Near-field patterns of uniplanar compact photonic bandgap (UC-PBG) and non-UCPBG finite-width conductor-backed co-planar waveguides (FW-CBCPWs) are characterized using an electro-optic near-field mapping system. This system is very effective in visually showing the role of the UC-PBG structure in the suppression of microstriplike (MSL) modes in the FW-CBCPWs. © 2005 Wiley Periodicals, Inc.