Abstract: A temperature stable bandpass folded filter for microwave radio communication, made from standard waveguide sections. Two waveguide sections are divided into cavities using metal plates made from a temperature stable material, to construct the filter. The sections are connected juxtaposed and the cavities of each section are coupled through holes in the coupled broadwalls of the section. Low insertion loss and very good temperature stability is obtained with the use of copper clad INVAR waveguide material. The method of constructing the temperature stable folded waveguide filter of reduced length is also disclosed.