An apparatus comprising: a dielectric structure having a circular-shaped cross section and configured for placement in a waveguide having a circular shape, wherein the dielectric structure and the waveguide have an axis; and a plurality (306, 308) of conductive segments located within the dielectric structure and having centers that are substantially aligned with the axis, the plurality of conductive segments comprising: a first ring-shaped conductive segment having a shape selected from the group consisting of a cylinder, circular, octagon and hexagon, a first gap, and a second gap, wherein the first gap is opposite of the second gap; and a second ring-shaped conductive segment having a shape selected from the group consisting of a cylinder, circular, octagon and hexagon, a third gap, and a fourth gap, wherein the third gap is opposite of the fourth gap, wherein the positioning of the first conductive segment and the second conductive segment within the dielectric structure is radially symmetric, a distance separating the first conductive segment from the second conductive segment, and each of the plurality of conductive segments is configured to reduce a passing of a number of frequencies of electromagnetic signals traveling through the dielectric structure. a dielectric structure having a circular-shaped cross section and configured for placement in a waveguide having a circular shape, wherein the dielectric structure and the waveguide have an axis; and a plurality (306, 308) of conductive segments located within the dielectric structure and having centers that are substantially aligned with the axis, the plurality of conductive segments comprising: a first ring-shaped conductive segment having a shape selected from the group consisting of a cylinder, circular, octagon and hexagon, a first gap, and a second gap, wherein the first gap is opposite of the second gap; and a second ring-shaped conductive segment having a shape selected from the group consisting of a cylinder, circular, octagon and hexagon, a third gap, and a fourth gap, wherein the third gap is opposite of the fourth gap, wherein the positioning of the first conductive segment and the second conductive segment within the dielectric structure is radially symmetric, a distance separating the first conductive segment from the second conductive segment, and each of the plurality of conductive segments is configured to reduce a passing of a number of frequencies of electromagnetic signals traveling through the dielectric structure. a first ring-shaped conductive segment having a shape selected from the group consisting of a cylinder, circular, octagon and hexagon, a first gap, and a second gap, wherein the first gap is opposite of the second gap; and a shape selected from the group consisting of a cylinder, circular, octagon and hexagon, a first gap, and a second gap, wherein the first gap is opposite of the second gap; and a second ring-shaped conductive segment having a shape selected from the group consisting of a cylinder, circular, octagon and hexagon, a third gap, and a fourth gap, wherein the third gap is opposite of the fourth gap, a shape selected from the group consisting of a cylinder, circular, octagon and hexagon, a third gap, and a fourth gap, wherein the third gap is opposite of the fourth gap, wherein the positioning of the first conductive segment and the second conductive segment within the dielectric structure is radially symmetric, a distance separating the first conductive segment from the second conductive segment, and each of the plurality of conductive segments is configured to reduce a passing of a number of frequencies of electromagnetic signals traveling through the dielectric structure.