Measurement and analysis of horn antennas with integrated high impedance surfaces

Rectangular horn antennas with integrated Sieven-piper high-impedance surfaces are presented. This high-impedance surface approximates a magnetic conductor, allowing TEM propagation within its stopband. This enables the horn antennas to operate at frequencies that would otherwise be below the TE_1,0 cutoff frequency. Because the unit cell of a Sieven-piper high-impedance can be arbitrarily small, such an antenna can be reduced in volume arbitrarily. Four antennas in two geometries with metal and high-impedance sidewalls are designed, measured, and compared.