An experimental completely overlapped subarray antenna

A completely overlapped subarray antenna was designed, fabricated, and tested to demonstrate its broad-band, low sidelobe, wide scan angle performance. It uses time delay steering at the inputs to a transform feed, which illuminates a phase-shifter steered objective lens. The transform feed is a Rotman lens and the objective is a cylindrical bootlace lens, both of which are parallel plate waveguide cavities with coaxial probe elements. The signal bandwidth goal of 20 percent (8.1-9.9 GHz) at scan was met easily, however, achieving the peak sidelobe goal of - 30 dB proved more difficult because of internal reflections in the Rotman lens beamformer. A brief summary is presented of the completely overlapped subarray antenna (COSA) concept to explain the detailed design of our experimental model. Antenna pattern and S-parameter measurements illustrate the operating principles, the difficulties encountered, and the results achieved.