed impedance and that are electrically connected/disconnected each other and with the corresponding antenna unit10, for example shorted to ground or left open, according to the needs.

Also the variable loads12A,12B may comprise one or more meta-material (CRLH) cells and/or variable capacitors (varactors) and/or be coupled to a passive network of lumped elements.

The variable loads12A are operatively associated to the antenna unit10to selectively configure the radiating properties of said antenna unit, when this latter radiates electromagnetic waves according to a first polarization.

Similarly, the variable loads12B are operatively associated to each antenna unit10to selectively configure the radiating properties of said antenna unit, when this latter radiates electromagnetic waves according to a second polarization.

According to some embodiments of the present invention (FIGS. 4-5), one or more antenna units10(preferably each antenna unit10) comprise a plurality of active radiating elements11, each of them being fed by at least a feeding line501.

Also in this case, each antenna unit10may comprise one or more passive radiating elements16that are electromagnetically coupled with the active radiating elements11.

As described above, the passive radiating elements16are positioned in the proximity of the active radiating elements11, so as to be electromagnetically coupled with said active radiating elements, when these latter radiate electromagnetic waves W.

Also in this case, the number of the passive radiating elements16may vary according to the needs.

Preferably, the variable loads12of each antenna unit10are electrically connectable to the passive radiating elements16.

In the embodiment shown inFIG. 5, each of the active radiating elements11is fed by two independent feeding lines501A,501B, according to the dual polarization scheme described above.

Similarly, first and second variable loads12A,12B are connectable to the passive elements16.

The antenna system1may be realized in practice according to various technologies.

Preferably, a printed circuit technology is advantageously adopted for realizing the antenna units10.

The radiating elements11,16can be formed by conductive patches arranged on an insulating layer.

Similarly, the feeding lines501may be formed, at least partially, by conductive microstrips or vias arranged on an insulating layer.

In the example ofFIG. 7, the active radiating element (patch)11is slot-fed, which means that a cut is made in the ground plane of the feeding microstrip501.

Such a cut allows the energy provided by the feeding signal51to pass through the ground plane and to couple to said radiating element.

In a similar way, the passive radiating elements (patches)16are slot-coupled to a truncated microstrip line120connected to the variable loads12.

Preferably, the antenna units10comprises each a planar substrate200that may advantageously comprise a feeding layer200A, where the feeding lines51,120are arranged, and a radiating layer200B, when the radiating elements (patches)11,16are arranged.

According to some embodiments of the present invention, the substrate200is covered by at least an upper radiating structure300, advantageously planar, that comprises a plurality of second passive radiating elements301.

The second passive radiating elements301are positioned so as to be electromagnetically coupled with the radiating elements11,16, when these latter radiate electromagnetic waves W.

To this aim, the maximum distance between the radiating elements301and the radiating elements11,16must be lower than the carrying wavelength λ.

The radiating structure300may be a single layer or multi-layer structure.

The passive radiating elements301may be conductive patches formed on a dielectric substrate or slots/holes formed in a metal sheet.

The passive radiating elements301may be formed by meta-material cells.

In this case, each radiating element301may be advantageously designed to present non-conventional electromagnetic properties that allow concentrating the electromagnetic waves W coming from the radiating elements11,16towards the radiation direction, with which said electromagnetic waves have been emitted. In this way, the directivity of the antenna system1can be remarkably enhanced, thereby increasing the overall antenna gain.

Preferably, the second passive radiating elements301have a different geometrical shape and/or distribution, depending on their position in the radiating structure300(FIG. 9).

This solution allows remarkably increasing the antenna gain without changing the direction of radiation determined by the radiating elements11,16.

Therefore, the radiating structure300does not affect the reconfigurability of the radiating lobes of each antenna unit10and it allows achieving relatively high gain values for different directions of radiation, according to the needs.

In the embodiment shown inFIG. 8, each antenna unit10is covered by a different dedicated radiating structure300.

As an alternative, a single radiating structure300is used to cover all the antenna units10.

In a further aspect, the present invention relates to an antenna system100that comprises one or more reconfigurable antennas101.

In principle, the reconfigurable antennas101may be of any type.

Preferably, at least one of the antennas101comprises one or more antenna units10.

The radiating antennas101are operatively associated to at least a radiating structure103, which comprises a plurality of radiating elements104.

The radiating structure103may be a planar structure, as shown inFIG. 10, and it may be a single layer or a multi-layer structure.

In principle, however, the radiating structure103may have any shape or dimension, according to the needs. For example, it may be a suitably shaped 3D radiating structure.

The radiating elements104are positioned so as to be electromagnetically coupled with the antennas101, when these latter radiate electromagnetic waves W.

To this aim, the maximum distance between the radiating elements104and the antennas101must be lower than the carrying wavelength λ of said antennas.

The radiating elements104may be conductive patches formed on a dielectric substrate or a slots/holes formed in a metal sheet.

The radiating elements104may be formed by meta-material cells.

In this case, each radiating element104may be advantageously designed to present non-conventional electromagnetic properties.

The radiating structure103allows concentrating the electromagnetic waves W coming from the antennas101towards the radiation direction, with which said electromagnetic waves have been emitted.

In this way, the directivity of the whole antenna system100can be remarkably enhanced, thereby increasing the overall antenna gain.

The radiating elements104may have a different geometrical shape and/or distribution, depending on their position in the radiating structure103(FIG. 10).

This solution allows remarkably increasing the antenna gain without changing the direction of radiation that is determined by the antennas101.

Therefore, the radiating structure103does not affect the reconfigurability of the radiating lobes of the antennas101and it allows achieving relatively high gain values for different directions of radiation, according to the needs.

In the embodiment shown inFIG. 10, a single radiating structure103is used to cover all the antennas101.

As an alternative, each antenna101or groups of antennas101may be covered by a different dedicated radiating structure103.

The antenna system, according to the invention, allows the achieving of relevant advantages.

The antenna system, according to the invention, allows scanning the surrounding space according to continuously different directions with a high gain.

When an isolated receiver is located at a certain position, the antenna system is capable of focusing the radiated energy towards that direction, without wasting power in the surrounding space.

On the other hand, when multiple users are located within a certain space sector, the antenna system is capable of configuring its radiation lobes so as to continuously scan said space sector. In this case, the antenna system is capable of behaving as a static sector antenna, without coverage reductions at the edges of the space sector. The continuous scanning activity with high gain reconfigurable lobes, in fact, allows a more uniform coverage. The achievable high gain values further allow covering wider space sectors.

From the above, it is apparent how the antenna system, according to the invention, is characterised by remarkable beam-steering capabilities, relatively high gain values and a relatively small form factor.

The antenna system, according to the invention, has proven to be of relatively easy and cheap realization at industrial level and practical installation on the field.