Buckingham uses a simple unshaded vertical array in a waveguide. The simple unshaded vertical array is an inefficient receiver because it does not match the eigenfunctions of the waveguide. For his noise sources he uses free space functions instead of the eigenfunctions of the waveguide. This letter clarifies these aspects of his paper and gives a procedure for designing an optimum array processing system. The analysis shows that the main advantage of using a vertical array is to filter the different modes and when the mode spectrums of the signal transmission and noise are the same there may be little or no gain of the signal‐to‐noise power ratio. The procedure also gives upper and lower limits of the signal‐to‐noise ratio for vertical arrays in waveguide transmission.