1. Field of the Invention
The present invention relates to a phase shifter, in more particular, to a transmission line phase shifter.
2. Related Art
As a phase shifter used for beam control or phase modulation of a phased array antenna, a transmission line phase shifter has been conventionally used. For example, Japanese Patent Laid-Open No. 5-14004 discloses a phase adjustment circuit, comprising a first substrate, a U-shaped pattern formed on the first substrate, a second substrate, and first and second patterns formed on the second substrate, each of the first and second patterns having a part provided in parallel with each other, in which parallel parts in the U-shaped pattern are overlapped with the parallel patterns of the first and second patterns to contact to each other, and the first and second substrates are configured to be continuously movable.
According to the phase adjustment circuit disclosed by Japanese Patent Laid-Open No. 5-14004, a length of the U-shaped pattern is determined as a length of an integral multiplication of a ½ wavelength of a signal to be transmitted, so that the first and second substrates are continuously movable in a state where the respective parallel parts in the U-shaped pattern are overlapped with and in contact with the parallel patterns of the first and second patterns. According to this structure, in the phase adjustment circuit of Japanese Patent Laid-Open No. 5-14004, it is possible to continuously change a transmission path length of the signal, so as to continuously change a signal phase while confirming circuit characteristics.
In addition, Japanese Patent Laid-Open No. 2001-237605 discloses a phase shifter, comprising a first dielectric substrate, a plurality of input side microstrip lines and a plurality of output side microstrip lines provided on the first dielectric substrate, a second dielectric substrate which is movable with respect to the first dielectric substrate, a plurality of coupling microstrip lines provided on the second dielectric substrate, and an insulator provided between the first dielectric substrate and the second dielectric substrate, in which a plurality of the input side microstrip lines and a plurality of the output side microstrip lines are overlapped with a plurality of the coupling microstrip lines respectively to be facing to each other.
According to the phase shifter disclosed by Japanese Patent Laid-Open No. 2001-237605, it is possible to change lengths of overlapped portions, in which a plurality of the input side microstrip lines and a plurality of the output side microstrip lines are overlapped with a plurality of the coupling microstrip lines via the insulator, simultaneously with a constant proportion. According to this structure, it is possible to change phases of the signals transmitted through the input side microstrip lines the respective coupling microstrip lines at the same time. For example, the phase shifter disclosed by Japanese Patent Laid-Open No. 2001-237605 may be installed in an array antenna used for an antenna for a portable telephone base station as an apparatus for changing a directivity orientation.
However, in the phase adjustment circuit disclosed by Japanese Patent Laid-Open No. 5-14004, a total length of the U-shaped pattern is previously set (fixed) as the length of the integral multiplication of the ½ wavelength of the signal to be transmitted.
In the phase shifter disclosed by Japanese Patent Laid-Open No. 2001-237605, a total length of a plurality of the coupling microstrip lines is previously set (fixed) as the length of the integral multiplication of the ½ wavelength of the wavelength of the signal to be transmitted respectively.
Therefore, in both of the phase adjustment circuit disclosed by Japanese Patent Laid-Open No. 5-14004 and the phase shifter disclosed by Japanese Patent Laid-Open No. 2001-237605, it is difficult to improve transmission characteristics and return loss characteristics when a signal at a frequency other than a frequency of the signal that is supposed to be used when designing the phase shifter.