Abstract: A microstrip transmission line comprising a dielectric substrate including a series of periodic sinusoidal undulation portions defining spaced apart peaks and troughs, where a distance between the peaks and troughs defines a period of the microstrip line, and where each peak defines a maximum height of the substrate and each trough defines a minimum height of the substrate. The transmission line further includes a conductive strip formed to a surface of the substrate so that the conductive strip follows the undulation portions. The conductive strip includes a modulation portion in a width direction of the conductive strip perpendicular to a signal propagation direction along the strip, where the modulation portion includes a minimum width portion provided at each peak and a maximum width portion provided at each trough so that a variation of a ratio between the width of the conductive strip and the height of the substrate is maximized.