Patent Publication Number: US-7589603-B2

Title: Phase shifter having power dividing function for providing a fixed phase shift and at least two phase shifts based on path length

Description:
TECHNICAL FIELD 
   The present invention relates to a phase shifter; and, more particularly, to a phase shifter having power dividing function, which performs tilting of a vertical radiation beam in a base station of a mobile communication system. 
   BACKGROUND ART 
   In general mobile communication systems, since a density of subscribers is different at every region and at every time, the tilt control is frequently required in order to optimize the mobile communication system. For optimization of the air interface network, in a conventional mobile communication system, a mechanical tilt is used. The beam tilt of the antenna in a vertical direction means an angle of the beam radiated by the antenna slopes to the horizontal. 
   A conventional antenna is mechanically tilted to vary the radiated beam tilt of the antenna, using a mechanical tilting device mounted on the antenna. 
   Mechanical tilting of the antenna is a cost-effective way to manufacture the antenna. However, in this case personnel have to climb up toward the antenna to manually adjust antenna beam tilt. It is neither economically viable nor time-conscious. In other words, when the beam tilt of the antenna is required, the person should climb up toward the antenna, unfasten bolts fixing the tilting apparatus, adjust the angle of the antenna, and fasten the bolts, which takes much more time to tilt the antenna. 
   To solve the abovementioned problem, an electric beam tilting device capable of adjusting antenna beam tilt at a distance is developed. Such electric beam tilting device includes a phase shifter for shifting a phase of the beam radiated by the antenna. 
   A phase shifter for adjusting antenna beam tilt is disclosed in Korean Patent Laid-open No. 2002-0041609 which describes the phase shifter in which the beam tilt is varied by both adjusting the phase of the radio waves radiated by the antenna and controlling the power division. 
     FIG. 1  is a view showing a conventional phase shifter. 
   As shown, the conventional phase shifter includes a power divider  51 , a first phase shift unit  52 , a second phase shift unit  53 , a first delay unit  54  and a second delay unit  55 . 
   A radio signal is fed into the power divider  51  via an input port (IP). The power divider  51  divides up the radio signal in a predetermined ratio and then feeds them into the first and second phase shift units  52  and  53 . The first phase shift unit  52  adjusts the phase of the radio signal and then sends it out to both a first output port (OP 3 ) and a second output port (OP 4 ). The second phase shift unit  53  divides the radio signal into two separate parts moving away in opposite directions to obtain phase shifts between them. The first and second delay units  54  and  55  are electrically connected to the second phase shift unit  53 , facing each other. On the one hand, the first delay unit  54  delays the radio signal and then pass the delayed radio signal on to a third output port (OP 5 ). On the other hand, the second delay unit  55  delays the radio signal and then send them out to a fourth output port (OP 6 ). Ideally, the phase difference between output signals at the OP 5  and the OP 6  is constant. 
   When the power divider  51  divides the radio signal into two parts in the ratio of 1 to 2, the intensity of one part fed into the second phase shift  53  is two times stronger than that of the other part fed into the first phase shift units  52 . That is, one part of the power divider  51  has a degree of zero and an amplitude of 1 (i.e., 1&lt;0). The other part of the power divider  52  has a zero degree and an amplitude of 2 (i.e., 2&lt;0). 
   The radius of a circular shape formed by the microstrip transmission line making up the first phase shift units  52  is roughly  3  times larger than that of the second phase shift units  53 . If the phase of the radio signal received via the IP is not changed, The output signals at the OP 3 , OP 5 , OP 6  and OP 4  are outputted at the same time. 
   When the first and second phase shift units  52  and  53  are rotated by certain degrees, the phase difference between input and output signals at the OP 3 , OP 5 , OP 6  and OP 4  are 3 Θ/2 , Θ/2, −Θ/2 and −3 Θ/2 respectively. That is, the OP 3  has a degree of +3 Θ/2 and an amplitude of 0.5. The OP 5  has a degree of +Θ/2 and an amplitude of 1. The OP 6  has a degree of −Θ/2 and an amplitude of 1. The OP 4  has a degree of −3 Θ/2 and an amplitude of 0.5. In this case, the phases of the adjacent output signals differ by Θ. 
   Following from the above, the function of the first and second phase shift units  52  and  53  is to vary the phase of the radio signal fed into the antenna via the OP 3  and OP 6 , thereby varying its power distribution. 
   However, the main drawback to the conventional phase shifter is that there is a need for an additional power divider capable of acquiring an output signal that has the same phase as the input signal. In addition, as the phase shift units are turned by certain degrees to vary the phase of the input signal, the radio signal fed into a metallic contact between a fixed part and a variant part is likely to go through an intermodulation. In this case, attainable variation in the angle of antenna beam tilt in vertical directions is limited largely due to a one-dimensional way the delay units delay the radio signal. Here, the delaying of the radio signal is done by making use of the distance between the radio signals. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a phase shifter having a power dividing function. 
   It is another object of the present invention to provide a phase shifter for preventing inter modulation of a signal. 
   It is further another object of the present invention to provide a phase shifter having a larger range of variable angle of the beam tilt. 
   In accordance with an aspect of the present invention, there is provided a phase shifter, including: an input port for receiving a radio frequency (RF) signal; a power dividing means for dividing the RF signal into a first divided signal of which phase is to be varied and a second divided signal having a fixed phase value; a first output port for outputting the second divided signal having the fixed phase value; a phase shift unit for dividing the first divided signal into a third divided signal and a fourth divided signal wherein the third divided signal and the fourth divided signal move in opposite directions and for shifting phase of the third divided signal and the fourth divided signal based on a difference in a path length of the third divided signal and the fourth divided signal, to thereby generate phase-shifted signals; a phase delay means for delaying of the third divided signal and the fourth divided signal based on the phase-shifted signals; and at least two second output ports connected to the phase delay means, for outputting the phase-shifted signals. 
   The phase shifter includes: a first induction unit electrically connected to the first output port, wherein the first induction unit is a copper plate having a semicircle shape formed on the same plane as the input port; a second induction unit wherein the second induction unit is a copper plate having a ring shape formed on the same plane as the phase shift unit; and a dielectric located between the first induction unit and the second induction unit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a diagram showing a conventional phase shifter; 
       FIG. 2  is a diagram showing an electrical tilting antenna to which a phase shifter in accordance with the present invention is applied; 
       FIG. 3  is an exploded diagram illustrating a phase shifter in accordance with the present invention; 
       FIG. 4  is a schematic diagram illustrating a phase shifter in accordance with the present invention; 
       FIG. 5  is a front view illustrating a phase shifter in accordance with the present invention; 
       FIG. 6  is an exemplary view illustrating phase difference of output signals due to a phase shifter in accordance with the present invention; 
       FIG. 7  is a diagram illustrating multiple phase delay units of the phase shifter in accordance with the present invention; 
       FIG. 8  is a front view illustrating a phase shifter in accordance with another embodiment of the present invention; 
       FIG. 9  is a view illustrating vertical beam patterns obtained by controlling an electrical tilting apparatus having five output ports in accordance with another embodiment of the present invention; and 
       FIG. 10  is a view illustrating vertical beam patterns obtained by controlling an electrical tilting apparatus having five output ports in accordance with another embodiment of the present invention. 
   

   MODE(S) BEST FOR CARRYING OUT THE INVENTION 
   Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter. 
     FIG. 2  is a diagram showing an electrical tilting antenna to which a phase shifter in accordance with the present invention is applied. 
   As shown, a phase shifter  200  is electrically connected to five antenna array elements numbered  210 ,  220 ,  230 ,  240  and  250 . A first array element  1  ( 210 ) has a degree of Θ1 and an amplitude of P 1 . A second array element  2  ( 220 ) has a degree of Θ2 and an amplitude of P 2 . A fourth array element  4  ( 240 ) has a degree of Θ4 and an amplitude of P 4 . A fifth array element  5  ( 250 ) has a degree of Θ5 and an amplitude of P 5 . A handle  260  controls the phase shifter  200  in such a way that the phase difference between radio frequency (RF) signals fed into the array elements has a scale factor of Θ. In detail, the phase difference between two adjacent RF signals fed into the array elements is Θ. Typically, the handle  260  incorporates a remote-controlled step motor. 
   The phase shifter  200  includes a power dividing unit for dividing the RF input signal into separate output signals, each of which has a fixed phase value. 
   In this embodiment, the number of the array elements electrically connected to the phase shifter  200  is five (5). However, the number of the array elements is not limited. 
     FIG. 3  is an exploded diagram illustrating a phase shifter in accordance with the present invention. 
   As shown, the phase shifter includes a basis plate  21 , a circuit board  30 , a dielectric  20 , a phase shift unit  15 , guide units  18 A and  18 B, a bolt  19 A and a nut  19 B. 
   The circuit board  30  is supported by the basis plate  21  made of copper. The circuit board  30  has, on one side, an input port  10 , a first output port  11 , phase delay units  17 A and  17 B, a first induction unit  13  and second output ports  12 A,  12 B,  12 C and  12 D. The first output port  11  outputs a signal that has a fixed phase value. The first induction unit  13  is semicircle in shape. The phase delay units  17 A and  17 B put together are shaped like a circle in full view. Each of the second output ports radiates a signal whose phase is variable. 
   The dielectric  20  transports an electric power by electromagnetic bond. The dielectric  20  is evaporated on the upper side of the circuit board  30 . Teflon can be used as the dielectric  20 . 
   The phase shift unit  15  is shaped like the hands of a clock, which are rotatable at a pivot point located on the center of the circuit board  30 . On the underside of the phase shift unit  15  is located one copper plate facing the other copper plate mounted on the circuit board  30 . 
   The bolt  19 A and the nut  19 B fasten together the phase shift unit  15  and the circuit board  30  so that the phase shift unit  15  turns around a pivot made up of the bolt  19 A and the nut  19 B. Here, the phase shift unit  15  turns either clockwise or counterclockwise by certain degrees. The turning motion of the phase shift unit  15  is guided by the guide units  18 A and  18 B. 
     FIG. 4  is a schematic diagram illustrating a phase shifter in accordance with the present invention. The same reference numeral is given to the same element, although the element appears in different drawings, and may not be described in further detail. 
   As shown, a rotating shaft made up of a bolt  19 A and a nut  19 B goes through a basis plate  21 , a circuit board  30 , a dielectric  20  and a phase shift unit  15 . The guide units  18 A and  18 B guide the rotating motion of the phase shift unit  15  so that the phase shift unit  15  is rotated within a predetermined angle. 
     FIG. 5  is a front view illustrating a phase shifter in accordance with the present invention. 
   As shown, an image of a semicircular copper plate mounted on the underside of the phase shift unit  15  is projected onto the frontal view of the circuit board. 
   The function of the semicircular copper plate mounted on the bottom side of the phase shift unit  15  is to transfer an electric power from an input port  10  to the phase delay unit  17 A or  17 B. On the bottom side of the phase shift unit  15  is mounted the semicircular copper plate facing another semicircular copper plate mounted on the circuit board  30 . The dielectric  20  is located between the two semicircular copper plates. The phase delay unit  17 A or  17 B includes a micro strip line and open stubs. The capacitance between the stubs and the circuit board ground plane causes the RF signal to be propagated slowly. Input impedance of the phase delay unit  17 A or  17 B is adjusted by the length of an open stub. The open stub is connected to one part of the input port  10 , and the length and width of the open stub is adjusted so that the input port  10  has the impedance of 50Ω. 
   The operation of a phase shifter is described below in conjunction with  FIGS. 3 to 5 . 
   As an RF signal is fed into the input port  10 , a power divider divides the RF signal into two parts. One part is a signal of which phase is variable. The other part is a signal having a fixed phase value. The power divider includes a first induction unit  13 , a second induction unit  14  and a dielectric  20 . The first induction unit  13  is a copper plate shaped like a semicircle and is mounted on the circuit board  30 . The first induction unit  13  transmits a first divided signal to a first output port. The second induction unit  14  is a ring-shaped copper plate and is mounted on a side of the phase shift unit  15 . The second induction unit  14  transmits the other divided signals to the phase delay unit  17   a  or  17   b . The dielectric  20  is positioned between the first and second induction units  13  and  14 . 
   Referring to  FIG. 3 , the input port  10 , the induction unit  13  and the phase delay units  17 A and  17 B are formed on the same plane. Referring to  FIG. 5 , the second induction unit  14  and the phase shift unit  15  are formed on the same plane. 
   The one part of the RF input signal, a first divided signal, is transmitted to the first output port  11  via the first induction unit  13 . The first divided signal has the same phase as the RF input signal. The other part of the RF input signal is transmitted to the phase delay units  17 A and  17 B via the second induction unit  14 . 
   The power divider determines on how the electric power is shared between two different portions of the RF input signal. In which case, one portion has a fixed phase value and the phase of the other portion is to be shifted. Here, the power divider controls power energy of the first divided signal and the second divided signal by varying the length of the semicircular arc of the first induction unit  13  and the size of the second induction unit  14 . Another embodiment of the present invention implements a phase shifter in which an input port  10  branches off to carry the portion of a RF input signal having a fixed phase value. 
   The RF signal from the phase shift unit  15  is fed into the phase delay units  17 A and  17 B. The RF signal from the phase delay unit  17 A is divided into two parts moving away in opposite directions and is transmitted to the second output ports  12 C and  12 D. The RF signal from the phase delay unit  17   b  is divided into two parts moving away in opposite directions and is transmitted to the second output ports  12 A and  12 B. In which case, the way the RF signal is transferred from the phase shift unit  15  to the phase delay unit  17 A is similar to that used in the power divider. In detail, the dielectric  20  transfers the electric power from the third induction units  16 A and  16 B to the phase delay units  17 A and  17 B. 
   Following from the above, the function of the dielectric  20  is to prevent metallic components from coming into contact with each other, thereby safeguarding against a signal intermodulation. 
   The electric power among the output ports is controlled by adjusting the width of the copper plate formed on the underside of the phase shift unit  15 . In other words, the amount of power applied to the third induction unit is decided by the width and the length of the phase shift unit  15 . 
     FIG. 6  is an exemplary view illustrating phase difference of output signals due to a phase shifter in accordance with the present invention. 
   As the phase shift unit  15  turns clockwise by a certain degree, the path length of a RF signal fed into the phase delay units  17 A and  17 B varies. In which case, the path length of a RF output signal from the second output port  12   b  is shorter than that of a RF output signal from the second output port  12 A by  2 L, whereas the path length of a RF output signal from the second output port  12   d  is longer than that of the second output port  12 C by  2   l.    
   The phase delay units  17 A and  17 B are shaped like an arc-shaped comb. An output signal from each output port of the phase delay units  17 A and  17 B has a different phase value. This is due to the fact that the radius of the arc formed by the phase delay unit  17 A differs from that of the phase delay unit  17 B. 
   The phase of the output signal from the second output ports  12 A,  12 B,  12 C or  12 D is shifted by varying the angular degrees by which the phase shift unit  15  turns. Referring to  FIG. 2 , a phase shifter proposed by the present invention produces output signals that have phase values of θ1, θ2, θ3 and θ4. 
   Unlike in a rod-shaped phase delay unit included in a conventional phase shifter, the phase delay units  17 A and  17 B are shaped like an arc-shaped comb so that a signal delay is maximized. In other words, since a small change in the angular displacement made by the phase shift unit  15  makes a big difference in delay of the signal, thereby maximizing the beam tilt of an antenna in vertical directions.  FIG. 7  shows multiple phase delay units of the phase shifter in accordance with the present invention. 
     FIG. 8  is a front view illustrating a phase shifter in accordance with another embodiment of the present invention. 
   As shown, the phase shifter includes a first output port  11 , second output ports  12 A,  12 B,  12 C,  12 D,  12 E,  12 F,  12 G and  12 H and phase delay units  17 A,  17 B,  17 C and  17 D. Each phase delay unit  17 A,  17 B,  17 C or  17 D has a different radius and has a repeated pattern. As is described in the preceding embodiments of the present invention, the phase shifting of a RF signal is effected by rotating the phase shift unit  15 . The operation of the phase shifter having  9  output ports is similar to that of a phase shifter having  5  output ports. Accordingly, for only easy description, detailed description of the phase shifter having  9  output ports will be skipped. 
   Following from the above, the number of phase shift units incorporated in a phase shifter is varied according to the number of output ports. In which case, the phase shifting of an input signal comes in a many varieties. 
     FIG. 9  is a view illustrating vertical beam patterns obtained by controlling an electrical tilting apparatus having five output ports in accordance with an embodiment of the present invention.  FIG. 10  is a view illustrating vertical beam patterns obtained by controlling an electrical tilting apparatus having five output ports in accordance with another embodiment of the present invention. 
   As shown in  FIGS. 9 and 10 , the phase shifter in accordance with the present invention changes angles of radiation patterns of the antenna, without the mechanical beam tilt. 
   In a phase shifter proposed by the present invention is included a dielectric for preventing metallic components from coming into contact with each other, thereby safeguarding against a signal intermodulation. 
   The phase shifter has a power dividing unit for outputting a signal having the same phase as the input signal, to thereby manufacture a small size of the phase shifter having the power dividing function. 
   In the phase shifter, the dielectric is inserted between the fixed element and the variable element so as to electromagnetically transfer a signal, thereby preventing inter modulation of the signal. 
   Unlike in a rod-shaped phase delay unit included in the conventional phase shifter, the phase shifter in the present invention includes phase delay units that are shaped like an arc-shaped comb, distances between the signals between the output ports and the phase shift unit are larger so that a signal delay is maximized. Accordingly, a range of variable angle of the beam tilt of the antenna is larger than the conventional phase shifter. 
   Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.