Separate excitation of the characteristic waves in the ionosphere results in two orthogonal propagation channels on the same frequency, which may be used in diversity and multiple-input, multiple-output (MIMO) systems. In this article, a method to measure the isolation between these paths is proposed and demonstrated in a near vertical incidence skywave (NVIS) experiment at a frequency of 7 MHz over a 105-km distance. Characteristic wave isolation exceeding 25 dB is measured during "Happy Hour": the interval when the propagation path just opens or closes and only the extraordinary wave propagates.
Witvliet, B. A., van Maanen, E., Petersen, G. J., Westenberg, A. J., Bentum, M. J., Slump, C. H., & Schiphorst, R. (2015). Measuring the isolation of the circularly polarized characteristic waves in NVIS propagation. IEEE antennas and propagation magazine, 57(3), 120-145. https://doi.org/10.1109/MAP.2015.2445633