Patent ID: 9627733
Date: 2017-04-18
CPC Classifications: H01P

Claim:
1. A millimeter waveband filter comprising: a first waveguide which has a transmission line to allow electromagnetic waves in a predetermined frequency range of a millimeter waveband to propagate in a TE10 mode; a second waveguide which has a transmission line to allow the electromagnetic waves in the predetermined frequency range to propagate in the TE10 mode and is connected to the first waveguide in a state where at least one end portion of the second waveguide is inserted into the first waveguide; a pair of flat electric wave half mirrors which have characteristics to transmit a part of the electromagnetic waves in the predetermined frequency range and to reflect a part of the electromagnetic waves and are arranged to face each other at an interval in a state where the transmission line of the first waveguide and the transmission line of the second waveguide are blocked; and variable interval means for relatively moving the first waveguide and the second waveguide in a longitudinal direction of the transmission line in a state connected together to change the interval between the pair of electric wave half mirrors, wherein frequency components centering on a resonance frequency of a resonator formed between the pair of electric wave half mirrors are selectively transmitted, and a groove which has a length along the longitudinal direction of the transmission line corresponding to a ¼ wavelength of electromagnetic waves to be a leakage prevention target is formed on the outside of the second waveguide facing the inside of the first waveguide, and leakage of the electromagnetic waves from the interval between the outside of the second waveguide and the inside of the first waveguide is prevented by the groove, wherein the pair of electric wave half mirrors respectively have rectangular plates which have a predetermined thickness and reflect electromagnetic waves propagating through the transmission line, and slits which are formed in central portions of the plates along a long side direction of the plates and transmit a part of the electromagnetic waves propagating through the transmission line, the slits are of a ridge type in which a central portion has a height smaller than both side portions, and the thickness of the plates and the height and width of each of both side portions and the central portion of the slits are set such that transmittance to the electromagnetic waves propagating through the transmission line becomes flat in the predetermined frequency range, the predetermined frequency range is 75 to 110 GHz, and the transmittance of the electric wave half mirrors is about −20 dB.