A method of designing two-dimensional complex coefficient FIR digital filters for broadband digital beamforming antennas by a combination of spectral transformation and a window method

Abstract

In digital beamforming (DBF) antennas, received propagation signals are first converted down into baseband inphase and quadrature signals, then DBF signal processing is done. We propose a method for designing two-dimensional (2D) digital filters utilized in such DBF networks to handle the signals with wide fractional bandwidths up to 40%. First, we consider the relationship between DBF and its 2D normalized frequency description. Here, we show that 2D complex coefficient digital filters with nonsymmetric characteristics are necessary to form broadband beams. Next, based on this consideration, we describe the proposed method, which combines spectral transformation and a window method. Note that approximation is achieved such that the beam pattern, including its sidelobe characteristics, from the resulting broadband DBF network is virtually frequency-independent. As a result, it has become possible to design DBF networks suitable for a multibeamforming network for use in the broadband beamspace adaptive array antenna proposed in Sekiguchi, Miura, and Karasawa [9]. © 1998 Scripta Technica. Electron Comm Jpn Pt 3, 81(3): 22–34, 1998