In this paper, a novel concept to implement millimeterwave substrate integrated waveguide-based circuits for chipless identification application has been demonstrated. The proposed design utilizes a pair of compact half mode SIW cavity to encode the interrogating signal and resend the signal through the open-end aperture of the cavity. Thus, the encoding resonator itself has been utilized as radiator of the interrogating signal which helps to improve the compactness of the design. The complete design has been realized in K band making physical size of the circuit very small which makes it attractive for practical application. © 2019 URSI. All rights reserved.