Filter having switch function and band pass filter

A filter having a switch function which comprises:

• a waveguide structure having a plurality of resonators inside a metal case;
• and
• a plurality of branch waveguides branching from a primary waveguide, said filter selectively transmitting a transmission signal through one of the plurality of branch waveguides,
• wherein each of said resonators is disposed on said plurality of branch waveguides, each of said resonators including i) an inner conductor which is disposed in a space inside said metal case, one end of said inner conductor being grounded to said metal case, and ii) a short-circuiting portion allowing a neighborhood of an open end of the inner conductor to be selectively conducted to said metal case,
• wherein electrical conductivity in a region between the neighborhood of the open end of said inner conductor and said metal case is switched between a conductive state and a non-conductive state, so that a selection from said plurality of branch waveguides is performed, and
• wherein said short-circuiting portion comprises i) a short-circuiting plate connected between the neighborhood of the open end of said inner conductor and said metal case, ii) a short circuit line disposed on the short-circuiting plate to electrically connect the neighborhood of the open end of said inner conductor with said metal case, and iii) an active device disposed on the short circuit line to switch, between said conductive state and said non-conductive state, electrical conductivity in said region between the neighborhood of the open end of said inner conductor and said metal case.