The SIW antenna suffers from the narrow bandwidth for a single cavity and single resonant. Defected ground structure (DGS) with a dual cavity was the solution to solve narrow bandwidth by resulting in hybrid resonance. The hybrid resonance with 14.83% impedance bandwidth is proposed in this antenna design. The first resonance resulted from the combination of the TE101 modes from inner and outer HMSIW cavities while the second resonance resulted from the combination of the strong TE101 and the weak TE102 mode from the inner HMSIW cavity and the addition of the weak TE101 from the outer HMSIW cavity. The measurement antenna design has a broadband antenna with a 14.31% (5.71 – 6.59 GHz) impedance bandwidth by using substrate Rogers RO 5880.

Designing microstrip antennas with wide bandwidth and low-frequency capabilities presents several challenges. These difficulties mainly arise due to the relatively small size of the microstrip in comparison to the operating frequency. Therefore, achieving a combination of enhanced bandwidth and lowerfrequency cut-off becomes crucial to support a broad frequency range of communication technologies. This paper presents a method for enhancing the bandwidth of a circular microstrip antenna based on an inverted C-shaped ground configuration. The proposed method successfully creates an antenna with extended bandwidth while lowering the operating frequency. The antenna was simulated and then fabricated using an RO5880 duroid substrate with a relative permittivity of 2.2, a thickness of 1.575 mm, and a loss tangent of 0.0009. The simulation and measurement results demonstrate that the antenna can operate effectively within a wide frequency range of 3.5 GHz to 18 GHz. Additionally, utilizing this method enables the antenna to function at even lower frequencies and wider bandwidth without the need for additional dimensions.