WIDEBAND DUAL-POLARIZED RADIATION ELEMENT AND ANTENNA

OF SAME

FIELD OF THE INVENTION

The present invention relates to a base station antenna for mobile communication system, especially to a high performance wideband dual-polarized radiation element and its antenna.

BACKGROUND OF THE INVENTION

At present, under the circumstance of the coexisting 2G and 3G networks, the requirement for antennas which are compatible for 2G and 3G networks are continuously increasing. With the development of communication technology, higher performances of multiple band antennas are also desired.

Basing on the above development tendency, the design that two pairs of cross-polarized dipoles form in the shape of square or circle is commonly applied in the present market. U.S. Pat. NO. 6333720B 1 disclosed an antenna, of which the low band radiation element module included two pairs of cross-polarized dipoles arranged like a dipole square. By embedding the high band radiation elements among the low band radiation elements achieves the performance of multiple band antennas.

There are some defects in the low band radiation element and its multiple band antennas as following: (1 ) the linear dipoles cause a big dimension of dipole square; it also degrades the performance of high band radiation between low band radiation elements. Besides, the coupling between low band radiation elements degrades its electrical performance. (2) The structure of the balun is linear, which makes low band radiation element close to the high band, and the impedance and pattern of the high band radiation elements is effected by the low band radiation elements, which causes lower electrical performance and bad pattern.

Compared with U.S. Pat. NO. 6333720B 1 , the design in Chinese Patent published No. CN201 134512Y had some improvements. But it still had some defects as following: (1 ) since the high band radiation element is embodied in low band radiation element to achieve multi-band antenna, the high band radiation element is positioned near the low band balun, which badly affects the VSWR (Voltage Standing Wave Ratio) and radiation performance of high band radiation element. (2) Although the design reduced the radiation dimension, all the dipoles at one end are bent downwards, so it increases the bad impact on high band radiation element. (3) Different size of dipoles, specially the end thereof being enlarged to expand the operation band, also increases the difficulty of manufacturing and decreases the reliability of the radiation element. SUMMARY OF THE INVENTION

A main object of the present invention is to provide a wideband high performance dual-polarized radiation element, which has simple structure for easily manufacturing, and has smaller dimension, thus improving electric and radiation performance.

Another object of the present invention is to provide a single band or multiple-band antenna, which can reduce cross coupling, and improve electrical and radiation performance.

To obtain the above object, a wideband dual-polarized radiation element comprises a plurality of dipoles and baluns which feed current to dipoles in balanced manner. Bottoms of the baluns are fixed on an annular connector. Each dipole has a pair of unit arms aligned on top of the corresponding balun. Therein, one end of each unit arm of the pair are respectively fixed at two sides of the top of the balun, and the other ends are respectively bent downwards or inwards, thus form a downward loaded line and an inward loaded line.

Preferably, the loaded lines are respectively bent downwards at a right angle with respect to dipole polygon, and bent inwards to center of the dipole polygon. Adjacent dipoles have loaded lines parallel. The pair of dipoles are arranged as orthogonal polarization, with the unit arms of dipole linear or fold line and forming a sharp of octagon or hexadecagon. The wideband dual-polarized radiation element is made by integral die- casting ₀

The baluns are in the shape of arc at a height of 0.2-0.3 of operation wavelength, and preferably its length is 0.25 of wavelength of central frequency. Each balun defines a groove in lower surface thereof for running feeding cable therein. A hole is defined in one side of top of the balun, and a metallic pillar is set at other side of the top. The feeding cable, which comprises a core wire and outer metallic shielding layer, goes through the hole in the balun from the groove, the core wire thereof and the metallic pillar are respectively welded to either end of a dielectric slice in order to support the slice on the top thereof, and the outer metallic shielding layer is welded in the groove close to the hole. Other end of the feeding cable is welded in the groove close to the annular connector as well. Therefore, the baluns feeds current to the corresponding dipole in balanced manner. A wideband antenna comprises a metal reflector and at least one wideband dual-polarized radiation element above. The radiation element is fixed on the metal reflector via fasteners engaging with fixed holes defined in the annular connector. The reflector has a vertical sidewall, and the dipoles of the radiation element are bent downwards near the vertical sidewall.

In another implementation, there are at least two wideband dual-polarized radiation elements installed linearly on the metal reflector.

In the third implementation, there are also several high band radiation elements set on the metal reflector, and at least one is embedded among the wideband dual-polarized radiation element.

Preferably, as the wideband dual-polarized radiation element positioned on the reflector, the dipoles thereof near the vertical sidewall of the reflector are bent downwards, and the dipoles near other radiation element are bent inwards. Namely, the wideband dual-polarized radiation element is arranged on the reflector with the downward loaded lines of the dipoles near the sidewall, and the inward loaded lines adjacent to other radiation element on the reflector.

Benefits of this invention are as follows:

Such design that the dipoles are bent downwards or inwards at ends, and form a shape of octagon or other polygon, greatly reduces the dimension of radiation element on the condition of the same electrical length, in other words, extends the length of radiation current.

Besides, the wideband dual-polarized radiation element of the present invention is high efficiency, good radiation performance, and can be flexibly applied to single band antenna and multi-band antenna. The integral structure of the radiation element made via die-casting, ensure a simple structure with excellent performance.

The loaded lines which are bent inwards, increase the distance between radiation elements aligned on the reflector, especially increase the distance between the high band radiation elements and the lower band radiation elements, therefore, greatly reduces the interference to the high band radiation element.

The loaded lines, which are bent downwards, compensate the asymmetry of polarization so that it improves greatly the performance of cross polarization discrimination ratio.

Furthermore, the radiation element adopts arc baluns, which simultaneously enhance above feature.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail in the following text with reference to the drawings in which, in detail:

FIG. 1 is a perspective view of a radiation element in accordance with an embodiment of the present invention;

FIG. 2 is a top view of FIG. l ;

FIG. 3is a side view of FIG. 1 ; FIG. 4 is a perspective view of the radiation element in accordance with another embodiment;

FIG. 5 is a perspective view of a wideband dual-polarized antenna in accordance with an embodiment of the present invention;

FIG. 6 is a perspective view of a dual-band dual-polarized antenna in accordance with embodiment of the present invention;

FIG. 7 illustrates H- panel pattern of a dual band antenna in accordance with an exemplary embodiment; and

FIG. 8 illustrates another H- panel pattern of a dual-band antenna in another exemplary embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS 1 -3, a high performance wideband dual-polarized radiation element 100, comprises a plurality of cross-polarized dipoles arranged in a dipole polygon, baluns correspondingly feeding current to each dipole in balanced manner, and an annular connector 1 1 1 for fixing the baluns at the bottom thereof. In the exemplary embodiment, the radiation element 100 comprises two pairs of cross-polarized dipoles 1 1 , 12, 13, 14 arranged in a shape of octagon and aligned on top of baluns 21 ,22,23,24. The radiation element 100 is made by integral die casting.

In a preferable embodiment, the dipoles 11 , 12, 13, 14, have similar structures, and each includes a pair of unit arms 11 a and l ib, 12a and 12b, 13a and 13b, 14a and 14b. One end of each unit arm is fixed respectively to two sides of top of the corresponding balun, the other ends are bent downwards or inwards in such way that forms a downward loaded line and inward loaded line 61a and 61b, 62a and 62b, 63a and 63b, 64a and 64b. More preferably, the loaded lines are respectively bent downwards at a right angle with respect to dipole polygon, and bent inwards to a center of the dipole polygon. Adjacent dipoles have loaded lines parallel to one another.

Taking dipole 11 as example, it includes a pair of unit arms 11a and l ib aligned on top of balun 21. Unit arm 11a and l ib both have one end respectively fixed at two sides of the top of balun 21, the other end of unit arm 11a bends inwardly, thus forms loaded line 61a, and the other end of unit arm l ib bends downwardly to form loaded line 61b. More preferably, the other end of unit arm 11a or l ib bends orthogonally downwardly to the dipole octagon to form the downward loaded lines 61b, or bends inwardly to a center of the dipole octagon to form the inward loaded lines 61a. The configuration of loaded lines 61a and 61b well shrink the diameter of the radiation element 100. In other words, the radiating current length is highly extended. Meanwhile, it can minimize the structure of radiation element 100. Furthermore, the inward loaded line 61a can decreases the influence from lower-frequency radiation element (short for LFRE in the below description) to higher-frequency radiation element (Short for HFRE in the below description) in multiple band application. Therefore, the electrical and radiation performance will be improved.

Similarly, one end of unit arms 12a and 12b of dipole 12 are respectively connecting on the top of balun 22, and the other ends bend to form downward loaded line 62b and inward loaded line 62a.

One end of unit arms 13a and 13a in dipole 13 are connecting on the top of balun 23 , and the other ends bend to form downward loaded line 63b and inward loaded line 63a.

One end of unit arms 14a and 14a in dipole 14 are connecting on the top of balun 24, and the other ends bend to form downward loaded line 64b and inward loaded line 64a. Thus, loaded-lines 61 a and 64a are aligned parallel to one another, 62a and 63a are parallel aligned, which are all bending inwardly and parallel to reflector 20 as shown in FIG. 5.

Meanwhile, downward loaded lines 61b&62b and 63b&64b are parallel to each other, and vertical to reflector 20 as shown in FIG. 5.

The two pairs of dipoles forms ±45° polarization, and dipoles in the same direction are spaced at 2/5-3/5 of the operation wavelength away from each other. Bottom of each balun is orthogonally fixed on the annular connector 1 1 1.

The cross profile of dipoles 1 1 , 12, 13, 14 is in the shape of circle, square or polygon, and the shape of circle or polygon will offer better impedance characteristic. To reduce the weight of the radiation element 100, the dipoles, such as its cross-section in the shape of polygon structure, are configured as hollow interior, as a result, manufacturing cost is reduced, and the radiating dimension remains unchanged as well.

Cross profile of dipoles 1 1 , 12, 13, 14 can also be designed in the shape of "L", "T" or stub line. The shape of stub line can confirm the best impedance characteristic. Considering the difficulty of manufacturing, the dipoles with cross-section in the shape of "L" is more preferable as shown in the drawings.

In preferable embodiment, baluns 21 -24 are in the shape of arc, and respectively feed current to dipole 1 1 , 12, 13, 14 in the radiation element 100 in balanced manner. The height of the balun is 1/5-3/10 of the operating wavelength, and preferably is 1/4 of central frequency wavelength. Arc balun expands the distance between the LFRE and HFRE, which can restrain the influence from the LFRE to the HFRE, and improve the cross-polarization performance thereof in this way.

Baluns 21 ,22,23,24 have similar structure. The bottom of each is orthogonally fixed to annular connector 1 1 1 , and the top is connecting with dipoles 1 1 , 12, 13, 14. A groove (not labeled) is designed in a lower surface of each balun for accommodating cables and feeding network for electrically connection and feeding current to their corresponding dipoles.

Balun 21 is illustrated to explain the detail structure of baluns and its feeding network. Referring to FIGS 1 -3 again, the bottom of balun 21 is orthogonally connected on the annular connector 1 1 1. Feeding cable 91 , which comprises core wire 51 and outer metallic shielding layer (not labeled), is fixed inside of the groove in the lower surface of the balun 21. On the top of balun 21 , one side thereof defines a hole 101 , and the other side sets a metallic pillar 41. The hole 101 communicates to the groove for installing feeding cable. A feeding slice 31 is welded on the top of the metallic pillar 41.

In specific application, feeding cable 91 goes through the hole 101 , then the core wire 51 thereof is connected with one end of the feeding slice 31 , and the other end of the feeding slice 31 is electrically connected with the metallic pillar 41. Thus, electrical connection between the core wire 51 of cable 91 and the unit arm l ib of dipole 1 1 achieves in this way. A pair of dielectric rings 71 is respectively set around outside of the core wire 51 and the metallic pillar 41 so as to support the feeding slice 31.

At a point near the hole 101 in the groove, outer metallic shielding layer of feeding cable 91 is welded to the unit arm 1 1 a. Moreover, the other end of cable 91 goes along inside of the groove, and is welded to the balun 21 at welding point 121 in the groove where close to connector 1 1 1 , which can avoid the electric and radiation performance of the radiation element 100 to get worse because of the electricity leakage from cable surface.

Baluns 22, 23, 24 and the way to electrically feed to corresponding dipole 12, 13, 14 are similar to the balun 21. Cable 92, 93, 94 respectively goes along inside of the groove in the lower surface of the corresponding balun, and is respectively welded to the balun at welding points 122, 123, 124 in the groove where close to annular connector 1 1 1. On the top of each balun, one side thereof defines a hole 102, 103 , 104, and the other side sets a metallic pillar 42, 43 , 44. The hole 102, 103, 104 respectively communicates to the groove for installing feeding cable. A feeding slice 32,33,34, is respectively welded on the top of the metallic pillar 42,43,44. A pair of dielectric rings 72, 73, 74 respectively sleeve around the core wire 52, 53 or 54 and metallic pillar 42, 43 or 44, thus supports feeding slice 32, 33 or 34 on the top as well. In actual use, cable 92, 93 or 94 respectively goes through hole 102, 103, or 104 at one side of the top of balun 22, 23 or 24, its core wire 52, 53 or 54 is connecting with one end of feeding slice 32, 33, or 34, and metallic pillar 42, 43, or 44 is connecting with the other end of feeding slice 32, 33 or 34, so as to achieves the electrical connection between core wire 52, 53 or 54 of feeding cable and one unit arm of the corresponding dipole. At a point close to hole 102, 103 or 104, outer metallic shielding layer of feeding cable is welded in the groove so as to achieve electrical connection between feeding cable 92, 93 or 94 and the other unit arm of the corresponding dipole.

The wideband dual polarized radiation element 100, wherein, its two pairs of dipoles are cross polarized, and arranged in the form like an octagon or other polygons. The unit arms of dipole are linear or like polygonal line. The loaded lines of each dipole are respectively bent inwards and downwards. Therefore, at the same electrical wavelength, the dimension of the radiation element 100 is reduced.

FIG. 4 explains another embodiment of the radiation element 100, wherein the two pairs of cross-polarized dipoles forms a hexadecagon, which makes the dimension of the radiation element much reduced.

One unit arm of the dipole is inwardly bending, which lessens influence on higher-frequency radiation element caused from the end of the loaded line. The other unit arm is downwardly bending, which offsets the asymmetry of the borders of the dipoles, thus improves the electrical performance.

Each balun is arc, at a height about 1/5-3/10 of the operating wavelength, such design can effectively reduces the interaction from different operating frequency bands, which ensures the consistency of electrical performance and a stable structure of the radiation element.

Furthermore, radiation element 100 is made by integrated casting. It has simple structure for easily manufacturing, is widely applicable for single band or multiple band antennas with excellent electrical and radiating performance, and mainly applicable for base station antenna for mobile communication.

Fig. 5 shows the radiation element 100 applied in dual polarized antenna 10 for a single operating band. Radiation element 100 is fixed on the metallic reflector 20. The annular connector 1 1 1 defines a plurality of fixing holes 81 , 82, 83, 84 therein, via which fastening pieces are inserted, therefore, the radiation element 100 is mounted to the reflector 20. Reflector 20 includes a vertical sidewall 200. According to the direction of the dipoles positioned with respect to the sidewall of reflector 200, two pairs of dipoles can form polarization at ±45°, horizontal or vertical polarization.

In the application of single band antenna array, two or more radiation elements 100 are linearly fixed on the metallic reflector 20.

The loaded lines close to the reflector sidewall 200 are downwards bending to offset the asymmetrical borders of the radiation element 100, thus improving the electrical performance of the antenna. Other loaded lines close to radiation element array are inwards bending. Loaded lines are arranged in such way that can increase the distance between radiation elements, namely, it can lessen the interaction therebetween.

Referring to FIG. 6, in the application of dual band antenna 10, at least two wideband dual polarized radiation elements 100 are linearly fixed on the metallic reflector 20 as LFREs. Beside, there is a plurality of higher-frequency radiation elements (namely, HFREs) 30 fixed on the reflector as well. At least one HFRE 30 is embedded in LFRE 100 to form a coaxial array. The loaded lines of dipoles close to radiation element array are inward bending, which can increase the distance from LFRE 100 to the HFRE 30 positioned between two LFREs 100. Therefore, it can lessen the influence caused by LFRE 100 on the HFRE 30.

The invented antenna radiation element 100 is in a shape of octagon, hexadecagon or other polygon. The design lessens the dimension of the LFRE 100 in the application of multiple band antenna, and it can decrease the coupling between radiation elements.

Moreover, loaded-lines in dipole combine with inward bending and downward bending, which can lessen the influence on higher-frequency radiation element 30 caused by the end of the loaded line.

Baluns of the radiation element in the antenna are arc. It is advantageous to diminish the coupling between different operating frequency bands.

The following description is an analytical comparison on radiating and electrical performance in application of dual band antenna.

In a first exemplary embodiment, the LFRE 100 and HFRE 30 construct a 65° dual band antenna. The impacts on the electrical and radiation performance for different bending directions of loaded lines are compared.

The two antennas, each comprises a lower-frequency radiation element (LFRE) module and a higher-frequency radiation element (HFRE) module located within the former. The only difference therebetween is that, the first antenna includes the LFRE with loaded lines of dipoles all downward bending, but the second antenna 10 includes the LFRE 100 of the present invention with loaded lines of dipole respectively downward and inward bending. The simulation data of Section Power Ratio (short for SPR) for LFRE is shown in Table 1. In the application of dual band antenna, the comparison on the simulation data for HFRE is shown in Table 2. Wherein, SPR means section power ratio, HBW means horizontal half-power beam width, CFBR means central-polarization front to back ratio, XFBR means cross-polarization front to back ratio, CPR0 means cross polarization front to back ratio at 0 degree, CPR60 means cross polarization front to back ratio at ±60°, and CPR10 means cross polarization front to back ratio at gain l OdB .

Table 1 Comparison on the simulation data SPR of LFRE

Operating Frequency first antenna Antenna 10

790 4.79 4.38

875 3.59 3.06

960 2.65 1.99 Table 2 comp arison on the simulation data of HFRE

table 1 shown above, the loaded lines of LFRE 100 in the present invention combing inward and downward bending, improve the LFRE' s electrical performance.

From the comparison in table 2, it indicates that LFRE with all loaded lines downward bending worsens the electrical performance of HFRE. In other words, the LFRE 100 in the present invention can greatly improve the electrical and radiation performance and the cross polarization discrimination ratio as well.

Also referring to FIG. 7, wherein 7(a) shows H panel pattern of LFRE in the first antenna; 7(b) shows H panel pattern of HFRE in the first antenna; 7(c) shows H panel pattern of LFRE in the second antenna 10 of the present invention, and 7(d) shows H panel pattern of HFRE in the second antenna, which show that the loaded lines inward and downward bending in LFREI OO can optimize the radiation performance of HFRE in the application of dual band antenna 10.

In other exemplary embodiment, a third dual band antenna, which is different to the second antenna 10 in the above first exemplary embodiment, is that the baluns of the LFRE are linear other than arc. The electrical performance of LFRE is shown in Table 3, and its influence to HFRE on electrical and radiation performance is shown in Table 4. Wherein FREQ means frequency, XPBR means front to back cross polarization ratio. FIG. 8(a) indicates the H panel pattern of HFRE of the third antenna; FIG. 8(b) indicates the HFRE' s H panel pattern of the second antenna 10 of the present invention.

Table 3 electrical perfor mance comp arison between arc b alun and linear b alun in LFRE

Table 4 electrical perfor mance comp arison between arc b alun and linear b alun in HFRE

From Tables 3-4 and FIG. 8, they come to a result that arc balun' s impact to HFRE is slight, XFBR be superior to linear balun. Furthermore, it can ensure the consistency of electrical performance and a stable structure.

In conclusion, the wideband dual-polarized radiation element of the present invention greatly improves the performance of cross polarization discrimination ratio, function in high efficiency with good radiation performance, and can be flexibly applied to single band antenna and multi-band antenna.

While the invention has been described in conjunction with specific embodiments, it is evident that numerous alternatives, modifications, and variations will be apparent to those skilled in the art in light of the forgoing descriptions. The scope of this invention is defined only by the following claims.