Abstract: A quarter-mode substrate integrated waveguide (QMSIW) is equivalent to an isosceles right triangular waveguide with two magnetic walls and one electric wall at the hypotenuse of the triangular. The mode solutions of the QMSIW are determined based on the cavity model of an isosceles right triangular waveguide, both transverse electric and transverse magnetic mode shapes are presented in this paper. Single microstrip-fed antenna based on QMSIW with planar compact circular polarization is proposed and designed. The simulation results show that this antenna exhibits right-handed circularly polarized radiation with a high gain of 6.18 dBic and 3 dB axial ratio bandwidth of 3.44%.