Inset-microstrip-line-fed dual-frequency circular microstrip antenna and its application to a two-element dual-frequency microstrip array

A new dual-frequency design of an inset-microstrip-line-fed circular microstrip antenna with an arc-shaped slot is proposed and experimentally studied. The two operating modes of the proposed antenna are associated with the perturbed TM₁₁ and TM₀₁ modes and have the same polarisation planes and similar broadside radiation characteristics. By varying the length of the arc-shaped slot, the proposed antenna can provide a tunable frequency ratio of about 1.29 to 1.43 for the two operating frequencies. The application of the proposed antenna to the design of a two-element dual-frequency microstrip array is also demonstrated. Details of the obtained dual-frequency performances of the proposed dual-frequency design are presented and discussed