In this communication, a filtering slot antenna design scheme that manipulates the mixed electric/magnetic couplings between slots is introduced. Firstly, the mixed electric/magnetic (E/M) couplings between two identical slots, which can contribute to a radiation null (RN), are investigated and detailed with resort to the equivalent circuits. Then, based on mixed E/M coupling theory, two modified versions of the dual slot antenna are proposed for altering the balance between E/M coupling, aiming to effectively shift this RN to either the upper or lower band edge. Finally, following the former design methodology, a wideband bandpass filtering slot antenna enabled with three slots is attained. The three slots are further shaped into split rectangular rings to achieve a compact design. With the utilization of microstrip feeding, three in-band resonances are created to realize a wide impedance bandwidth of 33.8%. Meanwhile, a good bandpass response with out-of-band rejection up to 12.1 dB is accomplished by introducing two RNs based on abovementioned E/M coupling theory and one extra RN from the folding slot. This compact filtering slot antenna is eventually fabricated, assembled, and tested. The measured results of the prototype are found in good agreement with simulated ones, thereby confirming the design concept.