Spectra of the radio bridge for various models. The solid black line shows the fiducial model presented in Sect. 3. Models 1 and 2 yield spectra that are similar to the fiducial one, shown by the dashed and dotted black lines, respectively. The blue curves correspond to η_B = 0.02 (model 3; dashed) and η_B = 0.08 (model 4; dotted), while the orange curves show the cases with ψ = 0.4 (model 5; dashed) and ψ = 0.6 (model 6; dotted). For comparison, all spectra are normalized to match the 60 MHz radio power of A399–A401. The model parameters are summarized in Table 2.