Microstrip antenna arrays for airborne high-performance, polarimetric SAR systems

Many dual-linear polarization antenna arrays, e.g. for polarimetric synthetic aperture radar (SAR) systems, are required to have very low cross-polarization levels. In order to improve the cross-polarization performance of the entire array over that of the basic dual-polarization element from which the array is constructed, a well-known element mirroring technique has often been employed. This technique improves the cross-polarization performance of the array, but it may also cause generation of grating lobes. A new principle is described for obtaining very low cross-polarization levels in dual-linear polarization antenna arrays and simultaneously avoiding the generation of grating lobes. This paper reviews the new principle and presents its implementation in a wideband, dual-linear polarization microstrip antenna array used in the Danish airborne L-band polarimetric SAR system “EMISAR”. The antenna array, comprising 8 × 2 probe-fed stacked patch elements, exhibits a 10 % bandwidth, a peak directivity of 18 dBi and a cross-polarization level of 40 dB below the co-polar. Suggestions for further enhancements to the novel principle are given.