Wideband microstrip patch array with low sidelobes and a high polarisation purity for high resolution imagin radars

The design and the measured performance of a wideband microstrip patch array for a high resolution imaging radar is described. The array consists of aperture-coupled microstrip patch elements based on low-permittivity foam materials. The array is designed by a method of moments approach under consideration of mutual coupling effects. The manufactured 8×8 element cosine tapered X-band array shows a bandwidth of 1.8 GHz (VSWR<2), which is more than 18% of the centre frequency. Within this bandwidth the sidelobes remain below ¿20 dB. The cross-polarisation level is below ¿30 dB for all aspect angles and even below ¿38 dB for aspect angles between ±60°.