In this paper, a substrate integrated waveguide (SIW) based self-triplexing antenna (STA) with non-linear replicated hybrid slot (NLR-HS) is presented. To the author's best knowledge, the concept of NLR is the first of its kind in the literature used for obtaining self-triplexed operation. Initially, the SIW cavity is loaded by a hexagonal slot merged with two rectangular transverse slots that together produce two distinct resonances around 5.23 and 7.50 GHz. The variation in resonant frequencies of both lower and upper frequency bands can be modelled by applying NLR on the hexagonal slot. To achieve the self-triplexing operation, a coaxial probe-fed parasitic hexagonal patch is placed concentrically inside the hexagonal slot. The third resonance is centered around 10.82 GHz and can be modelled with the help of the gap between the hexagonal slot and parasitic patch.To validate the proposed idea, the design is fabricated and experimentally tested. Moreover, the antenna shows a front-to-back ratio (FTBR) better than 25 dB, average isolation of 43 dB and measured gain (efficiency) values of 7.33 (97.39%), 6.66 (95.82%), and 6.28 (97.83%) dBi at three resonances. Good agreement between the simulated and measured results makes the proposed STA a good candidate for practical applications.INDEX TERMS 5G, cavity-backed antenna, non-linear replication (NLR), self-triplexing, sub-6 GHz, substrate integrated waveguide (SIW).