- 1 DESCRIPTION MULTIBRANCHED DIVISION PHASE SHIFTER Technical Field [00011 The present invention relates to a multibranched distributed phase shifter, and more particularly, to a multibranched distributed phase shifter which is applied to a phase circuit which controls a tilt angle of an array antenna and the like. Background Art [0002] In an array antenna for a mobile phone base station and the like, for example, for the purpose of optimizing a service area of the base station, a tilt angle of an emission beam which is emitted from the array antenna of each base station is controlled. In order to change the tilt angle of the emission beam, it is necessary to change, by using a phase shifter, the phase distribution of excitation electric power supplied to each array antenna element. For example, distributed phase shifters described in Patent Document 1 and Patent Document 2 below have been known as such a phase shifter.
- 2 Figure 7 is a perspective view illustrating an example of a conventional distributed phase shifter. In the distributed phase shifter illustrated in Figure 7, an input-side strip conductor 3 and an output side strip conductor 2 having a partially opened circular ring shape are disposed on a dielectric substrate 10, and one end of the input-side strip conductor 3 in the center (a central axis is indicated by P) of the circular ring is positioned at the center of the circular ring of the output-side strip conductor 2. In addition, sliding portions (5a, 5b) which slide on the output-side strip conductor 2 are provided, and the lengths thereof are X/4 to the left and to the right, respectively. Both ends of the output-side strip conductor 2 serve as output ends. Moreover, one end of an arm portion 5c on the central side of the circular ring is positioned at the center of the circular ring. Further, high-dielectric insulators (4a, 4b) which are an insulating material of a general high-frequency electric cable, such as polyethylene fluoride, are interposed between the arm portion 5c and the input-side strip conductor 3 and between the sliding portions (5a, 5b) and the output-side strip conductor 2. In the distributed phase shifter illustrated in Figure 7, a high-frequency signal inputted through the input-side strip conductor 3 is coupled to the arm portion Sc via the high-dielectric insulator 4a, and - 3 passes through the arm portion 5c to reach the left and right sliding portions (5a, 5b) at leading ends of the arm portion 5c. Then, at the left and right sliding portions (5a, 5b), the high-frequency signal is coupled to the output-side strip conductor 2 via the high dielectric insulator 4b. Then, when the arm portion is rotated, a predetermined phase difference can be provided between excitation electric powers which are outputted from both the ends of the output-side strip conductor 2. [0003] It should be noted that prior art documents relating to the invention of the present application are as follows. Patent Document 1: Japanese Patent Laid-Open No. 05 121915 Patent Document 2: Japanese Patent Laid-Open No. 2000 196302 Disclosure of the Invention Problem to be Solved by the Invention [0004] However, as is apparent from Figure 7, the distributed phase shifter illustrated in Figure 7 can distribute an inputted high-frequency signal only into two.
-4 Therefore, in order to distribute the inputted high frequency signal into three or more and to obtain an output having a predetermined phase difference, a multibranched distributed phase shifter as illustrated in Figure 8 is used. Figure 8 is a view for describing an example of the conventional multibranched distributed phase shifter. In Figure 8, reference symbols 30a, 30b, and 30c each denote the distributed phase shifter illustrated in Figure 7, reference numeral 31 denotes a three-branched distributer, and reference numeral 32 denotes a linkage mechanism (or gear mechanism). In the multibranched distributed phase shifter illustrated in Figure 8, the inputted high-frequency signal is distributed into three by the three-branched distributer 31, and the high-frequency signals which are distributed into three are inputted to the distributed phase shifters (30a, 30b, 30c), respectively, to be synchronized by the linkage mechanism (or gear mechanism) 32 for rotating a conductive slider. As a result, it is possible to obtain excitation electric power having a desired phase difference between the distributed phase shifters (30a, 30b, 30c) and also a predetermined phase difference between outputs of each of the distributed phase shifters (30a, 30b, 30c). However, the multibranched distributed phase shifter illustrated in Figure 8 requires the linkage mechanism - 5 (or gear mechanism) 32 in addition to the distributer 31, so that the structure is complicated, the area is large, and moreover, the number of parts is large, which leads to a problem of high cost. The present invention has been made in order to solve the above-mentioned problem of the conventional technology, and therefore has an object to provide a multibranched distributed phase shifter in which the structure is simple, the area is small, and moreover, the cost can be reduced. The above-mentioned and other objects and novel features of the present invention will be clarified by the description given herein and the accompanying drawings. Means for Solving the Problem [0005] The outline of the representative aspects of the invention disclosed in the present application is briefly described as follows. In order to achieve the above-mentioned object, the present invention provides a multibranched distributed phase shifter including: a dielectro-substrate; first to nth output-side strip conductors which are formed on the dielectric substrate, each have a circular arc shape, and each have both ends serving as output ends, the circular arc shape constituting, when (n 2) circular rings which - 6 are concentrically disposed with respect to an arbitrary point as a center are assumed and first to nth circular rings are assigned thereto in order from a circular ring having a smallest radius of the (n 2) circular rings, a part of corresponding one of the first to nth circular rings; an input-side strip conductor which is formed on the dielectric substrate and has one end positioned at the center of the circular rings; first to nth sliding portions which each have a circular arc shape constituting a part of corresponding one of the first to nth circular rings and are shorter than the output-side strip conductors; and an arm portion which includes the first to nth sliding portions and can rotate around the center of the circular rings, in which an insulator is interposed between the first to nth output-side strip conductors and the first to nth sliding portions each having the circular arc shape, and an insulator is interposed between the input-side strip conductor and the arm portion. In addition, according to the present invention, a characteristic impedance of a part of the arm portion reaching each of the first to nth sliding portions is changed, to thereby change an amplitude ratio of a high frequency signal outputted from each of the first to nth output-side strip conductors. In addition, according to the present invention, the arm portion includes: a ring-shaped conductor at one end -7 thereof on a central side of the circular rings, the ring-shaped conductor being formed so as to surround the center of the circular rings; and a first line and a second line which each have one end connected to the ring-shaped conductor and another end at which the first to nth sliding portions each having the circular arc shape are provided. Advantage of the Invention [0006] The effect obtained by the representative aspects of the invention disclosed in the present application is briefly described as follows. According to the present invention, it is possible to provide the multibranched distributed phase shifter in which the structure is simple, the area is small, and moreover, the cost can be reduced. Brief Description of the Drawings [0007] Figure 1 is a plan view illustrating a schematic structure of a multibranched distributed phase shifter according to an embodiment of the present invention; Figure 2 is a view for describing a relation between an arm portion and an input-side strip conductor of the multibranched distributed phase shifter according to the embodiment of the present invention; Figure 3 is a view for describing a relation between a sliding portion, and a first line and a second line of the distributed phase shifter according to the embodiment of the present invention; Figure 4 is a perspective view illustrating a schematic structure of a modified example of the multibranched distributed phase shifter according to the embodiment of the present invention; Figure 5 is a graph showing simulation results of a distribution loss characteristic and a return loss characteristic of an example of the multibranched distributed phase shifter according to the embodiment of the present invention; Figure 6 is a perspective view illustrating a schematic structure of a modified example of the multibranched distributed phase shifter according to the embodiment of the present invention; Figure 7 is a perspective view illustrating an example of a conventional distributed phase shifter; and Figure 8 is a plan view illustrating an example of a conventional multibranched distributed phase shifter. Description of Symbols [0008] 2, 2a, 2b, 2coutput-side strip conductor 3 input-side strip conductor 3a, 6a ring-shaped conductor - 9 4a, 4b high-dielectric insulator 5a, 5b, 7a, 7b, 7c sliding portion 5c arm portion 6b first line 6c second line 10 dielectric substrate 11 rotating substrate 30a, 30b, 30cdistributed phase shifter 31 three-branched distributer 32 linkage mechanism (or gear mechanism) Best Mode for Carrying Out the Invention [0009] Hereinafter, an embodiment of the present invention is described in detail with reference to the drawings. It should be noted that, throughout the drawings for describing the embodiment, components having the same function are denoted by the same symbols, and repetitive description thereof is omitted. Figure 1 is a plan view .illustrating a schematic structure of a multibranched distributed phase shifter according to the embodiment of the present invention. In the multibranched distributed phase shifter according to the present embodiment, three output-side strip conductors (2a, 2b, 2c) each having a partially opened circular arc shape and an input-side strip conductor 3 are disposed on a dielectric substrate 10. A - 10 grounding conductor (not shown) is formed on a rear surface of the dielectric substrate 10. Here, when three circular rings which are concentrically disposed with respect to an arbitrary point as a center (a central axis is denoted by P) are assumed, first to third circular rings are assigned thereto in order from the circular ring having the smallest diameter of the three circular rings. In this case, the output-side strip conductor (2a) constitutes a part of the first circular ring, the output-side strip conductor (2b) constitutes a part of the second circular ring, the output-side strip conductor (2c) constitutes a part of the third circular ring, and both ends of each of the output-side strip conductors (2a, 2b, 2c) serve as output ends (here, six output ends). In addition, sliding portions (7a, 7b, 7c) are provided on the output-side strip conductors (2a, 2b, 2c), respectively. The sliding portions (7a, 7b, 7c) slide on the output-side strip conductors (2a, 2b, 2c), respectively, and a length of a circular arc shape of each of the sliding portions (7a, 7b, 7c) is set to be equal to or smaller than Xo/2 (ko is a designed center frequency). [0010] An arm portion, which is formed of a first line 6b and a second line 6c, allows each of the sliding portions - 11 (7a, 7b, 7c) to rotate around the center (the central axis P in Figure 1) of the circular ring. As illustrated in Figure 2, the arm portion includes, at one end thereof on a central side of the circular ring, a ring-shaped conductor 6a which is formed so as to surround the center of the circular ring. In addition, the input-side strip conductor 3 also includes a ring shaped conductor 3a which is formed so as to surround the center of the circular ring. An insulator 4a is interposed between the ring-shaped conductor 3a of the input-side strip conductor 3 and the ring-shaped conductor 6a of the arm portion. In addition, an insulator 4b is interposed between the sliding portions (7a, 7b, 7c) and the output-side strip conductors (2a, 2b, 2c). Here, the insulators (4a, 4b) are formed of, for example, an insulating material of a general high-frequency electric cable, such as polyethylene fluoride. In addition, as illustrated in Figure 3, the first line 6b and the second line 6c are connected to the sliding portions (7a, 7b, 7c) at positions the same distance away (Tl = T2) from the center of each of the sliding portions (7a, 7b, 7c). [0011] Similarly in the distributed phase shifter according to the present embodiment, a high-frequency signal inputted through the input-side strip conductor 3 reaches - 12 the ring-shaped conductor 3a, is coupled to the ring shaped conductor 6a of the arm portion via the high dielectric insulator 4a, passes through the first line 6b and the second line 6c to reach the sliding portions (7a, 7b, 7c), and at the sliding portions (7a, 7b, 7c), is coupled to the output-side strip conductors (2a, 2b, 2c) via the high-dielectric insulator 4b. Then, a rotation axis is inserted into the center (P in Figure 1) of the circular ring, and the arm portion is rotated by rotating the rotation axis, that is, the sliding portions (7a, 7b, 7c) are rotated thereby, which makes it possible to obtain, as excitation electric powers outputted from both the ends of each of the output-side strip conductors (2a, 2b, 2c), excitation electric powers having a desired phase difference between the output-side strip conductors (2a, 2b, 2c) and also a predetermined phase difference between terminals of each of the output-side strip conductors (2a, 2b, 2c). It should be noted that a method of reducing an interval between the ring-shaped conductor 6a of the arm portion and the first sliding portion 7a or a line interval of the first line 6b and the second line 6c between the sliding portions is used, to thereby change characteristic impedances of the first line 6b and the second line 6c reaching each of the sliding portions (7a, 7b, 7c), which makes it possible to change an amplitude - 13 ratio of the high-frequency signal outputted from each of the output-side strip conductors (2a, 2b, 2c). [0012] Figure 4 is a perspective view illustrating a schematic structure of a modified example of the multibranched distributed phase shifter according to the embodiment of the present invention. The multibranched distributed phase shifter illustrated in Figure 4 is different from the multibranched distributed phase shifter illustrated in Figure 1 in that the output-side strip conductor is formed of two output-side strip conductors (2a, 2b). Other structure thereof is the same as that of the multibranched distributed phase shifter illustrated in Figure 1, and hence repetitive detailed description is omitted. Figure 5 is a graph showing simulation results of a distribution loss characteristic and a return loss characteristic of an example of the multibranched distributed phase shifter illustrated in Figure 4. The graph of Figure 5 is a graph showing calculation results when characteristic impedances of the input-side strip conductor 3 and the output-side strip conductors (2a, 2b) are assumed as 50 Q. In addition, in the graph of Figure 5, an abscissa indicates a frequency and has a scale unit of 0.5 GHz, - 14 and an ordinate indicates a loss and has a scale unit of -5 dB. [0013] A curve indicated by A in Figure 5 shows a return loss of an input terminal (01 in Figure 4). In addition, a curve indicated by B in Figure 5 shows a distribution loss from the input terminal (01 in Figure 4) to an output terminal (02 in Figure 4) and a distribution loss from the input terminal (01 in Figure 4) to an output terminal (03 in Figure 4). Further, a curve indicated by C in Figure 5 shows a distribution loss from the input terminal (01 in Figure 4) to an output terminal (04 in Figure 4) and a distribution loss from the input terminal (01 in Figure 4) to an output terminal (05 in Figure 4). It should be noted that the distribution loss from the input terminal (01 in Figure 4) to the output terminal (02 in Figure 4) and the distribution loss from the input terminal (01 in Figure 4) to the output terminal (03 in Figure 4) exhibit substantially the same characteristic, and hence in Figure 5, the curve of B is drawn as one curve. Similarly, the distribution loss from the input terminal (01 in Figure 4) to the output terminal (04 in Figure 4) and the distribution loss from the input terminal (01 in Figure 4) to the output terminal (05 in Figure 4) also exhibit substantially the same - 15 characteristic, and hence in Figure 5, the curve of C is drawn as one curve. As is apparent from the distribution loss characteristics (B, C) shown in Figure 5, in the multibranched distributed phase shifter according to the present embodiment, the distribution losses each have a substantially constant value. [0014] Figure 6 is a perspective view illustrating a schematic structure of a modified example of the multibranched distributed phase shifter according to the embodiment of the present invention. The multibranched distributed phase shifter illustrated in Figure 6 is different from the multibranched distributed phase shifter illustrated in Figure 1 in that the arm portion is formed of a single first line 6b. Other structure thereof is the same as that of the multibranched distributed phase shifter illustrated in Figure 1, and hence repetitive detailed description is omitted. In the case where the arm portion is formed of the first line 6b and the second line 6c as illustrated in Figure 1, it is possible to vary a phase of a high frequency signal in a band wider than in the case where the arm portion is formed of the single first line 6b as illustrated in Figure 6.
- 16 It should be noted that the description is given above of the case where the length of the circular arc shape of each of the sliding portions (7a, 7b, 7c) is Xo/2. It is desirable that, when the length of the circular arc shape of each of the sliding portions (7a, 7b, 7c) is assumed to be Lo, the length of the circular arc shape of each of the sliding portions (7a, 7b, 7c) be (2xko)/5 Lo (3xko)/5, more preferably, (9xXo)/20 Lo (11xXo)/20. Hereinabove, the invention made by the present inventors has specifically been described on the basis of the embodiment. The present invention is not limited to the embodiment, and, as a matter of course, can variously be changed within a range which does not depart from the gist thereof. Industrial Applicability [0015] The present invention relates to a multibranched distributed phase shifter, and more particularly, is effectively applied to a phase circuit which controls a tilt angle of an array antenna and the like.