GB2526282A

GB2526282A - Selective antenna system combining phased array and lens devices

Info

Publication number: GB2526282A
Application number: GB1408857.9A
Authority: GB
Inventors: Hervã Merlet; Philippe Le Bars; Mohammed Himdi; Olivier Lafond; Jonathan Bor; Benjamin Fuchs
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2014-05-19
Filing date: 2014-05-19
Publication date: 2015-11-25
Anticipated expiration: 2034-05-19
Also published as: GB201408857D0; GB2526282B

Abstract

An antenna 300 comprises radiating elements 342 arranged in an array 341 with sub-arrays 344. Each sub-array 344 has individual power supply control means and phase shifters allowing it to generate a signal beam in a predetermined direction. The signal beams generated by the sub-arrays 344 are arranged to be received and directed by an electromagnetic lens 310. Different sub-arrays 344 may generate signal beams in different directions. The lens 310 may be a spherical or hemi-spherical or semi-spherical dielectric material Luneburg lens or fish-eye Maxwell lens and where the focal length of the lens is inside the said lens at a given focal distance. The length of the feed network conductive lines may be used to adjust the phase of the signal reaching the radiating elements 342 of a sub-array 344 consisting of four elements 342. The array 341 may be formed on a planar printed circuit board 340 and the lens 310 may be integrally formed with the antenna casing 320. The antenna 300 may provide a simple compact antenna which is cheap and easy to manufacture which can operate efficiently to transfer data at a high bit rate using high- frequency signals.

Description

SELECTIVE ANTENNA SYSTEM COMBINING PHASED ARRAY AND LENS

DEVICES

The present invention relates to multi-beam forming antennas and radiating devices having plenty of technical applications, in particular in the domain of indoor and/or outdoor wireless transmission.

Communication devices are increasingly numerous today and require an increasingly higher quality of service. There is a growing need for reliable communication devices with high recording capacities that are user friendly and offer high image quality. These may be for example digital cameras, high-definition digital camcorders (hand-held cameras or shoulder cameras), etc. When images such as videos or photographs are being viewed on a display device such as an UHD (Ultra high-definition) television set, due to the nature and the very high resolution of the information that is being transmitted, the data bit rates for the transmission of data between the imaging device and the display devices are very high, in the range of some gigabits per second (here below denoted as Gbps).

Similar bit rates are necessary for the transmission of data between an imaging device and a storage device or physical carrier dedicated to the storage of multimedia data (audio and/or video data).

To prevent loss of quality during the transfer of images, the use of a digital wire link able to transfers high-definition non-compressed multimedia data, such as an HDMI (high-definition multimedia interface) cable, may prove to be necessary.

Indeed, HDMI data is transmitted in raw mode i.e. with little or no processing and/or compression.

Raw data as recorded by the sensor of the imaging device can therefore be rendered without loss of quality.

Furthermore, in order to maintain high man/machine interactivity in a home system such as the one formed by a digital camera and a HD television set, the raw data must be transmitted almost in real time.

This is for example deemed to be the case when the maximum latency time is in the range of 3Oms.

When a user makes connects a HD television set to a digital camera using an HDMI cable and then views the recorded images, the digital camera becomes a sender device transmitting the images stored in its mass memory to the HD television set. On the other hand, the HD television becomes a receiver device receiving the images sent out by the digital camera and displays them on a projection screen.

It must be noted that the HDMI technology, taken here purely by way of an illustration, can be used to reach data bit rates of up to 5 Gbps without compression, loss or delay. Other standards can be used also to reach such data bit rates, such as for example the 1EEE1394 standard.

However, the use of a wire link in home communication systems has several drawbacks.

On the television side, the connection systems may be difficult to access, especially when they are located behind the television set. They may also be unavailable because other devices may already be connected to them.

On the camera side, the connection systems are often very small-sized and can also be concealed by covers, thereby making it difficult to connect the cable. In addition, it can be very difficult to move the camera or the screen when all devices are connected.

Similarly, in case cables are integrated in the walls of the house it is impossible to modify the installation.

One known approach for overcoming these drawbacks is the use of wireless connection between the television set and the camera. A However, said systems need to support data bit rates of several Gigabits per second.

Current WiFi systems operate in the 2.4 GHz and 5 GHz radio bands (as stipulated by the 802.11 a/bIg/n standard) and are thus not suited to reach the target bit rates. It is therefore necessary to use communications systems in a radio band of higher frequencies. The radio band around 60 GHz is a suitable candidate.

When using an extensive bandwidth, 60 GHz radio communications systems are particularly well suited to transmitting data at very high bit rates.

In practice, in order to obtain high quality radio communications (i.e. low error bit rate) and sufficient radio range between two communication devices (for example a camera and a television set), it is necessary to use directional (or selective) antennas with positive gain enabling line of sight (LOS) transmission of data. Consequently, narrow beam forming techniques are necessary for wireless communication with high throughputs bit rate.

During discovery phase, each pair of nodes of the wireless network has to initiate the communication parameters. It is therefore necessary to configure the antenna angle in order to obtain the best quality with radio frequency (RF) link.

Communication parameters can be transmitted with a low bit rate and therefore allow decreasing needs in the budget of the RE link (e.g. antenna gain). This in turn allows a wide antenna beam to be formed in order to detect all the nodes in the range.

Consequently, the antenna has to form both a narrow and a wide beam during subsequent phases.

The so-called smart antennas or reconfigurable antennas are used to reach the distances required by the audio and video applications. A smart antenna mainly comprises a network (e.g. an array) of radiating elements distributed on a support. This network enables the use of beam forming techniques in which each radiating element of the antenna is electronically controlled in phase and power (or gain) in order to form a narrow beam or a set of beams in sending and/or reception mode. Each beam can be steered and controlled. Consequently, this requires a dedicated phase controller and a power amplifier for each antenna element which increases the cost of the antenna.

In order to obtain a narrow beam, several antenna elements have to be powered, which may therefore result is a considerable consumption of energy. Power consumption is a serious handicap, especially for battery-powered portable devices for which maximum autonomy is sought.

Moreover, beam steering is obtained by changing the phase and the magnitude between the antenna elements. This requires the capacity to adapt the amplitude and phase of the signal to be sent to each radiating elements.

Such an operation is costly at 60 GHz frequency.

In addition, the geometrical dimensions of the smart antenna are also a strong limitation to small portable device.

The smart antennas known in the prior art comprise a network of radiating elements (for example 16) laid out in a square array on a substrate.

The radiating elements have each a dimension of half the wavelength (i.e. 2.5mm in case of 60GHz range) and the space between the antennas elements has to be at least of one quarter of the wavelength of the signal. Consequently, the surface of a smart antenna is rather large, which is not very convenient for being integrated in portable devices.

This leads to high costs, particularly when the materials used in the manufacture of the antenna comprise a substrate based on semiconductor technology. In the latter case, the final costs for mass market production of portable devices may be too high.

Figure Ia illustrates a smart antenna embodiment 100 transmitting video data through a 60GHz link. This embodiment 100 comprises an electronics board 101 with a baseband circuit 110 connected to a radio frequency circuit 120.

As illustrated on Figure Ib, the radio frequency 120 circuit comprises an antenna array 121. Antenna array 121 itself comprises several active antenna radiating elements 122 integrated in a substrate 123.

Antenna radiating elements 122 each have a dimension of half the wavelength A. (i.e. 2.5mm in case of 60GHz range) and the space between the antennas elements is around one quarter of the wavelength A.. The antenna directivity and gain depend on the number of antenna radiating elements 122.

As schematically illustrated on Figure Ic, each radiating element is connected to an amplifier (not represented) and a phase shifter 124. A phase shifting of 180 degrees is applied to some radiating elements 122 and a phase shifting of zero degree on others. The resulting radiation pattern 130 is shown on Figure Id.

As mentioned before, the fact that all antenna radiating elements 122 have to be power supplied leads to high power consumption. There is thus a need to improve the global power consumption, but also material costs, and the antenna radiation pattern.

A solution to some of the aforementioned problems lies in using a planar steerable antenna with a printed circuit board (PCB) patch.

However, planar antennas have drawbacks such as mutual inductance between the antenna elements resulting in a waste of energy through coupling. Also, the inherent symmetry causes energy to be sent in undesired directions and creates unwanted lobes.

Another drawback is the necessity to adapt both the amplitude and phase of the signal sent to each element. Such operation is costly at 60 GHz frequency.

A solution is proposed in EP2538491, in which a low cost planar steerable antenna operates in two dimensions in the azimuthal plane (assuming a spherical referential). In the elevation plane however, the beam width is fixed, thus disabling steering possibilities.

While this technology is adequate in most cases, there is a need to either increase the antenna directivity and gain or make beam steering possible in the elevation plane.

Both aspects are linked considering the fact that as the antenna gain increases, the directivity also increases and the radiation pattern of the beam becomes narrower. Consequently, in order to recover the signal sent by the transmitter to the receiver, there is a need to implement antenna beam steering capability in the elevation plane.

As described in EP2538491, the radio frequency sources are located around a cylindrical lens, thus giving beam steering capability in the azimuthal plane. The sources are easily implemented on the PCB substrate.

An antenna according to EP 2538491 is illustrated on Figure 2a, 2b and 2c comprises a cylindrical lens 210 (as shown on Figure 2b) that is encapsulated by a top shield 220 (as shown on Figure 2a) and a bottom shield 230 (as shown on Figure 2c).

Cylindrical lens 210 is illuminated by wave guides 240 that are edged in the shields, and fed by electronics board 250 where radio frequency components such as power amplifiers (PA) or low noise amplifiers (LNA) are implemented around the circular shape of the lens.

Such an antenna implements sixteen beams in the azimuthal plane with the possibility to switch to only one or several beams. The beam width in the elevation plane is fixed and sufficient to reach the target.

Improvements regarding the elevation control capability can nevertheless be made. Positioning of the different components (e.g. waveguides, shielding and adjustment of the substrate or electronics board) around the circular shape of the lens can also be improved, in particular in order to simplify the structure of the final product casing.

In order to add a beam steering function to the antenna in the elevation plane, the lens must have another shape, such as a sphere or a hemisphere.

It is however difficult to implement radio frequency sources around a spherical lens in three dimensions. In particular, such an implementation is not possible with a two-dimension substrate.

There is thus a need for a multi-beam forming antenna array that both minimizes power consumption and the required surface, but also reduces industrial costs by simplifying the positioning of the radiating sources and the lens.

The invention has been designed with the foregoing in mind.

According to a first aspect, the invention concerns an antenna that comprises radiating elements arranged into clusters, each cluster comprising a plurality of radiating elements, control means for individually controlling the power supply of each cluster, for each cluster, passive phase shifters arranged to shift the phase of the radiating elements of the cluster, when under power supply, in order for the cluster to generate an electromagnetic signal in a predetermined direction, and an electromagnetic lens arranged to receive and direct the electromagnetic signal generated by the radiating elements of each cluster.

An antenna according to the invention makes it possible to control the steering of a beam in both the azimuthal and elevation planes.

To that end, the antenna may be constituted of a lens placed in the casing, while the antenna elements are placed on a substrate or PCB, thus facilitating the assembly of the device.

The solution improves the BOM (Bill Of Material) cost (semiconductor cost), the antenna efficiency (power consumption is limited to the activation of the phased array sub set (e.g. 2 x 2)), improves the radiation pattern: side lobes, directivity (gain), limited the hardware resources, is easy to implement, have a high gain obtained by the lens characteristic (better directivity than the array antenna alone).

The lens itself may be is produced using the method described in EP2538491 by the same applicant. Advantageously, the concept is easy to manufacture and can be carried out in various low-cost devices and various frequencies.

According to said first aspect of the invention, each cluster advantageously generates an electromagnetic signal in a different direction than another cluster.

In a possible interesting implementation of the invention, the radiating elements being power supplied through electrical lines, the phase shift of the clusters is performed by adjusting the length of the electrical lines.

In a possible particular implementation of the invention, a cluster is constituted of four radiating elements.

In another possible particular implementation of the antenna, the electromagnetic lens is a dielectric lens.

In a possible interesting implementation of the invention, the focal point of the lens is inside the lens at a given focal distance.

In a particular implementation of the invention the electromagnetic lens has the shape of a hemisphere.

In a further implementation of the particular implementation of the invention, the electromagnetic lens is a Maxwell-type cell.

In another particular implementation of the invention, the electromagnetic lens has a spherical shape.

In a further implementation of the particular implementation of the invention the electromagnetic lens is a Luneburg-type cell.

Thanks to the Lunenburg (or Maxwell) lens, high gain and better directivity can be obtained rather than with the sole array of radiating elements.

Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which: -Figure Ia (prior art) illustrates a printed circuit board of a smart

antenna according to the prior art;

-Figure lb (prior art) illustrates an antenna array of radiating elements of a smart antenna according to the prior art.

-Figure Ic (prior art) further illustrates the antenna array as shown in Figure lb; -Figure Id (prior art) shows the radiation pattern obtained through the use of a smart antenna according to the prior art -Figure 2a (prior art) represents an embodiment of a smart planar steerable antenna (multi-beam antenna) according to the prior art; -Figure 2b (prior art) illustrates a cross-section of the embodiment of the smart planar steerable antenna as shown in Figure 2a; -Figure 2c (prior art) illustrates the embodiment of the smart planar steerable antenna and an electromagnetically shielding member encapsulating the electromagnetic lens partially.

-Figure 3 illustrates a first particular embodiment of an antenna according to the invention -Figure 4 shows a first radiation pattern of the antenna according to the invention as shown in Figure 3; -Figure 5 shows a second radiation pattern of the antenna according to the invention as shown in Figure 3 -Figure 6a illustrates an antenna array of radiating elements of a particular embodiment of an antenna according to the invention -Figure 6b is a schematic of the electrical lines supplying power to the array of the array of radiating elements of Figure 6a.

-Figure 7a is a schematic representing a Luneburg lens and the position of its focal point in spherical coordinates.

-Figure 7b is the schematic of Figure 7a where the lens is cut according to the invention.

-Figure 7c is a cross-section of the lens used as a simulation model.

-Figure 8a, 8b, and 8c show the result of a simulation of the electromagnetic field inside and outside the lens of the antenna of Figure 7c; -Figure 9a, 9b and 9c show the radiation patterns obtained through the use of three active antenna transmission beams.

Considering passive array antennas have lower performance than an active array antenna, passive antenna 300 according to the invention illustrated on Figure 3 uses the focusing propriety of a lens 310 to increase its directivity and gain.

To that end, lens 310 is directly integrated and/or fastened in an antenna casing 320, thus facilitating the assembly of passive antenna 300.

Passive antenna 300 also includes a Printed Circuit Board (PCB) or substrate 340 including an array 341 of Radio Frequency (RF) components, or passive radiating components 342, that are mechanically independent from lens 310. Here, PCB 340 and lens 310 are not on the same support.

The distance "d" between lens 310 and PCB 340 can range from some millimeters to some lambda (4 lambda being the wavelength of the signal.

In order to obtain good beam focusing and therefore a high antenna directivity and gain, lens 310 can be a Luneburg spherical lens or a fish-eyes Maxwell lens.

Here in this first embodiment, lens 310 is a fish-eyes Maxwell lens.

Thanks to such a configuration, there is no need to add a wave guide, and thus no need to ensure an accurate contact between said wave guide, shields and the lens itself.

As illustrated on Figures 3 to 5, antenna array 341 comprises several passive radiating elements 342 arranged into clusters such as first cluster 344 which is represented on these figures as switched on.

In particular, a cluster, such as first cluster 344, is constituted of four passive radiating elements 342.

As illustrated on Figures 4 to 5, clusters emit an electromagnetic wave signal, or radiation pattern 430. in a predetermined direction. Lens 310 is arranged to receive and direct said signal.

More specifically, radiation pattern 430 is directed towards a focus point of lens 310.

Considering the distance between lens 310 and the clusters is low enough, radiation pattern 430 is not constituted of plane waves but spherical waves.

The waves emitted by clusters, such as first cluster 344, pass through lens 310 with a predetermined angle associated to the predetermined direction of radiation pattern 430.

The result is a first beam 420, the signal of which benefits from increased directivity and gain, depending on the law of lens 310.

Figure 4 illustrates the result of the combination of array 341 and lens 310.

Array 341 comprises control means (not represented) individually controlling the power supply of each cluster.

Array 341 also comprises, for each cluster, passive phase shifters that are configured to shift the phase of radiating elements 342 in order for the cluster to generate an electromagnetic signal in a predetermined direction.

Said passive phase shifters are achieved through the design of the array.

Therefore, with each cluster is associated a particular angle determined by design.

Advantageously, this allows for adapting the beam-width and the gain according to the predetermined (chosen) beam direction, without having to add any extra hardware. In other words, this allows for beam steering capability in both the azimuthal and the elevation plane. This is the crux of the invention, adding more details could be beneficial.

Figure 5 illustrates yet another beam obtained in another direction.

A second beam 520 is generated by switching on, through the control means, a second antenna cluster 443, while first antenna cluster 344 is switched off.

Second beam 520 is an electromagnetic signal that has another direction than first beam 420, both in elevation plane and in the azimuthal plane.

Therefore a three-dimensional beam forming antenna is obtained.

Figure 6a and 6b illustrate the passive antenna array design and its power supply.

As mentioned before and as shown on Figure 6a, an antenna array 610 according to the invention is composed of clusters 620, each of which corresponding to one beam direction.

In the following example, four passive antenna radiating elements 621, 622, 623 and 624 constitute one cluster 620 and are power supplied by electrical lines 625 as shown on Figure 6b.

The phase shift between the passive radiating elements 621 622, 623 and 624 of a cluster 620 is performed by adjusting the length of the electrical lines 625, i.e. using the length differences between the different electrical lines 625.

In particular, for each beam direction, therefore for each radiating cluster 620, the length of the associated electric line is adjusted to create a phase shift.

In a second embodiment, an antenna according to the invention comprises a modified Luneburg lens as shown on Figure 7a and 7b.

Here, a modified Luneburg lens 710 is simulated in one plane.

Indeed, the lens having a symmetric shape (spherical or semi-spherical) for the other planes, the result can be transposed directly for all planes.

According to this second embodiment, in order to obtain a lens with good focusing and multiple beam properties and comprising a flat side so that the antenna can be easily integrated in an apparatus. The classical Luneburg law is modified in order to move the focal points of the lens from its surface to the inside of lens 710 at a given focal distance F as illustrated by the dash circle on the Figures 7a. A flat side is created on the cylinder surface (or spherical surface), as illustrated to the Figure 7b, to constitute a flat lens surface 714.

Flat lens surface 714 is parallel to the plane where the sources are implemented, i.e. the electronic board (PCB or substrate). In this case, the distance d" between the radiating elements and the lens is reduced to the minimum. Thus, plane waves are incoming on the modified Luneburg lens.

Figure 7c shows an implementation of this particular solution, where three different sources 711, 712 and 713 are laid out at different places to simulate the three-beam steering.

The result of a simulation of the electromagnetic field inside and outside a lens of the antenna of Figure 7 is shown on Figures 8a, 8b and 8c, which respectively correspond to the activity of first source 711, second source 712 and third source 713.

In each case, the spherical wave or quasi-spherical wave is transformed through the lens into a plane wave.

These results demonstrate that the antenna directivity increases through the use of the lens.

Figures 9a, 9b and 9c show examples of radiation patterns as emanated by the antenna according to the invention illustrated on Figure 7.

Radiation patterns illustrated in Figures 9a, 9b and 9c respectively correspond to first source 712, second source 713 and third source 711.

In each case, the radiation patterns confirm the beam steering capability of the antenna.

An antenna according to the invention thus offers the possibility of directing the beam in both in the azimuthal plane and the elevation plane without any additional hardware components.

Such an antenna is therefore easy to implement, greatly reducing the manufacturing costs.

In addition, its limited need in hardware resources and its low power consumption that is limited to the activation of the phase array clusters makes it even more cost-effective.

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention.

Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate.

In the claims, the word comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used.

Claims

CLAIMS1. An antenna comprising: radiating elements arranged into clusters, each cluster comprising a plurality of radiating elements, control means for individually controlling the power supply of each cluster, for each cluster, passive phase shifters arranged to shift the phases of the radiating elements of the cluster in order for the cluster, when under power supply, to generate an electromagnetic signal in a predetermined direction, and an electromagnetic lens arranged to receive and direct the electromagnetic signals generated by the radiating elements of each cluster.
2. An antenna according to claim 1, wherein each cluster generates an electromagnetic signal in a different direction than another cluster.
3. An antenna according to any one of the previous claims, wherein, the radiating elements being power supplied through electrical lines, the phase shift of the clusters is performed by adjusting the length of the electrical lines.
4. An antenna according to any one of the previous claims, wherein a cluster is constituted of four radiating elements.
5. An antenna according to any one of the previous claims, wherein the electromagnetic lens is a dielectric lens.
6. An antenna according to any one of the previous claims, wherein the focal point of the electromagnetic lens is inside the electromagnetic lens at a given focal distance.
7. An antenna according to any one of the previous claims, wherein the electromagnetic lens has the shape of a hemisphere.
8. An antenna according to claim 7, wherein the electromagnetic cell is a Maxwell-type cell.
9. An antenna according any one of the previous claims, wherein the electromagnetic lens has a spherical shape.
10. An antenna according to claim 9, wherein the electromagnetic lens is a Luneburg-type cell.
11. An antenna substantially as hereinbefore described, with reference to, and as shown in, Figure 3, 4, 5 or 6a of the accompanying drawings.
12. A circuit substantially as hereinbefore described, with reference to, and as shown in, Figure Gb of the accompanying drawings.
13. An electromagnetic field substantially as hereinbefore described, with reference to, and as shown in, Figure Sa, Sb, or Sc of the accompanying drawings.
14. A radiation pattern substantially as hereinbefore described, with reference to, and as shown in, Figure 9a, 9b or 9c of the accompanying drawings.