This article presents the designs of planar inverted-F antennas (PIFAs) at frequencies of 0.835 GHz, 0.9 GHz, 1.8 GHz, 1.9 GHz, 2 GHz, and 2.6 GHz. Initially, the designs of rectangular-shaped PIFAs are determined through the parametric studies concerning the dimensions of the antenna’s patch length, shorting plate, ground plane, and substrate. Afterward, rectangular-shaped slots are introduced into radiating element of two antennas that operate at a lower frequency range of less than 1 GHz, to tune the resonant frequency to the respective 0.835 GHz and 0.9 GHz. Different configurations of partial or full ground plane are implemented to improve the reflection coefficient, <em>S</em><sub>11</sub> performance to be below -10 dB in both simulation and measurement. The proposed six PIFAs have gain that are greater than 2 dB with the nearly omnidirectional radiation patterns. All the designs and analyses are performed using the CST Microwave Studio utilizing Rogers 4003C substrate.