In this paper, a novel design of substrate integrated waveguide (SIW) cavity backed slot antenna for dual frequency and broadband application is demonstrated. In the proposed design, a parasitic slot is placed along with the conventional central slot at the top metallic plate of the cavity to generate dual frequency resonances at 10.08 GHz and 11.96 GHz. The central slot is placed at the center of the cavity and it is excited by TE120 mode of the cavity to radiate into free space. However, the placement of parasitic slot in the cavity modifies the surface current distribution at top metallic plate at higher frequency and as a result, a hybrid mode resonance is achieved. Both these resonances contribute to the dual frequency operation of the antenna with unidirectional radiation pattern, high gain, high front-to-back ratio (FTBR) at both operating frequencies. The proposed antenna achieves a bandwidth of 108 MHz (1%) and 100 MHz (0.83%), a gain of 5.5 dBi and 5.3 dBi and front to back ratio of 10 dB and 12 dB respectively at first and second resonant frequency. The slot lengths can be varied to achieve a frequency ratio of two resonant frequencies in a broad range of 1.18-1.5. The length of the slot pair can also be tuned to merge the dual resonances to achieve a broadband response. A design example of broadband antenna is also demonstrated. The proposed design shows a bandwidth of 380 MHz (3.6%), a gain of 5.2-5.8 dBi and FTBR of 15 dB throughout the operating bandwidth. © 2015 EurAAP.