This paper presents a wideband low-profile cavity backed slot antenna for wireless transmission. A low-profile cavity antenna comprises a circular substrate integrated waveguide (SIW) based backed cavity and octa-star shaped slot on top as a radiating element fed by a coax probe feed at the center of the cavity. The antenna executes a wide impedance bandwidth response due to dual resonance of octa-star slot when excited by probe feed. To validate the design concept, a prototype has been manufactured and measured, which displays a −10 dB impedance bandwidth of 16.35%, extending from 9.26 to 11.02 GHz with the flat gain and conical radiation characteristics. Owing to the single layered integrated cavity, this antenna can be easily mounted with other radio frequency (RF) circuitry. © 2020 Wiley Periodicals, Inc.