Breakdown limitations on the transmission of microwave power through the atmosphere

One of the limiting factors in the transmission of the increasingly large amounts of microwave power available is voltage breakdown of the atmosphere. Almost all of the published work dealing with voltage breakdown at microwave frequencies has been concerned with breakdown in the presence of surfaces to which particles can diffuse. This paper describes laboratory experiments which have been performed using a focused microwave system to produce a discharge in the absence of proximate surfaces. The experiments have been concerned with 1) the determination of the power level at which breakdown occurs, and 2) the ability of the atmosphere to act as a medium for the transmission of power after breakdown has occurred. The paper presents a theory for predicting the power level at which breakdown will occur and then demonstrates the agreement of this theory with measured breakdown levels. An experiment is then described which shows that the power per unit of input power, received beyond the discharge plasma by a test antenna, decreases as power is increased after breakdown.