Dual-mode cavity for waveguide bandpass filter

A dual-mode cavity for a waveguide bandpass filter, said dual-mode cavity consisting essentially of:

• a first end waveguide section having a first iris lying in a polarization plane of one mode at an end of said first end waveguide section and shaped to support two modes including said one mode and a mode having a polarization plane perpendicular to said one mode, said first iris enabling coupling of said first end waveguide section to an adjoining waveguide;
• an intermediate waveguide section coaxial with and aligned with said first end waveguide section at an end thereof opposite said end at which said first iris is provided, said intermediate waveguide section being of rectangular section with sides tilted at an angle .beta. greater than 0.degree. and less than 90.degree. with respect to said polarization plane of said one mode and of said first iris;
• and
• a second end waveguide section coaxial and aligned with said intermediate waveguide section and adjacent said second end waveguide section opposite said first end waveguide section, said second end waveguide section having a second iris lying in said polarization plane of said one mode and of said first iris at an end of said second end waveguide section opposite said intermediate waveguide section, said second end waveguide section being shaped to support two modes, said second iris enabling coupling of said first end waveguide section to an adjoining waveguide, said wave-guide sections forming a single adjustment-screw-free cavity between said irises.