Broadbanding of microstrip antennas by orthogonal polarizations

Microstrip antennas are inherently narrow band because they constitute a resonant cavity with radiation, medium, and copper losses. However, if two resonant cavity modes with two slightly different resonant frequencies can be excited independently without coupling, then this can become a broadband antenna. This coupling is achieved by the orthogonal polarizations for two resonant modes. Several antenna structures based on this concept have been analyzed and tested experimentally, showing the expected increase in bandwidths.