Adaptive control of a broadband array using frequency independent coefficients

Adaptive antenna arrays in broadband signal applications utilise tapped delay lines (TDL) in order to obtain the necessary frequency variation in the aperture distribution. This implies the adjustment of a total of N·L parameters corresponding to L taps at each of the N antenna elements. This paper discusses the adaptive control of a broadband antenna array using a gradient search-type algorithm wherein only a single coefficient vector of size M+1 is adjusted, where M is the aperture size in half-wavelengths at a reference frequency f_u. This is accomplished by utilising frequency-invariant (FI) beamformers, obtained specifically via a 2D-DFT-transformation. Simulations verify the effectiveness of this technique and the subsequent improvement in convergence speed in adaptive broadband nulling