Slow-wave structure for ridge waveguide

A ridge waveguide having a slow structure, comprising:

• an elongate hollow tube defined by a conductive top wall, a pair of conductive sidewalls, and a conductive bottom wall, the elongate hollow tube having a first characteristic impedance;
• and
• at least one series of ridge segments protruding from the conductive top wall into the hollow tube and extending along an elongate direction of the hollow tube;
• wherein
• each of the ridge segments has a pair of opposing side surfaces parallel to and separate from the conductive sidewalls of the hollow tube and is spaced from the ridge segment adjacent thereto by a distance to result in a second characteristic impedance equal to or larger than the first characteristic impedance.

A method of forming a ridge waveguide filter having a slow-wave structure, comprising:

• a) forming a body portion of an elongate hollow tube, wherein the body portion has an open top;
• b) providing a planar plate having a first surface and a second surface opposite to the first surface;
• c) pressing the first surface to form a ridge recessed from the first surface and protruding from the second surface;
• d) processing the second surface to form a plurality of trenches recessed from a top surface of the ridge;
• and
• e) covering the open top of the body portion by attached the planar plate to the body portion, wherein the second surface of the planar plate faces the body portion.

A method of maintaining a characteristic impedance of a slow-wave structure of a waveguide operating at a certain frequency, comprising:

• a) processing a top wall portion of the waveguide to form a ridge extending into the waveguide along an elongate direction of the waveguide;
• and
• b) processing the ridge into a plurality of ridge segments separated from each other by a gap, so as to effectively introduce a plurality of inductances between the ridge segments, which themselves capacitively couple to a bottom wall of the waveguide, such that the ridge segments and the gaps form a transmission line operating in such a way as to slow a wave propagating down the waveguide;
• and
• c) configuring the gap to increase a characteristic impedance of the transmission line when a wave traveling therethrough.