(a) SED template of an FR II lobe adopted to estimate the contribution to the EGB (red line). (b) The radio and X-ray luminosities of the lobes in the C05 FR II sample (black dots). The red square indicates the 1 keV and 178 MHz luminosities estimated from our SED template (upper panel). The cyan dots show synthetic sources generated from the model luminosity function described in Section 5.