Analysis, Design, and Measurement of Directed-Beam Toroidal Waveguide-Based Leaky-Wave Antennas

Leaky-wave antennas (LWAs) have been widely investigated for wireless systems. Most LWAs reported to date are open-path based, i.e., their guided traveling waves follow a non-closed path. A substrate-integrated (SI) toroidal waveguide-based LWA is developed in this article. A coaxial-fed probe structure effectively excites traveling waves that propagate along a closed path in the toroidal waveguide. Inverted L- and planar helical-shaped radiators, whose pickup structures extract power from the waveguide through its top wall, are introduced to radiate, respectively, linearly-polarized (LP) and circularly-polarized (CP) directed beams. The dispersion properties of the closed waveguide's traveling wave are determined and the associated propagation phase along circular paths with specific radii guides the placement of these radiators to achieve a directive beam at a specified angle. Prototypes of both the LP and CP toroidal LWA (TLWA) systems were fabricated and tested. Good agreement between the simulated and measured results was obtained. The measurements of the compact, low-cost LP and CP prototype systems confirm they radiate beams pointed in their distinctly different, specified directions with realized gains of 13.2 dBi and 13.9 dBic, respectively, at 9.75 GHz.