In this paper, a novel structure of a circular patch microstrip antenna based on external corrugations is designed, simulated, and measured to operate in S and C-bands applications. The parameters of this antenna structure, such as input impedance, bandwidth, gain, surface currents, and radiation patterns were studied and improved. This antenna design includes modifying the shape of the radiating patch by cutting seven parts of the tip patch as semi-oval with a diameter and depth of 2 mm between each part, 450 angles. The antenna ground plane was reduced to the size of 40×13 mm2. The insulating substrate has dimensions of 50×40×1.6 mm3. The obtained results showed a good improvement of the antenna performance with resonant frequencies of 3.1 GHz, 7.1 GHz, and fractional bandwidth of 40.8%, 12.4% respectively. This design is simulated using Ansoft High-Frequency Structure Simulator (HFSS), and it is compared with the obtained measurement data. Interestingly, the comparison results are in good agreement. The antenna design is helpful for many services operations at these bands of frequencies and their applications.