RF propagation from a flatplate array antenna with polarizing lenses

Under a previous IR&D project the capability of an airborne Ku-band slotted flatplate array was expanded to include polarization diversity for automatic target recognition (ATR). A lightweight meanderline polarizer lens was designed, which transmits linearly polarized RF and receives simultaneously both co-polarized and cross-polarized target returns. An optional configuration, obtainable using an RF switch, transmits right-hand circular and receives simultaneously right- and left-hand circularly polarized returns. Either configuration detects two time-correlated polarization scattering states. Such data are useful in target identification either through partial polarization whitening of the image or by supplying feature information for matching against a target model. The addition of a second RF switch to the design allows pulse-to-pulse alternating transmission of both polarizations, in which case the full polarization scattering matrix can be obtained. The linearly polarized aperture of the original array design permits the antenna to support air-to-air pulse doppler monopulse, high resolution synthetic aperture radar ground mapping, and ground moving target track radar modes. The high gain and efficiency of the flatplate array, combined with pulse compression techniques and high transmitter power, give the system a long range, high resolution, ground mapping capability unusual in a nose mounted radar system. With the incorporation of the polarizer lens, the new ATR capability makes this antenna a more powerful tool in air-to-ground combat and surveillance.