A METHOD OF DESIGNING 2-DIMENSIONAL COMPLEX COEFFICIENT FIR DIGITAL-FILTERS FOR BROAD-BAND DIGITAL BEAMFORMING ANTENNAS BY A COMBINATION OFSPECTRAL TRANSFORMATION AND A WINDOW METHOD

In digital beamforming (DBF) antennas, received propagation signals ar e first converted down into baseband inphase and quadrature signals, t hen DBF signal processing is done. We propose a method for designing t wo-dimensional (2D) digital filters utilized in such DBF networks to h andle 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 filter s with nonsymmetric characteristics are necessary to form broadband be ams. Next, based on this consideration, we describe the proposed metho d, which combines spectral transformation and a window method. Note th at 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 Sekiguc hi, Miura, and Karasawa [9]. (C) 1998 Scripta Technica.