Patent Publication Number: US-8994603-B2

Title: Cross polarization multiband antenna

Description:
This invention concerns a radiating element such as those which are present in multiband telecommunications antennas. It relates in particular to multiband antennas known as panel antennas which are used specifically in cellular telephone applications. 
     Cell telephony uses miscellaneous frequency bands corresponding to different known telecommunications systems. Several telecommunications systems are currently used simultaneously such as, for example, the “Global System for Mobile communications” GSM (870-960 MHz) and the “Universal Mobile Telephone Service” UMTS (1710-2170 MHz). 
     Telecommunications network operators must therefore have access to a network of antennas which transmit data on the various frequency bands used. Certain operators install additional antenna networks for this purpose, each of which operates on the basis of a telecommunications system. The operators therefore use a network of GSM antennas and a network of DCS antennas even though they install a network of UMTS antennas. However, when it comes to deploying their network, the operators find it difficult to obtain authorisation for the installation of new antennas. The current sites are already extremely overloaded in terms of their visual impact. Moreover, the increasing number of antenna networks is generating additional costs for operators (purchasing of antennas, renting of positions, installations) as well as environmental damage. 
     For all these reasons, operators are trying not to add to the number of antenna already installed. One solution to this problem would be to use multiband antennas based on a combination of radiating elements belonging to several telecommunications systems respectively within a single antenna chassis. These antennas incorporate several single band antennas in a reduced volume whilst maintaining the same service quality. 
     For example, there are two-frequency band or three-frequency band antennas in which radiating elements assigned to each frequency are aligned either parallel to each other according to a longitudinal periodic structure, for example staggered and alternating, so as to create a similar radioelectric environment for all radiating elements corresponding to the same frequency. These configurations significantly increase the width of the antenna and degrade the radiation performances, at least for the highest frequency. For both types of configuration, there is a strabismus effect of the azimuth diagram caused by asymmetry in the azimuth alignment plane of elements radiating at high frequency. A strong degradation in cross polarisation is also observed in the ±60° angular section due to this asymmetry. 
     A dual polarization radiating element consists of two independent dipoles each of which comprises two collinear conducting arms with a given polarization (positive or negative) to send and receive radiofrequency signals. The length of each arm is more or less equal to a quarter of the wavelength of the working wave. The radiating elements are assembled in a longitudinal alignment above a reflector which refines the directivity of the radiation pattern of the set created by reflecting the rear radiation of the dipoles. Each dipole of a radiating element is linked by a feed line to an external energy source. These radiating elements are dedicated to sending/receiving a single frequency. 
     A certain type of radiating element exists which comprises four more or less triangular conducting arms which are arranged orthogonally in relation to one another on a horizontal plane and which are known as a cross bow tie. 
     Another type of radiating element exists, known as a butterfly, which consists of four conducting arms folded axially in a V shape and arranged orthogonally in relation to one another. 
     There are also printed elements, also known as patch elements, which comprise four conducting arms marked by a conducting layer applied to a dielectric substrate. 
     The aim of this invention is, therefore, to provide a radiating element for a multiband antenna which is capable of reducing the space occupied. 
     This subject of this invention is a multiband antenna radiating element consisting of a first pair of dual cross-polarization dipoles each of which comprises two collinear conducting arms, whereby the four conducting arms define a first radiating plane corresponding to a low frequency band. The radiating element also consists of at least a second pair of cross-polarization dipoles each of which comprises two collinear conducting arms, whereby the four conducting arms define a second radiating plane corresponding to a higher frequency band. The first and second radiating planes are parallel; the second radiating plane is positioned above the first from which it is electrically insulated and the surface of the first radiating plane covering the conducting arms of the first pair of dipoles is larger than the surface of the second radiating plane covering the conducting arms of the second pair of dipoles. 
     It is necessary to superimpose two separate radiating planes, which are electrically insulated from one another, in parallel. The lower radiating plane, with a lower frequency, is designed to provide a sufficient surface for the upper radiating plane with a higher frequency so that it can be assimilated with a ground plane in relation to the upper radiating plane. This is obtained with as large as possible a surface covered with the dipoles of the lower radiating plane. 
     According to a first embodiment, the first radiating plane is defined by a pair of printed dipoles and the second radiating plane is defined by a pair of dipoles chosen from cross dipoles, butterfly dipoles and printed dipoles. 
     According to a second embodiment, the first radiating plane is defined by a pair of cross dipoles and the second radiating plane is defined by a pair of dipoles chosen from cross dipoles, butterfly dipoles and printed dipoles. 
     According to a first embodiment, the cross dipoles comprise triangular-shaped arms. 
     According to a second embodiment, the cross dipoles comprise square-shaped arms. 
     According to a third embodiment, the cross dipoles comprise arms made up of a solid fractal pattern. 
     According to a fourth embodiment, the cross dipoles comprise arms made up of separate strands. The strands should preferably be separated by a distance smaller than or equal to λ HF /10 where λ HF  is the wavelength of the high frequency RF signal. 
     In one variant embodiment, the radiating element comprises three parallel superimposed radiating planes: a first lower radiating plane, a second intermediate radiating plane positioned above the first radiating plane from which it is electrically insulated and a third upper radiating plane positioned above the second radiating plane from which it is electrically insulated. 
     A further aim of the invention is to provide a multiband telecommunications antenna comprising the radiating elements described above. 
     The advantage of this invention is that it reduces the width of the antenna and therefore its surface which reduces its manufacturing cost and provides it with a reduced wind surface area. 
     Moreover, the characteristics of the antenna comprising elements according to the invention are better than configurations in the prior art for two reasons. On the one hand, the radiating elements of one frequency band will be less disrupted by the radiating elements of the other frequency bands as the latter become “invisible” to them due to the position of the dipoles above one another. On the other hand, all the dipoles are in a symmetrical environment. 
    
    
     
       Other characteristics and advantages of the present invention will become apparent upon reading the following description of one embodiment, which is naturally given by way of a non-limiting example, and in the attached drawing, in which: 
         FIG. 1  represents a radiating element according to a first embodiment, 
         FIG. 2  shows a multiband antenna comprising radiating elements similar to those in  FIG. 1 , 
         FIG. 3  represents a radiating element according to a second embodiment, 
         FIG. 4  represents a radiating element according to a third embodiment, 
         FIG. 5  represents a radiating element according to a fourth embodiment, 
         FIG. 6  represents a radiating element according to a fifth embodiment, 
         FIG. 7  represents a radiating element according to a sixth embodiment, 
         FIG. 8  represents a radiating element according to a seventh embodiment, 
     
    
    
     The embodiment illustrated in  FIG. 1  represents a radiating element  1  comprising a lower radiating plane  2  defined by a first pair of cross dipoles consisting of a first dipole  3  and a second dual cross-polarization dipole  4  whose length is more or less equal to ½λ BF , where λ BF  is the wavelength of the low frequency RF signal, arranged orthogonally in relation to one another presenting orthogonal polarizations of ±45°. The first dipole  3  comprises a first conducting arm  5  and a second conducting arm  6  which are collinear with a negative polarization (−45°), each with a length more or less equal to ¼λ BF . Each conducting arm  5 ,  6  is more or less triangular in shape. The arms could naturally also adopt another shape (square for example). The first  5  and second  6  conducting arms are arranged as an extension of one another in a horizontal plane so that their apexes are close to one another without coming into contact. Similarly, the second dipole  4  comprises a first conducting arm  7  and a second conducting arm  8  which are collinear with a positive polarization (+45°). The conducting arms  7 ,  8  are more or less triangular in shape. The first  7  and second  8  conducting arms are arranged as an extension of one another in a horizontal plane so that their apexes are close to one another without coming into contact. The cross dipoles  3 ,  4  are supported by a base  9 . The four conducting arms  5 ,  6 ,  7 ,  8  are all supported by a shaft  10  attached to a shared base plate  11  forming the base  9 . Each dipole  3 ,  4  is provided with a balanced power supply to generate a linear polarization. 
     According to one embodiment of the invention, the radiating element  1  also comprises an upper radiating plane  13 , similar for example to the lower radiating plane  2 , defined by a second pair of cross dipoles consisting of a first dipole  14  and a second dual cross-polarization dipole  15  whose length is more or less equal to ½λ BF , where λ BF  is the wavelength of the low frequency RF signal, arranged orthogonally in relation to one another presenting orthogonal polarizations of ±45°. The dipole  14  comprises a first conducting arm  16  and a second conducting arm  17  which are collinear with a negative polarization (−45°) and the dipole  15  comprises a first conducting arm  18  and a second conducting arm  19  which are collinear with a positive polarization (+45°). The arms  16 ,  17 ,  18 ,  19  are more or less triangular in shape and arranged as extensions of one another in a horizontal plane. The cross dipoles  14 ,  15  are supported by a base  20 . All the conducting arms  16 ,  17 ,  18 ,  19  are supported by a shaft  21  attached to a shared base plate  22  forming the base  20 . Each dipole  14 ,  15  is provided with a balanced power supply to generate a linear polarization. 
     The lower plane  2  is assembled on a flat reflector  24  which serves as a ground plane through the intermediary of its base plate  11 . The upper radiating plane  13  is positioned above the lower plane  2  from which it is electrically insulated, for example by a layer of dielectric material  23  and is attached to the latter by means of its base plate  20 . The conducting arms  5 ,  6 ,  16 ,  17  with negative polarization (−45°)are superimposed as are the conducting arms  7 ,  8 ,  18 ,  19  with positive polarization (+45°). In this case, the conducting arms  5 ,  6 ,  7 ,  8  of the dipoles  3 ,  4  on the lower plane  2  have a metallic surface which is sufficiently developed to serve as an RF energy reflector for the upper plane  13 . 
       FIG. 2  illustrates a beneficial embodiment of a telecommunications antenna  30  comprising radiating elements  31  assembled on a reflector  32 . The radiating element  31  comprises an upper radiating plane  33  dedicated to the UMTS frequency band and a lower radiating plane  34  dedicated to the GSM frequency band. The antenna  30  may also comprise elements including a radiating plane  35 , similar to the upper radiating plane  33 , dedicated to the UMTS frequency band, which are interspersed between the radiating elements  31 . The radiating planes  35  and  33  must either be physically positioned at the same height or be compensated for electrically by the addition of a cable in order to generate a flat wavefront. 
       FIG. 3  presents a second embodiment of a radiating element  40  comprising a base  41  mounted beneath a radiating plane  42 . The lower radiating plane  42  is defined by a first pair of cross dipoles made up of two dipoles  43  and  44  with dual cross polarization. The dipole  43  with negative polarization (−45°) comprises a first conducting arm  45  and a second conducting arm  46  and the dipole  44  with positive polarization (+45°) comprises a first conducting arm  47  and a second conducting arm  48 . An upper radiating plane  49  defined by a first pair of dual polarization printed or metallic dipoles, known as patch type dipoles, is mounted beneath the lower radiating plane  42  from which it is electrically insulated. As stated above, the conducting arms  45 ,  46 ,  47 ,  48  are all supported by a shaft  50  attached to a base plate  51 . Each dipole  43 ,  44  is therefore provided with a balanced power supply to generate a linear polarization. 
       FIG. 4  depicts a third embodiment of a radiating element according to the invention. The radiating element  60  comprises a base  61  supporting a lower radiating plane  62  defined by a first pair of cross dual polarization dipoles consisting of a first dipole  63  and a second dipole  64  arranged in a cross shape, each with two arms  65 ,  66  and  67 ,  68  respectively. Each arm  65 ,  68 ,  67 ,  68  is made up of separate strands whose length is more or less equal to ¼λ BF , where λ BF  is the wavelength of the low frequency RF signal. The strands are separated by a distance smaller than or equal to λ HF /10, where λ HF  is the wavelength of the high frequency RF signal. 
     An upper radiating plane  69  is superimposed on the lower radiating plane  62  from which it is electrically insulated. The upper radiating plane  69  is defined by a second pair of dual cross-polarization dipoles supported by a base  70 , a first dipole  71  and a second dipole  72  arranged in a cross shape, each with two arms  73 ,  74  and  75 ,  76  respectively which are more or less triangular in shape and arranged as an extension of one another in a horizontal plane. 
     It may be possible in a similar way to create radiating elements consisting of a different number of superimposed radiating planes, for example a lower radiating plane, an intermediate radiating plane and an upper radiating plane. In this case, the lower radiating plane must naturally embody the same characteristics with regard to the intermediate plane as the ones which have already been described in relation to the upper radiating plane. Similarly, the intermediate radiating plane must embody the same characteristics with regard to the upper radiating plane as the ones which have already been described in relation to the lower radiating plane. 
     The radiating element  80  represented in  FIG. 5  is a fourth embodiment of a radiating element according to the invention. The radiating element  80  comprises a lower radiating plane  81  defined by a first pair of dipoles, which is a printed circuit forming dipoles  82  and  83  each of which possesses two arms  84 ,  85  and  86 ,  87  respectively fed by a conductive line  88 . A radiating plane  89  defined by a second pair of dual cross-polarization dipoles is superimposed on the lower radiating plane  81  from which it is electrically insulated. The upper radiating plane  89  comprises two cross dipoles supported by a base similar to the upper radiating plane  69  in  FIG. 4  which has already been described. 
       FIG. 6  depicts a fifth embodiment of a radiating element according to the invention. The radiating element  90  comprises a lower radiating plane  91  defined by a first pair of dipoles which is a printed circuit forming dipoles  92  and  93  in a cross shape similar to the lower radiating plane  81  in  FIG. 5  which has already been described. A radiating plane  94  defined by a second pair of cross dipoles is superimposed on the lower radiating plane  91  from which it is electrically insulated. The upper radiating plane  94  comprises two cross dipoles  95 ,  96  of the “butterfly” type which are arranged orthogonally and supported by a base  97 . Each dipole  95 ,  96  consists of two conducting arms folded axially in a V shape. 
       FIG. 7  depicts a seventh embodiment of a radiating element according to the invention. The radiating element  100  comprises a lower radiating plane  101  defined by a first pair of dipoles which is a printed circuit forming dipoles  102  and  103  in a cross shape similar to the lower radiating plane  81  in  FIG. 5  which has already been described. An upper radiating plane  104  is superimposed on the lower radiating plane  101  from which it is electrically insulated. The upper radiating plane  104  is a printed circuit forming dipoles  105  and  106  in a cross shape. 
     It may be possible in a similar way to create radiating elements consisting of a different number of radiating planes. For example, a radiating element  110  comprising a lower radiating plane  111 , an intermediate radiating plane  112  and an upper radiating plane  113  superimposed as shown in  FIG. 8 . In this case, the lower radiating plane  111  must naturally embody the same characteristics with regard to the intermediate plane  112  as the ones which have already been described in relation to the upper radiating plane  113 . Similarly, the intermediate radiating plane  112  must embody the same characteristics with regard to the upper radiating plane  113  as the ones which have already been described in relation to the lower radiating plane  111 . 
     The lower radiating plane  111 , defined by a first pair of dipoles, is a printed circuit forming dipoles  114  and  115  in a cross shape similar to the lower radiating plane  81  in  FIG. 5  which has already been described. An intermediate radiating plane  112  defined by a second pair of cross dipoles is superimposed on the lower radiating plane  111  from which it is electrically insulated. The intermediate radiating plane  112  is also a printed circuit forming dipoles  116  and  117  in a cross shape. An upper radiating plane  113 , defined by a third pair of dipoles, is superimposed on the intermediate radiating plane  112  from which it is electrically insulated. The upper radiating plane  113  is also a printed circuit forming dipoles  118  and  119  in a cross shape.