True time-delay bandpass beamforming: A new implementation

Beamforming as a basic approach of array signal processing has been widely used in many important applications such as radar, sonar, and communications. Typical algorithms include time-delay-based and FFT-based, and various implementation structures have been developed. For bandpass sampled signals, a true time-delay beamformer involves three processes: signal demodulation to obtain its complex envelop; delay of the complex envelop; and phase rotation of the delayed complex envelop. Those processes can be realized using FIR filters. In this paper, a few improvements are proposed for the above bandpass beamforming implementation, including a new way of filter coefficient selection and a polyphase filter structure. The new implementation generates exactly identical results as the conventional zero-padding interpolation beamformer, and meanwhile can readily fit into a low-power, highly-parallel processing unit such as FPGA.