Investigation of class J continuous mode for high-power solid-state RF amplifier

The class J design space is investigated with half wave current excitation for a solid-state RF amplifier capable of delivering hundreds of watts. Unlike conventional class J designs, the present analysis aims to explore a continuous design space in order to operate a commercially available device, within its practical limits of drain voltage. This design analysis together with package effects and the inclusion of non-linear capacitor is verified experimentally by fabricating a high-power (550 W CW) high-efficiency (62.8%) solid-state amplifier operating at 505.8 MHz. This power was obtained by in-phase combining two similar continuous class J stages, each one contributing half of the total power. For high-power lateral diffused metal-oxide semiconductor devices, the class J design space is found to be more realisable than popular modes of operation in view of the large non-linear output capacitance of the device. The measured output power, efficiency, spurious response and large signal output reflection coefficients are satisfactory and as anticipated from the design analysis. Since the final application of this amplifier is for a solid-state transmitter, a study of repeatability in terms of phase and amplitude imbalances was carried out by fabricating and evaluating multiple amplifiers, each one working with the proposed design principle.