Anomalous leaky-mode dispersion of coupled-cavity wideband leaky-wave antennas

We report the anomalous modal dispersion in leaky-wave antennas composed of two coupled resonant cavities tuned for wideband response. The increase in gain bandwidth has been previously associated with the synthesis of a positive-slope phase response which satisfies the resonant condition at the desired scanning angle over a wide frequency band. In this paper, we demonstrate that this type of design also provides an anomalous, quasi-oscillatory response on the resulting leaky-mode dispersion. This type of dispersion shows stabilization of the effective leaky-mode radiation angle around the desired scanning direction over a broad frequency band, which is in accordance with the wideband resonance condition. Numerical results are presented for a two-dimensional Fabry-Pérot antenna radiating at broadside, and for a one-dimensional substrate-integrated waveguide antenna scanning at 30º, both of them operating at Ku band and composed of two resonant cavities. A final discussion and interpretation of this anomalous modal dispersion is also given, recalling the excitation and coupling of two leaky modes supported by the double-cavity antennas.