A slot-coupled microstrip antenna includes a first substrate, a second substrate, and a support base. The first substrate having a first surface and a second surface, in which a ground surface that is formed on the first surface, and a plurality of slots are formed on the ground surface. A feeding network is formed on the second surface. A plurality of antenna corresponding to the slots are formed on the second substrate disposed above the first surface. The support base having two fillisters at two side of the support base. The design of slot structure often has adverse influence on cross polarization and a front-to-back ratio of antenna radiation. The support base having two fillisters of the slot-coupled microstrip antenna can effectively inhibit the influence on the cross polarization and raise the front-to-back ratio from the slots.