In this paper, a new cavity-backed antenna configuration, called strip, slot, air, inverted patch (SSAIP) is proposed. The SSAIP is the cavity-backed version of the standard strip, slot, foam, inverted patch (SSFIP) antenna concept, and this paper compares the electrical performances of both types of antennas. Results reveal that similar to their SSFIP counterparts, SSAIP antennas also exhibit large frequency bandwidth but now combined with clean and versatile radiation patterns and can thus be used in broadband communication applications. The analysis of these antennas is carried out with a specific integral equation formulation, described in the paper. To facilitate the physical understanding of the new structure, an equivalent filter model of the real SSAIP antenna is also derived. This equivalent model allows standard filter design techniques to be used for an easy electrical design of the antenna. In addition to theoretical results, experimental results are also presented showing good agreement between numerical predictions and measurements. ¿ 1998 American Geophysical Union