Frequency dependence of beam sizes for NenuFAR and LOFAR, shown alongside the angular size of Cas A. The LOFAR beam is represented for the two CRRLs experiment: Salas et al. (2017) (circles) and Oonk et al. (2017) (squares). Oonk et al. (2017) cropped the images from LOFAR in squares whose sizes are fixed in two frequency windows. Salas et al. (2017) cropped the images from LOFAR in circles centred on Cas A, with continuous values for its diameter. The Nenu-FAR beam size function is shown with the solid line. The red dotted line represents the angular extension of Cas A at radio frequencies (Green 2014). The source is spatially resolved for neither setups, at any frequency.