  The possibility of controlling Fano lineshapes in the electronic transmission
is addressed in terms of a simple discrete model within a tight binding
framework, in which a finite sized ordered chain is coupled from one side to an
infinite linear chain (the `backbone') at one lattice point. It is found that,
the profile of Fano resonance is strongly influenced by the presence of
impurity atoms in the backbone. We specifically discuss the case with just two
substitutional impurities sitting in the otherwise ordered backbone. Precise
analytical formulae relating the locations of these impurities to the size of
the side coupled chain have been presented. The nature of the transmission
spectrum and the reversal of the pole-zero structures in the Fano resonance are
discussed with the help of these formulae.
