A thin wall leaky waveguide antenna

A thin wall leaky waveguide antenna (TLA) obtained by replacing one of the narrow walls of a rectangular waveguide by a film of metal with thickness less than the skin depth is discussed. The radiation pattern for TLA has been evaluated by using Kirchhoff-Huygens approach. In using this method, the dispersion relation has been solved for the complex propagation constants in a parallel plate waveguide with an imperfect plate (
\sigma < \infty
), the thickness of which is less than the skin depth. Separate approximate expressions for the propagation constants for TEM,
TM_{n0}
, and
TE_{n0}
modes in this parallel plate structure have been obtained by considering the mode of propagation as a perturbation of the waveguide mode. Experimental results at
X
band frequencies with thin bismuth films are reported and are found to be in fair agreement with the theoretical results. Phase velocity (
c/\upsilon
) variation of TLA is essentially that of a simple rectangular waveguide. Very low values of attenuation constant can be obtained so that a long antenna can be used even with the beam directed away from endfire.