\[fig:fig5\]e). In analogy to cylindrical NWs, this first order resonance can only be excited in the TM geometry, TE polarized illumination results in a very weak scattering in the corresponding spectral range. While small nanowires have spectrally broad optical resonances (figure \[fig:fig5\]a-b), narrower higher order resonances appear with increasing NW width (figure \[fig:fig5\]c-d). In contrast to the omnidirectional TM scattering in the smallest wires, the first occurrences of strong forward scattering seem to be the result of interference between a sharp quadrupolar resonance and a broad dipolar contribution. We deduce this conclusion from the similarity in field intensity distributions in cylindrical and rectangular NWs (compare Figs. \[fig:fig3\]d and \[fig:fig5\]e,f,i).

Under TM excitation, we also observe branches of a different kind of Fano-like resonances where the FW/BW ratio is almost unity (see Fig. \[fig:fig4\]c-d and Fig. \[fig:fig5\]c-d, bottom row). In a narrow spectral window the otherwise strong forward scattering is suddenly suppressed while BW scattering increases. Resonances with such field profiles are observed neither under TE polarization, nor in symmetric SiNWs ([see SI Figs. S11-S15]{}, where scattering from rectangular wires is compared to different symmetric geometries). We attribute these sharp features to horizontal guided modes along the SiNW width ($X$-direction), the 