Two SIW bandpass filters (BPFs) are presented using rectangular cavities and loaded posts for 5.8GHz WLAN system using rectangular cavity and loaded posts. Except that both of them use two rectangular cavities to create a passband, they are different in setting the feed-line locations. In design, two loaded posts are introduced as inductive coupling elements to restrain the fundamental resonant mode in SIW cavity at 5.8GHz for WLAN system. In Type-A BPF, TE102mode is used to generate transmission zero (TZ) at a specific frequency out of the desired passband. In Type-B BPF, the source-load cross-coupling is further introduced to improve the out-of-band rejection. In final, two prototype SIW bandpass filters are fabricated to prove the predicted frequency responses in experiment. © 2015 IEEE.