A low-profile self-triplexed slot antenna is proposed for multiple system integrations. The antenna comprises of hybrid substrate integrated waveguide (SIW) cavity (a combination of a half-mode circular and half-mode rectangular SIW), radiating slot, and feeding network. A slot is imprinted on the upper metal-layer of the SIW which splits the cavity into three radiating sections. It offers tri-frequency bands when each section is excited separately. By finely tuning the antenna dimensions, it produces three frequency-bands around 5.57, 7.17, and 7.65 GHz simultaneously utilizes a single slot with maintaining the intrinsic input-port isolation better than 20 dB. This property helps to introduce the self-triplexing phenomenon. Compared with the conventional multiband antennas that use an extra circuitry to ensure the port isolations, this design preserves compactness and easy to integrate with planar circuits Moreover, the proposed antenna is fabricated and the measured results mutually agreed with the simulated counterparts. The proposed design can be a feasible option for mobile transceiver applications. © 2018 Wiley Periodicals, Inc.