The present invention relates to a slot antenna for radiating and/or receiving mm-wave signals. Specifically, the present invention relates to a slot antenna which is adapted to transmit and/or receive electromagnetic signals in a wireless communication system operating in a high-frequency range, such as the GHz frequency range or the mm wavelength range and is suited for high data rate communication.
The object of the invention is hereby to propose such a slot antenna for radiating and/or receiving mm-wave signals which has a simple structure and can therefore be produced at low-cost while still being adapted to be used in a high frequency bandwidth and for high data rate applications.
The above object is achieved by an antenna for radiating and/or receiving mm-wave signals as defined in the enclosed independent claim 1. The antenna according to the present invention comprises a substrate, a planar contacting layer formed on said substrate and a radiation element being formed as a slot in said planar contacting layer, said slot comprising a middle part and two outer parts being connected by said middle part and extending away from said middle part, said antenna further comprising a feeding structure adapted to feed signals to the middle part of said slot.
The antenna of the present invention therefore has a simple structure and can be manufactured at low-cost while still providing a very good performance for high data rate applications in high frequency bandwidth.
It is to be understood that the antenna of the present invention could be used as a pure receiving antenna or a pure radiating/transmitting antenna, or could be used in applications in which electromagnetic signals are radiated from as well as received by the antenna.
The antenna of the present invention is particularly suitable for high frequency bandwidth applications, i.e. applications in the GHz frequency range, such as a frequency range between 20 and 120 GHz. These frequency ranges typically enable high data rate applications since they provide a large frequency bandwidth availability. It would, however, also be possible to use the antenna of the present invention in different frequency ranges and bandwidths depending on the wanted application.
Hereby, by varying the measures of the antenna of the present invention, such as the width and the length and the proportions of the different elements of the present antenna, a specific adaptation to the respectively required frequency range and bandwidth can be achieved. Also, the simple structure and low-cost solution of the antenna of the present invention makes the antenna specifically useful for consumer electronic applications. However, the antenna of the present invention can also be used in other applications if wanted and/or necessary.
Advantageous sub features of the present invention are defined in the dependent claims.
Advantageously, two outer parts of the slot are parallel to each other. Further advantageously, the middle part and the two outer parts form a U together. In other words, the slot has a U-shape. Such a shape is advantageous as it leads to the radiation of electromagnetic signals with linear polarization. Signals with linear polarization are advantageous for indoor applications, specifically for indoor with line of sight and also for non line of sight signals. Such an antenna shape, however, may also be advantageous in selected outdoor applications. The U-shape of the slot leads to a quite large frequency bandwidth around the operation frequency of about 10 percent. For example, in case that the operation frequency is around 60 GHz the achieved frequency bandwidth is around 6 GHz with such a shape. Further advantageously, the width of each of the two outer parts of the slot increases in the direction away from the middle part. By such a tapering of the two outer parts, the antenna impedance can be reduced and matched to the impedance of the feeding structure, which is typically 50 Ohm.
Alternatively, the width of each of the two outer parts of the slot can remain constant, i.e. untapered.
Further advantageously, both outer parts of the slot have the same length and width. In other words, the two outer parts could be mirror-symmetric in relation to a symmetry axis extending between the two outer parts and perpendicular to the middle part of the slot. Further advantageously, the width of each of the two outer parts of the slot is more than two times of the width of the middle part. Further advantageously, the distance between the two outer parts, i.e. the length of the middle part, is larger than the width of each of the two outer parts. Further advantageously, each of the two outer parts is longer than wide.
Further advantageously, the feeding structure is a microstrip feeding line arranged on a side of said substrate opposite to the planar conducting layer. Hereby, the decoupling of the feeding structure from the radiation element has the advantage of suppressing side lobes in the antenna characteristics as compared to structures in which the feeding structure is placed in the same layer as the radiation element. Thus, in the antenna of the present invention, only the shape of the radiation slots determines the antenna radiation pattern, since the side lobe radiation is greatly reduced and therefore the axial ratio of the radiation pattern is greatly decreased, so that the antenna of the present invention is particularly advantageous to be used in an array antenna in which a high gain can be realized and in which the radiation beam can be steered.
Further advantageously, the planar conducting layer and/or the feeding structure are printed elements. By printing the planar conducting layer, for example a copper layer, onto a single layer substrate, the slot can be simply etched with simple etching technology, so that a low-cost structure is achieved. If additionally a simple 50 Ohm microstrip feeding line is printed onto the opposite side of the substrate, i.e. onto the other side opposite to the planar conducting layer, a simple and low-cost feeding structure is achieved.
Further advantageously, the antenna of the present invention has a reflector plane arranged in a predefined distance from the side of the substrate opposite to the planar conducting layer. Such a reflector plane arranged below the antenna is advantageous to avoid backside radiation and is helpful to direct the radiation pattern to the side of the substrate on which the planar conducting layer with the slot is located, therefore increasing the antenna gain in one direction. Between the reflector plane and the substrate, a low dielectic material or air can be provided.
Advantageously, the length and width dimensions of the planar conducting layer are in the range of half of the wavelength of the operation frequency. These dimensions make the antenna of the present invention quite suitable for applications in the mm-wave frequency range.
The present invention is further directed to an antenna array comprising a plurality of antennas according to the present invention. Hereby, the plurality of antennas advantageously have a common substrate and the radiation direction can be changed. For example, the antenna array may comprise beam steering elements adapted to change the radiation direction of each of the antennas. Advantageously, the beam steering elements hereby comprises phase shifters adapted to shift the signal face for each antenna.
Particularly, the arrangement of the feeding structure on the substrate side opposite to the side on which the planar conductive layer is located and therefore decoupling the feeding network from the radiation structure suppresses the side lobes in the radiation patterns so that an antenna array with a very high gain can be achieved. Further, a very reliable beam steering with a high accuracy can be provided due to the fact that—if at all—only very small side lobes are present.
The present invention will be further explained on the basis of the following description of advantageous embodiments relating to the enclosed drawings, in which
The antenna 1 comprises a substrate 2 which can be formed from any suitable material, such as a dielectric material or the like, and may be formed as a single layer. A planar conducting layer 3 is formed on the substrate 2, for example, by forming a copper layer on the upper side of the substrate 2, for example by a printing technique. In the planar conducting layer 3, a radiation element 4 is formed, which has the shape of a slot. The slot is for example formed by etching technology.
On the side of the substrate 2 opposite to the conducting layer 3, a feeding structure 5 is provided, by which electromagnetic signals are supplied to the radiation element 4 in order to be transmitted or by which electromagnetic signals received by the radiation element 4 are supplied to processing circuitry connected to the feeding structure. Further, in a predetermined distance from the side of the substrate 2 on which the feeding structure 5 is provided, a reflector plane 6, formed by a conducting, for example metal, plane is located. The reflector plane operates as an electromagnetic wave screen to reflect electromagnetic waves transmitted and/or received by the radiation element 4 to cancel or suppress radiation on the backside of the substrate 2 and to increase the antenna gain in the main direction of the antenna, which is the direction perpendicular to the plane of the conducting layer 3 pointing away from the substrate 2. There might be applications, however, in which the antenna of the present invention can be implemented without such a reflector plane 6.
The feeding structure 5 can be any kind of suitable feeding structure, but is advantageously embodied as a microstrip feeding line which is applied to the backside of the substrate 2 by printing technology. Hereby, the microstrip feeding line advantageously has a 50 Ohm impedance.
The operation principle of the antenna 1 of the present invention is as follows. An exciting electromagnetic wave is guided to the radiation element 4 through the feeding structure 5. In the radiation element 4, i.e. the slot, the magnetic field component of the exciting electromagnetic wave excites an electric field within the slot. Hereby, in order to achieve a large frequency bandwidth at the operation frequency, for example a frequency bandwidth of 10 percent of the operation frequency, the radiation element 4 according to the present invention comprises a middle part 4a and two outer parts 4b which are connected by said middle part 4a and extend away from said middle part 4a, so that a slot antenna is formed. The specific shape of the radiation element is shown in more detail in the perspective view of the planar conductive layer 3 and the feeding structure 5 of
In the shown embodiment of the antenna 1, the slot of the radiation element 4 generally has a U-shape, in which the two arms of the U are formed by the mentioned outer parts 4b and the base connecting the two outer parts 4b is formed by a middle part 4a. The two outer parts 4b generally extend parallel to each other and perpendicular to the middle part 4a. The shown U-shape of the slot leads to the frequency bandwidth of approximately 10 percent of the operation frequency, for example a frequency bandwidth of 6 GHz and an operation frequency around 60 GHz. In the shown embodiment, the transition between the middle part 4a and the two outer parts or arms 4b is rounded. However, in different applications, the transition between the middle part 4a and the two outer parts 4b could be rectangular with corners.
As indicated in
The planar conductive layer 3 and thus the substrate 2 have two symmetry axis A and B which split the conductive layer 3 in half in the length as well as in the width direction. Hereby, the feeding structure 5 extends along and symmetrically to the symmetry-axis A and the slot of the radiation element 4 is arranged mirror symmetrically to axis A. In other words, the two outer parts 4b of the radiation element 4 extends generally parallel to the axis A and are mirror symmetric with respect to it. The base line of the middle part 4a of the radiation element 4 is arranged on the symmetry axis B. In other words, the distance between the base line of the middle part 4a is half of the length of the conducting layer 3 in this direction.
Generally, it is advantageous, if the two outer parts 4b are tapered, i.e. if the width of the two outer parts 4b increases away from the middle part 4a. Hereby, the imaginary part of the complex impedance of the radiation element can be decreased so that the over all impedance of the antenna 1 is decreased and can be matched to the impedance of the feeding structure of for example 50 Ohm.
Further, in case that the two outer parts 4b are tapered, the width w1 of the two outer parts at their ends is larger than the width w2 of the middle part 4a. Advantageously, the width w1 of the ends of the two out parts 4b is more than two times larger than the width w2 of the middle part 4a. Further, the length 13 of the middle part 4a is larger than the width w1 of the ends of the two outer parts 4b. In other words, the distance between the two outer parts 4b is larger than the respective width w1. Further, the over all width w3 of the radiation element 4 is larger than its length 12, whereby each of the two outer parts 4b has a length 12 which is longer than its width w1. The shown shape and dimensions of the planar conducting layer 3 and the radiation element 4 are particularly suitable for radiating and receiving signals in the 50 to 70 GHz frequency range.
The phase shifters 9 are used to shift the signal phase at each antenna 1 in order to obtain the desired beam steering pattern direction. Any kind of broad bandwidth microstrip phase shifter can be used and implemented with the antenna array 10 in order to steer the beam pattern.
The shape instructor of antenna 1 of the present invention is therefore particularly useful and advantageous for implementation in antenna arrays, such as antenna array 10, with beam steering due to the simple and low-cost structure and the high gain in GHz frequency range.
Number | Date | Country | Kind |
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07 122 149.3 | Dec 2007 | EP | regional |