An electromagnetic dispersive delay line (10) includes a dielectric strip (28) as well as a coupler (24, 34, 36, and 38) for launching surface electromagnetic waves into the dielectric strip. The upper surface of the dielectric strip (28) is left exposed to the air in order to provide an interface with a lower-permittivity medium of propagation. This permits a surface-electromagnetic-wave propagation mode. The thickness of the dielectric strip (28) is varied along its length so as to result in a linear relationship of delay to frequency throughout a predetermined frequency range. Preferably, a conductive strip (26) spaced from the dielectric strip extends along the surface-wave propagation path in the region occupied by the evanescent field external to the dielectric strip (28). This conductive strip (26) modifies the phase relationships between the electric and magnetic fields in the evanescent-field region so as to cause some of the power transmission to occur outside of the dielectric strip. This modifies the dispersion curve so as to extend the bandwidth of significant dispersion.