An apparatus (100) is provided for causing a phase-shift in reflected signals (R) that are a reflection of surface-traveling wave signals (S) of a select signal frequency. The apparatus (100) comprises a conductive strip (102) having a plurality of slots (104) therein alternatingly arranged orthogonal to each other, each slot (104) having an effective length (L) that is a fraction between 9/16 and 7/8 of the wavelength associated with the select signal frequency, and a plurality of conductive enclosures (106) respectively disposed under each of the plurality of slots (104). Each of the conductive enclosure (106) have a width and length sufficient to enclose a respective corresponding slot (104), and a depth that is a fraction of between 1/8 and 3/8 of the wavelength associated with the select signal frequency when transmitted in the dielectric material (110). The plurality of slots (104) and plurality of conductive enclosures (106) cause a phase-shift in the range of 150 to 210 degrees in reflected signals (R) that are a reflection of surface-traveling wave signals at the select signal frequency which impinge the apparatus (100).