An analysis of microstrip line fed antennas has been presented theoretically using circuit theory concept. The theoretical investigations of F-shape antenna parameters such as return loss, VSWR, gain and efficiency have been calculated. It is found that antenna resonate at 2.4 and 5.2 GHz for lower and upper resonance frequencies respectively. The bandwidth of the F-shape antenna at lower resonance frequency is 20.08 % (simulated) and 17.05 % (theoretical) whereas at upper resonance frequency, it is 5.93 % (simulated) and 5.78 % (theoretical). The characteristics of the F-shape antenna is compared with other microstrip line fed antennas. It is found that F-shape antenna is linearly polarised along the X direction. The theoretical results are compared with IE3D simulation results as well as reported experimental results and they are in close agreement.