The studies of the filtering antenna have performed many methods and type of resonators used in co-design between the filter and antenna. But none of them using the interdigital resonator with a via through hole. Interdigital resonator with a via through hole has a unique characteristic for it is short-circuited at one end and open circuited at the other. This condition is expected to have an effect to the electric field and the surface current direction. This paper performs a second order of the interdigital filter co-design with a proximity fed rectangular patch antenna. The simulation shows that the interdigital resonator with a via through hole affects the polarization of the antenna from a vertical polarization alter to a slant polarization. The design is fabricated and measured, both the simulation and measurement show a good agreement with a bandwidth of 330 Mhz at 4.65 GHz center frequency, maximum gain of 6.72 dBi and a -75° slant polarization.