The effect of an air gap on the radiation pattern of a microstrip leaky wave antenna radiating into a half space

In various antenna applications it is not desirable to have the antenna in direct contact with the medium the radiation is trying to penetrate. In ground penetrating radar, the antenna is moved over the ground, so that data can be obtained about subsurface features. Clearly in this application, if the antenna was in direct contact with the ground the antenna would be damaged very quickly. Hence the need for an air gap. Researchers investigating the effect of a dielectric coating on a leaky wave long slot waveguide antenna, concluded that some slight discrepancies between measured and theoretical results in backlobe radiation, may be due to the presence of a small air gap between the antenna´s metalization surface and the dielectric coating, as a result of the adhesive process (Whetten and Balanis, 1996). In this paper, the effect of a small air gap between a microstrip leaky wave antenna (LWA) and a half space is examined. The propagation constant and power radiation pattern is evaluated for various air gap spacings.