In this paper, a novel compact microstrip patch antenna that intrinsically combines unique self-decoupling and filtering performance is presented. Being in a single-layer, low-profile, and compact configuration as a typical microstrip patch antenna, the developed antenna consisting of a rectangular patch and a cascaded inverted-F radiator exhibits the same operation bandwidth as the referenced microstrip antenna. The integrated inverted-F radiator not only acts as an isolator to effectively suppress mutual coupling between array elements, but also provides two additional deep out-of-band radiation nulls to achieve good out-of-band roll-off characteristics benefiting from the two quarter-wavelength open stubs located in the inverted-F radiator. Prototypes of the self-decoupled filtering patch antenna have been designed, fabricated, and measured. The measured results agree well with the simulated results, showing an isolation improvement of at least 8.2 dB over the entire operation bandwidth and good filtering performance with two deep nulls allocated at two edges of the passband.