Error-controlled high power linear amplifiers at VHF

Two amplifiers, each covering a different band in the VHF range, were constructed for test set applications. These amplifiers were required to meet stringent specifications beyond the general scope of previous art. These specifications related to the simultaneous availability of relatively large output power, tight linearity, minimal delay distortion across a 40 per cent band, high input and output return loss, large dynamic range, and time stability. The performance problems were solved by using: (i) Quadrature couplers in a corporate structure array to provide a high multiplicity of “paralleled” transistors, yielding both the power and return loss capabilities. (ii) The emitter follower configuration as the basic amplifier element, providing broad band, high level performance owing to the large self degeneration of that configuration. (iii) A “feed-forward,” instead of a feedback, system for error control and noise cancellation.