Directive dual-band CP shorted ring-slot antenna

In order to maximize the power captured from incident wave a directive antenna is required. As an example, high directivity is desired for rectifying antenna (rectenna) operating at low power densities, because the rectifier efficiency decreases at lower input power levels. Ring-slot antennas-being attractive for their simplicity and ease of integration, among others-are, however, bidirectional by their nature. Unidirectional radiation pattern can be achieved e.g. by reflector- or cavity-backing. In this paper, improved broadside CP performance of a microstrip-fed dual-band circularly polarized shorted ring-slot antenna is demonstrated when a single reflector is added to the structure.