Microwave waveguide filter having rectangular cavities, and method for its fabrication

A microwave waveguide filter comprising

• a main-line cavity structure comprising a group of at least two rectangular main-line cavities arrayed along a main propagation path and including a first main-line cavity and a second main-line cavity, wherein each main-line cavity includes a sidewall, and wherein each pair of adjacent main-line cavities has a common transverse wall therebetween perpendicular to the main propagation path and a main-line aperture in the common transverse wall;
• and
• a rectangular first feedback cavity in microwave communication with each of the first main-line cavity and the second main-line cavity through the respective sidewall of the first main-line cavity and the second main-line cavity, there being
• a first-cavity feedback aperture between the first feedback cavity and the first main-line cavity, and
• a second-cavity feedback aperture between the first feedback cavity and the second main-line cavity,
• wherein each of the main-line cavities and the first feedback cavity have a base wall that lies in a common filter plane, and
• wherein a first-cavity sidewall of the first main-line cavity and a second-cavity sidewall of the second main-line cavity are parallel and both of a first-sidewall length, and the first feedback cavity has a length measured parallel to the first-cavity sidewall selected from the group consisting of about the first-sidewall length and about twice the first-sidewall length.

A method for fabricating a microwave waveguide filter, comprising the steps of

• providing a single filter block of material;
• and
• fabricating the single filter block of material to have therein
• a main-line cavity structure comprising a group of at least two rectangular main-line cavities arrayed along a main propagation path and including a first main-line cavity and a second main-line cavity, wherein each main-line cavity includes a sidewall, and wherein each pair of adjacent main-line cavities has a common transverse wall therebetween transverse to the main propagation path and a main-line aperture in the common transverse wall, and
• a rectangular first feedback cavity in microwave communication with each of the first main-line cavity and the second main-line cavity through the respective sidewall of the first main-line cavity and the second main-line cavity, there being
• a first-cavity feedback aperture between the first feedback cavity and the first main-line cavity, and
• a second-cavity feedback aperture between the first feedback cavity and the second main-line cavity.