In the June 2022 issue of IEEE Antennas and Propagation Magazine, there was an error in Figure 4 and also in the text in [1], in the “Gravitational Redshift” section. In Figure 4, the quantity ${v}_{\text{emit}} / {v}_{\text{obs}}$ is plotted rather than ${v}_{\text{obs}} / {v}_{\text{emit}}$. The graph no longer asymptotes at the Schwarzschild radius but goes to zero: physically, the frequency is infinitely redshifted and nothing escapes the black hole. The corrected figure and its caption are given.
Figure 4. Gravitational redshift.
Throughout the “Gravitational Redshift” section, between and including equations (21) and (26), the labels ${v}_{\text{emitted}}$ and ${v}_{\text{observed}}$ should be swapped, except in the example of Friedmann–Lemaître–Robertson–Walker spacetime found above the subsection “Stationary Observers.” We sincerely apologize for these errors and any confusion they may have caused and would like to express our thanks and gratitude to Ankit Mishra at the National Institute of Technology Rourkela, Inda, for bringing this to our attention.
[1] C. R. D. Bunney and G. Gradoni, “Electromagnetism in curved space–time: Coupling doppler shifts and gravitational redshifts,” IEEE Antennas Propag. Mag., vol. 64, no. 3, pp. 40–51, Jun. 2022, doi: 10.1109/MAP.2021.3099714.
Digital Object Identifier 10.1109/MAP.2023.3323116