Abstract The design and synthesis of a compact, low-profile, flexible substrate integrated waveguide (SIW) wearable filtering antenna (filtenna) along with two parasitic resonator patches has been proposed for 5G communication. For the purpose of minimizing circuit size, a half-mode rectangular-shaped substrate-integrated (HMRSI) cavity has been used as a resonating patch initially. HMRSI cavity has located in close proximity with two parasitic truncated corner patches serve as both the radiator and the final stage resonators, therefore optimizing the filtering performance and expanding the operating bandwidth. In order to enhance the roll-off rate, two different radiation nulls are achieved first at the upper band-edges & second at lower band-edges: one is produced by the parasitic patches’ interaction with the HMRSI cavity, while the other is created by the corner truncation and notching on the parasitic patches with defected ground. Filtenna design is guided by typical filter synthesis technology. A manufactured and measured optimized prototype has been done. The proposed flexible filtenna exhibits excellent out-of-band selectivity and measurement shows well agreement with simulated ones and attain an 8.2% fractional bandwidth (FBW), a max. realized gain of 6.1 dBi with a flat passband gain response. The proposed filtenna has also studied on human body and achieved low SAR which enables it on-body wearable filtenna.