Suppressed Side-lobe, Beam Steered, C-band Circularly Polarized Array Antenna for Airborne Synthetic Aperture Radar

A circularly polarized antenna array was designed for use with an airborne C-band synthetic aperture radar (SAR) measurement system. SAR performance parameters were designed and used as the performance requirements of the array antenna. A single patch antenna was first designed to conform to the required operating frequency and axial ratio for circular polarization. This was then followed by the linear array and feed design. Several important antenna performance parameters customized for our SAR measurements were achieved in this study. Among them are low axial ratio of under 3dB with 125 MHz bandwidth via corner truncated square patches for circular polarization; steep scanning angle of 40 degrees using phased delayed 10-element array at 0.53 lambda element spacing; suppressed side-lobe level utilizing the Dolph-Chebyshev synthesis method; and reduced radiation from spurious feeds through optimized feed network using T-junctions and mitered bends. The antenna performance was estimated, followed by full electromagnetic wave simulation at each design step. The optimized design was used for fabrication of the antenna and the array antenna performance parameters was verified through measurements in an anechoic chamber. Results show agreement between theoretical and simulated data which match the design parameters. A planar array structure is also proposed to increase the total array gain.