Annular ring microstrip leaky-wave antenna

We investigate the first higher order leaky mode of an annular ring microstrip, which can be viewed as two-dimensional leaky-wave antenna (LWA). The frequency bandwidth of the radiation region of an annular ring microstrip line with a thin strip width or with a small curvature can be estimated from that of the rectangular microstrip line of the same strip width. An aperture-coupled microstrip feeding structure is used to excite this first higher order mode of an annular ring microstrip. The resonant modes and the first higher order leaky mode can be identified by the current distributions on the microstrip line. Simulation and measurement results illustrate the leaky-wave characteristics.