In this article, a fully 3-D printed embedded passive harmonic sensor tag with improved read range and better clutter rejection is presented for detecting assets located underground. The sensor tag receives the query signal from a 3-D printed Vivaldi antenna at the fundamental frequency (f 0 ) and radiates back to the interrogator at the second harmonic frequency (2f 0 ). The sensor tag consists of a linearly polarized double slot antenna that operates at both the fundamental as well as the second harmonic frequency. Utilizing the capabilities of 3-D printing, a nonlinear diode is embedded onto the substrate and coupled to the antenna for generating the higher order harmonics is designed. The 3-D printed tag is compatible with direct printing onto the buried assets, such as plastic pipelines, as markers for localization. The polarization of the antenna is used for identifying the location and the direction of the pipeline. The sensor tag has higher signal-to-noise ratio and can be readily interrogated with any hand-held readers from above the ground.