Measuring the Isolation of the Circularly Polarized Characteristic Waves in NVIS Propagation [Measurements Corner]

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.