A theoretical and experimental study of the matching network linking the antenna of a helicon plasma system to its rf power source is described. It is shown that the introduction of a rf step-down transformer into the conventional L-section network has a number of benefits. The transformer increases the reflected antenna impedance seen by the network, bringing it closer to the output resistance of the rf source. The resulting low-Q network is shown to be insensitive to changes in the antenna impedance and the values of the matching elements. It is found that in general only one component in this broad-band network needs to be adjusted rather than the iterative adjustment of two components in the conventional network. The importance of this simplification with respect to the automatic control of the matching network is discussed.
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Rayner et al. (1996) studied this question.