Research that combines antenna miniaturization and increasing the fractional bandwidth simultaneously is still rarely found. There are still few studies that get the percentage of ultra wideband bandwidth. Thus, this research develops the fractional bandwidth enhancement in the half mode SIW antenna structure (HMSIW) by resulting four resonances close together. The half-mode SIW antenna structure can provide up to 50% miniaturization of the full SIW dimensions while combining several adjacent resonant frequency modes in two half-mode SIW ports can increase the bandwidth percentage above 30%. The first research that has been done to increase the fractional bandwidth is to combine the TE101 and TE102 modes in the full mode SIW structure. The combination of the two modes is obtained by modifying the slot into the shape of the letter T. The 3% of fractional bandwidth is achieved. The second study used a half-mode SIW structure with triangular slots to combine the TE101 and TE102 modes. The fabrication of this antenna design gives an impedance bandwidth measurement of 380 MHz at a frequency of 3.66-4.04 GHz at VSWR = 2, which means that this antenna has a fractional bandwidth of 9.87%. This antenna has a unidirectional radiation pattern in the H and E planes with a measurement gain of 4.2 dBi. The last research used a half pentagon ring slot and a combination of two half mode SIW cavities. This antenna design has four resonant frequencies that is combination of TE101-inner, TE102-inner, TE202-inner and TE202-outer modes. The measurement results prove that these four resonances have increased the fractional bandwidth up to 31.83% in the frequency range 9.14-12.6 GHz with a reflection coefficient of less than -10 dB. This antenna has an omnidirectional radiation pattern in the H plane and unidirectional in the E plane. This antenna has a linear and circular polarization with a maximum measurement gain of 7.62 dBi at a frequency of 10.48 GHz.