Millimeter waveband filter and method of varying resonant frequency thereof

A millimeter wave band filter comprising:

• a transmission line that is formed by a plurality of waveguides and into which electromagnetic waves with a predetermined frequency range of a millimeter wave band are incident and which propagates the corresponding incident electromagnetic waves from one end to the other end in a TE10 mode;
• and
• a pair of radio-wave half mirrors that are disposed opposite each other with a space interposed therebetween so as to block the inside of the transmission line and have planar shapes and a characteristic of transmitting a part of the electromagnetic waves with the predetermined frequency range and reflecting another part thereof,
• wherein in the electromagnetic waves incident from a side of the one end of the transmission line, a frequency component centered on a resonant frequency of a resonator, which is formed between the pair of radio-wave half mirrors, is selectively output from the other end of the transmission line,
• wherein in order to change an electrical length between the pair of radio-wave half mirrors, at least one of space-varying means, which varies a space between the pair of radio-wave half mirrors, and permittivity-varying means, which varies permittivity of a dielectric material inserted between the pair of radio-wave half mirrors, is provided,
• wherein the transmission line is formed of
• a first waveguide which has an internal rectangular size capable of propagating the electromagnetic waves with the predetermined frequency range from one end of the first waveguide to the other end of the first waveguide in the TE10 mode, and
• a second waveguide which has an internal rectangular size capable of propagating the electromagnetic waves with the predetermined frequency range from one end of the second waveguide to the other end of the second waveguide in the TE10 mode and is connected to the first waveguide so as to be circumscribed around a portion of the one end of the first waveguide,
• wherein one of the pair of radio-wave half mirrors is mounted on the first waveguide, and the other is mounted on the second waveguide, and
• wherein the space-varying means varies the space between the pair of radio-wave half mirrors by telescopically sliding the first waveguide and the second waveguide in a state where the waveguides are connected.