A novel microwave periodic structure—the ladder microstrip line—is proposed. A preliminary investigation has shown that the novel transmission line has a lower phase velocity as compared with the conventional microstrip line even when they occupy the exact same surface area and have the same outline contour. This makes it attractive for monolithic microwave integrated circuits (MMIC) and microwave superconductive circuits, where size reduction is of primary importance. © 1995 John Wiley & Sons, Inc.