Abstract: A thin plate member of electrically conductive material is disposed within a rectangular waveguide. The plate member has the thickness less than one tenth of the wavelength of a frequency to be suppressed, an opening whose maximum dimension is less than the length of the short side of the waveguide, and a gap formed between two opposite projections extending from the edge of the opening. The plate member is arranged, in said rectangular waveguide, parallel with the electric field and perpendicular to the magnetic field.

Abstract: A microwave oscillator has a cavity resonator enclosed by conducting walls and containing a microwave oscillator element therein. A biasing device applies a bias voltage to the microwave oscillator element to generate a microwave signal. A microwave coupling circuit takes the microwave signal from the resonator in a direction which is perpendicular to the direction of the propagation of the microwave signal in the resonator and applies the taken-out microwave signal to an output means. The microwave coupling circuit is located at a position corresponding to one of the nodes of the electric field appearing in the cavity. The coupling circuit also is preferably at a position on the resonator wall which is a quarter wavelength away from the oscillator element. The undesired signals can be effectively suppressed in the output means, by -44 dB, or more, without making use of a filter.

Abstract: In the preparation of diaminomaleonitrile by polymerization of hydrogen cyanide, the improvement which comprises employing, as a reaction solvent, at least one mononitrile compound selected from the group consisting of saturated aliphatic mononitriles containing 2 to 4 carbon atoms, methacrylonitrile and aromatic mononitriles.