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.