Closed-Loop Feed Architectures for RCS Beam Broadening of Retro-Reflective Arrays

This communication presents a novel architecture for a one-dimensional, large radar cross section (RCS) retro-reflective array. This array is tailored to aide in the standoff detection and localization of large metallic objects in a warehouse setting. This application scenario requires this retro-reflective array to be planar, provide a high RCS, and a wide beam in the elevation plane. Traditional methods to increase the RCS of planar arrays employ an increase in the number of array elements which typically results in a narrowing of the beam in this plane. The approach presented eliminates this problem. To maintain a wider beam in elevation, a unique series fed grounded coplanar waveguide (GCPW) patch element is designed to radiate off boresight at a specified degree. This linear array is fed from both terminal ends of the array through a unique `closed-loop' interconnection scheme. In this arrangement, a resonant structure is created through circular loops that are formed by the interconnection of the linear series arrays and associated feed lines. The result is a broadened beam in elevation when compared to that of traditional Van Atta interconnection schemes while maintaining the broad RCS expected of a retro-reflective array in the horizontal plane. This compact array has a large RCS and is implemented at 26 GHz. The design of the array elements themselves is discussed along with the development of this novel feed architecture. RCS pattern measurements from the fabricated arrays are presented and performance enhancements quantified when compared to traditional retro-reflector feed geometries.