A planar dual-band sequentially-rotated array is proposed to cover the radionavigation bands at 1.19 and 1.57 GHz. The antenna consists of a two-port ring microstrip line that series feeds four radiating elements. The basic radiator is the so-called complementary strip-slot, a microstrip-fed slot that has its complementary stub superimposed to it on the microstrip layer, in order to cancel the slot resonant behaviour and provide ultra broad impedance matching. Thanks to this element feature, the antenna can cover the two bands and diplex them into the two ports without the need of additional passive or active components. The detailed design and results of the reflection coefficient, axial ratio and radiation patterns are provided, which confirm the good performance of this simple antenna.