Under the excitation of a pair of shifted inclined slots, TE ₁₀₁ , TE ₀₁₁ and TM ₁₁₀ modes in a single rectangular cavity are excited, and exploited to form a passband of bandpass filter (BPF). The pair of slots are fed through microstrip lines at the input and output port. Based on the single triple-mode rectangular cavity, a dual-cavity BPF is designed, fabricated and measured to enhance the selectivity of filter by cascading two single ones. The BPF could achieve about 32 MHz bandwidth at center frequency of 2.98 GHz, and two transmission zeros (TZs) at 2.925 and 3.005 GHz, leading to the suppression outside passband larger than 50 dB in the vicinity of center frequency.