- 1 DESCRIPTION DISTRIBUTED PHASE SHIFTER Technical Field (0001] The present invention relates to a distributed phase shifter, and more particularly, to a 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. Figure 6 is a perspective view illustrating an example of a conventional distributed phase shifter.
- 2 In the distributed phase shifter illustrated in Figure 6, 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 on a central side (a central axis is indicated by A) of the circular ring is positioned at the center of the circular ring of the output-side strip conductor 2. In addition, a conductive slider 5 is provided, and one end of an arm portion 5c of the conductive slider 5 on the central side of the circular ring is positioned at the center of the circular ring. In addition, the conductive slider 5 includes sliding portions (5a, 5b) which slide on the output-side strip conductor 2, and the lengths thereof are X/4 to the left and to the right, respectively. In addition, both ends of the output-side strip conductor 2 serve as output ends. 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 of the conductive slider 5 and the input-side strip conductor 3 and between the sliding portions (5a, 5b) of the conductive slider 5 and the output-side strip conductor 2. [0003] -3 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 [0004] In the distributed phase shifter illustrated in Figure 6 described above, a high-frequency signal inputted through the input-side strip conductor 3 is coupled to the arm portion 5c of the conductive slider 5 via the high-dielectric insulator 4b, and passes through the arm portion 5c to reach the left and right sliding portions (5a, Sb) 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 4a. Then, when the conductive slider 5 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. However, the above-mentioned distributed phase shifter has a problem that a bandwidth of the high- 4 frequency signal in which a phase can be varied (delayed) is narrow. Object of the Invention It is the object of the present invention to substantially overcome or at least ameliorate one or more of the foregoing disadvantages. Summary The present invention provides a distributed phase shifter including: a dielectric substrate; an output-side strip conductor which is formed on the dielectric substrate, has a circular arc shape, and has both ends serving as output ends, the circular arc shape constituting, when a circular ring having a center thereof at an arbitrary point is assumed, a part of the circular ring; an input side strip conductor which is formed on the dielectric - 5 substrate and has one end positioned at the center of the circular ring; a sliding portion which has a circular arc shape constituting a part of the circular ring and is shorter than the output-side strip conductor; and an arm portion which includes the sliding portion at a leading end thereof and can rotate around the center of the circular ring, in which: an insulator is interposed between the output-side strip conductor and the sliding portion having the circular arc shape, and an insulator is interposed between the input-side strip conductor and the arm portion; the input-side strip conductor includes a ring-shaped conductor at one end thereof on a central side of the circular ring, the ring-shaped conductor being formed so as to surround the center of the circular ring; the arm portion includes a ring-shaped conductor at one end thereof on the central side of the circular ring, the ring-shaped conductor being formed so as to surround the center of the circular ring; and a first line and a second line which each have one end connected to the sliding portion and another end electrically connected to the ring-shaped conductor of the arm portion; and the ring-shaped conductor of the input-side strip conductor and the ring-shaped conductor of the arm portion are opposed to each other via the insulator. [0006] - 6 In addition, according to the present invention, the arm portion further includes a third line which has another end connected to the ring-shaped conductor of the arm portion, the another end of the first line and the another end of the second line are connected to one end of the third line, and the one end of the first line and the one end of the second line are connected to the sliding portion at positions the same distance away from a center of the sliding portion. Advantage of the Invention [0007] The effect obtained by the representative aspects of the invention disclosed in the present application is briefly described as follows. According to the distributed phase shifter of the present invention, it is possible to vary the phase of the high-frequency signal in the bandwidth wider than ever before. Brief Description of the Drawings [0008] Figure 1 is a perspective view illustrating a schematic structure of a 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 -7 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 graph showing simulation results of a distribution loss characteristic (B) and a return loss characteristic (A) of an example of the distributed phase shifter according to the embodiment of the present invention; Figure 5 is a perspective view illustrating a schematic structure of a modified example of the distributed phase shifter according to the embodiment of the present invention; Figure 6 is a perspective view illustrating an example of a conventional distributed phase shifter; and Figure 7 is a graph showing simulation results of a distribution loss characteristic (B) and a return loss characteristic (A) of the example of the conventional distributed phase shifter. Description of Symbols [0009] 2 output-side strip conductor 3 input-side strip conductor 3d, 6d ring-shaped conductor -8 4a, 4b insulator 5 conductive slider 5a, 5b, 7 sliding portion 5c arm portion 6a, 6b, 6c line 10 dielectric substrate 10s grounding conductor Best Mode for Carrying Out the Invention [0010] 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 perspective view illustrating a schematic structure of a distributed phase shifter according to the embodiment of the present invention. In the distributed phase shifter according to the present embodiment, an output-side strip conductor 2 having a partially opened circular arc shape and an input-side strip conductor 3 are disposed on a dielectric substrate 10. A grounding conductor 10s is formed on a rear surface of the dielectric substrate 10. Here, when a circular ring having a radius R with respect to an arbitrary point as a center (a central axis - 9 P in Figure 1) is assumed, the output-side strip conductor 2 constitutes a part of the circular ring, and both ends of the output-side strip conductor 2 serve as output ends. In addition, a sliding portion 7 which slides on the output-side strip conductor 2 is provided on the output side strip conductor 2. Here, a length of a circular arc shape of the sliding portion 7 is set to Xo/2 (Xo is a designed center frequency). An arm portion, which is formed of a first line 6a and a second line 6b, allows the sliding portion 7 to rotate around the center (the central axis P in Figure 1) of the circular ring. [0011] 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 6d 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 3d which is formed so as to surround the center of the circular ring. An insulator 4b is interposed between the ring-shaped conductor 3d of the input-side strip conductor 3 and the ring-shaped conductor 6a of the arm portion. In addition, an insulator 4a is interposed between the sliding portion 7 and the output-side strip conductor 2. Here, the insulators (4a, 4b) are formed of, for - 10 example, an insulating material of a general high frequency electric cable, such as polyethylene fluoride. It should be noted that, in Figure 2, only the first line 6a is illustrated and the second line 6b is omitted. In addition, as illustrated in Figure 3, the first line 6a and the second line 6b are connected to the sliding portion 7 at positions the same distance away (Tl = T2) from the center of the sliding portion 7. Similarly in the distributed phase shifter according to the present embodiment, a high-frequency signal inputted through the input-side strip conductor 3 reaches the ring-shaped conductor 3d, is coupled to the ring shaped conductor 6d of the arm portion via the high dielectric insulator 4b, passes through the first line 6a and the second line 6b to reach the sliding portion 7, and at the sliding portion 7, is coupled to the output side strip conductor 2 via the high-dielectric insulator 4a. Then, in the present embodiment, a rotation axis is inserted into the center (P in Figure 2) of the circular ring, and the sliding portion 7 is rotated by rotating the rotation axis, which makes it possible to provide a predetermined phase difference between excitation electric powers outputted from both the ends of the output-side strip conductor 2. [0012] - 11 Figure 4 is a graph showing simulation results of a distribution loss characteristic (B) and a return loss characteristic (A) of an example of the distributed phase shifter according to the present embodiment. Figure 7 is a graph showing simulation results of a distribution loss characteristic (B) and a return loss characteristic (A) of an example of a conventional distributed phase shifter. The graph of Figure 4 is a graph showing calculation results when characteristic impedances of the input-side strip conductor 3, the first line 6a, the second line 6b, and the output-side strip conductor 2 are assumed as 50 In addition, the graph of Figure 7 is a graph showing calculation results when characteristic impedances of the input-side strip conductor 3, the arm portion 5c of the conductive slider 5, and the output side strip conductor 2 are assumed as 50 Q and an impedance matching circuit is added to a part of the arm portion 5c of the conductive slider 5. Figure 4 and Figure 7 shows, in the case where the designed center frequency is 2 GHz, the return loss characteristic (A) when a high-frequency signal is applied to an input terminal connected to the input-side strip conductor 3, and the distribution loss characteristic (B) when the high-frequency signal is - 12 distributed from the arm portion to both the ends of the output-side strip conductor 2. In addition, in the graphs of Figure 4 and Figure 7, an abscissa indicates a frequency and has a scale unit of 0.1 GHz, and an ordinate indicates a loss and has a scale unit of -5 dB. [0013] As is apparent from the return loss characteristic (A) shown in Figure 7, in the conventional distributed phase shifter, the band in which the loss is equal to or smaller than -15 dB is approximately 0.6 GHz (~ 2.3 GHz 1.7 GHz). In contrast, as is apparent from the return loss characteristic (A) shown in Figure 4, in the distributed phase shifter according to the present embodiment, the band in which the loss is equal to or smaller than -15 dB is equal to or larger than 1.8 GHz (~ 3.0 GHz - 1.2 GHz). As described above, the distributed phase shifter according to the present embodiment is capable of varying the phase of the high-frequency signal in a band wider than the conventional distributed phase shifter. In addition, as is apparent from the distribution loss characteristic (A) shown in Figure 7, in the conventional distributed phase shifter, the distribution loss becomes larger as being farther from the designed center frequency (in Figure 7, 2 GHz). On the other hand, as is apparent from the distribution loss characteristic - 13 (B) shown in Figure 4, in the distributed phase shifter according to the present embodiment, the distribution loss has a substantially constant value. [0014] Figure 5 is a perspective view illustrating a schematic structure of a modified example of the distributed phase shifter according to the embodiment of the present invention. The distributed phase shifter illustrated in Figure 5 is different from the distributed phase shifter illustrated in Figure 1 in that the arm portion includes the ring-shaped conductor 6d, a third line 6c connected to the ring-shaped conductor 6d, the first line 6a, and the second line 6b. Even when the third line 6c is interposed between the first line 6a and the second line 6b, and the ring shaped conductor 6d as illustrated in Figure 5, it is possible to obtain the similar effect to that of Figure 1. It should be noted that the description is given above of the case where the length of the circular arc shape of the sliding portion 7 is ko/2. It is desirable that, when the length of the circular arc shape of the sliding portion 7 is assumed to be Lo, the length of the circular arc shape of the sliding portion 7 be (2xko)/5 Lo (3xko)/5, more preferably, (9xko)/20 5 Lo (llxXo)/20.
- 14 As has been described in the above, according to the distributed phase shifter of the present embodiment, it is possible to vary the phase of the high-frequency signal in a band wider than the conventional distributed phase shifter. In addition, the rotation axis is inserted into the center (P in Figure 2) of the circular ring, and the sliding portion 7 can be rotated by rotating the rotation axis, which makes it possible to simplify the structure for rotating the sliding portion 7. 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 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.