This paper introduces a novel triple-band, dual-polarized antenna triplexer, specifically designed for applications in Wireless Local Area Network (WLAN), Industrial Scientific and Medical (ISM) and IoT frequency bands, operating at 9.96 GHz, 10.85 GHz and 13.73 GHz. Utilizing Substrate Integrated Waveguide (SIW) technology, the design achieves compactness and enhanced performance while addressing the stringent requirements of off-body communication systems. The antenna comprises two SIW cavities a rectangular cavity and an embedded diamond-shaped cavity, both sharing a common aperture. These cavities incorporate diamond-ring-shaped slots that serve as radiating elements, excited using distinct methods. The rectangular cavity is excited via a microstrip feedline to achieve linear polarization at 9.96 GHz, while the diamond cavity employs a coaxial probe to generate circular polarization at 10.85 and 13.75 GHz. The design achieves superior decoupling, with isolation levels below -23 dB, high gain values of up to 8.6 dB in free space and 8.4 dB on-body, and low Specific Absorption Rate (SAR) values under 0.245 W/Kg. These features make it a compact, efficient, and safe solution for wearable and off-body communication systems.