To overcome the inherently narrow bandwidth of conventional microstrip antennas, this work proposes a wideband microstrip patch antenna using an L-shaped parasitic structure. The antenna consists of a main radiating patch and L-shaped parasitic elements, with an overall size of 0.83λ?×0.83λ?×0.083λ?, where λ? denotes the free-space wavelength at the 5 GHz center frequency. The main patch operates in the fundamental transverse magnetic (TM₁₀) mode, while multiple resonances are introduced via electromagnetic coupling with the parasitic elements, thereby significantly extending the bandwidth. A Rogers 5880 substrate with a relative permittivity of 2.2 and a loss tangent of 0.000 9 was used to reduce the quality factor. A 180° out-of-phase differential feeding scheme was applied to suppress radiation pattern distortion. Simulation results show that the proposed antenna achieves a voltage standing wave ratio (VSWR) below 2 from 3.6 GHz to 6.6 GHz, corresponding to a 60% fractional bandwidth—six times wider than that of traditional microstrip designs. The antenna exhibits a peak gain of 9.8 dBi at 6.2 GHz, with gain variation within 1.5 dB across the operating band. The main beam remains stable, with a pointing deviation within 5°, and cross-polarization levels remain below -15 dB over 3.6 GHz to 6.3 GHz, reaching as low as -38 dB at the center frequency. This single-layer configuration achieves both broadband and high-gain performance, demonstrating strong potential for broadband wireless applications, including 5G communication and Wi-Fi systems.