Calibration and Optimization of a Wideband Circular Array Using a Phase-Mode Beamformer
Abstract
Circular and cylindrical arrays are advantageous when 360-degree azimuthal coverage is desired, as they do not suffer the angle-dependent beam broadening and scan loss characteristic of linear and planar arrays. A phase-mode beamformer (implemented as a Butler matrix) transforms an ideal wideband circular array into a frequency-invariant virtual linear array, greatly simplifying wideband beamforming. The nonideal responses of a physical analog beamformer and antenna elements, however, necessitate equalization to realize this frequency invariance. In this report, we first define a signal-processing model of the entire beam former system, from antenna to final array weights. For the array, Butler matrix, and equalization filters, we define error metrics which can be used to evaluate the relative contributions of each component to the overall error. We focus on the design and performance of equalization filters located at the phase mode outputs, that can be implemented either as analog tapped-delay-line (TDL) filters or as digital FIR filters. We then compare wideband array patterns from the system using standard tapers, optimized array weights, and adaptive beamforming.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 15, 2021
- Accession Number
- AD1175346
Entities
People
- Dan P. Scholnk
Organizations
- United States Naval Research Laboratory