The open-ring microstrip antenna

The open ring microstrip structure has been studied in recent years for various applications in microwave circuits and as antenna element [1-3]. Even though a considerable amount of analytical and experimental work has been done on the resonant frequency, the corresponding field distribution for various modes, the Green´s function and the input impedance of such an open ring structure, the work on the radiation characteristics such as the radiation pattern and the directivity have been somewhat limited [1-5]. In this paper the expressions for the radiation fields of an open ring structure are derived by utilizing the simple theory based on the cavity model and the resultes for the radiation pattern for typical lower order modes are presented.