A single-layer microstrip-fed patch antenna with capabilities of both bandwidth enhancement and harmonic suppression is proposed. For this purpose, a pair of λ/4 microstrip-line resonators is introduced and coupled in proximity to a rectangular patch. The wideband property can be obtained by making effective use of the two resonances introduced by the radiating patch and nonradiating λ/4 resonators. Different from other reported dual-resonance patch antennas, the proposed antenna does not require the electrically thick substrate, so it has attractive low-profile property. Thanks to the good features of λ/4 resonators and capacitive feeding scheme, harmonic radiating modes of the patch antenna can be significantly suppressed as highly demanded in modern highly integrated communication systems. The working principle, equivalent circuit, and design procedure are extensively described. Finally, a prototype antenna operating at 4.9 GHz is designed and fabricated. The measured results show that its bandwidth is 2.7 times wider than that of the traditional insert-fed patch counterpart, and the harmful spurious radiation from other higher order radiating modes has been effectively suppressed.